} Technical Report =: HISTORIES June 1971 Sponsored by NAVAL FACILITIES ENGINEERING COMMAND SNAVAL Cl NG LABORATORY Port Hueneme, California 93043 Approved for public release; distribution unlimited. SEAFLOOR FOUNDATIONS: ANALYSIS OF CASE HISTORIES Technical Report R-731 3.1310-1 by D. G. Anderson and H. G. Herrmann ABSTRACT The characteristics, basic foundation design parameters, and foundation performance of a number of seafloor installations are summarized. These instal- lations include offshore towers, habitats, acoustic arrays, and numerous other objects located in water depths from 20 to 12,000 feet. A number of case his- tories are analyzed. Some findings indicate behavioral problems not normally considered during foundation design. Several unique foundation configurations are documented which have been devised and utilized by a few to overcome the conditions imposed by the unique seafloor environment. Results of this study reveal that a number of foundation failures and near failures have occurred. Of the approximately 400 installations studied, 4% had experienced performance problems and an additional 3% had experienced failure. The causes, or probable causes, of several failures are examined. The value of foundation performance monitoring, both to the operation of an installation and to the field of seafloor foundation design, and the value and need for continued cooperation in the sharing of such information and experience are discussed. Approved for public release; distribution unlimited. Copies available at the National Technical Information Service (NTIS), Sills Building, 5285 Port Royal Road, Springfield, Va. 22151 CONTENTS page INGER @DWCIHIONY ee eee ee ol oo me Geese eee ] ONCE ean a ne tae a aon oumne retort chien ec enaneS ] SCOWC MAN Mer ee ey RR es or ae Se Me AA, ee ] BackajnOuUnGia tr: cies cutee ce Sauer ey Oueip > e-Msenc 1 EVALUATION OF FOUNDATION PERFORMANCE ..... . 2 CASE STUDIES ty aeea stacey ce cn oe eer Teer Mot cir omecamic 8 PNCOUSHICUATAVS: enn ct, er eens Sateen es gies re 9 Miscellaneous Submerged Structures . ........ . 24 IUSTOUICS NES: BAe RA cas OAs AS So Ne leit ad 39 Onshore Towers eine Plaiionms . 2. s 6 oo o o 5 o 4 « / ANALYSIS OF CASE STUDIES . 5. 2. 1. os. 0 6 5 6 5 oo 68 Foundation RenionmancelenOblemSia sean ino ene 68 Uiniguea Foumekiion Feemures 2. 5 os 5 6 ob 5 6 oo val SUMMARY ANID CONCLUSIONS . 5 2. 5620546685008 & V3 RECOMIMENDATIONS - . 06 + o so 6 0 ao 6 6 6b 6 Oo 75 ACKNOWLEDGMIENT .. 6 0 1 0 6 © 59 © 6 6 0 @ 6 36 8 6 VS REFERENCES =, fo prec te cee ones Rena nn man et Renan ia nS wwe 0301 poyo1a? 3 INTRODUCTION Objective The objective of this effort was to collect and summarize all available information on the performance of seafloor foundations. This information, along with an analysis, was directed at understanding the parameters which affect performance and establishing guidelines for more effective foundation design. Scope This summary of foundation performance is incomplete, because the collection and analysis efforts are to be continued. Often the only available knowledge of performance is that the foundation exists and that it either did or did not apparently function satisfactorily. Efforts are continuing in the collection of more detailed information on installations discussed here and additional information on installations which may have been missed in this initial study. Background The Navy is currently utilizing numerous ocean-bottom installations which depend upon the seafloor soils for their support (positive, negative, and lateral). These installations include offshore towers, habitats, and bottom-sitting test structures on the continental shelves. Test structures and a surprisingly large number of acoustic arrays and similar devices located in the deeper oceans constitute the remaining portion of seafloor installations. All of these seafloor structures, or installations, require some form of founda- tion through which vertical and horizontal forces are transmitted to, and resisted by, the seafloor. A number of the foundations now in use have experienced difficulties— performance was sufficiently unsatisfactory to impair the mission of the installation. A few foundations have been involved in failures which have required remedial measures. Numerous other foundations have been overdesigned with what were thought to be large factors of safety to ensure satisfactory performance. This was typically a successful, but usually expensive, approach. All of the systems were designed with what was thought to be an adequate factor of safety. Ina few cases, however, because all of the performance parameters were not thor- oughly understood, one was neglected. In such cases, when poor performance occurred In that parameter, the overall safety factor of the system became less than one. As the national interest requires, and as the technology is developed, the Navy is planning more numerous and larger installations for the ocean bottom. With this increased activity on the seafloor, and with the increasing sensitivity of many of these installations (such as manned installations, which require a high degree of confidence in the design, since any unsatisfactory per- formance may endanger human life), there isa need to (1) improve the capability for designing seafloor foundations which will perform satisfactorily, (2) increase the confidence level in these procedures, and (3) use designs which are econom- ically consistent with safety. For these reasons, the Navy has undertaken research that will develop design guidelines for seafloor foundations. The overall development of this design capability can be significantly improved by the study of past successes and failures. The results of such a study can be used directly as design guide- lines (a strictly empirical approach); or, more appropriately, they can be used to point out past problems (leading to the delineation and understanding of additional design parameters) and to act as test cases against which various proposed design rules may be compared and evaluated. EVALUATION OF FOUNDATION PERFORMANCE Satisfactory foundation performance can be defined in several ways. However, satisfactory performance basically is performance that permits the installation to complete its mission as intended. Specific performance parameters contribute to this overall behavior. These parameters often include the following: (1) stability relative to bearing capacity; (2) stability relative to overturning; (3) stability relative to lateral motion; (4) tolerable differential settlements; (5) tolerable total settlements; and (6) sufficient rigidity (stiffness) to prevent motion. These parameters must consider dynamic (such as earthquake) as well as static (such as sub- merged weight) situations and soil behavior (such as compression or rupture) as well as other environmental influences (such as undermining, current scour- ing action, or slope instability). In addition, for each of these parameters there are different scales of satisfactory performance. For example, manned installations require a high degree of confidence in their stability and, therefore, can tolerate very little motion; whereas, unmanned and relatively insensitive seafloor installations are often capable of tolerating larger settlements without impairment of their mission. In the extreme case, an installation involving numerous identical structures (each of which is unmanned and duplicates to some degree the mission of the others) may be capable of tolerating (for the sake of economy) some failures. In a situation such as this, the scale of performance behavior may be such that fewer than two failures (in the overall installation involving a large number of individual implants) may be considered satisfactory. The scale of performance may also be influenced by factors such as soil or sediment province, physical environment (such as water depth, current velocity, and biologic activity), and design life of the installation. In spite of the wishes or needs of the owner or Operator of an installation, such factors may force a shift of performance scales. For example, performance satisfac- tory at 6,000 feet may be unacceptable at 60 feet. Such a shift is, in essence, attributable to the state-of-the-art of certain technologies which limit or restrict performance. To ascertain the scale of performance and the parameters affecting performance, the behavior of the in-situ foundation must be monitored. The monitoring of foundation performance serves six purposes: (1) it initially focuses objective thought on the type of performance which is required, on the level of performance which is satisfactory, and on the parameters which should be considered for satisfactory performance; (2) it keeps the operators informed of the condition of the installation so that remedial steps can be taken if they become necessary; (3) it evaluates the success of the foundation design procedure and the assumptions made therein; (4) it points out behavior parameters which may not have been considered at the time of the design; (5) it begins to give a statistical view of foundation behavior and failure; and (6) it forms a library of past experience or case histories, which can be used in future analyses and comparisons. Such monitoring of foundations on land has been common throughout the ages. Earliest design techniques were based strictly on observations and experience (the empirical approach). More recently, the need for performance monitoring, as a means of improving foundation design capabilities, has been pointed out in prominent technical literature (Casagrande, 1965; Feld, 1965). As discussed earlier, a variable and dissimilar number of behavior parameters collectively (and often mutually exclusive) contribute to an instal- lation’s degree of satisfactory behavior. The parameters which are most commonly important, and thus worth monitoring, are (in probable decreasing order of importance) the following: (1) total vertical penetration or settlement into the seafloor; (2) differential vertical motions (differential settlement) or rotation; (3) lateral motion (skidding); (4) soil behavior in the vicinity of the installation (such as excess pore pressure and location of soil strain resulting in installation movement); and (5) dislocation of soil mass (such as scour, fill, or mass movement—slope instability) in the vicinity of the installation. Applicable monitoring techniques are in use on land for all of these. These techniques can, and have been, modified for use on the seafloor for submerged installations. For observing immediate, large-scale movements of an installation shortly after deployment, simply visual (direct or by closed- circuit television) observations by divers, submersible, or some remote observation system [CURV (Cable-Controlled Underwater Research Vehicle), for example] have been successfully employed. Similar visual methods can be employed for monitoring smaller movements (or other behavior phenomena) over longer periods of time if some form of referencing foundation position is added. Another technique for monitoring smaller movements involves the usage of mechanical and fluid measuring systems such as shown in Figures 1 and 2. The mechanical system references movement to a vertically stable reference rod (isolated from surface movements) while the fluid system relates movement to a constant-elevation fluid interface. NCEL (Naval Civil Engineer- ing Laboratory) divers have monitored the performance of several model foundations which employ mechanical and fluid referencing techniques (Figures 1 and 2) in up to 130 feet of water. The fluid system concept has also been utilized to measure differential vertical movement of a structure. These measurements were made by attaching the reference stand to one end of a structure and locating the sighting tube (Figure 2) at the opposite end. The accuracy of measurements for the mechanical and fluid referencing sys- tems Is typically in the order of 0.125 inch. The periodic monitoring of installations in deeper water could be accomplished by employing the same measuring systems and a small submer- sible; however, it is typically more economical to use some sort of automated data collection system. The LOBSTER (Long-Term Ocean Bottom Settlement Test for Engineering Research) employs such a method. This device (Figures 3 and 4) uses the same mechanical reference system as shown in Figure 1; how- ever, data are automatically taken (rate is variable from once every 7 seconds to once per hour) from three sensors which measure total settlement (accuracy about 0.02 inch) and footing tilt (differential settlement) in two perpendicular planes (accuracy about 0.5 degree). The LOBSTER is deployable in water depths to 6,000 feet for durations of up to 1 year. All data are stored inter- nally on digital tapes which are recovered at the end of the deployment. measuring rod (carried by diver) —4' center well (allows 15° rotation) footing reference point NCEL LOBSTER concrete footing isolation tube | reference rod (with cone tip) Figure 1. Mechanical reference system (cross-section view). sighting tube /\) (transparent) measuring rod fluid ? fluid inter interface Buisce x light fluid (oil) seafloor : installation heavy fluid (colored water) [ee reference stand~ | WIT Al al a7 r reference footing be ~ 30’ 7) ales en == base 10’ = Figure 2. Fluid reference system. PINGER/TRANSPONDER ATTITUDE SENSOR DIGITAL TAPE RECORDERS SURFACE ACTUATED RADIO BEACON DATA ACOUSTIC COMMAND CONDITIONING _—~_ RECEIVER ciety - XENON FLASHER SETTLEMENT SENSOR 7 RELEASE COMMAND | DECODER RELEASE TIMER RECOVERY FOOTING FLOATATION COLLAR ISOLATING TUBE AND io REFERENCE PROBE é Figure 3. Artist's conception of NCEL automated performance monitoring device, LOBSTER. Another automated monitoring device is the NCEL Foundation Performance Monitoring System (FPMS) (Figures 5 and 6). The FPMS, which is composed of a Foundation Monitor and an Amplification Module, is designed for general use on a structure of any size, shape, and type (such as mat, spread footings, or piles). The system monitors vertical movement (settlement) by sensing the change in pressure head between the Foundation Monitor and the Amplification Module as the Foundation Monitor settles relative to the Amplification Module. The Amplification Module is physically isolated from the effects of the structure (by a distance of about 30 feet). The Foundation Monitor also records the differential movement of the struc- ture by utilizing two tilt transducers mounted at right angles to each other within the Foundation Monitor. As the structure tilts or rotates, the Foun- dation Monitor and tilt transducers undergo a similar movement. Precision of vertical settlement readings is better than 0.05 inch, while precision of tilt readings is better than 2 minutes. The Foundation Monitor, which can be deployed in up to 6,000 feet of water, senses the tilt and pressure transducers at various time increments (short during initial phase; longer during latter phase). Once the appropriate transducers are sensed, the Foundation Monitor conditions and stores the digitized data on magnetic tape for later processing. Figure 4. NCEL automated monitoring device, LOBSTER. The devices mentioned in the previous paragraphs are currently being used to monitor the performance of seafloor structures. These devices, and others not mentioned, succeed in answering some of the questions concerning the scale of foundation performance and the parameters affecting foundation performance and design. However, two points must be emphasized. A need still exists for other, new devices capable of monitoring parameters (such as earthquake response and pore pressure dissipation) presently not being moni- tored. Some of these devices will have to be sophisticated and expensive; therefore, only foundations which justify a high degree of performance monitoring will be able to afford them. Other devices can be inexpensive and permit low-cost foundation monitoring. The second, and perhaps most important, need is for an increase in the number of foundations being moni- tored. Whether the monitoring devices are sophisticated (such as LOBSTER) or unsophisticated (such as visual observations), much valuable design data are gained by recording some or all of the in-situ foundation behavior. By establishing a broad program of monitoring performance, it is probable that the reliability of future systems will be increased while the cost of construct- ing and placing the same system will decrease. seafloor installation Eoundation Monitor differential pressure transducer and fluid reservoir small-diameter water-filled Amplification Module flexible membrane TASH STARS H small-diameter mercury-filled line -~ 30' A > Figure 5. NCEL Foundation Performance Monitoring System (FPMS). CASE STUDIES Information has been gathered on the characteristics and performance of approximately 200 foundations which have been used on the seafloor. These case histories have been divided into four categories. The first three categories, Acoustic Arrays, Miscellaneous Structures, and Habitats, include all of the totally submerged structures. The fourth category, Offshore Platforms and Towers, includes the structures which extend to and above the ocean surface. The fourth category also summarizes information on over 300 offshore struc- tures for which specific performance information was unavailable. Figure 6. FPMS being readied for deployment. Acoustic Arrays A number of underwater ranges, most operating as three-dimensional acoustic tracking systems for training and testing of the Fleet and of various weapons systems, are listed in Table 1. These ranges are located in the nor- thern hemisphere (from Bermuda to Hawaii) and are utilized almost exclusively by the Navy and its contractors. The ranges are all similar in makeup; consequently, foundation requirements are much the same. The differences in seafloor conditions at the various range sites impose differing restrictions on foundation design. Soil conditions at the sites vary from sand with rock outcroppings to what is described as a silt-ooze. These underwater ranges utilize a number of hydrophones (varying from 5 to over 200) placed on the seafloor in a specific pat- tern. The ranges cover areas which vary from several square miles to as large as 200 square miles. The sound created by any object (or of a pinger attached to an object) within the range is received by these hydrophones at slightly different times, depending on the distance from the object to the particular hydrophone. The resulting electrical impulses are usually carried by underwater cable to a submerged termination chamber. In the termination chamber all signals are gathered, and, in some instances, con- ditioned. From the termination chamber, the data are carried through the surf zone by a smaller number of heavier cables, designed to withstand con- ditions in this most severe transition zone, to shore-based equipment for final conditioning and analysis. The underwater termination chambers are usually located in shallow water (60- to 80-foot depths) and are usually larger and heavier than the hydrophone structures which are designed simply to support one or more small hydrophones in a relatively fixed position on the deep-ocean seafloor. The hydrophones are located in water depths from 600 to 12,000 feet. Some individual underwater ranges vary in depth by as much as 9,000 feet. The hydrophone structures, which are usually identical within each range, have heights from 15 to 50 feet, mean lateral dimensions from 4 to 50 feet, and submerged weights from 300 to over 1,000 pounds. Although the basic nature of these structures is such that relatively small loads are involved, their foundations must still minimize settlement, tilt, and lateral movements. The foundation system in combination with the structure also must be designed for easy installation at a rather precise location. Design life for these systems is in the 5- to 20-year category. Some ranges now in existence are as much as 12 years old; most, however, are more recent. A number of foundation types have been utilized to support hydrophone structures. These include (in general chronological order of development and use) deadweight anchors, simple spread footings, multiple spread footings, and ring footings. Designers of earlier systems liberally employed universal joints and buoyancy elements to overcome the effects of differential foundation settlement. In this configuration, ocean-bottom currents can disrupt the performance of the hydrophones and, at one range, the system was modified to use a series of universal joints which were locked after a short period of time (Green, 1969; Daniels, 1969). The larger portions 10 Operator Installation Year Depth (ft) Location Table 1. Underwater Acoustic Arrays Structure Type Navy (Naval Under- Wt (Ib) in Water, W, or Air, A 12-ft-diam Mean Lateral Dimension Foundation Type Foundation Bearing Pressure (psf) Type Sediment Settlement water Weapons 4 silt size no sliding 1 -in.= e AUTEC Station, Naval 4,000 to 6,000 Bahamas hydrophones 55 400 (W) GIG OGI EA ring footing =127 carbonate | or excessive OS ain from * diam PVC submersible. Ordnance Station), material | settlement tubing Newport, R. I. 12-ft-diam 1 “iN é NevyalGau fic 2,200 to 5,500 hydrophones 37 360 (W) cl tote 10 ring footing =115 thin Missile Range), Kauai, diam PVC Performing as BARSTUR 1967 i veneer unknown Point Mugu, Hawaii tubing anticipated. Calif of sand i =1,000 (W) and moored spread ce sinetateIn eer l with grouted-in stakes mx cone footing 3,000 to 12,000 hydrophones 200+ Sx3ft frame unknown Navy (Naval assumed t 196! I Cncenveter a0 3,000 DOBACS 1 35,000 (A) 25 ftindiam | ‘Wbuler unknown to be Problems with Bermuda Range | Sound Labora- and Bermuda frame unknown coral DOBACS. tory), New London, 1966 “ frames and material Conn. miscellaneous 10+ varies varies paris unknown —————— a Straits of WevyiNavel Georaley Malet) siliceous eae Canadian Range | Torpedo Station), 1965 =1,350 British hydrophones 6 10,000 (A) three 3x3 ft | apparatus on unknown obie =1 ft ceeoianat Keyport, Wash, Columbia, three footings eae ae Canada p - Navy (Naval Daybob Bay ° Hood Canal, concrete silty no settle- T t Faded orpedo Station), 1958 650 Wash. hydrophones 15 1,000 (W) 4x4ft Blacks 62.5 sediments limenuneted Keyport, Wash. 12-ft-diam circle of 2-in.- - me GrElectronies 4200 ee hydrophones 5} 385 (W) diam PVC ring footing =123 Rolcuidence ates SCARF General Motors 1965 Sane tubing sand of soil fail- Corp., Goleta, Calif IELEWGL (GAlins mee by submersi- ix ; . ballasted to compensate ble, DOWB. 60 junction chamber 1 for 15,000-Ib positive four legs unknown buoyancy Santa Cruz 12-ft-diam Sandia Corp., Island adja- circle of 2-in.- no problems Sandia Facilit 1 1 NGA FdsieiaseucyNhib 965 2,400 penn hydrophones 6 385 (W) diam PVC ring footing =123 penarten SCARF tubing concrete St. Croix silty no settle- Structure slid St. Croix Range | Na’ 1964 *. x a vy gi 3,000 Virain Islands hydrophones 11 3x3 ft blocks and unknown ea} Prentinntodl||(nonnclaness open boxes a continued 1 Operator University of Miami, Coral Gables, Fla. Other Ranges Lockheed Ocean Laboratory, San Diego, Calif. Woods Hole Oceanographic Institute, Woods Hole, Mass.* New York, N. Y.* Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada* Project CAESAR* * No data available. Columbia University, Installation Year early 1960's Table 1. Continued Location Straits of Florida San Clemente Island hydrophones Structure transducer hydrophone Wt (Ib) in Water, W, or Air, A low weights Mean Lateral Dimension Foundation Type Foundation Bearing Pressure (psf) Sediment Type Settlement Remarks 12 of differential settlement were presumed to occur before the systems were locked. The locking process prevented subsequent movement due to current drag. At another range, a simple spread footing slid down a shallow slope (Linger, 1969). This problem was prevented on later foundations by using footings with cutting edges designed to key the footing into the underlying soil and, thereby, prevent lateral movement. More recent trends in structural design have been toward the use of simpler configurations. This change was facilitated to a degree by advances in fields related to range design and layout. The change has resulted in the use of lower total weights and larger widths on the footing systems. This more recent and now somewhat standardized design, the ring footing, has experienced no known foundation performance difficulties during use in several diverse soll types. The following sections summarize the characteristics of several acoustic ranges. Information includes structural aspects (size, weight, con- figuration) of the system, environmental data (soil parameters, depth of water, currents, terrain) at the site, and performance (settlement, sliding) of the structure with respect to foundation behavior. Data on the systems were generally sketchy; therefore, only an empirical performance investigation can be attempted. AUTEC Range. The Atlantic Undersea Test and Evaluation Center (AUTEC) was completed in early 1967 (Jackson and Grant, 1967; Busby, 1965 and 1969; Covey, 1967; Austin, 1964). In addition to providing three- dimensional tracking, the range conducts temperature, salinity, and pressure measurements. AUTEC is located about 180 miles southeast of West Palm Beach, Florida, in the Tongue-of-the-Ocean (TOTO)—a sheltered expanse of water parallel to Andros Island in the Bahama Islands. The body of water is approximately 100 nautical miles long by 15 nautical miles wide and has a depth which varies from 3,600 feet in the south to 6,600 feet in the north. The tracking system is composed of weapons, acoustic, and sonar ranges. The Weapons Range occupies an area 5 miles wide by 35 miles long off the southern end of Andros Island. Three-dimensional tracking Is pro- vided by 55 individual hydrophones geometrically arranged into two separate groups at opposite ends of the range. The Acoustic Range is located between the Weapons Range and New Providence Island. Two hydrophones occupy this 5- by 5-mile area. The Sonar Range, scheduled for later completion, will include sonar transponders accurately located on the seafloor. During 1961 and 1962, approximately 100 sediment cores were taken by the Naval Oceanographic Office (NAVOCEANO). The constituents of the TOTO bottom sediments were predominantly silt size, skeletal and nonskeletal carbonate particles representing both shallow- and deep-water environments (Huddel et al., 1965). Organic carbon content of the sediment ranged from 1% to 2%. The general variations of water content, void ratio, density, and undrained strength with depth in the soil profile all indicated a normally consolidated soil profile. Coarse-grained materials, which formed more than 50% of some of the cores, were attributed to deposition by turbidity currents. Sediment undrained shear strength (vane shear strength) in the northern area ranged from 1 to 3 psi over the length of the cores. In the southern area, strength averaged less than 1 psi. Sediment sensitivity varied from slightly insensitive to slightly quick. Bottom photographs show an almost feature- less ooze with a few benthic organisms. In the central northern portion of the channel at a water depth of 6,000 feet, there is a series of cavities and depressions. The hydrophone structures are designed with the hydrophone attached to the top of a 15-foot-tall conical frame. The 12-foot-diameter base is con- structed of 2-inch-diameter polyvinyl! chloride (PVC) tubing. Figure 7 shows an almost identical hydrophone structure. Weight of the entire apparatus in water is about 400 pounds. Visual performance observations were made 6 months and again 3 years after the system was installed. The observations were made from the submersibles Aluminaut and Alvin. No unusual activities or problems (sliding or excessive settlement) were noticed (Austin, 1964). BARSTUR. During the spring of 1967, the Navy established a highly instrumented three-dimensional underwater tracking range in Hawaiian waters (Prince, 1968; Okura, 1969). The site is located in the north central Kaulakahi Channel (Kaulakahi Channel separates the Island of Kauai from the Island of Niihau to the west) (Garrison, 1965). Barking Sands Tactical Underwater Range (BARSTUR), composed of an underwater communications system (UQC) and 37 tracking hydrophones, is located in a 5- by 10-mile area (Figure 8). Water depths within the range vary from 2,200 to 5,500 feet. Each hydrophone is located with respect to a center hydrophone, which, in turn, is referenced (within a 175-foot-diameter circle) to shore facilities. An underwater junction box, located beyond the surf zone in 65 feet of water, forms a terminus for connecting the smaller individual phone cables to a single, multiconductor, heavily armored cable. Figure 7. Typical dual hydrophone structure, SCARF range. (From Momsen, 1970. Photo courtesy of AC Electronics.) 15 22° 15° it) 5 10. «15 beet} Scale in Thousands of Feet 22° 10° Makaha Poi Kauai 22° 05° Barking Sands complex operations building 22° 00° : Ss 160° 00° 159° 55° 159° 50° 159° 45 Figure 8. Hydrophone locations for Barking Sands Tactical Underwater Range (BARSTUR). (From NPOLA, 1969.) Specific seafloor studies were made by NAVOCEANO and others during 1964 (Belshée, 1967). Records from the seven sediment cores (from water depths of 2,400 to 6,000 feet) and various underwater photographs indicated that a thin veneer of sand covered nearly 70% of the seafloor at the site. Outcrops of basaltic rock accounted for most of the other 30%. About two-thirds of the seafloor at the site had a slope of 5 degrees or less. Nearshore investigations indicated patches of sand distributed in pockets formed in the bedrocks. The greatest thickness of sediment measured in the nearshore region was 18 inches. Maximum relief in the area was 3 feet. Each hydrophone structure, weighing 360 pounds in water, supports a single hydrophone. These structures are similar to the units used at AUTEC. The detailed configuration is shown in Figure 9. The 4-foot-wide by 20-foot-long by 1-foot-high junction box rests directly on the seafloor and is secured by five grouted-in stakes. 16 Weight in Air : 502 Ib BARSTUR has performed Weight in Water : 360 Ib - . Hydrophone Height Above Base: 15 ft satisfactorily to date (Okura, 1969). Diameter of Base Ring : 12 ft Difficulties have been experienced C. G. Above Base in Air : 32.45 in. with only two hydrophones. One C. G. Above Base in Water wsO!Osiin- f Yoke Pivot Above Base : 34.0 in. hydrophone has become inoperative Free Fall Velocity : 2.86 ft/sec and will be replaced. A second hydro- phone is experiencing a shadow effect which may possibly be caused by the proximity of a rock outcropping or ledge. Neither difficulty appears attributable to unsatisfactory foun- dation performance. Tracking Is still good in the rest of the range; however, a shift of more than 20 feet would have been required before variations would be noticed. A detailed survey and inspection were planned for the fall of 1969, but have been postponed. Some difficulty has also been expe- rienced with the hydrophone cables at the junction box (Good, 1970). During the winter storms of 1969- 1970, several were torn loose from their bottom securing system (dead- weight bags) and became entangled about the junction box (Black, Bruce, and Herrmann, 1970). Remedial steps were taken during the summer of 1970. mast (aluminum) yoke (aluminum) (in up position) The yoke is horizontal when the assembly is installed in water. base ring (pve) Figure 9. BARSTUR hydrophone Bermuda Range. An acoustic pas (Pei INAOey range was established in 1961 by the : Navy near the Island of Eleuthera in the Bahamas (Moothart, 1969). Water depths at the site vary from 3,000 to 12,000 feet. Although no sediment records are available, nearshore material was assumed to be coral, and offshore sediments were assumed to be even harder. The bermuda system is composed of numerous acoustic arrays supported by a variety of footings. Difficulties with the Deep Ocean Basin Acoustic Cable Source (DOBACS) have been reported. These problems are apparently not the result of unsatisfac- tory foundation performance. The DOBACS, which weighs 35,000 pounds in air and is approximately 25 feet in diameter by 50 feet high, was positioned at a water depth of 3,000 feet on a relatively small, steeply sloped (30 degrees) plateau. The plateau is approximately 200 by 400 yards in area. The struc- ture was leveled by a gimbal system after placement. Canadian Range. The Navy maintains an acoustic range in the Straits of Georgia, northeast of Nanaimo, British Columbia, Canada (Green, 1969; Daniels, 1969). The range, established in 1965, contains six hydrophones located in approximately 1,350 feet of water. Bathymetry in the area Is relatively flat, and sediments are predominantly siliceous oozes. Two configurations have been used for supporting the acoustic instrumentation. The older hydrophones are attached to buoyant spheres and anchored to the bottom. This configuration is flexible, and bottom cur- rents of about 0.1 knot cause undesirable hydrophone movements. The newer and more successful supporting structures consist of a 50-foot tripod apparatus with each corner supported on a 3- by 3-foot concrete footing. The entire apparatus weighs approximately 10,000 pounds in air. Since sediments in the area were extremely soft, a unique device was designed to minimize attitude change due to differential footing settlement. A universal joint was placed between the hydrophone and the tripod, anda buoyant sphere was attached to the hydrophone. If the base settles differen- tially into the sediment so that the tripod tilts, the buoyant sphere moves the hydrophone back to a vertical position by rotating the system about the flexible joint. The entire system remains flexible for approximately 2 weeks, after which time the hydrophone’s position is fixed rigidly relative to the tripod. The magnitude of settlement during the first 2 weeks was approximately 1 foot. This value varied according to the buoyant force supplied by the sphere and the properties of the bottom sediments at the specific location. Although some further tilting has been noted subsequent to clamping of the hydrophones, operation of the range has been satisfactory. Daybob Bay Range. !|n 1958, the Navy established an acoustic range west of Seattle, Washington, in Daybob Bay (Green, 1969; Daniels, 1969). Fifteen hydrophones were placed in approximately 650 feet of water ona silty sediment. Each hydrophone is attached to a 15-foot length of pipe atop a 4- by 4-foot concrete anchor block. A buoyant sphere and two universal joints maintain vertical position. No unusual performance problems have been noted with the 1,000-pound negatively buoyant configuration. SCARF. The Santa Cruz Island Acoustic Range Facility (SCARF) is a three-dimensional acoustic tracking range belonging to General Motors Cor- poration’s A.C. Electronics—Defense Research Laboratory (A.C. Electronics, 1968; Chalfant and Buck, 1968; Engstrom, 1969; Momsen, 1970). The hydro- phone arrays were implanted in 1965 at an average water depth of 4,200 feet some 6 miles south of Santa Cruz Island (Figure 10). BLUE CAMERA STATION (1320' ELEV.) WHITE STATION MAIN SITE (161’ ELEV.) 2 4 9 A 16 Se 2 i; yi 1 , 5 20 be. 5 WL aise ay n Pacis ” =——_ \ STATION (976’ ELEV.) A \ ks SHALLOW WATER ‘Hh, 6 \\\\ (UNDERWATER CABLE Ue DROPEZONE \ mn TERMINATION CHAMBER | AUN AY | BATHYMETRY SURVEY zs RV SWAN SEPT 13-1965 SURFACE CONTROL - DECCA HIFIX FATHOMETER - GIFFT GDR COMPUTER CONTOURED - IBM 7040 Figure 10. SCARF and Sandia underwater ranges. (From Momsen, 1970. Photo courtesy of AC Electronics.) 19 The submerged portion of the facility consists of four dual tracking hydrophones, a string of three noise-measurement hydrophones, and a UOC. The tracking and communication hydrophones are supported on 15-foot-tall by 12-foot-diameter aluminum conical frames each weighing 385 pounds in water (Figures 7 and 11, respectively). The noise-measurement string includes three hydrophones attached to a buoyed cable. All sea cables are connected to an underwater termination chamber in approximately 60 feet of water, 1/2 mile offshore. The 6-foot-diameter by 12-foot-tall cylinder is supported on a sandy bottom by four legs. Ballast is used to overcome the 15,000 pounds of positive buoyancy developed by the chamber. Slight reception problems at one of the four hydrophone structures led to the performance of an inspection of the entire range by the General Motors submersible, DOWB (Deep Ocean Work Boat), in late 1968 and early 1969 (Engstrom, 1969). Asa result of this inspection it was discovered that several structures were lying on their sides. This was determined not to have been the result of soil-related problems. The structures were righted during the summer of 1969 using the DOWB (Figure 12). Output from the tracking hydrophones indicates that the foundations have performed satisfactorily since that time. It is interesting to note that for all but one of the structures there was no obvious indication of improper orientation of the structures. The range inspection and subsequent remedial actions resulted in an overall improvement of the range effectiveness. Sandia Facility. In 1965, an acoustic range was installed adjacent to SCARF for the Sandia Corporation by the owner and operators of SCARF (Engstrom, 1969). The six hydrophones are located in approximately 2,400 feet of water (Figure 9). Other physical and mechanical characteristics of the system are similar to those at SCARF. A common underwater cable-termination chamber is used by the two ranges. No foundation problems have been reported. Saint Croix Range. The Applied Physics Laboratory (APL) at the University of Washington designed and installed for the Navy an underwater tracking range off the west coast of Saint Croix in the Virgin Islands (Garrison, 1963; Rooney, Eppert, Huddel, 1965; Linger, 1969). Four hydrophone struc- tures were emplaced in 1964 at a water depth of approximately 3,000 feet. The range was enlarged to 11 hydrophone structures in 1967. Sediment investigations were made at the site in 1962 and 1965 by NAVOCEANO and in 1963 by APL. Typical sediment properties as deter- mined by NAVOCEANO were as follows: 20 Total walt weet, o.oo 6 6 2 ee os on IWSTO 105 per SOSCHIG CHEMI, ss 5 5 sk tk AIA UWO 270 Weiter Gomient . « 5 5 oc 2 eo a 0 oo o WO tO SOR WoldifeulO: shine 6s on ol ee ee TAO wods0 Unconfined compressive strength . . . . . 1.0 to 4.3 psi The seafloor topography was relatively smooth with slopes varying from 3 to 20 degrees. Each hydrophone structure included: (1) an open space-frame, with a major lateral dimension of 30 feet, for supporting the individual hydrophones, (2) a universal joint and buoyant sphere for maintaining the hydrophones on the space-frame in a fixed, stable plane; and (3) a base for anchoring the con- figuration. The bases for the first structures were concrete cubes with 3-foot sides. The newer hydrophone structures have a 3-foot-square open box base. Immediately after the first structures were placed, difficulties were noted with one (Linger, 1969). An anchoring base and its attached frame slid down a 10- to 15-degree slope dragging an umbilical cable. A lateral distance of approximately 1,000 feet was traversed. The possibility of sliding was reduced on the seven more recent structures by designing the base with a hol- low interior and open bottom so that the perimeter became a cutting edge. During emplacement of these seven, the bases were dropped from approxi- mately 50 feet above the seafloor in order to increase penetration into the sediments. |t was intended that any downslope motion would be resisted by the lateral stress mobilized against these ‘’keying edges.’ No subsequent dif- ficulties with foundation performance have been reported. Other Acoustic Ranges. The University of Miami installed a transducer and two receivers for measuring environmental fluctuations in the Straits of Florida between Miami and the Island of Bimini (Sykes, 1969; Steinberg, 1969). Bottom sediments were hard, and equipment weights were low. No foundation performance problems have been reported. The Lockheed Ocean Laboratory, San Diego, installed a hydrophone system off San Clemente Island in the early 1960's (Inderbitzen, 1969). The purpose of the range was to demonstrate the Laboratory’s ability to perform oceanographic work. A concrete block base held the hydrophone array in place for 3 months without incident. Other similar structures have been used by Woods Hole Oceanographic Institute, Columbia University, Bedford Institute of Oceanography, and on Project CAESAR. No foundation problems have been reported; however, in these cases, the only information available is that the structures exist. 21 Figure 11. SCARF communications hydrophone (UQC) structure. (From Momsen, 1970. Photo courtesy of AC Electronics.) Li Figure 12. SCARF hydrophone structure during righting by submersible, DOWB. (From Momsen, 1970. Photo courtesy of AC Electronics.) 23 Miscellaneous Submerged Structures A great number of structures other than acoustic arrays and habitats have been placed on the seafloor (Table 2). Many of the structures included in this category are scientific or experimental devices and packages. Some of the structures are installed semipermanently, while others are deployed many times but only for short durations. The foundation types include both pile and footing configurations. NCEL DOTIPOS System. The NCEL DOTIPOS (Deep Ocean Test-In-Place and Observation System) is a tethered, bottom-sitting plat- form (Figure 13) with observation systems, control mechanisms, power source, and data telemetry (Kretschmer, 1969; Padilla, 1969 and 1970). Figure 13. NCEL DOTIPOS. DOTIPOS has a pyramidal frame with an 18-foot-square base and an overall height of approximately 16 feet. The platform is supported by three 4-foot-square pads. The total submerged weight varies from 1,900 to 4,000 pounds, depending upon the type of accessories attached. At maximum 24 submerged weight, the bearing pads apply a stress of 85 psf. Short-term settlements from 0.5 to 1.5 inches have been observed in soft cohesive sedi- ments. No foundation performance difficulties have been experienced during more than 30 deployments on the seafloor in water depths to 5,600 feet. ESSA Bottom-Sitting Observation Stand. The Seattle, Washington, Division of the Environmental Science Services Administration (ESSA) used an observation stand equipped with a camera and current meter array to observe ocean-bottom currents in the Tasman Sea (Ryan, 1969). The device, which weighs 200 to 300 pounds in water, is pyramidal with a 12- by 12-foot base fabricated from 1-inch-diameter pipe. Water depths at test locations varied from 2,600 to 15,000 feet. Sediments were predominantly calcareous oozes. Although bottom penetration and settlement varied from site to site, no foun- dation performance difficulties were experienced. Performance data are being assembled by ESSA for future publication. ESSA Plate Load Device. Two series of plate bearing tests were performed by Harrison and Richardson on sandy marine sediments in the shallow waters of lower Chesapeake Bay (Figure 14) (Harrison and Richardson, 1967; Harrison, 1969). The behavior of the sediments was compared to the theoretical behavior as predicted by the Terzaghi and Taylor equations for terrestrial soil. A load frame (Figure 15), which weighed 82,000 pounds in air and was estimated to weigh 48,000 pounds in water, supplied the reaction for each of the in-situ load tests. The frame had a bearing area of approximately 48 square feet (giving an applied stress of 1,000 psf). A 20,000-pound calibrated hydraulic jack on the frame was used to apply loads to the 12-, 19-, and 24- inch-diameter plates. Before tests were performed, soil at the site was evaluated for grain size, void ratio, density, and wet unit weight. A series of triaxial tests, con- ducted in the laboratory, established the sediment’s angle of internal friction. When the load frame was slowly placed on the seafloor, the frame settled 1-1/2 to 3 inches into the sediment at Site A and 1 inch at Site B. Once SCUBA divers had instrumented the frame, the plate bearing tests were performed. Values of ultimate in-situ bearing capacity as determined by this procedure were found to be generally higher (by factors of 2 to 3) than pre- dicted by theory. The amount of settlement under a given stress increased as the plate diameter increased, as predicted by existing terrestrial theory. NCEL LOBSTER. The NCEL LOBSTER (Long-Term Ocean Bottom Settlement Test for Engineering Research) was designed to measure the in-situ long-term compression of soft sediment under typical foundation loads. 25) (‘uoIssiuiad Aq pas-) “sseiqg S!our||| $0 AysuanluM © “£96 | ‘uospseyoiy pue UosIWeH WO14) “Sas 1S9} Bulieaq aze\d WSSq 4O uOl1e907 “P| aanbi4 SS 3GNLISNO1 mi ich £1 o9L on e\ I \ \ | wmeq MW 01 pa4saj9y SuIEqOS| = dasy |4 S = =| --wg S See am G0oLE £ assis 26.614 z eat TW ad WSHHO [. S3T9NV LNVIX3S @ ILis o9E 26 Name NCEL DOTIPOS (Deep Ocean Test- In-Place and Observation System) ESSA Bottom- Sitting Observation Stand Operator NCEL (Naval Civil Engineering Laboratory) ESSA (Environ- mental Science Services Admini- stration), Seattle, Wash. Table 2. Miscellaneous Submerged Structures No. of Structures Depth ’ or Location (ft) Deployments off Southern Oto 5,600 California coast numerous 2,600 to 15,000 | Tasman Sea Bay Chesapeake Lateral ESSA Plate Load ESSA, Norfolk, Device Va, NCEL LOBSTER (Long-Term Ocean Bottom Settlement | NCEL Test for Engineer- ing Research) NCEL Plate Bearing Device MSL NASL Deep-Sea NaS teva (Sprean War Applied Science Be ul Laboratory) NCEL STU (Submersible Test NCEL Unit) NRL (Naval NRL’s STU Research Laboratory) NUSL Transponder | NUSL (Naval Block Underwater Sound Laboratory) California coast 20 4to 1,200 120 to 6,000 California coast Bahamas 120 to 6,780 California coast Bahamas near Fort Lauderdale, Fla. near Fort Lauderdale, Fla. Long Island Sound, New London, Conn. off Southern off Southern Tonque-of- 4,500 the-Ocean, off Southern Wt (Ib) in Water, W, or Air, A} Dimension (ft) 1,900 to 4,000 (W) 18x18 square spread 200 to 300 (W) 12x12 base of 1-in.- 82,000 (A) two 5 x S-ft 48 000 (W) Binge spread footings 1,300 (W) 6-ft diam fits inside 12-ft-diam circle 3,000 to 6,000 (W) =5,000 (A) 200 to 300 (A) 200 to 300 (A) 1,000 (A) 5 x2 (diam) =730 (W) 3x3 spread footing Foundation Sediment Type three 4-ft- 12x 12-ft diam pipe soft cohesive sediments predominantly calcareous ooze 0.5 to 1.5 in. circular spread three 2x 5-ft strip footings 10 x 10-ft base of 1-1/2-in, +— sandy marine sediments 1to3in. Settlement Remarks In-situ vane shear Strength and cone penetration avail- able. No difficulties encountered. In-situ load-versus- deflection curves available. —— soft cohesive sediments cohesionless and cohesive silts 6 x 6-ft base of spread footing deactivated sands and silty clays to clayey silts silt size calcareous sands calcareous sand calcareous ooze predominantly sands 1to8 in. versus-time records Oto Zin, deflection curves no excessive settlement thought to be less than 1 ft no sinking noted no settlement noted base was par- tially covered with sand In-situ settlement- available. In-situ load-versus- available. Shear strengths available. Settlement esti- mates based upon mudline markings. Settlement esti- mates based upon mudline markings. Observed with television. Observed with divers. continued Table 2. Continued sand atop no problems | Resist a maximum Ran lateral-load- versus-deflection test. Predicted depth of equation. Initial No. of Structures Lateral ' Foundation 7 it R Sediment Operator Installation or aye Location Wt (Ib) in Water, W, or Air, A | Dimension hee Bearing Type Settlement Remarks Year Deployments (ft) Pressure (psf) Wil cate loose coarse iison vi ., " 30-ft-diam mat sand atop no problems 1958 1 115 au Ss up to 400,000 (W) 30-ft diam tect Ginna eae ELIAS over bedrock wil cate four 14-in.- loose coarse Differential move- ison vi " , J diam piles sand atop no problems | ment of 1/8-in. NUC (Naval huey) y 70 =a Sa fede lal alee) a9) embedded dense sand noted would have been NUC Pop-Up Undersea) Research Seg aaa 65 ft over bedrock detected. ; and Development Test Site Center), Pasadena, loose coarse Calif. Wilson Cove, 24-in.diam 2 165 a Sen unknown 24-in. diam | piles BS cence maeal of 410,000 ft-lb. Hellas over bedrock | lateral Wilson Cove, 24-in.diam See Rb = 21 170 San Clemente unknown 24-in. diam | piles embedded A Island, Calif 36 ft eb elt ete ‘ over bedrock | 50,000-Ib load St. Andrews Bay ESSA, Miami St. Andrews 8) sipyrecting silty clay to penetration from M r 1961 3 7 2,100 each (W) 3x3 spread footing " - 5 lodel Studies Beach, Fla. Bay, Fla. 4-ft diam spread footing silty sand bearing capacity Petroleum : . I ' Miscellaneous Gompanter =20 varies varies varies eens varies unknown Institute of Miami three 12-in.- University of Marine Science, 1964 1 85 es any diam pipe piles unknown calcareous ne. eeereey Miami’s Reflector University of e driven 20 ft send nat and Cameras Miami, Coral Gables, Fla, numerous 50 to 100 spread footings dense /arenuler jfino'settlements material noted APL (Applied FORAC Physics Labora- Stations tory), University varies 100 to 2,600 varies unknown unknown unknown unknown of Washington, Seattle, Wash. University of Pipe Sections Rhode Island, =1968 unknown bay sediments Kingston, R. |. 28 o SALVAGER (CLEVIS) PADS CRANE PADS SNUBBING PADS JACKING PLATE BARS 4" x'/2" x 4/4" I BEAM 10WF60 I BEAM 10WF33 I BEAM 6WF155 pra-eoon0e Ti % - eth i 7 1m Gi: A CROSS BARS (On F H concrete blocks) i £ | me: Y Ly mE i ass 10" (0 26m) CF | L 36" (108m) 5 Se CH Ss —— hee ee ie pe 31 3° ——— (1. 48m) (954m) Figure 15. Load frame for ESSA plate bearing tests. Top: drawing and specifications. Bottom: photograph of frame being transferred (by crane) from wharf to suspension cables of U.S.S. Salvager. (From Harrison and Richardson, 1967. © University of IIlinois Press. Used by permission.) 2S) Concrete blocks, 48 inches in diameter, which apply 100 psf to the sediment surface, are employed as the standard footings during the LOBSTER tests. Settlement is measured relative to a stationary reference rod extending 10 feet into the sediment. The reference rod is protected from intermediate settlement by a 9-foot-long outer casing or isolating tube. In one test (Figure 16) multiple reference rods were utilized to monitor soil compressions at var- ious depths. Movement is recorded by either SCUBA divers (Figures 1 and 2) or an automated electronics package (Figure 3). Nine long-term tests (duration of observation up to 2 years) have been performed at sites near Port Hueneme, California, in water depths varying from 4 to 1,200 feet. The soils in all cases were soft cohesive materials with grain sizes predominantly in the silt and clay ranges. The sediments’ vane shear strengths at a depth of 12 inches varied from 0.2 to 0.5 psi. In general, the settlement data generated by these deployments (Figure 17, typical example) have confirmed analytical predictions based upon the magnitude of pri- mary consolidation measured during laboratory consolidation tests. Settle- ment predicted in this manner typically varied from 1 to 3 inches. However, the in-situ results also indicated a sur- prisingly large amount of continuing long-term settlement, apparently caused by secondary compression (about 4 inches in one case). Results of the in-situ deployments also indi- cated that undermining of the foundation by burrowing animals instrumentation LOBSTER footing sediment layer reference probe Figure 16. Early, shallow-water LOBSIERIstructure and hydraulic scour can cause large and reference systems settlement and, in some instances, for investigation of long- render the foundation useless. These term foundation behavior two effects have caused up to 7 and OM ne Semler. 8 inches of foundation settlement at One particular site. In the latter case, 7 inches of settlement caused by scour was accompanied by a tilting of about 20 degrees. This tilting is equivalent to a differential settlement of about 18 inches. A more typical value of differential settlement, resulting from primary and secondary compression only, was 1 inch. 30 Settlement of Model Seafloor Footings eS Pitas Point 2 a S—~a~r BD 9 i 3 Mugu Lagoon a] \ a a} s Be © « \ ze 4 7 a \ 5 5 Ve ® oh = animals ia] o 6 undermining \ a F footing \ = 7 \ 4 1 1.0 10 100 1,000 Log Time (days) Figure 17. Typical settlement data from LOBSTER tests. NCEL Plate Bearing Device. The NCEL plate bearing device (Figure 18) was developed in 1965 to determine the short-term in-situ bearing pres- sure and settlement response of marine sediments (Kretschmer, 1967). The tripod frame is approximately 7 feet tall and has overall lateral dimensions which allow it to fit within a 12-foot-diameter circle. Three articulated sup- port pads (each approximately 2 feet by 5 feet) connected to the legs of the framework transfer the weight of the device to the seafloor. Total pad bear- ing pressure when fully loaded is approximately 200 psf. Circular and square bearing plates, ranging in diameter from 6 to 18 inches, transfer loads of 0 to 5,500 pounds to the sediment during a controlled penetration-rate test. About 100 tests have been performed in water depths from 120 to 6,000 feet, at a number of sites off the Southern California coast. No difficulties have been experienced with the foundation system for the device. Results of the individual in-situ plate tests are discussed in detail by Kretschmer (1967), Kretschmer and Lee (1970), and Taylor (1970). NASL Deep-Sea Exposure Arrays. The Naval Applied Science Laboratory (NASL) placed two specimen racks in the TOTO as part of a material evaluation program (Macander, 1969). The racks, which were installed Sil in early 1967, were 13 feet tall and had a 10-foot-square base. The bearing surface area was approximately 15 square feet; the total weight of the struc- tures in air was 650 pounds. The tests were conducted in 4,500 feet of water. Sediments at the site were predominantly silts with shear strengths of 1 to 3 psi. One unit was removed in 1968, and the other will be removed later. No excessive settlement was noted on the recovered rack. Figure 18. NCEL plate bearing device. NCEL Submersible Test Unit. Seven Submersible Test Units (ST Us) (Figure 19), which expose material specimens to the seafloor environment at and just above the sediment line, have been placed by NCEL in water depths of 2,370 to 6,780 feet (Jones, 1965; Hironaka, 1966; Reinhart, 1969). An eighth STU was placed in 120 feet of water. The test units have remained on the bottom for intervals of 4 to 24 months. In most cases, the STUs were supported by two strip footings. The footings applied approximately 110 psf to the sediments. Sediments gener- ally varied between silty clays and clayey silts. The soil at the shallow-water location was predominantly sand size. 32 aMMRe A, Akhil + eater is Figure 19. NCEL STU. Estimates of total settlement were determined from mudline markings on test specimens. Total penetration values varied between negligible and 8 inches. No distinctions could be made between dynamic, immediate, and long-term settlement processes. Naval Research Laboratory STUs. |n 1961, a cooperative program of deep-sea test panel exposures was initiated in TOTO by the Naval Oceano- graphic Office, the Naval Research Laboratory, and the Naval Underwater Ordnance Station (De Palma, 1962 and 1969; Hersey, 1969). Three test units were placed in 5,800 feet of water about 3 miles off Andros Island, in the Bahamas. The 200- to 300-pound pyramidal arrays, supported on a silt-size calcareous 00ze, were constructed of 1-inch-diameter pipe with a 6-foot- square base. Of the three units placed in the spring of 1962, one was recovered 3 months later, another 34 months later, and the last has yet to be recovered. Settlement for the two recovered arrays was thought to be less than 1 foot, since test plates located above that elevation showed no effects from burial in the sediment. 39 The Naval Research Laboratory also has placed submerged test units at two shallow-water sites. During 1961, a cagelike structure was recovered monthly from a water depth of 300 feet near Fort Lauderdale, Florida. The array, which had a 3- by 4-foot concrete base weighing 200 to 300 pounds, was placed on a calcareous sand bottom. No sinking was ever noted. Another unit was deployed near Fort Lauderdale in 500 feet of water for 12 months. Sediments at the site were calcareous oozes. The unit, which used a deacti- vated mine for a base, weighed approximately 1,000 pounds. No settlement was noted when observed with television camera just prior to recovery. NUSL Transponder Block. A small transponder block was placed in the Long Island Sound near New London, Connecticut, by the Naval Under- water Sound Laboratory (NUSL). The water depth at the site was approximately 60 feet, while sediments in the area were predominantly sands. Divers observed that the 3- by 3- by 1-foot concrete block base and the acoustic relay cables have been partially covered with sand (Moothart, 1969). NUC Pop-Up Test Site. Two foundation types have been used by the Naval Undersea Research and Development Center (NUC), Pasadena (formerly Naval Ordnance Test Station), for pop-up tests conducted off the northwest tip of San Clemente Island (Gardner et al., 1969; Sutton, 1969; Ridlon, 1969). The first foundation was installed in 1958 to test Polaris-type missiles. The foundation, which was in 115 feet of water, employed a 30-foot-diameter by 9-foot-high concrete-filled steel caisson. This caisson was embedded 7 feet into the soil. The soil profile consisted of 8 feet of loose coarse sand atop a 6-foot layer of dense sand. A fractured andesite with pockets of gravel lay beneath the sand. This foundation supported a 400,000-pound launcher; additional dynamic compression loadings as large as 140,000 pounds resulted during individual tests. No foundation problems were reported. In 1960, a more complex launch system (Figure 20) was installed in 170 feet of water at a nearby site. The soil profile was essentially the same. This system had a static weight of over 700,000 pounds and resisted dynamic compression loads of up to 220,000 pounds during individual tests. The test structure was supported on four 14-inch-diameter by 65-foot-long drilled-in, grout-filled, pipe piles. Over 200 simulated launchings have been performed. Although no foundation monitoring was provided, it is known that the thresh- old sensitivity of other electronic equipment mounted on the structure (differential movement of less than 1/8 inch) was not exceeded. Two camera mounting piles, which extend to the ocean surface, have also been installed at the Pop-Up Test Site. These 24-inch-diameter piles were drilled in 36 feet and filled with grout. The piles were designed primarily to resist a maximum overturning moment of 410,000 ft-lb caused by wind and wave forces. The two structures have exhibited no serious foundations pro- blems. 34 a ; ‘ e = a - & — ——— a fitta Figure 20. NUC’s Pop-Up Launcher II. (From Gardner et al., 1969.) Twenty-one mooring piles were also installed in the seafloor surrounding the pop-up launchers. These 24-inch-diameter by 36-foot-long, drilled-in, grout- filled, pipe piles are similar to those used for the camera support. One of the mooring piles was tested in 1964 to evaluate its lateral load capability. Figures 21 and 22 show the in-situ test setup. A lateral load of 50,000 pounds caused a maximum deflection of 1/2 inch and maximum angle of deflection of 25 min- utes. 35 3/4-in.-diameter wire rope > ' height indicator, ; existing peg-top chain to pote nrometels le removed from pile instrument mounting four-part line stand fi load cell VE Pom (NS mi £ = STI UES aS 1! ‘ ny Uy i} eee pile no. 21 ‘2 pile no. 1 pile no. 15 mi i (8-5/8-in. OD) Ht (24-in. OD) (24-in.OD) yr os Figure 21. Pop-Up Site pile load test. (After Sutton, 1969.) St. Andrews Bay Model Studies. |n 1961, Keller (1964 and 1969) placed three concrete blocks on the shallow seafloor (water depth averaged 17 feet) to study the bearing capacity of spread footing foundations. Two test sites in St. Andrews Bay, Florida, were used during the investigation. The concrete blocks were rectangular, square, and circular in plan (Figure 23). Each weighed approximately 2,100 pounds in water. Applied pressures ranged from 164 to 246 psf. The soil at each site was sampled and evaluated. It varied froma silty clay to a silty sand classification and, in all cases, would be considered a weak and compressible cohesive soil. Results of the laboratory study were then used to estimate the bearing capacity at various levels of object penetration. Laboratory data indicated that the undisturbed strength of the soil could not support the blocks at the soil surface; thus, a bearing capacity failure was expected. The extent of block penetration was predicted by determining the depth at which the bearing capacity, based upon undis- turbed soil strength, had increased enough (assuming soil strength increased with depth) to support the block. However, the blocks penetrated beyond the estimated depths. Subsequent analysis of the data has shown that use of 36 remolded strength values in the bearing capacity equation predicts fairly closely the observed depth of penetration. The strains imposed on the soil mass as a result of the initial bearing capacity failure possibly caused remold- ing and the reduction in soil strength. 3/4-in.-diameter wire rope EA four-part line Cf (OF a “to pile no. 15 height indicator me - potentiometers instrument mounting 1-1/4-in.-diameter wire rope instrument orientation line (1/4-in.-diameter rope) to pile no. 21 Figure 22. Pop-Up Site mooring pile load test setup. (After Sutton, 1969.) Submerged Petroleum Production Facility. The petroleum companies maintain a few totally submerged structures. At least 20 production facilities (flow-line manifolds, separators, heat treaters, oil storage tankage, gas compres- sors, etc.) are currently in use on the seafloor. Most of these facilities utilize mat foundation systems. Mat foundations were generally selected because of the extremely weak soil conditions and because this type of foundation pro- vides good resistance to scour effects. No foundation performance difficulties have been reported. University of Miami Reflector and Cameras. The Institute of Marine Science at the University of Miami has been using a reflector and various pad- mounted cameras on the seafloor periodically for the past 5 years (Kronengold, 1969). The reflector is 24 feet in diameter and is supported by three 12-inch- diameter pipe piles driven to refusal (approximately 20 feet). The water depth 37 at the site is 85 feet; sediments are calcareous sand. No settlement has been noted. The cameras, supported on flat pads, were placed in 50 to 100 feet of water. Sediments at the site were a dense granular material. No settle- ments were observed. Rectangular Block Weight in air: 3,974 Ib Weight in water: 2,219 Ib Bearing pressure in water: 1.14 psi Square Block Weight in air: 3,970 Ib Weight in water: 2,214 Ib Bearing pressure in water: 1.71 psi Circular Block Weight in air: 3,700 Ib Weight in water: 2,076 Ib Bearing pressure in water: 1.15 psi Figure 23. Dimensions and weights of concrete blocks used in St. Andrew's Bay model studies. (After Keller, 1964.) Other Structures. The Applied Physics Laboratory (APL), a division of the University of Washington, maintains FORAC stations at various localities (Linger, 1969). The devices, placed in 100 to 2,600 feet of water, consist of tripods with transducers. No indication of unsatisfactory performance has been reported. 38 The University of Rhode Island has observed the settlement of simulated pipe sections on bay sediments. Results are to be compared to predicted values (Nacci, 1969). Habitats A number of manned habitats (Table 3) have been deployed on the seafloor. General observations of their performance are available. Other habi- tats are in the design or fabrication stages. In these cases, the details of the selected foundation systems are useful as case histories, since the systems display the thinking of the designer relative to his past experience and knowledge of foundation performance. Habitats represent a somewhat specialized set of case histories for several reasons. To date, the deepest deployment of a habitat for which any information is available has been 328 feet. Site selection for such deployments is usually heavily influenced by the requirement for good diver visibility. This requirement typically results in selection of sandy sites. In addition, considera- tion of the consequences of any sort of foundation failure (in terms of possible loss of human life) usually leads to an extremely conservative approach to site selection and foundation design. The following sections summarize some of the pertinent characteristics of various habitats. Conshelf One. During September of 1962, an 8-foot-diameter by 17-foot-long steel cylinder was anchored horizontally in the Mediterranean near Marseilles, France (Cousteau, 1963). Conshelf One (Continental Shelf Station One) became Captain Jacques Yves Cousteau’s first in a series of manned underwater habitats. The station, which housed a crew of two men for a week at a water depth of 33 feet, experienced no foundation problems. Conshelf Two. Cousteau placed his second underwater manned station, Conshelf Two (Figure 24), in June of 1963 (Cousteau, 1964). Con- shelf Two was located in the Red Sea approximately 5 miles northeast of Port Sudan. The main structure, Starfish House, sheltered five men for a month at a depth of 36 feet. Five telescopic legs with 4- by 4-foot bearing plates sup- ported Starfish House on a coral sand ledge. Lead ballast of 200,000 pounds was added to the habitat to provide negative buoyancy. During Conshelf Two, Deep Cabin, a 20-foot-long rocket-shaped underwater chamber, housed a two-man crew for a week at a depth of 80 feet. Although three telescopic legs with bearing plates were intended for support, extremely steep rocky terrain precluded their use. Instead, the Deep Cabin was anchored on the steep slope. A third structure, the diving saucer hangar, allowed Cousteau’s diving saucer to operate from a dry base 36 feet below the water surface. 3g The round hangar was supported by three 3- by 3-foot bearing plates on telescopic legs. Negative buoyancy was established by 120,000 pounds of lead. Except for the required revision of the foundation system for the Deep Cabin, no foundation difficulties were reported. Conshelf Three. A third station, Conshelf Three, was placed near Villefranche, France, in October 1965 (Cousteau, 1966). The 18-foot- diameter steel sphere was occupied at a water depth of 328 feet by a six-man crew for 3 weeks. The sphere weighed 280,000 pounds and rested on a 48- by 28-foot chassis that held 154,000 pounds of ballast, ballast tanks, and reservoirs of helium, oxygen, and compressed air (Figure 25). The entire assembly was supported by four legs with sediment bearing plates. Crew members obtained undisturbed sediment cores by forcing water cans into the bottom sediments. At the project’s completion, minor difficulties were encountered in breaking the feet free from the bottom. Several anxious minutes were required before breakout occurred. Sealab |. On July 18, 1964, the Office of Naval Research, in conjunction with other Navy activities, placed a manned undersea habitat next to Argus Island, approximately 27 miles south of Bermuda (O'Neal et al., 1965; Groves, 1965). Sealab | (Figure 26) was lowered by the Argus Island crane from the water surface 193 feet to the very dense coral sand bottom. The bottom, which was leveled prior to the deployment, exhibited a mini- mum amount of loose, soft material. The 9-foot-diameter by 40-foot-long station was fabricated by the Naval Ship Research and Development Labora- tory (NSRDL) (formerly Mine Defense Laboratory) at Panama City, Florida, from two mine sweeper floats. The Sealab’s 3,000 pounds of negative buoy- ancy were supported by two 3- by 40-foot rectangular bins which doubled as ballast tanks (Figure 26). The habitat housed a crew of four men for 11 days. No foundation problems were recorded. Sealab I|. Sealab || was the Navy's second major step in a continuing man—undersea research program. Three 10-man teams occupied Sealab || for approximately 15 days each (Pauli and Clapper, 1967). Habitation occurred between August and October of 1965, 3,000 feet off Scripps Pier at La Jolla, California, in 205 feet of water (Fehl, 1969; Tolbert, 1969). The habitat was essentially a nonpropelled submarine built to withstand an internal working pressure of 125 psi. The hull was constructed of 1-inch-thick mild steel, 12 feet in diameter and 57-1/2 feet long. When on the bottom, Sealab || was 26,000 pounds negatively buoyant. The bearing surfaces, two 3- by 18-foot pads extending fore and aft, were designed to provide a maximum bearing stress of 300 psf. 40 Table 3. Habitats a Foundation in , Name Operator Year No. of Structures Dest Location Wt (Ib) in Water, W, or Air, A Feubteuae eaten Bearing Seallnca Settlement Remarks (ft) Type Size (H) Type Pressure (psf) Mediterranean near ‘ Conshelf One | Jacques Cousteau 1962 1 33 Merselliesaerance anchored unknown No foundation problems. 36 Red Sea five bearing pads 4x4 unknown coral sand No foundation ean Terrain too rough for Conshelf Two | Jacques Cousteau 80 Red Sea anchored rocky planned footing founda- tion. 36 Red Sea three bearing pads 3x3 unknown No foundation problems. Conshelf aca estConsteatl 308 near Villefranche, foun bearionipada a5 x5 ‘unknown Encountered minor Three France i breakout problem. ONR (Office of Argus Island, , dense coral Sealab | NavallRecesren) 193 Pe nesetia 3,000 (W) strip footings two 3x40 12.5 nel No foundation problems. Oto 15.8 in. off Scripps pier at very fine of Extensive soils 26; IW 1 n . r * SealebiIl ONE as La Jolla, Calif. chee o ETAlds| [2 wolf 20 silty sand differential investigation performed, settlement coarse h 5 ; BOI feces neam Beech: 37,200 (W) fap fosting 20.66 x 18 100 calcareous | T° MOVEMENE | scour and fill. Florida Atlantic Fla. concrete detected Hydrolab ° sand University iF fi 50 near Riviera Beach, 37,200 (W) mat footing 20.66x 18 100 atrencnd differential Movement ASIC RG) Fla. concrete movement extensive scour and fill. Makeiliiebltatj tOceaniclenternrlses, OOM || Macen wu Oceagls 80,000 (W) strip footings | two9x70 >63 No foundation problems, 1 (Aegir) Inc, Center, Hawaii of Interior, NASA Beery, Tektite | rf 58 St. Johns, 20,000 (W) mat footing 15x37 36 coral sand No foundation problems. and General Electric Virgin Islands Co. Golubaya Bi hydrauli Used large surface buoy Chernomer | | Russia 1969 1 33 ai Ns HG 125,000 (A) ye unknown for support. Gale lifted jack! Sea ase sUPbons) and moved habitat. Chernomer II | Russia 1 115 144,000 (A) four legs unknown Deutsche, Babcock, and Wilcox 1968 1 33. East Sea four bearing pads 5-ft diam unknown (Germany) University of New two anchors, EDALHA\ 1 inknown ents) Hampshire AMEN ESV AINE Nb 6,000 |b each + my | —al Has adjustable legs to German 1969 1 75 off ele Ein two strip footings unknown compensate for uneven in North Sea bottom. areal Sprut Russia 1967-70 several 30 to 40 Black Sea anchored unknown Buoyant tent. continued 41 Table 3. Continued Fi i Foundation islet Sediment Operator No. of Structures fection Wt (Ib) in Water, W, or Air, A ey eon fea Bearing =e Settlement ipa ze Pressure (psf) Sublimnos Great Lakes four pads four2x2 unknown cohesive soils = No foundation problems. tL. soils with r University of Miami bearins Atlantis Bra anaes sed 1,000 continental shelf 64,000 (W) spread footing two 17x33 57 eens =| 72 pst —|— a= ifs = — | soils with planned 0 Bp =12,000 (W) four bearing pads | 12-ft diam ~26 pesting 6,000 capacity > 144 psf __| al =| Santa Barbara fanned 0 3 City College Remy 0 0:40 i aa 4 Wilson Cove, modified imil 11 Sealab I! ONR planned 1 610 San Clemente 26,000 (W) version of eel ~300 etre, Welle Island, Calif. Sealab |! ea lab graded sand Cobb Seamount, F \ no planned (0) 120 Pacific (near state appears'simllar simi lar to similar to ~63 of Washington) to Makai Habitat Makai Habitat Makai Habitat —~—— +} — ———— r same as Tektite | 1970 1 50 Virgin Islands similar to Tektite | similar to similar to similar to Tektite Il u 3 Tektite | Tektite | Bee Tektite | same as Tektite | 1970 1 100 Virgin Islands He 9 42 (‘uolssiuusad Aq pasq) “A1@190S a1ydeiBoayd jeuoien © “iaziay sine Aq Bunuleg “p9GL ‘neasnoDg Wo14) “asnoH YsseiS—ierqey OM] saysuOD “vz ainbi4 , Jo|!0} ay{146 Asojes0ge| = jooid>yseys woo14Jep uayo3! woo Buluip pue Bull} suauienb Buidaajs 43}U39 |04}U0D woo Apees sJaMous siayenb Buidaa|s 43 CAP FERRAT LIGHTHOUSE VILLEFRANCHE x “Power and communication cables R : from Cap Ferrat lighthouse hang “|; from steel-drum buoys. PHYSALIE \s oe Buoy exerts 3-1/2-ton oS : \ -__ upward thrust to keep “ : 7 J guide cable taut. Se se ; ONSHELF THREE dangles safely} beneath surface waves during | Sc ‘Telephone line speeds | orders from diving \ ' saucer, undersea eyes _ of the operation. SE LABOR lowers sea house. | Nylon guy from PHYSALIE ies CONSHELF THREE Jon guide cable. Bobbing column of buoys descends with the station. Sea pressure forces water into the drums’ air pockets and reduces their buoyancy, gently lowering the power id communication cabl es » CONSHELF THREE reaches OIL-WELL HEAD Figure 25. Conshelf Three. (From Cousteau, 1966. Painting by Davis Meltzer. © National Geographic Society. Used by permission.) 44 (G96L “le 39 [PANO Woy) ‘yeugey | qejeas “gz aunbi4 45 (‘LOG6L ‘4adde}D pue tineg Wos4) “rexgGeY || qejeas “Zz a4nBI4 “quwioo TEED) Asauiyoeus uolje}1]U9A adeosa Aduabiawa WOO JaMoUs pue ssaooe JajeMiapun Vag seyjeq 4a]eM ssaooe saddn 46 Corner spades, 15 inches in depth, increased resistance to lateral movements (Figure 27). Sediment in the vicinity of Sealab || was a dark- gray, micaceous, very fine silty sand with few marine animals and a trace of clay. Analysis of surface cores indicated that the material contained 81% sand, 19% silt and clay. Median diameter of the material was approximately 0.004 inch. Laboratory tests of sediment engineering properties gave the following results: angle of internal friction, 22 degrees; vane shear strength, 1.4 psi; buoyant unit weight, 52 pcf. In-situ tests of the seafloor indicated a minimum soil bearing capacity of 1,300 psf. A safety factor of three was used to minimize settlement. The seafloor at the site sloped to the southeast at approximately 8 degrees. Typical microrelief was of the order of 4 inches. When Sealab I! was positioned, instrumentation showed a 10-degree trim by the stern and a list to the port of 3 degrees. The habitat was then lifted about 10 feet from the bottom, rotated, and replaced. A check indicated a port list of 6.54 degrees and a bow-up pitch of 5.96 degrees; these angles did not change appreciably during the three weeks of occupancy. Since Sealab || was sitting at a lesser slope than the terrain, differential settlement was assumed to have occurred. Measurements on the footings indicated the following settlements: starboard aft, 9 inches; starboard forward, 15.8 inches; port aft, 9.2 inches; port forward, negligible. Later measurements found little additional settle- ment; therefore, settlement apparently occurred on impact or almost immediately thereafter. Hydrolab. During October of 1967, Florida Atlantic University placed an underwater research laboratory in approximately 50 feet of water, 3,100 feet offshore of Palm Beach, Florida (Stephan, 1969; Perry Oceano- graphics, 1970). The 12-foot-diameter by 20-foot-long habitat, which was designed and fabricated by Perry Oceanographics, was supported on a pre- stressed concrete foundation, 18 feet by 20 feet 8 inches (Figures 28 and 29). Bearing pressure exerted on the coarse calcareous sand bottom was approxi- mately 60 psf. Hydrolab remained in position for 11 months. During this period, no movement was detected. Scour and fill were noticeable but not large enough to cause undermining of the Hydrolab foundation. This habitat was modified to operate as a one-atmosphere, lock-in/ lock-out facility, and it was placed on the seafloor in 50 feet of water off Riviera Beach, Florida, during July 1969. The soil in the area was a dense sand. The same concrete base, with floodable ballast chambers, was used. In this instance, four 4-foot-diameter metal ‘‘cookie-cutter’’-type keys extended 1 foot below the concrete base. During October 1969, four men spent 2 days living in the Hydrolab during Project Powercel (Ocean Industry, Jan. 1970, p. 23). At the beginning of this project, no scour problems were noted; however, by the end of the 47 2 days, undermining of the concrete slab along a major portion of one side and a corner was obvious (Hallanger, 1970). The resulting pit was estimated to be 3 feet deep and to extend 3 to 5 feet under the foundation slab. Only a small portion of this pit extended beyond the slab. Bottom currents estimated at 3/4 knot were prevalent during the 2-day project. This strong bottom cur- rent obviously contributed to the undermining. Marine animals inhabiting the area may also have contributed to the pit’s existence and extent. An additional external effect may have resulted when a support ship was moored to one corner of the slab. Dynamic action of the mooring line might have caused an up—down movement of the habitat, resulting in a pumping action in the sediment. However, this movement was not noted by inhabitants. A slight increase in the inclination of the Hydrolab was observed by at least one of the aquanauts during the habitation. The inclination apparently had no adverse effect on the overall experiment. Makai Habitat || (Aegir). Aegir isa submersible habitat designed to support six men on missions for 14 days in water depths to 580 feet (FahIman, 1968). The 400,000-pound, three-section habitat is made up of two 9-1/2- foot-diameter by 17-foot-long cylinders which connect axially to a central 10-foot-diameter sphere. This structure is mounted athwart two large flood- able pontoons. The pontoons are 9 feet in diameter by 70 feet in length and rest directly on the seafloor during use. The structure is designed to be towed on the surface to the site, where ballast tanks are flooded. Two anchored lines are used as lowering guides. A third and fourth anchor block are suspended beneath the habitat complex and supply the additional weight required to make the complex negatively buoyant. Once these blocks are on the bottom, the complex becomes positively buoyant and must be winched down to the bottom. Additional ballast tanks, which are flooded after the complex is on the bottom, give a total negative buoyancy of 80,000 pounds. The system was designed to include four hydraulically oper- ated legs for leveling on slopes up to 10 degrees. Aegir underwent its first sea trial during November of 1969 when five men spent 2 days on the seafloor in 200 feet of water (Ocean Industry, Feb. 1970). Since no large difficulties were encountered during the overall test, it is assumed that the foundation performed adequately. Tektite | Program. The Tektite | habitat was placed on the ocean floor at Lameshur Bay, St. Johns, Virgin Islands, as a joint effort involving the Navy, Department of Interior, NASA (National Aeronautics and Space Administration), and General Electric Company (Pauli, 1969; General Elec- tric, 1969; Stevenson, 1969; and Pauli and Cole, 1970). A four-man crew occupied the habitat for 60 days beginning in February of 1969. 48 2 ks dead Shae Fos VEDA OLEAN SMIENCES INST ik aa Figure 28. Hydrolab Habitat. (From Perry Oceanographics, 1970. ©Perry Oceanographics, Inc. Used by permission.) The habitat was positioned in 58 feet of water on a 10-foot layer of coral sand. Bedrock underlies the sand. The sand surface at the habitat site was leveled using a bolted steel frame with a diver-manipulated traveling screed. This technique established a flat bearing surface within 2 degrees of horizontal. The undersea habitat structure consisted of two pressure hulls connected by a pressurized crossover tunnel and attached to a rigid base. Each pressure hull, a vertical cylinder with domed head, was 12-1/2 feet in diameter and 18 feet long (Figure 30). A reinforced rectangular box with. approximate dimensions of 15 by 37 by 6 feet formed the rigid base. After jetting embedment anchors in at the site, the 5,000-pound positively buoyant habitat structure was to be jacked down to these anchors. However, this plan was abandoned in favor of a deadweight anchor technique, primarily because no reliable embedment anchor performance data could be obtained. Four 2,500-pound steel clumps were used as anchors. Once the habitat structure was on the seafloor, ballast tanks were flooded, and addi- tional weights were added. The total resultant load, 20,000 pounds of negative buoyancy, was applied to the seafloor over the 555-square-foot bearing surface. No foundation problems were experienced. 49 (‘uoIssiuiad Aq pasq, “ou| ‘soi ydesbouessQ A11384@) ‘OL6L ‘so!ydesBoueasg Assag Wo14) *yNOAe7 qejoupAyH “6z aanbi4 uoljeAa} J apis uoljena| yuo 4 Mal/\ UBld (Mojaq uoljenaja Uuody ul UMOYS UO!}aS 4a]Uad) JOYDUY aja1NU0D Passaijsaig JO Mal / 49]U99 N1y} UO!IaS See BL =| ol |0 01 i 50 (‘UoIssiuiad Aq pasx “ed ‘e1ydjapeliyd ‘swesBo1g swiaysAs ues ‘UOISIAIG SWaISAS jeJUaWUOIIAU pue Ajjqua-ay “3 °DOO “OL6L ‘91439a/y jesauad Wos4) “jyeyiqey ay18a]1 “OF ainbi4 51 Other Deployed Habitats. Although a number of additional habitats have been used on the seafloor, little information exists on their performance. During the spring and summer of 1969, Chernomer |, a Russian habitat, was placed in 33 feet of water at Golubaya Bay in the Black Sea (Hydrospace, 1969). The 125,000-pound habitat utilized a large surface buoy for support. During a gale, the habitat was reported, in one instance, to have been lifted 3 feet off the seafloor—presumably by the surface support buoy. The habitat then dropped, and ‘’bounced on hydraulic base supports.’ Asa result of this treatment, the habitat assumed a cant of 40 degrees. Chernomer || was designed for use in water depths to 115 feet (Hydrospace, 1969). This habitat, which was to be nearly independent of surface support, is 10 feet in diameter by 25 feet long, weighs 144,000 pounds, and is supported on four legs. The German company of Deutsche, Babcock, and Wilcox deployed a habitat in 33 feet of water in the East Sea during the fall of 1968 and the sum- mer of 1969 (Ocean Industry, Jan. 1970, p. 12). The habitat was manned for 14 days and remained on the seafloor for 2-1/2 months. From photographs, the habitat appears to be supported on four footings. The footings are about 5 feet in diameter, and each is rigidly attached to a stiff leg. Students and faculty at the University of New Hampshire fabricated and deployed the 8-foot-diameter by 12-foot-long habitat, EDALHAB (Engj- neering Design and Analysis Laboratory Habitat), in Alton Bay, New Hampshire (University of New Hampshire, 1967; Undersea Technology, 1970). EDALHAB supported four men for 48 hours at a depth of 26 feet. The EDALHAB struc- ture is slightly buoyant. The foundation consisted of two 6,000-pound anchors. A second German habitat was deployed in 75 feet of water off Helgoland in the North Sea during the summer of 1969 (Hydrospace, 1969). Three teams of aquanauts spent a total of 22 days in the habitat. The habitat, which was left in place on the seafloor for use during the summer of 1970, is 8 feet in diameter, 30 feet long, and has a design depth capability of 330 feet. A large surface support buoy, moored by three anchors, provides required breathing gases and power. The foundation for the habitat consists of two strip footings, each approximately 2 feet wide by 30 feet long. The habitat is supported on footings by four adjustable legs designed to compensate for uneven seafloor topography. On several occasions during the past 3 years, the Russians have used a hemispherical fabric tent with a wooden floor as a habitat (Hydrospace, 1969). These habitats, called Sprut, have been used in the Black Sea to sup- port two men for 2 days at water depths of 30 to 40 feet. The fabric tents are buoyant and are anchored to the seafloor. In at least one instance, Sprut was secured to two submerged rocks. 52 Link demonstrated a similar rubber-walled habitat, Sea Igloo, in 1964. The rubber habitat supported a man for 24 hours in 33 feet of water (Link, 1964). An underwater diver rest station, named Sublimnos, has been used at 30-foot water depths in the Great Lakes (Somers, 1970). The 8-foot-diameter by 8-foot-long vertical cylinder is ballasted for negative buoyancy. The foun- dation consists of four pads, each about 2 feet square. This structure has been successfully located on cohesive soils. Other Planned Habitats. Atlantis was a joint planned program between the University of Miami and Chrysler Corporation (University of Miami, 1968; Chrysler Corporation, 1968; Breckenridge, 1969). The two organizations intended to emplace a 1-atmosphere manned laboratory on the continental shelf (to 1,000-foot water depths). The tentative habitat consisted of a horizontal cylinder, 12 feet in diameter by 80 feet long, applying a nega- tive buoyancy of 64,000 pounds to the seafloor through two 17-foot by 33-foot spread footings (Figure 31). Static bearing pressures would equal 57 psf. The overall design was based on the following criteria: 1. maximum bottom currents of 5 knots 2. soil bearing capacity of 72 psf 3. a maximum slope of 5 degrees Each spread footing is connected to the superstructure by a hydraulic leveling system. Preliminary designs for a similar manned underwater station (MUS) were developed by NCEL and several contractors (General Dynamics, 1968). The selected concept consisted of two vertical cylinders; one containing a nuclear power generator and the other housing six men. The habitat would be capable of 30-day missions in water depths to 6,000 feet (Figures 32 and 33). The structure was designed to be slightly buoyant until the addition of a 12,000-pound anchor clump. This clump would be placed on the seafloor and the station winched down to it. Upon approaching the seafloor, four boom-mounted footing pads would swing out and stabilize the station ina vertical position on slopes as steep as 15 degrees and in currents as large as 1 knot. The design was such that negligible loads would be applied to the seafloor soil by the 12-foot-diameter bearing pads. Design criteria assumed a soil bearing capacity of 144 psf. In the most critical situation, a Current- induced overturning moment would be resisted by a single boom-mounted footing pad. In this situation, a vertical force of 12,000 pounds (108 psf) and a horizontal force of 12,600 pounds would be transmitted by the pad to the seafloor. The circular pads were to be made of a permeable screen to aS) reduce the breakout forces. The pads were also to have a circumferential ring to protect against scour and presumably to act as a key to resist the horizontal forces. hydraulic package baseplate leveler Section A-A typical both ends Figure 31. Project Atlantis manned station. (From Chrysler Corporation, 1968. ©University of Miami and Chrysler Corporation. Used by permission.) Santa Barbara City College is fabricating an ambient pressure structure for temporarily sheltering several men (Hallanger, 1970). The structure, which will be deployed in 30 to 40 feet of water, will include a tower that extends above the air—sea interface. Three other habitats have been fabricated and will be utilized in the near future. Sealab III, the first of these habitats, is basically a modified ver- sion of the habitat used in Sealab I! (Eager, 1968; Dowling, 1969; Hallanger, 1970; Huh, 1969; Stiles, 1969). It was designed to be deployed in 610 feet of water near Wilson Cove on San Clemente Island, California. The seafloor at the site was investigated extensively by NAVOCEANO and was found to be basically a dense, weli-graded sand with occasional larger rocks. Average slope at the site was 3 degrees. 54 Figure 32. Artist's conception of NCEL Manned Underwater Station. 3) Figure 33. Model of NCEL Manned Underwater Station. The second habitat will be used during Project Seause (Battelle et al., 1968; Breckenridge, 1969). This project will study in detail Cobb Seamount, in the Pacific Ocean off the state of Washington. The rock summit of the sea- mount, which reaches to within 120 feet of the sea surface, has been studied indirectly with various types of instrumentation and directly by SCUBA divers. A habitat has been designed for use at the site. This habitat appears to be simi- lar to the Makai Habitat II (Aegir). The third habitat, a modified version of Tektite |, was used during the summer of 1970 in the Tektite 1! program (Ocean Industry, 1969). The same site in the Virgin Islands was utilized for a period of approximately 7 months. A new, two-man habitat, located at a 100-foot water depth, was also employed during a portion of the program. 56 Offshore Towers and Platforms Offshore towers and platforms differ from totally submerged structures in three major ways: 1. They are currently used only in the shallow portion of the continental shelf. 2. They extend through the air—water interface and are thus subjected to large wave forces. 3. They are often large and massive because of the magnitude of environmental factors encountered. Several hundred offshore platforms are in existence (Howe, 1967). These structures are located in water depths of up to 370 feet, have total weights in excess of 3,500,000 pounds, and use pile or caisson foundations almost exclusively as their permanent foundation systems (Figure 34). Platforms in shallower waters are often constructed on site, beginning with pile driving and continuing upward. For the larger offshore platform, the underwater substructure, which doubles as a guide for the pile driving, is usually prefabricated, towed to the site, and positioned on the bottom. The substruc- ture typically utilizes a spread footing or shallow caisson configuration for temporary support while the piles are being driven and grouted. These plat- forms are founded on soils ranging from sand to soft clayey silt. As much as 300 feet of pile penetration and as many as sixteen 56-inch-diameter piles may be required to resist the loads of larger platforms. In addition to these relatively permanent structures, there are about 100 drill rigs of the jack-up variety (Howe, 1969a). These rigs use large caissons, pads, or mats as their foundation system. The structures are movable and have been used in water depths to 300 feet. Total weights of the jack-up rigs range from 1,000,000 to 10,000,000 pounds. Maximum lateral dimensions may exceed 240 feet. Foundation pads or mats range from 20 to 120 feet in major lateral dimension (Figure 35). Specific information is available on a limited number of offshore platforms and towers (Table 4). Most information is considered proprietary and is, therefore, available only in generalized form. Generalizations concern- ing performance of petroleum structures (information collected from a number of sources) are summarized in the following paragraphs along with available specific performance information. Argus Island. Argus Island was constructed in the summer of 1960 as a Navy research platform (McDermott, 1960). This structure, which is similar to oil well drilling platforms, supports a two-story, 85- by 85- by OT TIILiL1L BSSSI Sele eieeelie Dn MAL NIVINY NIA tte DANA ANUTNVIIN VIN 1,200 tons XIX VA 20’ water depth = ats Sze| 340’ water depth 6,510 tons Figure 34. Typical offshore platforms for shallow and deep water. (From Schmid, 1969.) 58 24-foot-high building. The site is located 27 miles south of Bermuda in 193 feet of water. Sediments are dense coral sands. The platform is supported on four 30-inch-diameter by 5/8-inch-thick steel piles drilled approximately 50 feet into the sedi- ment and then grouted. No foundation problems have been reported. Khazzan Dubai 1. Khazzan Dubai | is a large submerged oil storage tank with a capacity of 1/2 million barrels (Chicago Bridge and lron, 1969). Pumping and control facilities extend above the water surface. Its physical appearance Is that of an inverted funnel, 270 feet in diameter and 205 feet high (Fig- ure 36 and 37). Khazzan Dubai | was installed in August 1969, 58 miles off the shore of Dubai in the Arabian Gulf. The 30,000 ,000- pound open-bottom structure rests ona perimeter footing in 160 feet of water. The perimeter footing also contains guides for 30 anchor piles spaced around the perimeter. These 36-inch-diameter piles pene- trate 90 feet into the seafloor. The structure—foundation interface was designed to withstand the scouring action caused by a 3-knot bottom current. No problems have been reported to date. NSRDL Towers. The Naval Ship Research and Develop- ment Laboratory in Panama City, Florida, has operated two oceano- graphic towers off the coast of Florida since 1957 (Mine Defense Laboratory, 1964; Toske, 1969). The larger tower, Stage One, is located in 100 feet of water and has overall dimensions of 105 by 105 feet. The struc- ture is supported by sixteen 30-inch-diameter piles embedded 60 feet into a medium dense to very dense gray silty sand. Pile capacity is 760,000 pounds. Stage Two, the smaller tower, is 60 by 84 feet and is located in 60 feet of water. Eight 24-inch-diameter steel piles arranged in a 60- by 60-foot square support the structure. The upper 50 feet of sediment at the site contain medium dense blue, green, and gray coarse sands. Below that depth is a dense gray silty sand. Each pile, which has a capacity of 540,000 pounds, is embedded approxi- mately 70 feet. No foundation problems have been reported. NELC Tower. An oceanographic research tower was constructed for Naval Electronics Laboratory Center (formerly the Navy Electronics Labora- tory, San Diego) in 1959 (LaFond, 1965). The tower is located in 60 feet of water off Mission Bay, San Diego. The main tower extends 90 feet above the waterline. Four 12-3/4-inch-diameter open-end steel piles support the struc- ture. Maximum load on each leg is 140,000 pounds compression and 115,000 pounds tension. Subsurface exploration with probing and drilling techniques was utilized at the site to establish sediment logs (Dames and Moore, 1959). Water-jet probing reached 63 feet below the seafloor. A weathered conglom- erate was encountered at that depth. Borings were made approximately 10 feet from the probings. A log of one of the borings is shown in Figure 38. Undisturbed samples were taken and tested. In addition to routine tests for soil engineering properties, the laboratory study established friction charac- teristics between soil and steel. An effective angle of friction of 21 degrees was measured between steel and medium- to coarse-grained sands with shells (material found in the upper 30 feet), and a value of 19 degrees was measured between steel and loam and fine-grained sands (material found below 30-foot depth). No foundation performance problems have been reported. Tektite | Pile Guide System. During the on-site preparation phase of the Tektite | program, a pile foundation system was used in 32 feet of water for stabilizing and guiding a habitat-transporting barge (General Electric, 1969; Hallanger, 1970). After the barge was flooded and lowered, the habitat was to be floated off. A steel pile (about 21 inches in diameter) was driven to refusal through each of the four corner guides on the barge. The barge was left moored and floating in this condition overnight with plans to commence the controlled flooding and lowering operation the following morning. Seas were reported to be calm during the night; however, the next morning It was found that all four piles had snapped off at the mudline. Subsequently, the piles were redriven, and the flooding and lowering operation commenced immediately. This approach was successful. Sg) transverse derrick skid carriage whirley UPPer helicopter deck deck safety net longitudinal skid carriage SS Bao ti-0 } © oh @ b fh) o ooo oo foo o & ) Mat and Drilling Platform Figure 35. Typical jack-up rig with mat foundation. (From Schmid, 1969.) 60 Table 4. Offshore Towers and Platforms J Load P Embedment 1 h Fi it i Name Operator pee No, of Structures Ry Location a Per Foundation pesaey Depth rear pe) Pat) Remarks v Member : (ft) Yeo pel | 27 miles south of dense coral Argus Island Navy 1960 1 193 Bade le le | four 30-in.diam 50 eee i No foundation aes 270-ft-diam 2 near Dubai footing and footing with Khazzan Dubai | 1969 1 160 Arabian Gulf piles Rlesecerel 90 No foundation problems. around perimeter off west coast of a “ “ very dense ‘ 1 1 7 . -in. [ NSRDL (Naval Ship 00 Florida piles 60 ,000-Ib capacity sixteen 30-in.diam 60 aiyalisy ena No foundation problems. NSRDL Towers | Research and Devel- 1957 opment Laboratory) medium dense P Y 1 60. similar piles 540 ,000-Ib capacity eight 24-in.-diam 70 blue-green No foundation problems. coarse sand medium to NELC (Naval 3 - is Mission Bay near é 140,000-lb compression four 12-3/4-in.- coarse sand “ E if i y NELC Tower Electronics Labora: 1959 1 60 San Diego piles 115,000:lb tension alae 63 eae beck No foundation problems. tory Center) silty loam Navy, Department , I ff [sess (Pile | of interior, NASA, 1969 1 aah ie Fameshure sey. piles four 21-in-diam | S¥8' | coral sand Flies Soap ren iostidariog Guide System) Virgin Islands refusal night. General Electric 5,300 ,000-Ib compression loceeand St. George's Bank “ 720 ,000-Ib horizontal 24,000 at 30-ft 4 itled. 55 east of Cape Cod caissons 1 800,000 ft-lb three 15-ft-diam 48 See eg Penarerion Dismant bending moment 7,100 ,000-Ib vertical off ; 1,100 ,000-Ib horizontal similar to - er 14-ft 60 Dismantled. Texas Towers Air Force 3 55 Nantucket Shoal caissons 33,000,000 ft-lb three -diam aaa i bending moment 75 mil 6 800,000-Ib vertical ae le goegteseae? caissons | 820,000:b horizontal | three 12-1/2-tt- Destroyed by sea-action, re 7 structural failure. Newvereiterbon negligible bending diam moment 61 6961 ’ (Auedwog uo4| pue abpig obeo1yg yo Asayinos ojJ0Y4g uos| pue abpiig obea1yD Wo14) “Az!0e4 |10 pabsawiqns yo Uo!}daouOd s IsIUIY “QE a4nbI4 ee 2 IAA Mai BBS sa ses 63 he. * Figure 37. Khazzan Dubai | being towed to site. (From Chicago Bridge and Iron, 1969. Photo courtesy of Chicago Bridge and Iron Company.) 64 water depth—57 feet at 12 noon, Dec. 22, 1958 brownish-gray medium to coarse sand with many shell fragments 10 indicates number of blows of a 350 pound buoyant weight dropping 24 inches, for \ 1 foot of sampler pene- tration 350 a5 20: 400 | Butsaauibuz |iAig jeaen ‘passnosip aie aoualsadxa pue UO!JeWOJU! YONs $o Bulseys ay} ul! UO!T -PJ8d009 PanuljUOD JO} Paau Puke anjeA ay} Pue ‘UBisap UO!JEPUNOJ 1OO}JeaS $O Pjaljy BY} OF pue uoljeyjeysul ue $O UO!e1ado ay} O} YIOQ ‘HulsOYUOW BDUeLUIOJJad UO!JEPUNOY $O anjen ay ‘Paullwexa ase sainjie} |eianas yO ‘sasned ajqeqoid Jo ‘sasneo ay] ‘ainjle} paouaisadxa pey %E |euoljIppe ue Pue sWajgoid aoueWO}Jad paoualiadxa pey %p ‘paipnys suoijzeyjeysul OOF Ajalewixoidde ayi yO “pasino9s0 aney sainjley eau pue sainjiey UO!}EPUNOY $oO Jaquinu eB }eY} [panei Apnys Siu} $O S}/NSay “JUaWUOJIAUA JOO}JeaS aNbiuN ayy Aq pasodw) suolj}IPUOS a4] BWODIAAO 0} Maj & Aq pazi|!zN Pue PasiAap Uaaq aney YdI4M paualUNoop ase suO!esnbyy -UOd UO!}EpUNO} aNbiuN jesaNag ‘UBlsap UOIJepUNOY Hulinp pasapisuOd AjjeW4OU YOU SWa|qoid Jesoineyaq ajeo!1pul Sbuipuly awWosg ‘pazAjeue ase SaliOj}siy ased Jo AaquINU YY “138384 Q0O0'ZL 0} OZ Wo4} syydap 41a}eM Ul pazed0] $}9alqo 19430 sNoJaWNU pue ‘sAe1e JI}sNode ‘sjeyIqey ‘ssaMO0} BIOYS}JO aPNoU! suO!}e]JeSUI aSaY | “PAZeLULUNS ase SUO!}e||e}SU! 100] eas 4O JaqUUINU e $O aoueWOJJad UOI}EpUNOY pue ‘SiajalWeJed UBIsap UO!NePUNOY Iiseq ‘S91}Si49jDe41eYS ay | L-OLELe | aouewojiad UOl}epuNO 4—Sainjonsys JaJeEMJapUup-) “| palyisse|our) LZ6L eunr sniii'd 7g LEH UUeWIa} “S °H pue uosiapuy “5° Aq ‘S3IHOLSIH 3SVO 4O SISAIVNY ‘SNOILVGNNO4 4¥OO1SV4AS Asoyesoge Buisaauibu gz jinid jeaen LL a ee eee ye Unclassified Security Classification DOCUMENT CONTROL DATA-R&D (Security classification of title, body of abstract and indexing annotation must be entered when the overall) report is classified) Me ar : : Unclassified Naval Civil Engineering Laboratory 2b. GROUP Port Hueneme, California 93043 a as eer 3. REPORT TITLE SEAFLOOR FOUNDATIONS: ANALYSIS OF CASE HISTORIES 4, DESCRIPTIVE NOTES (Type of report and inclusive dates) Not final; December 1969—June 1970 5. AUTHOR(S) (First name, middle initial, last name) D. G. Anderson and H. G. Herrmann 6. REPORT DATE 7a. TOTAL NO. OF PAGES 7b. NO. OF REFS June 1971 84 111 8a. CONTRACT OR GRANT NO 948. ORIGINATOR'S REPORT NUMBER(S) ES HO TR-731 9b. OTHER REPORT NO(S) (Any other numbers that may be assigned this report) 10. DISTRIBUTION STATEMENT Approved for public release; distribution unlimited. 11. SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY Naval Facilities Engineering Command Washington, D. C. 20390 13. ABSTRACT The characteristics, basic foundation design parameters, and foundation performance of a number of seafloor installations are summarized. These installations include offshore towers, habi- tats, acoustic arrays, and numerous other objects located in water depths from 20 to 12,000 feet. A number of case histories are analyzed. Some findings indicate behavioral problems not normally considered during foundation design. Several unique foundation configurations are documented which have been devised and utilized by a few to overcome the conditions imposed by the unique seafloor environment. Results of this study reveal that a number of foundation failures and near failures have occurred. Of the approximately 400 installations studied, 4% had experienced per- formance problems and an additional 3% had experienced failure. The causes, or probable causes, of several failures are examined. The value of foundation performance monitoring, both to the operation of an installation and to the field of seafloor foundation design, and the value and need for continued cooperation in the sharing of such information and experience are discussed. FORM (PAGE 1) DD 2%"..1473 Unclassified S/N 0101-807-6801 Security Classification Unclassified Security Classification KEY WORDS Seafloor foundations Ocean-bottom facilities Undersea installations Offshore towers Offshore platforms Habitats Acoustic arrays Deep-sea construction Manned underwater stations Foundation performance Seafloor soils engineering FORM DD J0r"..1473 (Back) Unclassified (PAGE 2) Security Classification TS stories TUES 8 | Reeth aN a, 4 12 |