US3604522A - Pile-driving system and apparatus - Google Patents

Abstract

A system for driving piles by a succession of blows struck from above by a hammer element wherein a driving head assembly transfers the blow to the upper end of a hollow elongated pile. The driving head comprises an anvil element to engage the upper end of a pile and includes an elongated hollow case extension portion containing the reciprocable hammer element. A cable connected to the hammer element extends upwardly to an outdoor work platform for hoisting and lowering the driving head assembly. A pulley driven by hydraulic actuator means provides reciprocating movement to the hammer element.

Description

United States Patent 12/1933 McNeilly 72 Inventor Samuel Clifford Doughty 1,938,459 173/86 Burlingame, Calif. 2,342,253 2/1944 Copley 173/88 [2]] Appl, No. 756,685 2,721,055 10/1955 Madson et a]. 175/293 [22] Filed Aug. 30, 1968 FOREIGN PATENTS 145] sew-14,1971 536,133 4/1922 France 61/535 {73] Asslgnce Santa Fe International Corporation Santa Fe springs, m Primary Examiner.lames A. Leppink AttorneyFlehr, Hohbach, Test, Albritton & Herbert [54] FILE-DRIVING SYSTEM AND APPARATUS C aims snrawmg Figs ABSTRACT: A system for dr1v1ng p1les by a successlon of U.S. blo tru k from above a hammer element wherein a driv- 175/17l ing head assembly transfers the blow to the upper end ofa holl w elongat d The driving head comprises an anvil ele- 501 Field of Search 173/81-89, mm to engage the upper end f a pile and includes an elm 80, 128133, 134, 136, 137, 139; 175/6, 17 gated hollow case extension portion containing the reciproca- 56 ble hammer element. A cable connected to the hammer ele- 1 References cued ment extends upwardly to an outdoor work platform for hoist- UNITED STATES PATENTS ing and lowering the driving head assembly. A pulley driven by 863,614 8/1907 Lake 175/6 hydraulic actuator means provides reciprocating movement to 948,989 2/1910 Coffey 173/86 the hammer element.

0 I I I M :4. 41 11 .1 a

n F a 11 PATENTED SEPI 4 |97l SHEET 1 OF 3 mvrsmon Samuel Clifford Doughty BY Attorneys PATENTED SEPI 419m " sum 2 or 3 IN'VENTOR.

Samuel Clifford Dou BY PATENTEU .SEP 1 4|91| SHEET 3 OF 3 12 F i g. 8

i l A A [ii 2 F i 7 INVEIJfOR Samuel Clifford Doughty w W M fW Attorneys PILE-DRIVING SYSTEM AND APPARATUS BACKGROUND OF THE INVENTION This invention pertains to a system for driving piles by a succession of blows struck from above by a hammer element and to apparatus for use in such system. This invention is particularly useful in driving piles into the ocean floor under great depths of water, though not limited exclusively to such application.

In the construction of offshore drilling platforms and other downwardly extending legs form the so-called jacket" or support tower structure for the offshore platform.

It is necessary to resist overturning forces of wind and sea as well as other overturning forces. This, in the past, has been done by means of providing elongated piles which penetrate to .great depths and to which the tower can be secured by means of locating the piles coaxially of the hollow legs of the tower.

In order to drive piles coaxially of such jacket legs at greater and greater depths, it is becoming increasingly necessary to apply greater and greater hammering energy to the pile, preferably from the convenience of outdoor work stations rather than from submarine locations. It has been ob- .served that losses in the transmission of energy can occur where a pile extension is disposed atop the upper end of the pile to permit the blow to be struck at such an outdoor work station above the surface of the ocean. Certain follower mechanisms have also been employed but are'also believed to suffer from the same disadvantage. However, in order to employ larger and larger hammer elements or rams for striking the pile and for other reasons, and notwithstanding the inherent energy losses, it has remained preferable to drive the pile from the outdoor work station rather than to insert compressed air and steam hammers down into the leg of the tower structure for operation below the surface of the water.

Thus, while it is desirable to transmit the hammer energy substantially directly to the pile without loss of energy and by extremely massive hammer elements which can be readily operated from the outdoor work station at the top of the tower ,or on the platform supported by the tower, these objectives have been somewhat incompatible.

Where underwater steam and air hammers have been attempted for use at submerged locations within the tower legs, trouble has'been experienced in discharging the exhaust of such devices into the air above the water since this is usually done by carrying a heavy hose downwardly through the water and coupling it to the hammer. This hose must be very strong to overcome the tendency to collapse under high external water pressure. Other difficulties to be overcome are condensation of both live and exhaust steam when carried to great depths throughcold water, whereby the hammer mechanism tends to become drowned in a pocket of water condensate which impairs its functioning.

Other difficulties in the past have stemmed from the presence of infiltrated water under-high pressure finding its way into the casing so as to come between the contacting surface of the falling ram or hammer and top of the driving block or anvil which transmits the blow to the pile. Any such intrusion of water, in view ofits incompressible nature, greatly dissipates the energy of the blow of the hammer and renders it significantly lesseffective. Such water intrusion difficulties in the past have been countered by introducing compressed air into the casing so as ,to provide sufficiently high pressure to drive out thewater. However, difficulties have impaired the driving efficiency of underwater hammers of this type. Furthermore, such underwater hammers have seldom been as used to apply a striking blow to the upper end of a pile to be used at great depths of water, for example, at depths appreciably exceeding more than a hundred feet.

OBJECTS It is, in general, an object of the present invention to provide an improved pile-driving system and improved apparatus therefor which overcomes the foregoing and other problems.

It is another object to provide a drop-hammer style of piledriving system for submarine driving of piles. I

It is another object of the present invention to provide a pile-driving system and apparatus which inherently'minimizes the loss of energy transmitted by the ram or hammer element driven.

It is yet another object of the invention to provide an improved pile driving apparatus wherein reactive forces derived from a column of water captured within the pile being driven are dissipated without substantial loss of energy from the piledriving blow.

SUMMARY OF THE INVENTION In general, there is provided a system for driving piles by a succession of blows struck from above by a hammer element. A driving head assembly is adapted to transfer the blows to the upper end of the pile and comprises an anvil element adapted to engage the upper end of the pile in blow-transmitting relation thereto. An elongated hollow case is secured at one end of the anvil element so as to form an extension thereof. A massive hammer element is movable between advanced and retracted positions within the case to strike the necessary blows against the anvil. A flexible cable, connected to one end of the hammer element, lifts and lowers both the hammer ele-' ment and driving head assembly and also serves to operate the drop hammer action by an actuator means supporting thecable. Actuator means located at an outdoor work station serves to lift and quickly release the cable repetitively to provide' a succession of rapid blows struck by the falling hammer element.

These and other objects of the invention will be'more clearly understood from the following detailed description of preferred embodiments when considered in conjunction with the accompanying drawings and general summary of the invention.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevation schematic view showing an offshore oil drilling platform of the type referred to above;

FIG. 2 is an enlarged elevation view (partly in further enlarged section) schematically showing a pile-driving system and apparatus according to the invention;

FIG. 3 is a section view taken along the line 3-3 of FIG. 2;

FIG. 4 diagrammatically shows a system for operating the actuator means for providing a drop hammer action;

FIG. 5 is an enlarged detail view, in section, of another embodiment of a driving head assembly according to the invention;

FIG. 6 is an enlarged detail view showing an improved-pile construction according to the invention;

FIG. 7 is an elevation view showing another embodiment of the system according to the invention;

FIG. 8 is an enlarged elevation section view of a detail portion of FIG. 7 taken in the region of the line 88;

DESCRIPTION OF THE PREFERRED EMBODIMENTS As noted above, the pile-driving system as disclosed herein may be advantageously employed in offshore pile-driving rigs of a type, for example, as shown in FIG. 1. Thus, the superstructure 11 of the rig is generally located on or above the surface of the water 12 by means of a rather tall support tower 13. In general, the support tower 13 has been referred to as a jacket" comprised of upstanding'legs 14 which are suitably braced and supported and generally angle downwardly and outwardly from the superstructure 11 at an angle to the vertical.

As they participate in the system disclosed herein, legs 14 are generally hollow tubular members forming pile guide channels. Tower 13 typically is secured to the ocean floor 16 by means of hollow piles coaxially inserted snugly into the hollow interior of legs 14 so that they may be driven downwardly into the ocean floor to great depths in order to penetrate well beyond the relatively soft upper material of the ocean floor. Piles 17 form a close sliding fit within legs 14.

The upper ends of piles 17 are typically left in place to extend upwardly above the ocean floor 16 an amount sufficient to provide the necessary stability to the rig.

A guide channel, other than legs 13 can, of course, be defined in other ways. For example, in the application of offshore drilling circumstances, for example, so-called skirt piles are driven through and guided by short tubular lengths secured to the exterior portions of the jacket. Further, annular guide rings are sometimes employed in circumstances of the above type wherein several piles are used within a single leg of the structure.

In view of the fact that the legs 14 and the piles 17 are of relatively large diameter, on the order of several feet in diameter, and in view of the exceptional length of such piles, for example on the order of several hundred feet, it is highly desirable to minimize the amount of pile extension lodged within the legs 14 consistent with safety to the tower.

Thus, where piles 17 extend the full length of legs 14, it will be readily evident that a considerable waste of expensive piles 17 has occurred in view of the fact that the uppermost portions of such piles are providing little or no supporting or stabilizing function.

In order to conquer this problem in the past, it has been suggested to employ the pile-driving follower or extension, as mentioned earlier, which can be struck at its upper end in the region of the outdoor work station on platfonn 18 where the energy will be transmitted indirectly through the pile extension or follower to the upper end of the pile located well down in the leg. As noted, these systems have been subject to severe energy losses in providing such indirect force-transmitting means.

Referring to FIG. 2, a pile driving system is shown wherein the upper end of a pile 17 is shown disposed in a hollow leg 14 of support tower 13. A driving head assembly 19 comprised generally of those components shown in the enlarged detail portion of FIG. 2 is seated in the open upper end of pile 17.

Thus, the driving head assembly comprises an anvil element 21 adapted to engage the upper end of the pile 17 in blowtransmitting relation. Anvil element 21 includes a tapered frustoconical portion 211 dimensioned and adapted to fit readily into the upper end of pile 17 and to be supported by an enlarged annular midsection 21b serving to form a shoulder 22 which rests upon the upper edge of pile 17. The other end of anvil element 21 is formed to include a portion 210 of slightly reduced diameter and formed with a top face 23, which preferably can be slightly domed, to constitute the striking face of the anvil element 21 which directly receives the blows of a longitudinally movable ram or hammer element 24.

Portion 21c serves to plug and seal the lower open end of an elongated hollow case 26 secured to the upper end of anvil element 21 in a manner to form an extension of anvil 21 whereby both anvil 21 and case 26 travel together in a following movement as the pile 17 penetrates into the earth. Anvil 21 and its case extension 26 fit closely within the leg 14 in sliding manner comparable to the sliding fit between pile l7 and leg 14.

Anvil element 21 may, forexample, be of solid steel material or may be formed in a manner described further below relative to an additional embodiment pertaining to same.

While anvil element 21 serves to seal the lower end of case 26, the upper end of case 26 is also substantially sealed whereby the interior of case 26 is subjected to air pressure from an airhose 27 connected to pressurize case 26 through a compressed air inlet 28. At the lower end of case 26, an outlet 29 of a type serving to pass water while retaining air pressure within case 26, and of known construction, serves to evacuate any accumulated liquid from within case 26 under the air pressure from inlet 28.

Hammer element 24, as noted, moves through a stroke 31 to supply a succession of blows against the striking face 23 of anvil element 21. In order to eliminate any dissipation of the striking energy derived from the falling hammer element 24by virtue of any accumulated cushion of air disposed between the lower end of hammer element 24 and the striking face 23, as might otherwise form at that location by virtue of the closely fitted guided relation existing between the periphery of hammer element 24 within the closed case 26, fluid passage means have been formed longitudinally of the case and hammer for transferring fluid (such as air) therealong during movement of the hammer within the case.

Thus, as shown best in FIG. 3, fluted portions 32 form longitudinally extending peripheral indentations in the cross section of hammer element 24 in the nature of grooves to provide sufficient clearance to transfer any entrapped air at the lower end of the falling hammer element 24 to the increasing space at the upper end of hammer element 24. In order to maintain a closely fitting guiding relation between hammer element 24 and case 26 to minimize any side movement and undesirable lateral vibration forces, longitudinally extending ribs 33 are provided. Ribs 33 formed between each adjacent pair of fluted portions 32 ride along the interior wall of case 26.

With the foregoing configuration, it becomes readily possible to employ an extraordinarily massive hammer element 24 on the order, for example, of many thousands of pounds. A hammer element of such scope, if not closely contained within its guiding case can, of course, cause serious lateral impact forces acting against and damaging to the structure of the support tower 13.

Means for reciprocating hammer element 24 serves to lift it through its predetermined stroke 31 and then release the hammer element to fall freely to an advanced position where it contacts the striking face 23. Flexible cable means have been provided connected to the upper end of hammer element 24 in the form of a flexible steel cable 34 anchored in the upper end of hammer element 24 by suitable known means for embedding a cable in a solid steel material. A watertight packing gland 36 located in the upper end of case 26 passes cable 34 outwardly thereof so that cable 34 is free to move in and out of case 26 to lift and release hammer 24.

Means for actuating the cable so as to move hammer ele ment 24 between lowered and raised positions as well as to continuously pay out additional cable to operate the hammer at increasing depths as the pile penetrates the earth includes the structure shown at the upper end of support tower 13.

Thus, at the outdoor work station 18, a work surface or mounting platform 37 supports hoisting means which serves to pay out and retrieve both case 26 and hammer element 24 as well as to anchor or hold the upper end of cable 34. Thus, the hoisting means is in the form of an engine 38 of a suitable type readily controllable by an operator or attendant 39. Engine 38 is suitably coupled, as by means of the drive connection 41, to rotate the Windlass portion 42 of a winch 43. Thus, winch 43 serves to wrap and unwrap cable 34 upon Windlass 42.

A pulley 44 formed with a relatively deep sheave groove 46 engages that portion of cable 34 defined between Windlass 42 and the upper end of leg 14. As Windlass 42 is operated in a direction to pay out the cable 34, the airhose 27 may also be paid out accordingly so as to extend downwardly along leg 14. Airhose 27 is, therefore, conveniently carried upon a retractable hose reel 47 mounted to platform 37 so as to permit the airhose to be readily paid out along the other end of reel 47.

The upper end of airhose 27 is coupled to an air compressor 48 carried by platform 37. 7

Means for actuating pulley 44 to move between advanced and retracted positions so as to quickly relieve the tension in cable 34 and permit hammer element 24 to fall freely under the force of gravity includes the hydraulically. operated actuator 49 (FIG. 4). Actuator 49 is a double-acting hydraulic piston operated by suitable fluid system means whereby lines 51, 52 are alternately and quickly respectively connected to pressure and exhaust lines of a hydraulic pump 53.

The system shown in FIG. 4 for alternately applying pressure and exhaust to the opposite ends of hydraulic actuator 49 is merely representative of a number of systems for providing the function of developing a great force quickly acting to raise and to lower the pulley 44 through its predetermined stroke. From the foregoing, it will be evident that, in the condition shown, the spool style control element 58 serves to couple fluid line 52 to pressure from pump 53 via line 54 while connecting fluid line 51 to exhaust fluid to the pump via line 57. It is to be further understood, of course, that suitable reservoirs and other conventional hydraulic system devices may be employed to round out the system. The system shown in FIG. 4, therefore, is merely representative of known systems for quickly and automatically reversing hydraulic drives.

Means are also provided of a conventional nature whereby as the piston rod 59 moves upwardly to a predetermined degree adequate toproperly lift hammer element 24 to a point of release, the valveconnections described above with respect to FIG. 4 will be quickly reversed so as to quickly hydraulically drive the piston of actuator 49 downwardly and thereby move pulley.44 rapidly out of the way of the falling cable 34 wrapped therearound. Thus, movement of a projecting finger or other protrusion 61 carried by rod 59 ultimately serves to close a pair of contacts 62 so as to close the circuit of a power supply 63 and thereby energize a solenoid 64. As solenoid 64 is energized, it will act against the urging of a spring 66 which otherwise serves to urge control element 58 to the position shown in FIG. 4.

Thus, when solenoid 64 is energized, it can serve to quickly shift control element 58 in order to reverse the hydraulic connections to actuator 49.

Having the above arrangement in mind, it is readily apparent that cable 34, as trained about pulley 44, forms first and second reaches 34a, 34b thereof. The first reach is directly coupled to move hammer element 24. Hoisting means, such as the winch 43, is coupled so as to anchor the end of the second reach 34b. The actuator 49 is provided with a predetermined stroke serving to move the pulley from a lower to an upper position in order to elongate the second reach 34b while shortening the first reach by a multiple of the stroke of actuator 49. In this manner, if the stroke of actuator 49 is on the order of 2 feet, the hammer element 24 will be raised a distance of 4 feet due to the interposition of the rising pulley 44.

Additional multiplication of the actuator stroke can, of course, be obtained by introducing additional pulleys forming additional reaches of cable 34.

Further, from the foregoing, it will be readily evident that pulley 44 has less distance to travel when it is being returned, and accordingly, can move to its retracted position in less time and thereby more quickly relieve the strain on cable 34 to permit hammer element24 to fall and strike its blow. It is apparent that pulley 44 only needs to be accelerated downwardly from its upper position at a rate exceeding one half the acceleration rate provided by the force of gravity along. This fraction may be further proportionately reduced by introducing additional pulleys to further subdivide the cable into additional reach portions.

In circumstances such as the above offshore support tower application where it is found necessary to drive piles below water level and where the piles are hollow, it has been observed that the column of water entrapped within the pile can rise to a point where the anvil element 21 acts directly against the column of water and thereby generates a compression wave, in the nature of a water hammer, capable of doing considerable damage due to the great forces developed by such wave.

In addition, a further problem exists of dissipating the energy of the blow which is struck by virtue of the column of entrapped liquid which must be forced from within the pile.

With reference to FIG. 5, another embodiment of the anvil element 21 serves to solve the foregoing problems. Ac cordingly, an anvil element 71 includes a striking face 72 at its upper end adapted to be struck by the hammer element 73. The lower end of anvil element 71 includes a hollow recess 74 containing an inflated gas-filled bladder 76. Bladder 76 may,

for example, be an inflated nylonneoprene hollow sphere" having an outside diameter on the order of 1 foot or greater and a sufficient capacity so that it can be inflated with air, for example, to accommodate the hydrostatic head developedat the top of the submerged pile for the depth at which the pile is being driven. I

Thus, if anvil element 7 I is directly engaged on the upper end of the thickened wall portion 77 of pile 78 and the water level has risen to a point where it may make direct contact with the exterior of bladder 76, the striking blow of hammer 73 will not transmit a shock wave through the liquid medium within pile 78 in view of the fact that the compressive air within bladder 76 serves to initially absorb the shock.

The striking blow will, of course, serve to drive thcvpile 78 downwardly somewhat and this can serve to develop additional compression by virtue of the upwardly displaced column of water contained herein. In order to vent this water column from within pile 78, flow passages 79 of substantial diameter, for example, on the order of 4 or 5 inches, and of a sufficient number are provided so as to quickly vent the liquid. In the event that the flow passages 79 are incapable of venting the liquid quickly enough to preclude the development of a shock wave in the liquid within pile 78, it will be readily apparent that bladder 76 will absorb the momentary increase in pressure and thereby'provide additional time for discharging the liquid without forming the compression wave.

Another embodiment for safe guarding against the development of a compression wave and for venting the water displaced by downward movement of the hollow pile is shown in FIG. 6.

Thus, a pile construction 81 has been provided comprised of an elongated rigid hollow member 82 adapted to be driven in an upstanding orientation by a succession of blows applied at the upper end thereof. The upper end has been prepared with a thickened wall portion 83. A closure plate 84 serves to seal the upper end of pile 81 so as to entrap a cushion of air in the region 86 when lowering pile 81 into a body of water for driving. Openings 87 are formed at a predetermined displacement beneath closure plate 84 so as to vent the column of water 88 in response to compression derived from the driving blows of the hammer element 89 as the pile moves downwardly into the earth. The cushion of air in the region 86 therefore serves to momentarily absorb the reactive forces of the column of water 88 and to permit the flow passages formed by openings 87 to vent the column.

In another embodiment of the system for driving piles, as shown in FIGS. 7 and 8, a support tower extension structure 91 supports the hoisting means and actuator structures described above at an elevation above the level of the top of the tower. An elongated cable 92 is suitably coupled to a bail 93 so as to lift and lower an improved hammer element 94, whereby a drop-hammer action can be obtained even while driving piles at a modest angle to the vertical.

Hammer element 94 is designed to strike blows upon the upper end 96 of a pile 97 and includes a massive elongated guide stem portion 98 of a pile 97 and includes a massive elongated guide stem portion 98 movable in sliding relation coaxially within the pile 97 and further includes a massive head portion 99 formed on the upper end of stem portion 98. The underside of head portion 99 projects laterally to form a shoulder 101, which moves through a predetermined stroke S, to strike the upper end 96 of pile 97 in driving the pile. A fluid passage 102 extends longitudinally of guide stem 98 for relieving or venting fluid surge during the striking movement of hammer element 94.

Thus, as in the case of driving piles deeply into the ocean floor at a slight slant, batter piles can be driven by the drophammer system as described above whereby the hammer is lifted and released from an outdoor work station and the hammer can strike the upper end of the pile as contained in a leg 103 or other means defining a channel in which to guide and lodge the piles 97.

As thus provided, the embodiment described lastly above provides the advantage of a drop hammer acting against the upper end of a pile being driven, while at the same time serving to permit the pile to be driven into the earth at a substantial angle to the vertical.

While the systems disclosed herein overcome the problems involved in using pile extensions and followers, it will be readily evident that the disclosed systems are not incompatible with the sue of such extensions and followers. Therefore, whenever they should necessarily be required in a given construction project, the disclosed systems can be employed.

It is also apparent that the systems disclosed herein open the door to practical use of much larger hammer elements having a mass an order of magnitude greater than conventional present day systems.

lclaim:

1. In a system for driving piles by a succession of blows struck from above by a hammer element, a driving head assembly adapted to transfer the blows to the upper end of the pile comprising an anvil element adapted to engage the upper end of a pile in blow-transmitting relation thereto, an elongated hollow closed case secured at one end to the anvil element to form an extension thereof, an outlet serving to vent liquid from within said case while generally retaining air pressure within the case, means serving to supply air pressure to the interior of the case, a massive hammer element movable between advanced and retractedpositions within the case to strike said anvil at said advanced position, flexible cable means connected to one end of said hammer element, and means for actuating said cable means to move said hammer element between said positions.

2. In a system for driving piles by a succession of blows applied to the upper end of a pile, a guide channel adapted to receive a pile longitudinally inserted therein, a driving head assembly in the channel for transferring hammer blows to the upper end of the pile, said head assembly including an anvil element in the channel disposed in blow-transferring relation with the pile to travel along said channel and follow penetration of the pile, and an elongated hollow closed case in the channel and secured at one end of the anvil element and movable therewith in the channel, means for supplying air and movable with said anvil to follow the pile during driving of the pile, and means for maintaining said case free of liquid during driving of the pile, means forming a work station located on or above said body of water and supported by said leg, actuator means carried by said work station and including a mechanical coupling to said hammer element extending from said work station for moving said hammer element to strike said blows.

Claims (3)

1. In a system for driving piles by a succession of blows struck from above by a hammer element, a driving head assembly adapted to transfer the blows to the upper end of the pile comprising an anvil element adapted to engage the upper end of a pile in blowtransmitting relation thereto, an elongated hollow closed case secured at one end to the anvil element to form an extension thereof, an outlet serving to vent liquid from within said case while generally retaining air pressure within the case, means serving to supply air pressure to the interior of the case, a massive hammer element movable between advanced and retracted positions within the case to strike said anvil at said advanced position, flexible cable means connected to one end of said hammer element, and means for actuating said cable means to move said hammer element between said positionS.

2. In a system for driving piles by a succession of blows applied to the upper end of a pile, a guide channel adapted to receive a pile longitudinally inserted therein, a driving head assembly in the channel for transferring hammer blows to the upper end of the pile, said head assembly including an anvil element in the channel disposed in blow-transferring relation with the pile to travel along said channel and follow penetration of the pile, and an elongated hollow closed case in the channel and secured at one end of the anvil element and movable therewith in the channel, means for supplying air

3. In a system for anchoring a structure supported by hollow legs therebeneath, a hollow tubular leg of said structure disposed beneath the surface of a body of water and engaging the floor beneath the body of water, a pile inserted longitudinally into said leg to be driven into the floor beneath said body of water, an anvil in said leg for transferring blows to said pile, a movable hammer element in said leg for striking blows upon said anvil, a closed case containing said hammer element and movable with said anvil to follow the pile during driving of the pile, and means for maintaining said case free of liquid during driving of the pile, means forming a work station located on or above said body of water and supported by said leg, actuator means carried by said work station and including a mechanical coupling to said hammer element extending from said work station for moving said hammer element to strike said blows.

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