TN- 1133 Technical Note N-1133 SPECIALIZED ANCHORS FOR THE DEEP SEA - PROGRESS SUMMARY By J. E. Smith, R. M. Beard, and R. J. Taylor November 1970 This document has been approved for public release and sale; its distribution is unlimited. NAVAL CIVIL ENGINEERING LABORATORY Port Hueneme, California 93041 SPECLALIZED ANCHORS FOR THE DEEP SEA - PROGRESS SUMMARY Technical Note N-1133 YF 38.535.004.01.001 by J. E. Smith, R. M. Beard, and R. J. Taylor ABSTRACT Five anchor design concepts have been explored in conjunction with the program to develop an improved deep sea mooring capability. The knowledge gained from study of these anchor concepts, (1) ''Free-fall", (2) "Pulse-jet", (3) “Explosive”, (4) “Padlock”, and ©) "Vibratory", are summarized in this report. The vibratory anchor is currently the center of the deep sea anchoring development effort. A first generation design has demonstrated the concept to be feasible. Tests have shown that improvements are required for the vibratory anchor. An analytical study has been performed to assist in optimizing a second generation design. Improve- ments incorporated in the second generation design will be based on information from tests of the first design and the analytical study. The improved design will be tested in a range of seafloor sediment types and water depths to rate its capabilities and establish its reliability. This sale; its 4d atat CONTENTS INTRODUCTION . Background. Requirements. Modified Anchor Criteria. ANCHORS SYSTEMS VREV DEW.) 0 ey ens ee The '"Free-fall" Anchor. Design Considerations. Description and Results. Explosive Embedment Anchors History. Description. Tests and Results. Pulse-jet Anchor Concept. Background... . Description. Results and Conclusions of Investigation . The Padlock Anchor. Background . Description. Mees eincl RESswIliess 5 6 6 6 5 6 wun i TL | 0301 0040 ataal page 24 27 page TSO, WATRVNITORA, AINCRIOIR SWS 56 6 o 6 066 oOo Sl Backeromnds, 6 6 0060600006000000050006050 3] Desert rloml o 5 6 0 oo 6 6 0 6 6 00 0 0 oo 0 oO 32 Appurtenant Instruments ..... +++ +++ ++ ees 35 Ganeicall MeEsic Ricogrcen einGl Wie@eScleF®S 5 co o 0 6 6 6 6 Oo 6 37) MWESE RESMITESs 6 6 o-0 6 16 0 6 0 0 6 6 6 610 56.6 6 & oO Oo 41 Operation I - Long Beach Harbor, harbor soil. . . 4] Operation II - Santa Catalina Island, sand... . 41 Operation III - Santa Catalina Channel, deep MESES woe lo OF GO. 6 0% 0 ro. ONS. Oo 42 Operation IV - Santa Barbara Channel, deep water . 42 Operation V - San Clemente Island, sand. ..... 43 OQoararilem Wil = Seneca lake, Gllay soo o:5 0000 6 43 Operation VII - Port Hueneme, sandy-silt ..... Ak OpErAENOM WAQLIL = Riiices Pome, Cllayestile, 5 0 0 5 6 4d Opitiml vation Oi Desdlemle o ¢ 6 0 6 0 6 0 oo Oo BOO 45 Backerouma 5 56-06 506006006000 00050000 45 Ameulyesleall Pimocecies o 0 5 6 0 6 56 00 0 8 OO 49 SUMMARY /NNID) CONGIDUSIONS, 6 56 0 6 0 00 600510060600 0 57) ISIOAEUIRU, WORK, 6G o 6 6 0 6 6 0 60 60006006000 50 0.6 0600 0 SY IRIIRIINGIES 6 5° 06 0 6 0.0 0 0 0 06 66 0 6 O10 6.00.60 6 0 0 60 iv INTRODUCTION Background Anchors and anchorage systems are an important but neglected area of development in the greatly expanding field of ocean exploration and exploitation. There are requirements for sophisticated structures and instrument arrays plus other constructions to be positively and reliably secured in position on and under the sea in depths and locations not normally associated with anchoring. Yet, while intense effort is being expended on design and development of the constructions, attempts are made to hold them in position with dead weights and/or with conventional anchors ill-suited to the unusual demands put upon them. The U. S. Naval Facilities Engineering Command is sponsoring a program at the U. S. Naval Civil Engineering Laboratory, Port Hueneme, California, concerned with improving anchoring capability for mooring Navy equipment in the deep sea. Early objectives are to obtain a functional anchor design with a working holding capacity in the range of 25,000 to 50,000 pounds and operational in depths to 6,000 feet in seafloor sediments. An anchor with this capacity would provide a practical advantage over use of dead weights and conventional anchors. The 6,000-foot depth affords a practical anchoring capability throughout all continental shelf areas plus many strategic ocean areas beyond the continental shelves, e.g., sea mounts. Later objectives include anchoring capacities in the 100,000 to 300,000 pound range and an operational depth capability to 20,000 feet. At this stage in the program, a vibratory anchor design that appears to approach the early objectives of anchoring in soft sediments has been achieved. Also, valuable knowledge on other anchor designs and techniques has been gained. This report traces the history of the program and describes the present status of the vibratory anchor. Requirements There is a wide variety of structures and constructions for which deep ocean anchorage requirements exist. Mooring configurations to meet these requirements may be placed in four major categories: surface- single leg; surface-multi-leg; subsurface-single leg; subsurface- multi-leg. In addition, new areas of construction effort involve bottom rest structures for which the term anchorage may properly be applied to refer to the means of supporting and restraining the structures. The types of structures for which deep water moors are needed include oceanographic data buoy stations, surface and subsurface instrument arrays, ships, submarines beneath the surface, and manned or unmanned sea platforms. As yet, it is not valid to label any deep sea moor as a typical design. Some significant deep sea moors have been accomplished that illustrate both the requirements and the problems. Among these are the Tongue of the Ocean II (TOTO IIL) moor for large surface vessels, Figure 1, Naval Oceanographic Meteorological Automatic Device (NOMAD) anchor system, Figure 2, and the U. S. Coast and Geodetic Survey, Undersea Stabilized Platform, Figure 3, (Smith, 1965). Several underwater instrument array anchoring methods are depicted in Figures 4 and 5. It is noteworthy with respect to problems of deep sea moors that a moor system similar to the undersea stabilized platform design that was installed in 4,000 feet was attempted in water 18,000 feet deep. It was unsuccessful and a major difficulty pertained to lack of adequate anchors specially adapted for use in the deep sea (Interstate Electronics Corporation, 1970). Modified Anchor Criteria Conventional anchors have evolved through the ages into efficient implements to meet holding requirements under many operational conditions. There is much diversification in sizes, shapes, and arrangement of components of conventional anchors. However, all conventional anchors share certain characteristics that can serve to good advantage in meeting conditions for which they are designed but which are detrimental in deep ocean applications. They must be dragged in order to embed and develop rated holding capacity. The dragging force must be applied parallel or near parallel to the seafloor. They then are able to resist maximum forces only from the direction in which they were dragged. Forces from other directions and/or uplift forces greatly reduce their holding capability. One other limitation is that the performance of conventional anchors in hard seafloors is erratic and unreliable. In such conditions, they do not embed but depend on holding by falling into a crevice or by snagging on a protrusion or outcropping. These characteristics demonstrate the unsatisfactory nature of conventional anchors for deep water applications. Large scopes of line and other connective gear are required first to apply the forces parallel to the seafloor to effect embedment and second to maintain the parallel force direction during use. Attendant surface operational and coordination problems in handling the immense amounts of line and in maintaining correct position and course of work platforms during placement are acute. 4 °(G96L ‘UatTWS) weasks o8et10yoUR TT OLOL ‘TT eansty Zoyoue IMT qI-000‘9 xoadde ,go¢‘¢ :yadaq See SS sepoue qT -O0V ,09€ oO *sioyqo oy. worz ROGE Peaverto sl Ue a = se “TH Pue TH S3eT uo pez TWO Seapouy GE ‘aTBOS 0} Jou 3mq ‘T SSS ,0SS°€ pEOHCN SSS SS = CH BT sgupaqs [= |S \\ epoue - 9 [2 =— ue ee iN Zz, | | | Hl) i | yy (! Della | | | OSL ° 2 aT qeo tests ,h/T-T sgn aTqeo TeAetazqer 7 /T-T apoue - ¢ eTqeo quepued ,.8/¢-T AON 9}eTpewz9jUT , omg ff es 7 7 A aleTpewizequt konq utew 1000 ‘T ,00T ‘9 ,009‘€ ,002*OT automatic weather station ocean surface , "NOMAD" buoy shackle thimbled eye 3/4" chain and shackle thimbled eye and shackle 5,000' 3/4" dacron cable 1,875 fathoms 10,000' 3/4" polypropylene cable thimbled eye and shackle 3/4" chain 500-l1b anchor 1-1/4" chain Figure 2. NOMAD anchorage system (Smith, 1965). nA NNN) “(S96L SURTWS) wWIOsFQeTd peZTTTqejis eestepun “E sANSTY unip [ee2q7S PeTTLJ—-eqe10uU0D aoyoue yzIOFUeG qT- he o 1 o 1) ns e BS 46 spunod QooT ‘peot Time, Minutes Typical load and displacement data. Figure 23. Information on the breakout forces necessary to extract objects that are embedded in the seafloor is not plentiful; however, there is considerable information on this subject regarding terrestrial soils. Unfortunately, most of this information is related to the breakout resistance of shallowly embedded objects. Common practice has been to extend shallow breakout theory to the case of deeply embedded objects. This procedure is not applicable to extending shallow foundation design theory to deep foundation theory so it is probable that this procedure is not applicable to the similar problem of anchor breakout. Therefore, new analytical techniques were required to determine the breakout resistance of deeply embedded objects. Results of the research on shallow anchors indicate that such anchors form failure surfaces that are dependent upon soil type and soil density. Small-scale model tests at Duke University (Equivel-Diaz, 1967; Ali, 1968; and Bhatnagar, 1969) show that the shape shown in Figure 24 occurs only in the case of relatively shallow anchors in dense sand or stiff clay. For shallow anchors in loose sand or soft clay, the slip surface, though not clearly established, is closer to being a vertical cylinder around the perimeter of the anchor. Figure 24. Slip surface for a shallowly embedded circular plate. Deeply embedded anchors do not fail the soil in general shear failure such as that shown in Figure 24, regardless of the relative density of the soil. Experiments indicate that they can be moved vertically for considerable distances by producing a failure pattern, Figure 25, similar to punching shear failures in deep foundations (Vesic, (1969). Only after being pulled up to relatively shallow depths may they eventually produce general shear failures such as shown in Figure 24. 47 Figure 25. Slip surface for a deeply embedded circular plate. As presented in the section on Tests and Results, NCEL and OS&E have tested the anchor in several types of soils. In some instances very good penetration did not produce adequate holding capacities. In other instances, rather poor penetration produced relatively high holding capacities. One extreme example is a series of tests conducted at Seneca Lake by OS&E where penetrations were not limited. (This particular test series was not part of the Laboratory program and is not included in the test results.) An anchor system similar to the NCEL vibratory anchor achieved exceptional penetrations (over 50 feet), but breakout resistances were minimal (less than 15,000 pounds). It should be noted that in these tests a more powerful vibrator unit was used and the support guidance frame was not used thus permitting the vibrator unit to follow the fluke-shaft assembly into the soft sediments. At the other extreme are tests conducted by NCEL in a sandy silt where desired penetrations were not achieved, but results indicated that the 48 holding capacities would have been more than adequate if the desired penetrations had been achieved. From these tests it was evident that the first generation vibratory anchor is not a balanced design; i.e., one that matches the energy required to achieve proper embedment with fluke size to obtain the rated holding capacity in different types of seafloors. A vibratory anchor with a balanced design would, for a fixed amount of energy, embed into most seafloors and develop the same rated holding capacity. Unfortunately, in some seafloors, such as coral or rock, the anchor may not be functional because all available energy might be expended with little or no penetration and no consequent holding capacity. However an approach to an optimum vibratory anchor should be possible for most seafloor sediment conditions. To develop such a design, the relationships between fluke size, depth of embedment, breakout force, vibrator driving capability, and soil characteristics must be established for the soil types to be encountered. Once these relationships are established, a vibrator can be selected that has sufficient energy or force to drive different sized flukes to appropriate soil depths to achieve the desired capacity. The resulting vibratory anchor design will utilize a vibrator of one size with a fixed amount of energy available and have different fluke sizes for different seafloor soils (i.e., large flukes for low strength soils and small flukes for high strength soils). This accommodation will best utilize the fixed amount of energy available. Analytical Procedure. The sequence of events for the attainment of an optimum vibratory anchorage system was: (1) Determine the relationship between breakout force, fluke size, depth of embedment, and soil shear strength for cohesive and non- cohesive sediments. (2) Determine the penetration capabilities of the existing vibrator (10 kip force) for various fluke sizes and sediment types. (3) Determine the adequacy of the existing vibrator to achieve desired penetration and capacity. (4) Determine the most suitable fluke sizes to utilize the fixed amount of force available (10 kip) for both cohesive and cohesionless soils. The first step of the optimization was the analysis of the breakout resistance of embedded anchors. An analytical procedure, based on Vesic's (1969) analysis of the problem of the expansion of a spherical cavity close to the surface of a semi-infinite plastic solid, was used to determine the relationships between breakout force, fluke size, depth 49 of embedment and soil characteristics. Vesic's theoretical analysis was chosen because his results show good agreement with model tests of anchor breakout in the case of soft clays and loose sands (both typifying ocean sediments). Vesic's analysis was based upon the assumption that the shape of the slip surface during pullout is as shown in Figure 24. This type of failure is referred to as general shear and as previously mentioned in the Background section, occurs with "shallow" anchors. Vesic's theoretical solution gives the ultimate radial pressure needed to breakout a spherical cavity below the surface of a solid. The relation- ship is as follows: va} I — nN + aT cN Tee (1) where q_ = radial pressure (holding capacity) c = soil cohesion Ne oe e @ N =F + 1/2 D/B q FF = cavity breakout factors = buoyant unit weight of the soil D = embedment depth B = circular plate diameter For each soil, there is a characteristic relative depth D/B (D/B = ratio of depth of embedment to fluke diameter) beyond which anchor plates start behaving as "deep" anchors and beyond which breakout factors reach constant final values (Vesic, 1969). The failure pattern for deep anchors is similar to that occurring under deep foundations and is referred to as a punching type failure, Figure 25. To account for the changes in failure patterns, Vesic's results were tempered with engineering judgment and used in this analysis. The analysis is best explained by referring to Figures 26 and 27 where graphs of long term static breakout force versus depth of embedment for various fluke sizes are presented for an ideal sand and an ideal clay. 50 Depth of embedment, D (feet) Static Breakout Force, Bs (kips) for c/p = .5 To determine Fo for other values of c/p use: 40 . c/p + Be Saw Figure 26. Breakout force versus depth of embedment for an ideal clay; ¢ =o, = 90 pcf. 50 60 Yq 51 OcT ‘god OTT = Lt “o = 5 ‘pues [eepr ue 1A0F jueupeque jo yjdep snsieaA adT0Z JNoYesIgG Je,owerp syNTF G< @/d 2e JUeIsUOD OOT 08 09 Ov (sdty) Ls ‘a010q Jnoyeerg O17eIS °/@ ernst y Oc SG oO N Ww) = (1207) Gd S‘jUeuUpeque jo yzdeq (2) -l 52 To simplify the analysis for ideal clay, Figure 26, depth was plotted for a single c/p ratio of 0.5 (c/p = ratio of undrained shear strength to vertical effective pressure). Most seafloor clays are normally consolidated and can be classified by a constant c/p ratio, whereas most terrestrial clays are overconsolidated and exhibit variable c/p ratios with depth. The results were plotted to separate the cohesive (F,) and the overburden (F,,) components of the total breakout force (Fp) and to permit calculation of breakout force for clays with various c/B ratios. Breakout force was calculated using the breakout factors provided by Vesic, in Equation 1; however, the breakout factor N, was limited to a maximum value of 12. Previous researchers (McKenzie, 1955; Hansen, 1953) have shown that ''deep" anchor blocks exhibit breakout factors N. of 11 to 12 which roughly correspond to bearing capacity factors for "deep" foudations (Skempton, 1959). The points at which anchor behavior changes from a shallow to a deep anchor are indicated by slope changes in the lines of equal fluke size. Figure 27 presents plots of breakout force versus depth for an ideal sand initially in the loose and dense state corresponding to friction angles of 30 and 40°, respectively. Most seafloor sands are thought to fall within this range. As previously mentioned, available data suggest that the limiting relative depth, D/B, in sand, where punching failure begins, may increase from 2 in loose sand to over 10 in dense sand. Seafloor sands will generally be of low density; however, anchor embedment by vibration will cause densification. Being moderately conservative, all sands prior to anchor breakout are assumed to be of medium density. It has been shown (Baker and Kondner, 1966; Kalajian, 1969) that sands of medium density will change from a shallow to a deep anchor at a relative depth D/B of approximately 5. Therefore, for relative depths >D/B = 5, the breakout factors N, used in Equation 1 are constant. The points at which anchor behavior changes from a shallow to a deep anchor (where Ng = const.) are noted by slope changes in the lines of equal fluke size. The breakout forces presented are long-term static forces and do not take into account the effects of creep in clays and loading conditions other than static. Modifications of the breakout forces in consideration of these factors will involve considerable engineering judgment and a thorough understanding of the loads applied to the anchor mooring system. The second step was to analyze the penetration of vibratory anchors. A simplified method for predicting the depth of embedment is to equate vibrator driving force to static soil resistance. This technique is based on experience gained with vibratory pile drivers, which under tough driving conditions, fail to advance the pile further into the soil when the total weight plus the maximum driving force generated by the vibrator is less than the total static soil resistance to penetration (Schmid, 1969). 53 The equation used to calculate anchor penetration in clay is: = 6 ar : Cae aS “rem a5 4 (2) where Qe = vibrator force (10 kip) A, = total surface area of anchor shaft Ay = total surface area of fluke c = remolded shear strength rem c = undrained shear strength The penetration resistance of the shaft is calculated using the remolded shear strength because the fluke has passed through the region the shaft is in disturbing the soil. The fluke resistance, however, is calculated using the undrained shear strength because the fluke is penetrating into undisturbed soil. End bearing resistance was neglected because it is neglibible compared to resistance of the shaft and fluke. Equation 2 takes two forms, depending on whether the anchor is fully or partially embedded. For an embedment depth, D, greater than the total shaft length (D> 20 feet) the equation is: Q =i Ati spupieie Jel ult iS Sema a *p z P (c/p) (3) Simplifying and assuming a soil sensitivity of 2 (c/c = 2) the equation is: y b = Ore “|, @> 1) s- * Ge D. | (c/p) (4) For D <20 feet the governing equation is: Cc i - /_rem = = = A D2 i=), pies) (5) Quit Simplifying, the equation is 2 Qi, = (al. +A, DY y, . (ef) (6) ult where At = shaft area per foot of length c/p = ratio of undrained shear strength to effective vertical pressure 54 The equation used to calculate anchor penetration in sand is: Q = (AWE. goleactaA - 6.5) k tan ¢ @)) vertical effective stress where fo) k = coefficient of passive earth pressure oS i] friction angle between steel and sand Equation 7 takes two forms, one for D >20 feet, and one for D <20 feet. The equation for D >20 feet is as follows: One = (A, (0-10) + A, 3 Disa) Me . k tan 6 (8) For D <20 feet the equation is: 5 = D = ' es Qn = Qo mg vA Dy o & eee (9) The value of > to be used in the above equations is independent of soil density (Lambe and Whitman, 1969, p. 143) and is taken as @ = 26°. The coefficient k is much more difficult to predict; various researchers studying the horizontal stress acting on piles in sand (Ibid, p. 501) have reported values of k from 0.5 to 3.0. It is doubtful that the full passive resistance of the soil will be developed during penetration because the fluke and shaft are small and will not cause excessive soil movement. Also, it would seem logical that the values of k used for the loose and dense sand should not differ by very much because densification of the loose sand should occur while the anchor is being embedded by vibration. Values of k between 1 and 2 are recommended (Ibid, p. 500) to calculate horizontal stress acting on piles in sand. For calculation purposes, k will be assumed to vary from 1.0 for loose sand (¢ = 30°) to 1.5 for dense sand (¢ = 409). Results of the penetration analysis are presented in Table 3 for both sand and clay. Since densities were assumed and since slight density variations have a minimal effect on penetration, only one density was used for the clay. Determining the adequacy of the existing vibrator was the third step. Knowing the penetration capabilities of the vibratory anchor system permits the use of graphs of breakout force versus embedment depth to determine the theoretical breakout force of the vibratory anchor. The vibratory anchor penetrations presented in Table 3 refer to the embedment depths of the fluke centers prior to anchor keying. Field test results have shown that keying occurs in a distance of approximately one-half the fluke diameter (B/2). Therefore, breakout forces in Table 3 were determined from Figures 26 and 27 by using a depth of embedment equal to Dias BY) De DS) ao10g qnoyeelg ssoras Butkey eto0jseg SATIOOFF_ Tewz10y uoT eA oUeg /uj38uer4S TeeUs uoTIOTAW ‘AeTO pue pues TOF SaezTS syNTJ snoTAeA ATOZ voAO0;J qnoyeeiq pue uotqzeajqoued aJoyoue AtoZeAqTA jo AzewUNS “3 SLM dod OTT pues ad4J, [TOS 56 As stated in the introduction, one of the primary goals in the development of the vibratory anchor was to achieve a holding capacity between 25 to 50 kips. Results in Table 3 indicate that this goal can be achieved by using the existing 10 kip vibrator with various size flukes for sand and clay. The decision as to which size fluke is most suitable for various seafloor conditions depends upon two factors. First the anchor breakout resistance must be from 25 to 50 kips and second the penetration must be sufficient to minimize both the effects of scour around a long term mooring and the effects of minor upward anchor displacements due to unanticipated momentary loads. From Table 3, it appears that a 2.5-foot fluke size satisfies the above requirements and is more desirable in sand than the comparable capacity, but shallower embedment of the 3-foot fluke. For clays, the deeper penetration of the 4-foot fluke and its comparable breakout resistance to the heavier 5-foot fluke indicates that a 4-foot fluke is the most suitable. The fluke sizes chosen for sand and clay are based upon analytical procedures not yet verified by full scale field tests. When data from full scale tests becomes available these procedures will be updated, if necessary to improve prediction capabilities. SUMMARY AND CONCLUSIONS Five anchor design concepts have been explored in conjunction with the program to develop an improved deep sea mooring capability. The knowledge gained from study of these concepts and the present status of the program are summarized as follows: 1. The 'Free-fall'" anchor failed to achieve sufficient holding capacity to make embedment of an anchor by free-fall impetus alone feasible. However, two things of significance to deep sea anchoring capability were gained from the work on this anchor. First, an important new fluke design that is especially suited to a direct embedment anchor was achieved. It is being used in the development of the vibratory anchor concept. Second, the free-fall cable bale payout system proved feasible and is judged to be worthy of further investigation for future placement of deep sea anchors. Elements of the "free-fall" anchor concept as they pertain to handling, placing, and utilizing deep sea anchors will continue to be considered in the program. 2. The ''Pulse-jet'' anchor concept was judged to be unworthy of further development. Difficulties with high-pressure, high-temperature seals plus complex critical relationships between the internal working parts of the anchor and the surrounding soil medium were judged too costly to solve. No further development is planned. 57 3. The small 'Explosive'' anchor concept was tested in shallow and deep water and was judged to be feasible for deep sea anchoring application. However, work on this small concept was suspended in favor of the vibratory anchor. The vibratory anchor offers more economical expendable parts and extended power application during embedment making it more accommodating to instrumentation for measuring penetration of the seafloor and predicting holding capacity. Future work on explosive anchors for deep sea applications appears justified to obtain greater holding capacities than practicable with the vibratory concept and/or to function in seafloors not suitable for the use of vibratory anchors. 4, The 'Padlock" anchor work resulted in a tripod framework and rewind mechanism that can be used to obtain increased capacity of explosive or other direct embedment deep sea anchors once they are perfected to a satisfactory reliable level. Also, it can provide bearing capability for bottom rest, structures in the sea. Ultimately, refinement and application of the 'Padlock'"' anchor concept to meet the anchor performance requirements of high capacity complex deep sea installations is contemplated. 5. The "Vibratory" anchor currently is the center of the deep ocean anchoring development effort. A first generation design has been achieved that demonstrates the concept is feasible. The design is adaptable to instrumentation to measure and confirm its penetration into the seafloor. The new quick-keying fluke design adapted from the free-fall anchor has proved to be functional and is a major improvement over other known flukes for direct embedment anchors. Instrumentation has been developed to signal confirmation of the vibratory anchor's proper attitude prior to embedding and to signal the amount of its penetration. Analytical procedures have been devised to optimize the vibratory anchor design relating fluke size, seafloor conditions, and power requirements to achieve proper embedments. Despite these developments, certain improvements are required for the vibratory anchor to be reliable and functional in deep water. A second generation vibratory anchor will be designed that will include improvements in the support guidance system, the fluke shaft linkage, and the battery power unit package. The second generation design will be tested to evaluate the mechanical improvements and to substantiate or modify the analytical procedures used to optimize the anchor. 58 FUTURE WORK Plans for the immediate ongoing deep ocean anchoring development are directed to the vibratory anchor concept. Prototypes of the second generation design will be fabricated. Controlled testing of the prototypes in both clay and sand will be conducted to confirm and/or modify the analytical procedures devised for predicting anchor breakout resistances for particular fluke sizes and seafloor sediments with a given vibratory power unit. Other testing with the prototype will be conducted in water 1000 to 6000 feet deep to evaluate the functioning of the anchor at these depths. Still another phase of the immediate ongoing work will be a model investigation. This study will attempt to establish the effect on the holding capacity of anchors subjected to random variations in loading as imposed by a structure on the sea surface. It is anticipated that a broadened deep sea anchor development program will follow the vibratory anchor work. A hard seafloor embedment anchor will be developed to provide anchoring capability in seafloor types not suited to the vibratory anchor. An operational depth of 6000 feet, a 50,000-pound holding capacity, and functionability in seafloors ranging from sediments to rock and coral with compressive strengths to 15,000 psi are the goals for the hard seafloor anchor. To increase embedment type anchorage potential to a greater percentage of the seafloor, the vibratory anchor will be modified to be functional at water depths to 20,000 feet. In addition to these efforts, a mooring system utilizing embedment anchors will be developed to provide from 100,000 to 300,000 pounds of holding capacity in water depths to 6000 feet. To achieve these goals, existing embedment anchors and/or new modular types will be studied. 59 REFERENCES Ali, M. S. (1968), ''Pullout Resistance of Anchor Plates and Anchor Piles in Soft Bentonite Clay," M. S. Thesis, Duke University, 1968, (available in Duke Soil Mechanics Series, No. 17, p. 50). Baker, W. H. and Kondner, R. L. (1966), "Pullout Load Capacity of a Circular Earth Anchor Buried in Sand," National Academy of Sciences, Highway Research Record 108, 1966, pp. 1-10. Balla, A. (1961), ''The Resistance to Breakout of Mushroom Foundations for Pylon," Proceedings, Fifth International Conference on Soil Mechanics and Foundation Engineering, Paris, France, 1961, Vol. 1, pp. 569-576. Bhatnagar, R. S. (1969), "Pullout Resistance of Anchors in Silty Clay," M. S. Thesis, Duke University, 1969, (available in Duke Soil Mechanics Series No. 18, p. 44). Christians, J. (1967), ''Development of Multileg Mooring System, Phase A, Explosive Embedment Anchor,'' U. S. Army Mobility Equipment Research and Development Center, Report 1909A, Fort Belvoir, Virginia, December 1967. Dantz, P. A. (1968), "The Padlock Anchor - A Fixed Point Anchor System," Naval Civil Engineering Laboratory, Technical Report R-577, Port Hueneme, California, May 1968. Esquivel-Diaz, R. F. (1967), ''Pullout Resistance of Deeply Buried Anchors in Sand,'' M. S. Thesis, Duke University, 1967, (available in Duke Soil Mechanics Series No. 8, p. 5/7). Hansen, J. B. (1953), "The Stabilizing Effect on Piles in Clay," Christiani Nielsen Post, 1953. Interstate Electronics Corporation (1970), 'Sea Spider Moor," presentation to NCEL, February 1970. unpub lished Kalajian, E. H. (1969), "Vertical Pullout Capacity of Marine Anchors in Sand,'' M. S. Thesis, University of Massachusetts, Amherst, Massachusetts, March 1969. Kananyan, A. S. (1966), “Experimental Investigation of the Stability of Bases of Anchor Foundation," (in Russian); Osnovaniya, Fundamenty; Mekhanika Gruntov, Vol. 4, No. 6, November-December 1966 (available in English translation from Consultants Bureau, New York, pp. 387-392. 60 Lair, J. C. (1967), "Investigation of Embedding an Anchor by the Pulse- jet Principle," CR 68.008 to the Naval Civil Engineering Laboratory, Sea Space Systems, Inc., Torrance, California, October 1967. Lambe, T. W. and Whitman, R. V. (1969), Soil Mechanics, John Wiley & Sons, New York, 1969. Mackenzie, T. R. (1955), "Strength of Deadman Anchors in Clay," unpublished Masters Thesis, Princeton University, New Jersey, 1955. Mardesich, J. A. and Harmonson, L. R. (1969), "Vibratory Embedment Anchor System," CR 69-009 to the Naval Civil Engineering Laboratory, Ocean Science and Engineering, Inc., Long Beach, California, February 1969. Meyerhof, G. G. and Adams, J. I. (1968), ''The Ultimate Uplift Capacity of Foundations,' Canadian Geotechnical Journal, Vol. 5, No. 4, November 1968, pp. 225-244. Sea Space Systems, Inc. (1966), "Project 'Pulse-jet', A Technical Proposal For An Improved Embedment Anchor," Response to RFP N62-66-R-0016 to the Naval Civil Engineering Laboratory, May 1966. Schmid, W. E. (1969), "Penetration of Objects into the Ocean Bottom, (the state-of-the-art) ," CR 69.030 to the Naval Civil Engineering Laboratory, March 1969. Skempton, A. W. (1959), "The Bearing Capacity of Clays," Proceedings, Building Research Congress, London, 1959. Smith, J. E. (1965), "Structures in Deep Ocean, Engineering Manual for Underwater Construction, Chapter 7. Buoys and Anchorage Systems," Naval Civil Engineering Laboratory, Technical Report R284.7, Port Hueneme, California, October 1965. Smith, J. E. (1966a), "Investigation of Free-fall Embedment Anchor for Deep Ocean Application,'' Naval Civil Engineering Laboratory, Technical Note N-805, Port Hueneme, California, March 1966. Smith, J. E. (1966b), "Investigation of Embedment Anchors for Deep Ocean Use,'' Naval Civil Engineering Laboratory, Technical Note N-834, Port Hueneme, California, July 1966. Turner, E. A. (1962), "Uplift Resistance of Transmission Tower Footings," Journal of the Power Division, Proceedings, ASCE, Vol. 88, No. P02, July 1962, pp. 17-33. 61 Vesic, A. S. (1969), "Breakout Resistance of Objects Embedded in Ocean Bottom,'’ CR 69.031 to the Naval Civil Engineering Laboratory, Durhan, North Carolina, May 1969. Winterer, Dr. (1967), "Deep Ocean Vibracorer," CR 336 to the Scripps Oceanographic Institute, Ocean Science and Engineering, Inc., Long Beach, California, 1967. 62 Unclassified Security Classification DOCUMENT CONTROL DATA-R&D (Security classification of title, body of abstract and indexing annotation niust be entered when the overall report is classified) 1 ORIGINATING ACTIVITY (Corporate author) 2a. REPORT SECURITY CLASSIFICATION Unclassified Naval Civil Engineering Laboratory SENGHSUE Port Hueneme, California 93041 | SPECIALIZED ANCHORS FOR THE DEEP SEA — PROGRESS SUMMARY H 4. DESCRIPTIVE NOTES (Type of report and inclusive dates) February 1968 - June 1970 5. AUTHOR(S) (First name, middle initial, last name) J. E. Smith, R. M. Beard, and R. J. Taylor Biiccenbes Me econ November 1970 64 25 6a. CONTRACT OR GRANT NO. 9a. ORIGINATOR’S REPORT NUMBER(S) s. prosectno. YF 38.535.004.01.001 TN-1133 9b. OTHER REPORT NO(S) (Any other numbera that may be aasigned this report) 10. DISTRIBUTION STATEMENT This document has been approved for public release and sale; its distribution is unlimited. 11. SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY Naval Facilities Engineering Command 13. ABSTRACT Five anchor design concepts have been explored in conjunction with the program to develop an improved deep sea mooring capability. The knowledge gained from study of these anchor concepts, 'Free- fall", (2) "Pulse-jet", (3) "Explosive", (4) "Padlock", and (5) "Vibratory" are summarized in this report. The vibratory anchor is currently the center of the deep sea anchoring development effort. A first generation design has demonstrated the concept to be feasible. Tests have shown that improvements are required for the vibratory anchor. An analytical study has been performed to assist in optimizing a second generation design. Improvements incorporated in the second generation design will be based on information from tests of the first design and the analytical study. The improved design will be tested in a range of seafloor sediment types and water depths to rate its capabilities and establish its reliability. DD "2y..1473 ‘Pace ) Unclassified S/N 0101-807-6801 Security Classification Unclassified Security Classification KEY WORDS Anchoring Mooring Deep water Ship's Floating platforms Underwater structures Underwater vehicles Deep ocean vehicles Ship anchors Free-fall anchors Pulse-jet anchors Explosive anchors Padlock anchors Vibratory anchors DD WATS (BACK ) Unclassified (PAGE 2) Security Classification