US3482409A - Thin walled pile and method of driving the same - Google Patents

Description

Dec. 9, 1969 w. c. cxx-:MENTS 3,482,409

THIN WALLED PILE AND METHOD OF DRIVING THE SAME 5 Sheets-Sheet l Filed June 29, 1967 0 j WLS?,

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L N W W Dec. 9, 1969 w. c. cLEMENT's 3,482,409

THIN WALLED PILE AND METHOD 0F DRIVING THE SAME Filed June 29, 1967 l 3 Sheets-Shed y2` Fiaj l/l//LL/AM C. @LEMA/TS,

wm 95,2 'm/ y ATTOR NEYS Dec. 9,'1969 w. c. cLEMENTs 3,482,409

THIN WALLED PILE AND METHOD OF DRIVING THE SAME 3 Sheets-Sheet Filed June 29, 1967 Fio Fic!!! 56 lNVENTOR/S m, MM @,m My,

United States Patent O 3,482,409 THIN WALLED PILE AND METHOD OF DRIVING THE SAME William C. Clements, Middletown, Ohio, assignor to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio Filed June 29, 1967, Ser. No. 650,018 Int. Cl. E02d 5/34 U.S. Cl. 61-53.5 16 Claims ABSTRACT OF THE DISCLOSURE Thin walled shell piles, each comprising a thin walled shell of a length suitable to form a pile, and one of a variety of tapered closure plugs to expand the lower end of the shell piles within a specified range. Additionally, the thin walled shell piles may be of a stepped-down diameter, in which case a tapered, drive t, stepped diam eter transition ring joins the varying diameters of the shells.

A drive core for driving thin walled shell piles which com-prises at least two tubular segments captively joined in telescopic fashion with a sliding t such that each segment may move from a non-load transmitting t to a load transmitting it. If the drive core is to be utilized for driving thin walled shell of two or more stepped-down diameters, the segments thereof may be stepped down to accommodate the shell.

A method of driving thin walled shell piles comprising the steps of causing a tapered closure plug to expand the lower end of a shell within a specified range, and applying driving pressure simultaneously and directly to said shell and said plug through a segmented drive core disposed within said shell until the lower end of said shell reaches a desired depth. If the shell is of two or more stepped-down diameters, a stepped-down segmented drive core is utilized.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to achieving stable building foundations, and in particular to piles which are formed by driving a steel shell into the ground and then lling the shell with concrete.

Description of the prior art In considering the selection of a pile section, the most economical pile section that will meet the following criteria should be chosen:

(1) The pile must develop the required structural column strength within permissible allowable stresses;

(2) The pile must develop the required resistance or reaction in the soil formation either by friction and/or end bearing within the limits of permissible settlement;

(3) The pile itself or in combination with a mandrel or drive core must be capable of lbeing driven into the soil formation without damage to the pile.

With allowable stresses permitted by regulations, codes and accepted engineering criteria, a pile comprising relatively thin smooth walled shell, filled with concrete in place, will meet requirement number (1). However, generally when the required energy for driving a shell is imparted to the top or butt of a shell having a diameter and thickness selected to fulll requirement number (1), the completed pile, in most cases, will not fulll requirement number (2), because it will either structurally fail under the imparted energy, or it will not transmit suicient effective energy to the pile tip to accomplish driving to the required end bearing and/or desired penetration. Thus,

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when the diameter and thickness of a smooth walled shell is selected using stress levels permissible in modern codes and criteria (12,000 to 20,000 p.s.i. for steel, and up to 0.45% of concrete compressive strength), the permissible wall thickness usually dictates that a mandrel or drive core device be employed to drive the shell to the required bearing and/or desired penetration to avoid structural failure of the shell during driving.

Driving ydevices for installing smooth walled Shell piles utilizing economical closure plugs and appurtenances with relation to the cost of heavier wall'ed shells have not been available to the engineer and contractor. Accordingly, engineers and contractors have been forced into using shells having thicker walls to accomplish driving to required bearing and/or desired penetration, resulting in an uneconomical utilization of this pile type. Since handling and driving hazards are the main obstacles to the use of pile shells having thinner walls, the most logical approach toward development of such piles was found to be along the lines disclosed by I H. Thornley in United States Patent No. 2,465,557, including further development of improved closure plugs, drive cores and methods of making the piles.

Briefly, Mr. Thornley discloses in his patent an improved pile shell core plug and method for driving a pile shell, known as the swage method. A tapered concrete plug is disposed in the ground at a location where the pile shell is to be driven. The open end of a thin walled shell is then placed over the plug and pressed down to drive the plug into the ground. The resistance of the plug to driving causes the lower end of the shell to telescope over the tapered plug to a predetermined distance, expanding the lower end of the shell, and then drive pressure is applied to the shell and to the plug. The concrete plug of Thornley comprises a precast body of concrete having an upwardly tapered shank with a flat driving face at the top and a downwardly convex working face for penetrating the soil. The tapered plug is generally about 18 inches long, with the top diameter 11 inches or less, and the maximum diameter 121/2 inches. The included angle is one inch per foot, the cone having a 4 degree and 46 minute included angle. Generally, the only requirement of Thornley is that the taper of the plug be less than the critical angle, whereby the plug and the pile shell are held together by friction between them.

While the disclosure of Thornley has proven to be satisfactory in some respects, in other respects it has proven to be most unsatisfactory. For example, it is undesirable to have single drive cores as long as feet, because s-uch long drive cores are difficult and expensive to make and transport, and require driving equipment of excess size and height. Further, such drive cores are often quite difcult, if not close to impossible, to retract from the shell because they provide negligible articulation and no acceleration of one portion of the drive core with respect to another portion thereof, such that the pull on the lower end of the drive core is maximized and the tendency of the lower end of the drive core to be retained within the shell is minimized. The closure plug of Thornley has been found to excessively expand pile shell ends, and thus pile tips, which may split the shells, permitting the entry of water, or enlarge the pile tip to such magnitude that frictional or shearing forces between the shell and soil interface are destroyed or substantially reduced. Additionally, the Thornley closure plugs very often sustain defects during the driving thereof.

A number of other prior art patents are of interest. United States Patent No. 3,190,078, in the name of F. Rusche, discloses a mandrel assembly composed of individual mandrel units which are joined together by coupling means to form a long assembly for driving pile shells having interior corrugations a relatively great distance into the ground. Each mandrel unit includes a plurality of axially spaced, angularly distributed, radially expandable individual shell engaging and gripping plugs which are expanded by bladder means so as to grip the interior of the shell and to hold the shell rigid with the mandrel during driving of the shell. After the shell has been driven to the depth desired, the plugs of the inserted mandrel are contracted and the mandrel withdrawn.

It should be pointed out that there is a great difference between mandrel assemblies and drive core assemblies. Mandrel assemblies generally grip the interior of the shell being driven, which generally is provided with corrugations, while drive cores apply pressure at the bottom of the shell being driven, or at various olfsets such as shoulders or drive rings, and do not ordinarily expand and engage the shell continuously for its length.

United States Patent No. 3,118,284, in the name of W. H. Cobi, discloses an expansible pile driving mandrel for driving thin walled pile shells having interior corrugations comprising continuous segments the outer surface of which engages the inner wall of the pile shell. Each segment extends downwardly independent from any other of the segments and is capable of flexural movement.

A further prior art patent of interest is United States Patent No. 3,269,128, in the name of F. Rusche. This patent discloses a coupled pile driving mandrel made up of a number of short mandrel sections joined together by a coupling device. The mandrel sections are provided with pressure uid such as compressed air to operate plugs which protrude from the mandrel sections to engage the corrugations in the casing or shell and form a driving connection between the mandrel section and the shell.

The known prior art references relating to mandrel sections have proven unsatisfactory in a number of respects when applied to drive cores. First, the prior art does not disclose a drive core which is readily adjustable in length with a minimal number of components. Additionally, the prior art does not disclose a drive core which can easily be retracted from the shell pile in the event of being retained therein. Further, mandrels of the prior art do not apply driving force at both the top and bottom of the shell being driven so as to maximize development of the thinnest possible shell wall. In fact, most mandrels of the prior art do not even provide for any engagement between the top of the shell and the mandrel, thus precluding the application of driving pressure to the top of the shell being driven.

SUMMARY OF THE INVENTION The instant invention discloses an improved thin walled pile and method of making the same. The shell will ordinarily be smooth Wall pipe or tube, but it may be longitudinally uted or corrugated if such deformations are of a nature as not to substantially reduce the column strength of the pile. More particularly, the instant invention provides a novel drive core for driving a thin walled shell, the shell being provided with a novel clos-ure plug. Additionally, a new method is provided for driving thin walled shell with the novel drive core.

The improved thin walled hollow pile of the' instant invention comprises a thin walled steel shell of a length suitable to form a pile, and a variety of closure plugs which have bodies with tapered sides. The lower end of the steel shell has been forced down over the tapered sides of a closure plug such that the circumference of the lower end of the steel shell is elongated within the range of 0.5 to Such a range of circumferential elongation of the lower end of the steel shell is not known in the prior art and has been found to alleviate the problems caused by excessive expansion of the pile tips which may split the shell, permit entry of water, or enlarge the pile tip to such a magnitude that frictional or shearing forces -l between the shell and soil interface are destroyed or substantially reduced. Additionally, if the thin walled shell is of a stepped-down diameter, a tapered, drive t, stepped diameter transition ring joins the varying diameters of the shell.

The improved drive core of the instant invention comprises at least two tubular segments captively joined in telescopic fashion with a sliding fit such that each segment may move from a non-load transmitting t to a load transmitting t. When the drive core is placed within the shell to be driven, the lowermost segment of the drive core rests upon the top of the tapered closure plug in a nonload transmitting position, and the top of the drive core rests upon the top or butt of the pile. As driving pressure is applied to the drive core, the shell is pressed down to drive the plug into the ground. After the lower end of the shell telescopes over the tapered closure plug, the lowermost segment of the drive core is pushed from a non-load transmitting it to a load transmitting tit so as to cause the drive core to apply driving pressure simultaneously and directly to the shell butt and to the closure plug.

If the drive core is to be utilized for driving shells of two or more stepped-down diameters, the segments thereof may be stepped down to accommodate the shell. It should also be pointed out that the segmented drive core permits substantial articulation and acceleration of each upper segment with respect to the next lower segment of the drive core, maximizing the pull on the lowermost segment of the drive core when the' drive core is removed from the shell pile, and minimizing the possibility that the lowermost segment of the drive core will be retained within the shell. Heretofore, when shells being driven were not plumb or in tangential alignment, drive cores were retained within the shells.

The novel drive core of the instant invention is readily adjustable in length with a minimum number of components so that it may be utilized in driving pile to meet varying pile requirements. lts ability to be dismantled also facilitates handling, shipping and storage. The use of large and costly pile driving equipment is substantially minimized because the drive core may be adjusted by interchanging its segments. Additionally, the segments are joined in such a manner that the splice precludes the driving load from shearing the connection. Further, the splice details facilitate rapid uncoupling of the various segments.

The instant invention provides a method of driving thin Walled shells by rst disposing a tapered closure plug on the ground at the location where* the pile is to be driven. Next, the open end of a tubular shell is placed over the closure plug and the improved segmented drive core is disposed within the shell, the lowermost segment of the drive core resting upon the top of the tapered closure plug in a non-load transmitting position. Drive pressure is then applied to the drive core causing the shell to press down and drive the closure plug into the ground, the resistance of the closure plug to driving causing the lower end of the shell to telescope over the tapered closure plug such that the circumferential elongation of the lower end of the shell is within the range of 0.5% and 10%, and push the lowermost segment of the drive core from a non-load transmitting t to a load transmitting tit. Driving pressure is then applied simultaneously and directly to the shell butt and the closure plug through the drive core until the lower end of the shell reaches a desired depth and/or bearing. The method may also include the additional step of retracting the drive core from within the shell, whereby the telescoping segments of the drive core permit articulation and acceleration of each upper segment with respect to the next lower segment, maximizing the pull on the lowermost segment in the shell and minimizing the possibility that the lowermost segment will be retained within the shell.

It should also be pointed out that the closure plug may initially be jammed into the lower end of the' shell so that driving pressure may be applied simultaneously and directly to the shell butt and the closure plug from the start.

In a still further embodiment of the method of driving thin walled shells, the shell and closure plug are initially driven into the ground until the lower end of the shell telescopes over the tapered closure plug such that the circumferential elongation of the lower end of the shell is within the previously stated range. The drive core is then disposed within the shell, the lowermost segment thereof resting upon the top of the closure plug in a load transmitting fit, and driving pressure is simultaneously and directly applied to the shell butt and the closure plug until the lower end of the shell reaches a desired depth.

If the shell is of two or more stepped-down diameters, a stepped-down segmented drive core' is utilized, and the method for driving the shell is somewhat modified. The uppermost segment of a stepped diameter segmented drive' core is first retracted from a previously driven shell and then separated from the lowermost core segment while the lowermost core segment is retained in the retracted position. A first thin walled shell is threaded onto the uppermost segment of the drive core, and the uppermost segment of the drive core is rejoined with the remainder of the drive core which is being retained within the first previously driven shell. The stepped drive core and the first shell threaded thereon are then fully retracted from the first previously driven shell. A second thin walled shell of a diameter less than the diameter of the first shell is then placed in a second previously driven shell, the second shell being retained within the second previously driven shell such that the upper end thereof protrudes from the shell. A tapered, drive fit, stepped diamete'r transition ring is disposed around the upper end of the second shell, and the stepped diameter drive core is disposed within the second shell such that the lower end of the first shell, which is threaded onto the stepped drive core, is seated on the transition ring. The stepped drive core and the first and second shells are then fully retracted from the second previously driven shell and disposed over a tapered closure plug on the ground at the location where the new shell is to be driven. The first and second shell and the closure plug are then driven in the previously explained manner.

BRIEF DESCRIPTION OF THE DRAWING FIGURE 1 is -a broken-away side elevation showing the thin walled shell and the tapered closure plug which form the parts of the pile t be driven.

FIGURE 2 is a broken-away side elevation showing the pile to be driven after the drive core has been placed therein.

FIGURE 3 is a broken-away side elevation of the pile of the instant invention after it has been partially driven so that the plug is embedded within the lower end of the thin walled shell.

FIGURE 4 is a broken-away side elevation showing the pile of the instant invention driven to the desired depth and filled with concrete.

FIGURE 5 is an exploded cross-sectional view of a drive core according to the instant invention.

FIGURE 6 is a cross-sectional view of a segment of a stepped-down diameter drive core according to the instant invention.

FIGURE 7 is a broken-away side elevation at a reduced scale showing a stepped-down diameter drive core of the invention lifted to position within a first previously driven shell and having a holding pin engaged.

FIGURE 8 is a broken-away side elevation at a reduced scale showing the upper portion of the stepped-down diameter drive core of the invention disengaged from the remainder of the drive core so as to facilitate threading the uppermost portion of a first shell thereon.

FIGURE 9 is a broken-away side elevation at a reduced scale of the upper portion of the drive core of the invention which is lowered and captively engaged to the lower portion of the drive core within the first previously driven shell, the holding pin being removed.

FIGURE 10 is a broken-away side elevation at a reduced scale of -a stepped drive core assembly, the first shell being threaded thereon, as it is lowered into a second previously driven shell, a second shell of a smaller diameter than the first shell and having a stepped-down, tapered transition ring at one end thereof, being retained within the second previously driven shell.

FIGURE 1l is a broken-away side elevation at a reduced scale of the entire stepped drive core and shell assembly as being driven.

FIGURE 12 is a perspective view of a closure plug according to the instant invention, the tip of which has been reinforced by an embedded fabricated cross.

FIGURE 13 is a perspective view of a closure plug according to the instant invention which has been reinforced with a shield.

FIGURE 14 is a perspective view of the closure plug of FIGURE 13, the tip of which has been further reinforced with a fabricated steel cross.

FIGURE l5 is a perspective view of the closure plug according to the instant invention which has been reinforced at its lower end with another type of shield.

FIGURE 16 is a perspective view of a closure plug according to the instant invention wherein a plate having a fabricated steel cross depending therefrom is embedded in the plug.

FIGURE 17 is a perspective view of a closure plug according to the instant invention which is provided with at least two holding tabs extending from the periphery of its lower base.

FIGURE 18 is a cross-sectional view of a closure plug which comprises a precast concrete pile section.

FIGURE 19 is -a cross-sectional view of a pedestal closure plug according to the instant invention.

FIGURE 2O is a perspective view of another closure plug according to the instant invention and a cross-sectional view of the shell.

FIGURE 21 is a perspective view of another closure plug according to the instant invention and a cross-sectional view of the shell.

FIGURE 22 is a perspective View of `another closure plug according to the instant invention and a cross-sectional view of the shell.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides an improved construction and method for placing thin walled shell in the ground to form a pile. It will be understood that after the shell has been placed in the ground, it will be filled with concrete to complete the formation 0f the pile.

FIGURE 1 discloses the elements of the pile according to the instant invention. A shell 10 of a length sufiicient to form the desired pile is disposed over a tapered closure plug 11. The plug 11 is preferably of prec-ast concrete, but, as will be more fully explained hereinafter, it may be of metal or other suitable material so long as its tapered sides provide circumferential elongation of the lower end of the shell within the range of 0.5% to 10%.

, In a typical embodiment of the instant invention, the shell 10 has an inside diameter of 12 inches, and the wall thickness is within the range of 0.1 inch minimum to 0.3 inch maximum. The length of shell 10 which will be utilized preferably varies in l foot increments up to feet or more. The precast concrete plug 11 is typically of a length of l2 inches plus or minus 1A inch and is of a frusto-conical design, the larger base being of a diameter of 12% inches plus or minus 1/32 inch, and the smaller base being of a diameter of 111/2 inches plus or minues 1&2 of an inch.

It should be noted that an important requirement is that the taper of the plug 11 be such that when it is fully seated in the lower end of the shell 10, as will be more fully explained hereinafter, the circumferential elongation of the lower end 13 will be within the range of 0.5% to 10%. It has been found that when the circumferential elongation of the lower end 13 of the shell 10 is within this range, the lower end 13 of the shell 10 will more adequately transfer the loading upon the pile to the soil below, and provide a reliable water tight fit without danger of splitting the pile.

FIGURE shows a cross-sectional view of a drive core 14. The drive core 14 comprises tubular segments 15 captively joined in telescopic fashion with a sliding fit such that each segment may move from a non-load transmitting fit to a load transmitting fit. The lower end of each segment 15 receives a sleeve 17 in a tight fit. The sleeve 17 is welded or otherwise affixed to the inside of the segments 15. A slot 19 in each sleeve 17 provides an aperture for the passage of a pin 20, located in the top of each segment 15, to captively retain the segments 15 together. It will be clear that the segments 15 are joined in telescopic fashion and that they may slide with respect to each other the length of the slot 19. When the ends of the segments 15 are in contact with each other, they are in a load transmitting fit. However, when the ends of the segments 15 are not in contact with each other, the lowermost segment being posi tioned at the tapered or reduced end 18 of the sleeve 17, the segments 15 are in a non-load transmitting fit.

A drive core head 16, being the uppermost segment of the drive core 14, transmits force from the driving cap 19a to the pile, as will be more fully explained lhereinafter.

An adjusting sleeve 16a aids in adjusting the contact position 21a on the drive core 14 to accommodate shell of various lengths. The adjusting sleeve 16a may be slipped over or clamped on the drive head 16 of the drive core 14 to rest against the shoulder 16b thereof.

Intermediate segments may be provided to accommodate longer piles than provided for with only a two part drive core.

Joined to the lowest segment 1S of the drive core is a standard bottom 21. The standard bottom 21 is joined to the lowest segment 15 of the drive core in the same manner as the segments join together. In operation, it is the standard bottom 21 which contacts the driving face 22 of the closure plug 11.

If the drive core 14 is to drive stepped-down diameter shell, stepped-down diameter segments 15a, as shown in FIGURE 6, must be utilized. As can be seen from FIGURE 6, the stepped-down segments 15a of the drive core 14 are joined to segments 15 and the standard bottom 21 in the same manner as the segments 15 are joined together.

It should be pointed out that stepped segments 15a are used with the drive core 14 to facilitate threading the drive core 14 into a shell 10, as more fully explained hereinafter, eliminating long leads for the driving means. Additionally, stepped diameter segments 15a are used because the diameter of lower shells 10 may be reduced as the loading thereon is transferred by friction to the soil at upper levels of the shell 10.

The drive head 16, the segments 15 and 15a, and the standard bottom 21 are preferably provided with longitudinally extending spacer ribs 15b. The spacer ribs 15b are spaced equally around the periphery of the segments 15 and 15a and the standard bottom 21, and aidtin positioning the drive core 14 Within the shell 10, in minimizing the tendency of the shell 10 to sweep out of aligment, and in minimizing friction between the drive core 14 and the inside of the shell 10.

In the preferred embodiment of the invention, the drive core head 16 is 15 or 20 feet, the adjusting sleeve 16a is in increments of l, 2, 3 or 4 feet, the segments 15 are 5, 10, 15 or 2.0 feet, the standard bottom 21 is in increments of 5, 10, 15 or 20 feet, and the stepped-down diameter segment 15a is 5 feet. This, of course, enables the formation of a drive core 14 of a length sufficient to drive a pile to any desired depth.

Turning now to FIGURES 1-4, the method of driving a shell and closure plug according to the instant invention will be explained.

In FIGURE l, the Open end of a shell 10 is disposed over a closure plug 11 which has been placed on the ground at the location where the pile is to be driven. A segment 15 of the drive core 14, having thereon a standard bottom 21 and a drive head 16, is then disposed within the thin walled shell 10, such that the drive head 16 receives the butt of the shell 10 and the standard bottom 21 rests in a non-load transmitting position against the working face 22 of the closure plug 11.

It should be noted at this time that the position of the pin 20 in the slot 19 is such that the standard bottom 21 does not hang free within the shell 10. This is important, for when the shell 1f) is subsequently driven so that the plug is forced into the ground and into the lower end of the shell 10, inertia would cause the standard bottom 21, if free hanging, to be torn loose from the drive core 14.

The driving means (not shown) next applies the driving pressure to the head 16 of the drive core 14, whereby the shell 10 is pressed down to drive the closure plug 11 into the ground. The resistance of the closure plug 11 to driving causes the lower end of the shell 10 to telescope over the tapered closure plug 11. Additionally, the closure plug 11, when embedded within the lower end of the shell 10, pushes the standard bottom 21 upwardly against a segment 15 of the drive core 14 from a nonload transmitting fit to a load transmitting fit. The driv ing means now furnishes driving pressure through the head 16 simultaneously and directly to the shell 10 and through the drive core 14 to the closure plug 11 until the lower end of the shell 10 reaches a desired depth and/or bearing.

It should be pointed out that a pile of any desired length may be driven by the apparatus and method 0f the instant invention. All that is necessary is that after the butt of a particular shell 10 is driven substantially level with the ground, another shell 10 is placed atop thereof, the shells being sufficiently joined together. A further segment 15 of the drive core 14 is then captively joined by a pin 20 through the slot 19 to the preceding segment 15 of the drive core 14. It should also be emphasized that piles of any length may be driven by simply formulating a drive core 14 of the proper length from the increments available for the drive head 16, the adjusting sleeve 16a, the segments 15 and 15a, and the standard bottom 21.

The above referred to method may be successfully modified in several respects. First, the closure plug 11 may be jammed into the lower end of the shell 10 such that the circumferential elongation of the lower end is within the range of 0.5 to 10%. The shell 10 and plug 11 may then be disposed over the location where they are to be driven, the drive core 14 being inserted into the shell 10, the lower segment thereof resting upon the closure plug 11 in a load transmitting position, and the shell 10 and closure plug 11 driven to the desired depth and/or end bearing.

It will be understood that the shell 10 and closure plug 11, irrespective of whether or not the closure plug 11 is first jammed into the lower end of the shell 10 or whether it is seated in the end thereof when the shell 10 is trst driven, may first be driven into the ground by the driving means applying driving pressure to the butt of the shell 10 before the drive core 14 is inserted within the shell 10.

After the shell 10 has been driven to a desired depth and/or end bearing, the driving means withdraws the drive core from within the shell 10. Heretofore, great difficulty was experienced in withdrawing the drive core from piles because many piles very often were not driven in a near perfect plumb or tangential alignment and the drive core was retained therein. However, the segmented drive core 14 of the instant invention substantially eliminates this problem because the telescoping segments permit substantial articulation and deflection of the drive core 14 so that it can be more readily extracted from shells 10 which have not been driven in a near perfect plumb or tangential alignment.

In driving shells, it is common that uneven distribution of tip pressures tend to make the shells sweep or bend off theoretical vertical alignment. Without the benefit of articulation or deflection of the joints of the drive core 14 While the segments 15 and 15a thereof are in a non-load transferring position, the drive core 14 would tend to bind within the bent or swept shell, producing high friction forces between the outside of the drive core 14 and the interior of the shell 10. The articulation provided in the joints of the drive core 14 while the segments 1S and 15a thereof are in a non-load transferring position permits the drive core 14 to more nearly conform to the alignment of the bent or swept shells 10 without binding and producing high friction on the inside of the shell 10, which makes removal diicult. Depending upon the length of the shell 10, one or more joints may be provided in the drive core 14 to maximize the flexibility or articulation of the drive core. For example, as previously explained, drive cores may be made having joints at l foot, 15 foot, 20 foot or other suitable intervals.

Additionally, the telescoping joints between segments of drive core 14 of the instant invention permit acceleration of each upper segment 15 with respect to the next lower segment 15, to the extent of the length of the slot 19 in the sleeve 17 of each segment 1S, maximizing the pull on the lowermost segment 1S and the standard bottom 21 within the shell 10, and further precluding them from being retained within the shell because of any binding or frictional forces between the drive core 14 and the shell 10.

If shells 10 of stepped-down diameter are to be driven the drive core 14 will include the stepped-down segments 15a. Referring now to FIGURES 7 through 1l, the method for driving a drive core 14 having stepped-down diameter segments 15a will be explained.

The uppermost segment 15a of the drive core 14 is retracted from within a first previously driven stepped diameter shell 100. The splice pin is then retracted from the slot 19 in the sleeve 17 of the uppermost segment 15a, freeing that segment from the remainder of the drive core 14. The drive core 14 is preferably retained in the retracted position by inserting a holding pin 101 into the upper end of the lower segment 15a, of standard bottom 21, retaining the end of that segment slightly outside of the first previously driven shell 100.

A rst shell 10a to be driven is threaded onto the uppermost segment 15a of the drive core 14, as shown in FIGURE 8, and the upper segment 15a is rejoined with the remainder of the drive core 14 being retained within the first previously driven hole 100. The drive core, having threaded thereon the rst shell 10a to be driven, is then fully retracted from the first previously driven shell 100, as shown in FIGURE 9.

A second shell 10b of a diameter less than the diameter of the first shell 10a is disposed within a second previously driven shell 102, and a tapered drive t, stepped diameter transition ring 103 is placed around the upper end thereof, as shown in FIGURE 10. The fully retracted drive core 14, having threaded thereon the first shell 10a, is next disposed within the second previously driven shell 102 until the lower end of the lirst shell 10a is seated on the transition ring 103, circumferentially elongating the lower end of the rst shell 10a. The drive core 14 and the first and second shells 10a and 10b, respectively, are then fully retracted from within the second previously driven shell 102, and the first and second shells 10a and 10b, respectively, are driven in the manner previously explained until the second shell 10b and the closure plug 11 reach the desired depth and/ or end bearing, as shown in FIGURE 1l.

A great many of the reported pile collapse problems of presently driven shell piles are, in fact, failures due to the pile tip encountering an eccentric tip load during driving. This may be caused, for example, by the tip striking boulders, underground obstructions, irregular rock or hard pan formations. With flat closure plug ends there is no tip reinforcement to effectively distribute the eccentric load over the entire shell cross section just above the flat end, and extremely high localized stresses are developed which cause the shell wall to buckle just above the flat end of the closure plug. While the instant invention substantially eliminates these problems, since the tip of the shell 10 will be heavily reinforced by the closure plug 11, and the bulk of the driving energy will be transferred to the tip through the drive core 14 and closure plug 11 rather than through the shell Wall 10, various protective means are often necessary to protect the tip of the shell and to seat the shell adequately in hard rock or other impenetrable formations without damage to the lower face of the closure plug 11 or tip of the shell 10. FIGURES 12-16 disclose various closure plug reinforcements which have proven to be most satisfactory.

As was previously stated, the closure plug 11 has a body with tapered sides so that the lower end of the shell 11 telescopes over the closure plug 10. Preferably, the closure plug 11 comprises a precast body of concrete with the sides tapered upwardly in substantially frusto-conical form, and the top of the closure plug, the working face thereof, comprises a substantially flat face.

FIGURE l2 discloses a reinforcement for the closure plug 11, and hence the tip of the pile, which comprises at least two cross stiffener bars 50 cast into the closure plug 11, the bars protruding from the lower base of the frusto-conical body.

FIGURE 13 discloses a formed steel pan shield 51 which is placed beneath the closure plug 11 before the open end of the shell 10 is disposed over the closure plug 11. As shown in FIGURE 14, the pan or shield 51 may have other reinforcement attached thereto, such as, for example, the fabricated steel cross 52.

A steel plate shield 53 is disclosed in FIGURE l5. This reinforcement shield may be attached to the closure plug 11 by suitable means, such as, for example, a bolt 54 which is embedded in the closure plug 11. Additionally, a fabricated steel cross 55 may be provided to add further reinforcement.

A fabricated steel cross 56 attached to a plate 57 may be partially embedded within the lower end of the closure plug 11, as disclosed in FIGURE 16.

A further embodiment of the instant invention is the provision of at least two holding tabs 59 extending from the periphery of the larger base of the substantially frustoconical body of the closure plug 11, as shown in FIGURE 17. The purpose of the tabs is to preclude the entry of the closure plug 11 into the open lower end of the shell 10 beyond the full seating depth when the shell is partially driven without the drive core.

The closure plug 11, preferably of precast concrete, and as heretofore described, may include a precast concrete pile section 60 of any length or downward configuration, as shown in FIGURE 18. Additionally, reinforcement, such as the reinforcing bars `61, may be utilized as required.

A further embodiment of the closure plug 11 is shown in FIGURE 19, wherein the lower end of the closure plug 11 includes a precast pedestal 62 which rapidly mobilizes high tip bearing in weak soil strata. The pedestal closure plug 62 may, of course, be reinforced with the reinforcing bars 63, as required.

While a preferred closure plug 11 comprises a precast body of concrete with the sides tapered upwardly in substantially frusto-conical form, and having a top which comprises a substantially flat face, other closure plugs have also proven to be satisfactory. FIGURES 20-22 disclose other tapered closure plugs made from cast or fabricated metal which have been found to be acceptable in that they maintain the circumferential elongation of the lower end of the shell within the range of 0.5% to 10%, while at the same time, the standard bottom 21 of the drive core 14 is still provided with a surface upon which it may rest in a non-load transmitting position until such time as the driving cap 19a has furnished driving pressure through the drive head 16. The shell 10 is then pressed down to drive the plug 11 into the ground, the resistance of the closure plug to the driving causing the lower end of the shell 10 to telescope over the tapered closure plug, pushing the working head 21 of the drive core 14 from a non-load transmitting rit to a load transmitting t.

The closure plug 70 of FIGURE 20 comprises a substantially ilat circular section 71 having tapered sides 72 which depend outwardly and downwardly therefrom. Additionally, a cross stifener rib 73 may be provided on the under side of the circular section 71 between the tapered -sides 72 for additional reinforcement.

The closure plug 74 of FIGURE 2l comprises a sub` stantially flat circular section 75 having tapered sides 76 extending inwardly and upwardly therefrom. Fabricated cross stiifeners 77 depending from the at circular section 75 may be utilized for additional reinforcement. Further, the closure plug 74 may be fabricated with shoulders 78, as shown in FIGURE 22.

It will be understood that modifications may be made without departing from the spirit of the invention, and therefore, no limitations other than those specifically set forth in the claims are intended or should be implied.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of driving a thin walled shell which comprises the steps:

(a) disposing a tapered closure plug on the ground at the location where the shell is to be driven;

(b) disposing the open end of a relatively thin walled tubular shell over said closure plug;

(c) disposing a segmented drive core within said thin walled shell so that the lowermost segment of said drive core rests upon the top of said tapered closure plug in a non-load transmitting position, and providing the lower end of each segment of said drive core with a slot for the passage of retaining means located in the upper end of each adjacent segment of said drive core such that the segments are joined in telescoping fashion and may move with respect to each other the length of said slot from a non-load transmitting t to a load transmitting fit;

(d) applying driving pressure to said drive core so that said shell is pressed down to drive said closure plug into the ground, the resistance of said closure plug to driving causing the lower end of said shell to telescope over said tapered closure plug such that the circumferential elongation of the lower end of said shell is within the range of 0.5% to 10% and such that when said circumferential elongation of the lower end of said shell is within this range said closure plug pushes said lowermost segment of said drive core from a non-load transmitting t to a load transmitting lit; and

(e) applying driving pressure simultaneously and directly to said shell and said closure plug through said drive core until the lower end of said shell reaches a desired depth.

2. The method according to claim 1, including the additional step of retracting said drive core from within said shell, whereby said telescoping segments of said drive core permit articulation and acceleration of each upper segment of said drive core, maximizing the pull on the lowermost segment within said shell, and minimizing the possibility that the lowermost segment will be retained within said shell.

3. A method of driving thin walled shell, which comprises the steps:

(a) jamming a tapered closure plug into the open lower end of said shell such that the circumferential elongation of the lower end of said shell is within the range of 0.5% to 10%;

(b) disposing a segmented drive core within said shell so that the lowermost segment of said drive core rests upon the top of said tapered closure plug in a load transmitting position when said circumferential elongation of the lower end of said shell is within said range, and providing the lower end of each segment of said drive core with a slot for the passage of retaining means located in the upper end of each adjacent segment of said drive core such that the segments are joined in telescoping fashion and may move with respect to each other the length of said slot from a non-load transmitting iit to a load transmitting fit; and

(c) applying driving pressure simultaneously and directly to said shell and said closure plug through said drive core until the lower end of said shell reaches a desired depth.

4. The method according to claim 3, including the additional step of retracting said drive core from within said shell, whereby said telescoping segments permit articulation and acceleration of each upper segment of said drive core with respect to the next lower segment of said drive core, maximizing the pull on the lowermost segment of said drive core within said shell, and minimizing the possibility that the lowermost segment will be retained within said shell.

5. A method of driving thin walled shell, which comprises the steps:

(a) disposing a tapered closure plug on the ground at the location where the pile is to be driven;

(b) disposing the open end of a relatively thin walled tubular shell over said closure plug;

(c) applying driving pressure to said shell, whereby said shell is pressed down to drive said closure plug into the ground, the resistance of said closure plug to driving causing the lower end of said shell to telescope over said tapered closure plug such that the circumferential elongation of the lower end of said shell is within the range of 0.5 to 10%;

(d) disposing a segmented drive core within said thin walled shell so that the lowermost segment of said drive core rests upon the top of said tapered closure plug in a load transmitting position when the circumferential elongation of the lower end of said shell is within said range, and providing the lower end of each segment of said driv`e core with a slot for the passage of retaining means located in the upper end of each adjacent segment of said drive core such that the segments are joined in telescoping fashion and may move with respect to each other the length of said slot from a non-load transmitting tit to a load transmitting fit; and

(e) applying driving pressure simultaneously and directly to said shell and said closure plug through said drive core until the lower end of said shell reaches a desired depth.

6. The method according to claim 5, including the additional step of retracting said drive core from within said shell, whereby said telescoping segments of said drive core permit articulation and acceleration of each upper segment with respect to the next lower segment of said drive core, maximizing the pull on the lowermost segment of said drive core within said shell, and minimizing the possibility that the lowermost segment will be retained in said shell.

7. A method of driving thin walled shell, which cornprises the steps:

(a) jamming a tapered closure plug into the open lower end f said shell such that the circumferential elongation of the lower end of said shell is within the range of 0.5% to (b) applying driving pressure to said shell, whereby said shell is driven into the ground;

(c) disposing a segmented drive core within said shell so that the lowermost segment of said drive core rests upon the top of said tapered closure plug in a load transmitting position when the circumferential elongation of the lower end of said shell is within said range, and providing the end of each segment of said drive core with a slot for the passage of retaining means located in the upper end of each adjacent segment of said drive core such that the segments are joined in telescoping fashion and may move with respect to each other the length of said slot from a non-load transmitting fit to a load transmitting fit; and

(d) applying driving pressure simultaneously and directly to said shell and said closure plug through said drive core until the lower end of said shell reaches a desired depth.

8. The method according to claim 7, including the additional step of retracting said drive core from Within said shell, whereby said telescoping segments of said drive core permit articulation and acceleration of each upper segment with respect to the next lower segment of said drive core, maximizing the pull on the lowermost segment of said drive core within said shell, and minimizing the possibility that the lowermost segment will be retained within said shell.

, 9. A method of driving stepped diameter thin walled shell, which comprises the steps:

(a) retracting the uppermost segment of a stepped diameter segmented drive core from within a first previously driven stepped diameter shell, each segment of said drive core being captively joined in telescoping fashion with a sliding fit to another segment of said drive core such that each segment of said drive core may move from a non-load transmitting fit to a load transmitting fit;

(b) removing said uppermost segment from said drive core while said drive core is retained in said retracted position;

(c) threading a first thin walled shell onto said uppermost segment of said drive core;

(d) rejoining said uppermost segment of said drive core with the remainder of said drive core retained within said first previously driven stepped diameter shell;

(e) fully retracting said stepped diameter drive core and said first thin walled shell threaded thereon from within said first previously driven stepped diameter shell;

(f) disposing a second thin walled shell of a diameter less than said first shell within a second previously driven pile such that the upper end of said second shell is retained out of said second previously driven shell;

(g) disposing a tapered, drive fit, stepped diameter transition ring around the upper end of said second shell;

(h) disposing said stepped diameter drive core within said second previously driven shell such that the lower end of said first shell which is threaded onto said drive core is seated on said transition ring;

(i) retracting said stepped diameter drive core and said first and second shells from within said second previously driven shell;

(j) disposing a tapered closure plug on the ground at the location where the shell is to be driven;

(k) disposing the open end of said second shell over said closure plug such that the lowermost segment of said stepped drive core rests upon the top of said tapered closure plug in a non-load transmitting position;

(l) applying driving pressure to said stepped drive core, whereby said first and second shells are pressed down to drive said closure plug into the ground, the resistance of said closure plug to driving causing the lower end of said second shell to telescope over said tapered closure plug such that the circumferential elongation of the lower end of said shell is within the range of 0.5% to 10%, said closure plug pushing said lowermost segment of said stepped drive core from a non-load transmitting fit to a load transmitting fit; and

(m) applying driving pressure simultaneously and directly to said first and second shells and said closure plug through said drive core until the lower end of said second shell reaches a desired depth.

10. The method according to claim 9, including the additional step of retracting said stepped drive core from within said first and second shells, whereby said telescoping segments of said stepped drive core permit articulation and acceleration of each upper segment of said stepped drive core with respect to the next lower segment of said drive core, maximizing the pull on the lowermost segment of said stepped drive core within said first and second shells, and minimizing the lowermost segment being retained within said first and second shells.

11. A method of driving stepped diameter thin walled shell, which comprises the steps:

(a) retracting the uppermost segment of a stepped diameter segmented drive core from within a first previously driven stepped diameter shell, each segment of said drive core being captively joined in telescop-r ing fashion with a sliding fit to another segment `of said drive core such that each segment of said drive core may move from a non-load transmitting fit to a load transmitting fit;

(b) removing said uppermost segment from said drive core while said drive core is retained in said retracted position;

(c) threading a first thin walled shell onto said uppermost segment of said drive core;

(d) rejoining said uppermost segment of said drive core with the remainder of said drive core retained within said first previously driven stepped diameter shell;

(e) fully retracting said stepped diameter drive core and said first thin walled shell threaded thereon from within said first previously driven stepped diameter shell;

(f) disposing a second thin walled shell of a diameter of said first shell within a second previously driven pile such that the upper end of said second shell is retained out of said second previously driven shell;

(g) disposing a tapered, drive fit, stepped diameter transition ring around the upper end of said second shell;

(h) disposing said stepped diameter drive core within said second previously driven shell such that the lower end of said first shell which is threaded onto said drive core is seated on said transition ring;

(i) retracting said stepped diameter drive core and said first and second shells from within said second previously driven shell;

(j) jamming a tapered closure plug into the open lower end of said second shell such that the circumferential elongation of the lower end of said second shell is within the range of 0.5% to 10%, the lowermost segment of said stepped drive core resting upon the top of said tapered closure plug in a load transmitting position; and

(k) applying driving pressure simultaneously and directly to said first and second shells and said closure plug through said drive core until the lower end of said second shell reaches a desired depth.

12. The method according to claim 11, including the additional step of retracting said stepped drive core from within said lirst and second shells, whereby said telescoping segments of said stepped drive core permit articulation and acceleration of each upper segment of said stepped drive core with respect to the next lower segment of said drive core, maximizing the pull on the lowermost segment of said stepped drive core within said iirst and second shells, and minimizing the lowermost segment being retained within said lirst and second shells.

13. A drive core for driving thin walled shell, the open end of said shell being disposed over a closure plug on the ground at the location where each shell is to be driven, which comprises at least two tubular segments captively joined in telescopic fashion with a sliding fit such that each segment may move from a non-load transmitting t to a load transmitting tit, the lowermost segment of said drive core resting upon said closure plug in a non-load transmitting position, a drive head at the upper end of said uppermost segment which communicates with driving means, said drive head including an annular shoulder which contacts the butt of said shell, and a hollow adjusting sleeve which is positioned between said drive head and the uppermost segment of said drive core, the upper end of said adjusting sleeve being slidably received on said annular shoulder of said drive head and the lower end thereof slidably receiving the upper end of said upper segment, said adjusting sleeve being provided at a location intermediate thereof with an annular shoulder which contacts the butt of said shell, whereby the length of said drive core may be adjusted to accommodate a variety of shells of differing lengths, and whereby as driving pressure is applied to said drive core by said driving means, said thin walled shell is pressed down to drive said plug into the ground, the resistance of said plug to driving causing the lower end of said shell to telescope with said closure plug, said closure plug pushing said lowermost Segment of said drive core from a non-load transmitting t to a load transmitting t so that said drive core applies driving pressure simultaneously and directly to both said shell and said closure plug until such time as the lower end of said shell and said closure plug reach a desired depth, and whereby said segments permit articulation and acceleration of each upper segment of said drive core with respect to the next lower segment of said drive core as the drive core is retracted from said shell, maximizing the pull on the lowermost segment of said drive core within said shell, and minimizing the possibility that the lowermost segment of said drive core will be retained within said shell.

14. A drive core for driving thin walled shell, the open end of said shell being disposed over a closure plug on the ground at the location where each shell is to be driven, which comprises at least two tubular segments captively joined in telescopic fashion with a sliding tit, a splice pin located within the upper end of each segment, and a tight fitting sleeve located in the lower end of each segment, said tight fitting sleeve having a slot therein for receipt of said splice pin, whereby said segments may move with respect to each other the length of said slot from a nonload transmitting fit to a load transmitting tit, the lowermost segment of said drive core resting upon said closure plug, and a drive head at the upper end of said uppermost segment which communicates with driving means, said drive head including an annular shoulder which contacts the butt of said shell, whereby as driving pressure is applied to said drive core by said driving means, said thin walled shell is pressed down to drive said plug into the ground, the resistance of said plug to driving causing the lower end of said shell to telescope with said closure plug to a length substantially equal to the length of said slot so that said closure plug pushes said lowermost segment of said drive core from a non-load transmitting tit to a load transmitting t and said drive core thus applies driving pressure simultaneously and directly to both said shell and said closure plug until such time as the lower end of said shell and said closure plug reach a desired depth, and whereby said segments permit articulation and acceleration of each upper segment of said drive core with re spect to the next lower segment of said drive core as the drive core is retracted from said shell, maximizing the pull on the lowermost segment of the drive core within said shell, and minimizing the possibility that the lowermost segment of said drive core will be retained within said shell.

15. The drive core according to claim 14, wherein the periphery of said segments is provided with longitudinally extending spaced apart ribs, whereby said drive core is centered within said shell being driven and said friction between said drive core and the interior surface of said shell is minimized.

16. The drive core according to claim 14, wherein at least one of said segments is provided with a longitudinal cross section of stepped diameter, whereby said drive core can drive stepped diameter thin walled shell.

References Cited UNITED STATES PATENTS 1,771,312 7/1930 Pierce 61-53.7 2,465,557 3/1949 Thornley 6l-53.52 2,639,589 5/1953 Smith 6l53.7 3,263,431 8/1966 Phares 6l-53.5

JACOB SHAPIRO, Primary Examiner U.S. Cl. X.R.

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