TN-)28G Technical Note N-1286 DEEP-OCEAN PILE EMPLACEMENT SYSTEM: CONCEPT EVALUATION AND PRELIMINARY DESIGN By D. A. Raecke August 1973 Approved for public release; distribution unlimited. NAVAL CIVIL ENGINEERING LABORATORY Port Hueneme, CA 93043 TA Ui iNS WO, NI2%Te DEEP-OCEAN PILE EMPLACEMENT SYSTEM; CONCEPT EVALUATION AND PRELIMINARY DESIGN Technical Note N-1286 YF38.535.004.01.002 by D. A. Raecke ABSTRACT A previous review of the state-of-the-art of seafloor pile emplace- ment indicated that three types of mechanical systems could be developed for deep-ocean seafloor pile emplacement. The systems are: vibratory drivers, screw piles, and jack-in piles. Conceptual designs for multiple-pile emplacement systems utilizing each of these mechanical systems were developed and compared. The comparison showed that screw- piles would be the most effective in meeting the given operating re- quirements. A preliminary design for a pilot-model screw-pile emplace- ment system is presented, Approved for public release; distribution unlimited. ii CONTENTS TOMABRODWIGINON, 6 6 65650 oo OOOO oOo OO Bacherrowinsl Gogo o 6 010 6 6 0 016 6 6 00.6 6 SCOPA\ Oo o 6 oF 6G Oo Glo Oo a Oo oO old Oo & 50) 6 SELECTION OF PILE EMPLACEMENT SYSTEM CONCEPT .... QPSrRiENS MEGUHIATEMES og 6 6 05056000000 Commons Desten Characteristics uaesen sine enone WAAC IDielWaie SWSEMS 46 6156 6 6 6 c Jack-UnUSyStem yar wate ts ete a el relia etal oe SCHEVARLIS SYSEEM 6 o 6.0.6 670 0 0:6 0 6% Comparison of Conceptual Designs ... DUSCTSSLOM 6 9500.00 00000 0000006 PRELIMINARY DESIGN OF PILOT-MODEL EMPLACEMENT SYSTEM Genera iL e ° e e e e e e e e e e e e e e e e e e Foundation/Anchorage Subsystem ....... INEAinetom SUDSWSEEM “6 6 4 50 6.056000 6 DIECreLeaL SUbSYSEAM o 56 6 6.0606 00:0 0,0 6 Control and Feedback Subsystem ...... © e Load Handling and Surface Support Subsystem . . SIMPLIFIED, LIMITED-CAPABILITY SYSTEM FOR ANCHORAGES CONCLUSIONS AND RECOMMENDATIONS .... « © « «© « « ACKNOWLEDGEMENTS e e e e e e e oe e e e e e e e e e oe REFERENCE S O65 Ne ie. O06 Key 8: fon es 18°) a> ier ie. Xe! fen ier et lel eh ae MBL/WHO! QML 0 0301 0040235 ec ’ RTD ah TAK 1 AUAES | i eae raat load ! . ea 35 OM i WRAGT 4 ‘ P * Oia PEay nat) 2.7 14 Eby ev OA Ver eB, be Ha M Laz ye) y a & i * * £ Wot a he PT ae IEW, SAE Imei ee tee APTS re Bg abet: © daksen e a ' cr A oF P i i i” ar 44. oe Lp ONE Noseipn) aCe Viva Fey (eed Fy os ae he ‘i . 4 Ac Pe a: ’ : F G6 BENDA PRG, Spa, POURS US" marie eel ete Sri Dera: a Saha tale RO ARGH Nek He) Mirays TUE STRATA CET IE Bae bst ict t un ‘ ; : : aay a i i ; nw) Vile, Ae ame 5 Ris 3 i i . . * ‘ * e158 ' \ ¥ on . ‘ $ » j ‘1° uF ie hao or ee ee en ‘ ‘ * ' s bs Tera) te ta uy come: io, eomieva Yav art a A ae iat Te be ee ae , . we ae ’ . es 4 *\ 4 ; woo » 4 ‘ . s + , wet eY ¥C “ i ' ut ' , j i. ee Sd buh io iiss: hel: AA ou. So oe eee Tat: Oe ane oan ct (ie ph aigry he “ au 9 Ma a ae he ait t ou i 6 ty F a : aus ia @ ay c au: 7 Uy vat, wa, hero gene ee Peet sea Co ub tea: Pi s COOL Ake . Te z BO TP EE SEEIEELNE MD dea ee La REY, pert ia: ON. PY tbr: ahs Rae ae arr P, be AL P wes din etuk toacles't tim Tose wee Soak bis eyena 4WiN ROG yortayd hte wi te eee) Ps Noe Whe ebb Fe Wie 28 y RON Rega ST Ee eee * : : ae Fis HAS 2 Sp eo eh ees INTRODUCTION It is expected that future Navy seafloor and subsurface installa- tions will require foundations and anchorages of greater capacity and reliability than are provided by the foundation or anchorage systems ordinarily used (e.8., spread footings, mats, dead-weight anchors, and drag-type anchors). Piles and pile groups can often be designed to provide the required increase in capacity and reliability. However, the Navy has no means for emplacing piles in water deeper than about 100-150 feet. Few commercial organizations can emplace piles in water depths beyond 150 feet, and these operations are very expensive. Since further seafloor and subsurface installations frequently will be in greater water depths it will be necessary to develop economical means of emplacement to permit the use of piles for these installations. Background A review of the state-of-the-art of seafloor pile emplacement has shown that only marine drilling techniques could be adapted to emplace piles or pile groups for an immediate requirement in water deeper than 1000 feet.2 Pile emplacement using other state-of-the-art methods (e.g., underwater pile hammers and vibrators or surface-driving with followers) is currently limited to about 1000 feet by logistics problems. However, only moderate effort is required to develop a pile emplacement system operable to 6,000 feet, Three existing mechanical concepts were shown to be possible candidates for further development: vibratory drivers, screw piles, and jack-in piles. Scope In this report conceptual designs for pile emplacement systems based upon each of the three mechanical concepts are presented, and the advantages and disadvantages of each are summarized. A comparison of the advantages and disadvantages led to the selection of screw piles as the best system for further development. A preliminary design is presented for a pilot-model emplacement system based upon the use of screw piles. SELECTION OF PILE EMPLACEMENT SYSTEM CONCEPT Operating Requirements The operating requirements for a seafloor pile foundation were designed to apply to a generalized installation rather than a specific seafloor structure. This was done to ensure that the choice between alternatives would not be influenced by the special characteristics or design requirements of a given installation. In the initial phase of the selection process, the operating requirements were given as follows?: 1. The system must be operable in water depths to 6,000 feet. 20 The system must be able to emplace several piles in a multi- sided structure in correct relative positions. 3. Each pile must be within 2 degrees of plumb. 4. Pile emplacement must be possible in sea states up to and including sea state 3. De Each pile should have an ultimate uplift or bearing capacity of 200 kips. Based upon these criteria, concepts for several emplacement methods were developed and compared. The primary emphasis in the initial phase was upon the effectiveness of the emplacement device (i.e., vibratory driver, impact hammer, etc.) rather than upon the performance of an overall system. Details of the initial-phase comparison are given elsewhere.2 It was determined that vibratory driver, screw pile, and jack-in systems were feasible for development. The emphasis in the second phase was upon the performance of a complete pile emplacement system utilizing each of the three emplacement methods, In this comparison the operating requirements were modified to reflect the characteristics of the complete system. The operating re- quirements relating to water depth, verticality of the piles, and sea state were retained without change. For each system only the minimum required number of piles was considered, The minimum number for vibratory-driver and screw-pile systems is three piles; for the jack-in system, five piles are required, The minimum capacity requirement was reduced to an ultimate load capacity for the system of 150 kips in uplift or bearing, and a 75-kip ultimate lateral load requirement for the system was added. In addition to the above requirements, the following design goals were established: 1. The submerged weight of the system should be less than 40 kips to permit use of the NCEL-developed motion-compensating winch. 2. The power required for pile installation should be less than 100 horsepower. 3. The system should require less than two hours of on-bottom time to emplace the minimum number of piles. The time limit includes system checkout, leveling, etc. 4. The system should be able to emplace piles in a wide range of seafloor types; i. e., soft to stiff cohesive soils and loose to dense cohesionless soils. 5. The system should be capable of expansion in size (plan dimensions of structure) and number of piles. 6. All components should be within the state-of-the-art; i.e., minimum development required. 7. The system should utilize a minimum of mechanical operations and control functions. 8. The system should be handled by a single ship or a single tug- barge combination. Required deck space is a function of the plan dimensions of the installation, but the minimum space is approximately 12 ft x 12 ft for the emplacement system, 4 ft x 8 ft for a control van, 10 ft x 10 ft for a crane, and 10 ft x 20 ft for winches, prime mover, and miscellaneous equipment. The vessel must have a 20-ton crane to place the system overboard. Table I summarizes the operating requirements. Common Design Characteristics A schematic representation of a seafloor pile emplacement system is shown in Figure 1. The system comprises five subsystems: 1. The foundation/anchorage subsystem, which includes a template, piles and connections. 2. The installation subsystem, which includes the emplacement mechanism (i.e., vibratory drivers, or jack-in or screw-in mechanisms) and associated power conversion and distribution equipment (i.e., hydraulic pumps, lines, valves, reservoir, gears, etc.). 3. The electrical subsystem, which includes submerged electric motors, transformers, electrical cable, and generator. Table 1. Summary of Operating Requirements for a Seafloor Pile Emplacement System Water Depth 6000 feet Verticality Tolerance +2 degrees Sea State Capability Sea State 3 Capacity - Uplift or Bearing 150 kips ultimate Lateral Load 75 kips ultimate Submerged Weight 40 kips maximum Power Required 100 HP maximum Emplacement Rate 2 hours maximum to emplace all piles Number of Piles At least 3 piles placed in proper relative position* Seafloor Soils Adaptability Soft to stiff cohesive soils; loose to dense cohesionless soils Versatility Adaptable to emplacement of more than the minimum number of piles; adapt- able to changes in plan dimensions of structures Required Development Effort All components should be reasonably within the state-of-the-art; minimum development time desired Complexity Minimum number of mechanical operations and control functions desired; possi- bility of automation Ship Support Single ship or single tug-barge combination; approximately 500 sq. ft. deck space and 20-ton crane required * The jack-in system requires 5 piles for operation. 4. The control subsystem, which includes the controls of all sub- merged and surface equipment and any required instrumentation such as attitude sensors, safety alarms, etc. Do The load handling and surface support subsystem, which includes the cable, winch, surface vessel, crane, etc. The most influential requirement related to the physical configura- tion of the pile emplacement system is that several piles be emplaced in a given pattern. This necessitates the use of a template to properly position the piles, because the cost and difficulty involved in remotely positioning separate piles in a pattern in 6000 feet of water would be unreasonably large. The template provides a temporary base for power conversion and control equipment and acts as a guide to maintain verti- cality of the piles. It also can be designed to remain in place as part of the major structural support system. Thus, the seafloor installation need not have as heavy a base structure, and the installed weight of the installation can be reduced. The template will constitute a major portion of the weight of the emplacement system. Since all of the conceptual designs were based upon essentially the same installation plan dimensions, the weight of the template can be taken as constant. Differences in total system weight are thus due to differences in the weight of the emplacement mechanisms, the piles, and possibly the instrumentation and control systems required, The pile weights may vary because of different cross-sections and lengths required to obtain the specified load capacity. Because the piles are designed to be normal to the template the requirement concerning pile verticality is essentially a requirement for a maximum inclination of the template of + 2 degrees, It was concluded that the installation system would hang from the cable in an essentially vertical condition. Thus, if the piles are allowed to free- fall the final 3 to 5 feet they will enter the soil approximately vertically. This can be accomplished by providing a bottom-sensing probe and trip mechanism to release the piles. Also, a supplementary footing may be necessary to stabilize the template while one of the piles is being driven. The bottom-sensing probe and supplementary footing are shown in Figure 1. It was determined that hydraulic power is the optimum form for each of the three emplacement mechanisms. The use of hydraulic power at the planned water depth is not common, but the state-of-the-art was advanced considerably by the design for the NCEL seafloor deep corer>. It was determined that the best method of supplying power was by electrical transmission from the surface to a submerged electric motor driving a hydraulic pump*, This eliminates the difficulties involved with handling long hydraulic lines, The use of an electromechanical cable appears desirable to avoid cable entanglement problems, Control for the hydraulic motors and cylinders can be telemetered down the power cable. For the power levels tentatively proposed the use of a sea- floor source of electric power does not appear feasible. In the following sections, brief descriptions of conceptual designs based upon each of the emplacement mechanisms are presented. The relative advantages and disadvantages of each conceptual design are discussed, and a semi-quantitative method is employed to compare the designs and select the best system. Vibratory Driver Systems For vibratory driver systems, several designs are possible depend- ing upon the specific type of vibrator utilized and upon the mode of operation of the system. Two general types of vibrator are available: eccentric-weight drivers and linear oscillators2. Although the devices operate quite differently it was concluded that either could be used in an underwater system, and that neither type offers any significant advantage in meeting the operating requirements listed above. This factor was thus eliminated from the conceptual design. However, it should be noted that eccentric-weight devices have been developed to a greater extent than linear oscillators, which gives the eccentric- weight drivers a cost advantage. Three general modes of system operation were considered. In the first mode all of the piles are lowered with the template, and a separate vibrator is provided for each pile. Electric power would be supplied from the surface and converted to hydraulic power at the sea- floor. The control system would direct the power to one vibrator at a time. At the end of driving, the vibrators, electrical and control subsystem components would be detached and retrieved for reuse. In the second mode the system utilizes a single vibrator to drive all piles and an indexing system to position the driver from one pile to another. All piles are lowered with the template, as above. The electrohydraulic power system is also essentially the same as the first mode, The control system must control the indexing system as well as the power to the vibrator. It would also be necessary to provide a device for clamping the vibratory driver to the head of each pile, and for detaching the driver at the end of each driving cycle. This device must provide a rigid coupling of driver to pile for best efficiency of the vibratory driver. In the third mode the piles are lowered with the template and a single vibrator is handled on a separate line from the surface vessel. The system must provide means for locating and positioning the driver on the piles. The locating could be done acoustically, and the posi- tioning by water jets on the driver. The positioning could also be done by submersibles, either manned or unmanned. However, because of the likelihood of cable entanglement and the expense of submersible operations, this mode was eliminated from consideration. Jack-In System The jack-in concept for seafloor pile emplacement is shown schematically in Figure 2. This concept was developed to eliminate the need for a large reaction mass against which to jack. As indi- cated in Figure 2, the system uses five piles in a regular pentagonal template. At each corner of the template a jacking mechanism controls the position of the pile relative to the template. Piles are driven by jacking on one pile at a time in the sequence shown by the circled numbers in Figure 2. The reaction is derived from the weight of the emplacement system plus the skin friction on the two piles adjacent to the one being driven. Several types of jacking mechanism are feasible for this system. One promising concept uses a winch-and cable mechanism. Other possible mechanisms include rack-and-pinion jacks, chain jacks, and hydraulic cylinders. It was concluded that the specific type of jacking mechanism would not influence the choice between the conceptual designs. The control system for the jack-in concept would direct the power to one jack at a time. Several repetitions of the jacking sequence will probably be necessary because a given pile may meet a level of resistance that will overcome the available reaction, and that corner of the template will begin to rise. Jacking on that pile should be discontinued when the template reaches a predetermined inclination, and the next pile in the sequence should be jacked. The control system should permit the skipping of a given pile in the event it reaches maximum penetration before the other piles. At the end of driving the power and control subsystems would be detached and retrieved. Screw-Pile System A screw-pile system is shown schematically in Figure 3. The piles have one or more helical blades at the lower end, and are emplaced by rotating them about the longitudinal axis. The piles would be rotated individually to minimize power requirements. The driving torque would be resisted by lateral forces on the other piles in the template. At least two sequences of pile rotation may be required because the torque might be great enough to overcome the lateral soil resistance in the early stage of driving. Thus, the control subsystem would be quite Similar to the jack-in system described above. As shown in Figure 3, the screw piles are square and are rotated by a kelly drive that allows longitudinal motion of the pile while it rotates, An alternative drive system was considered with which two piles are driven at the same time by a drive unit attached at the upper end of the piles. The piles are counter-rotated to absorb the torque. It was concluded that this system is much less desirable than the kelly-drive system because the weight would be concentrated so far above the template, and the free-fall of the piles would be hindered. Comparison of Conceptual Designs Each conceptual design was carried only far enough to provide a reasonable basis for comparison. Because of the large number of oper- ating requirements that a seafloor pile emplacement system must meet, and because the four conceptual designs may differ in the manner or degree in which they fulfill any given requirement, a quantitative method of comparing the systems is necessary. The method adopted is essentially the same as was used to select the three emplacement mechanisms¢. Relative weights are assigned to each of the operating requirements identified in Table 1 to reflect the degree of importance they exert in concept selection. Then each system is rated according to how well it meets each operating requirement, employing a numerical rating scale, called an effectiveness number. The effectiveness number and the weight are multiplied and the products are summed for each system, The resulting aggregate number reflects comparative effective- ness of the systems. It was determined that all of the systems could be designed to meet the requirements for water depth, sea state capability, capacity, number of piles, and ship support in an equivalent manner. Thus, these require- ments can be neglected in comparing the various systems. The weights assigned to each of the remaining operating requirements are shown in Table 2, It should be noted that the requirement concerning versatility has been divided into two categories. The most important factore in comparing the systems are submerged weight, development re- quired and complexity. The submerged weight has a large effect upon the handling system, the range of choice of surface support system, and the likelihood of successful emplacement. The required development effort affects both the time and overall cost of procuring a prototype emplace- ment system. Systems utilizing the greater number of state-of-the-art components are superior, provided of course, that all other criteria are met satisfactorily. Complexity is related primarily to the reliability of the system and secondarily to cost. In general, systems utilizing fewer mechanical operations and control functions are more reliable and less costly; such systems are superior. The other operating requirements _have relatively less effect upon system comparisons, as reflected by the weight assigned. Table 2. Relative Weights of Operating Requirements for Concept Selection Requirement Submerged Weight Power Required Emplacement Rate Verticality Seafloor Soils Adaptability Versatility - Greater number of piles Versatility - Variable plan dimensions Required Development Effort Complexity A scale of 1 to 5 was adopted for assigning effectiveness numbers. As noted above, the effectiveness number attempts to quantify the degree to which each conceptual design fulfills the operating requirements listed in Table 2; the larger the number, the better the system meets the requirement. For the first four requirements, quantitative limits can be established for each of the effectiveness numbers, as shown in Table 3. For the remaining requirements, the effectiveness number represents the judgment of the relative quality of each conceptual design, Table 4 summarizes the conceptual designs, the effectiveness number assigned for each requirement, and the overall effectiveness rating of each system. Discussion All of the conceptual designs can meet the requirement that the submerged weight be less than 40 kips. However, the multiple-vibratory driver system will be just below this limit and is down-rated compared to the other systems, as shown in Table 4. The weight estimates for the vibratory systems are based on a driver-to-pile weight ratio of 3 to 1. This ratio is about average for successful commercial vibratory drivers. The required power is estimated to be the least for the jack-in system and the greatest for the vibratory systems. However, the vibra- tory systems have a potentially greater emplacement rate and may permit shorter on-bottom operation times, The lower relative rating of the emplacement rate of the jack-in and screw-in systems reflects their status as "static'’ emplacement methods. The jack-in system is rated much superior to the others in ability to assume and maintain a vertical pile attitude (i.e., level template attitude), because the jacks at each corner can be used to level the template at the beginning and end of the pile-jacking sequence. The attitude of the other systems depends upon how nearly vertical they hang when the piles are released from the template to free-fall the final 3-5 feet. The screw-in emplacement method is believed to be the most adaptable to differing soil conditions, Industry experience with this means of emplacing ground anchors for electric utility lines and pipelines has shown that screw piles can be configured to penetrate dense cohesionless and very stiff cohesive soils at the proposed power levels®. The vibra- tory driver systems are relatively inefficient in cohesive soils and would probably penetrate the stiff cohesive soils only with consider- able difficulty. The jack-in system is not expected to operate effectively in cohesionless soils because the point resistance of the driven pile would increase too rapidly with depth for the skin fric- tion on the adjacent piles to provide sufficient reaction force, 10 5 Table 3. Rating Scales for Effectiveness Numbers | Requirement 1 2 3 Ke 4 5 —t-—.. Estimated Submerged Weight, kips >40 30-40 20-30 10-20 Estimated Power Required, 80-100 60-80 | 40-60 20-40 HP Emplacement Rate, ft/min - - <5 5-10 | >10 a= = = Verticality, Degrees = Control i WI Subsystem Foundation/Anchorage a) Subsystem Figure 1. Schematic view of a seafloor pile emplacement system. 23 Concept for a jack-in emplacement system. Figure 2. 24 Power Cable Sas Electro-hydraulic Power Conversion a) > “d uy (=) > ta a cy) ™M 4 C\ eee © E ah oe g iS ALS Byes See ea een ee 7? \ > — ee ee 2 bo=s=4 ial eel ry Ne Ne, So? i Template 3) oat ak 30 ov HO Ue tal qm Conceptual design for a screw pile emplacement system. Figure 3. 25 "we sds JueueseTdme eTtd—-metos ‘iaqem-deep Toyz eouenbes [TeuotjetedQ ‘y siNnsTy epeW SuotToOeUU0D pue uf SeTtd ITV poosetTduq 3upteg etd TeAe7 aqeTduey pue TedTIIeA ATTetIUessY SeTTd ‘SeTtd sutd 4q PT9H SeTtd peseeToy pue powojj0g $u0730g F3J0 3sNe sey wstueyoow dtiy we sks JuomeoeTduy 26 Control Console Electrical Chamber Motor Controls Circuit Breakers (ean a Attitude Sensor | Power Supply Control & Feedback | | | | | | | Hydraulic Reservoir | | Hyd. Pump Motor | | Hyd. Pump | Hyd. Valves | Pressure Sensor | | Bypass Valve | | | | | | | | | | | | | Kelly Drive Pile Hold/Release Installation Leveling System Motors Mechanism Unit Release (if required) Kelly Drives LEGEND —— — — Control or Feedback Signal Le Le | | L Electrical Power Transmission t_}|Piles (Pile Travel & Umb. Hydraulic Power Transmission Catch Indicators) GE =Mechanical Power Transmission Figure 6. System block diagram for pilot-model seafloor screw pile emplacement system. 28 ' me As. wee ew ee oem — —F \ Figure 7. Load-Transfer Connectors