US3925998A

US3925998A - Method for forming cast-in-place caseless concrete piles

Info

Publication number: US3925998A
Application number: US491481A
Authority: US
Inventors: William R Lecorgne
Original assignee: INTERPILE USA Inc
Current assignee: INTERPILE/BARCUS Corp A FLA CORP
Priority date: 1974-07-22
Filing date: 1974-07-22
Publication date: 1975-12-16
Anticipated expiration: 1992-12-16

Abstract

The method of forming cast-in-place caseless concrete piles where pile holes to be driven in the earth into which concrete is to be fed occupy a proximity area such that transmission of forces during driving of some pile holes may damage the shape of others, wherein a respective hollow tubular driving mandrel and driving foot member releasably coupled thereto are driven into the earth to form each pile hole in the proximity area, and the mandrel for driving each hole is left fully inserted in its pile hole to protect the shape of the pile hole until all pile holes in such proximity area are driven, and the mandrels are then withdrawn after flowing concrete in the pile holes to leave castin-place caseless piles.

Description

United States Patent [1 1 LeCorgne Dec. 16, 1975 METHOD FOR FORMING CAST-IN-PLACE CASELESS CONCRETE PILES [75] Inventor:

[73] Assignee: lnterpile USA, Inc., New Orleans,

[22] Filed: July 22, 1974 211 Appl, No.: 491,481

[52] US. Cl. 6l/53.64; 61/50; 61/565 [51] Int. Cl. EOZD 5/34; EO2D 3/08 [58] Field of Search 61/50, 53.5, 53.52, 53.64,

{56] References Cited UNITED STATES PATENTS 3.638.433 2/1972 Sherard 61/535 X 12/1974 Steding.....

William R. LeCorgne, New Orleans,

Primary Examiner-Jacob Shapiro Attorney, Agent, or Firm-Mason, Fenwick & Lawrence [57] ABSTRACT The method of forming cast-in-place caseless concrete piles where pile holes to be driven in the earth into which concrete is to be fed occupy a proximity area such that transmission of forces during driving of some pile holes may damage the shape of others, wherein a respective hollow tubular driving mandrel and driving foot member releasably coupled thereto are driven into the earth to form each pile hole in the proximity area, and the mandrel for driving: each hole is left fully inserted in its pile hole to protect the shape of the pile hole until all pile holes in such proximity area are driven, and the mandrels are then withdrawn after flowing concrete in the pile holes to leave cast-inplace caseless piles.

10 Claims, 7 Drawing Figures U.S. Patent Dec. 16, 1975 Sheet 2 of2 3,925,998

METHOD FOR FORMING CAST-llN-PLACE CASELESS CONCRETE FILES BACKGROUND AND OBJECTS OF THE INVENTION The present invention relates in general to methods for forming castin-place caseless concrete piles, and more particularly to methods for forming such cast-inplace caseless concrete piles by driving into the ground a driving foot or boot member releasibly assembled on a hollow tubular driving mandrel to form the pile-forming hole or bore hole, then filling the bore hole with concrete and forming other pile bore-holes nearby without distortion or damage to the previously formed hole configuration or freshly poured concrete for closely adjacent piles.

For a long time, cast-in-place concrete piles of the type wherein a steel shell or outer casing was driven in the ground to be permanently left in the ground and concrete thereafter poured therein to form the pile, found widespread utility in the construction field. However, because of the cost and shortage of steel, delays in securing delivery of steel casings, and related factors, efforts have been made for many years to devise. effective methods of providing cast-in-place concrete piles which do not require a steel shell. Cast-in-place concrete piles which do not have such steel shells are generally termed caseless piles. The advantages to be gained by such cast-in-place caseless concrete piles lie principally in the reduction in material costs achieved by elimination of the steel shell, as a steel shell would be consumed in driving each pile and would not be recoverable, and avoidance of scheduling problems arising from slow steel deliveries.

Some problems which have been encountered with the so-called shell-less or caseless concrete piles are discussed in earlier US. Pat. No. 3,834,304, to Upson wherein it is stated that some efforts to produce caseless type piles involved first driving a temporary metal casing or shell into the ground, then pouring concrete into the interior of the temporary shell and pulling the shell upwardly before the concrete is set to leave a concrete pile without a protective shell. As recognized in the prior Upson patent, this method necessarily involved certain disadvantages, since a very heavy upward pull must be exerted to remove the casing with the result often being an upward dislodgement of the pile point which, no matter how slight, is very damaging to the ultimate construction since such a pile, when subsequently loaded, will sink down and cause a similar settling of the building or other load it supports. That patent described efforts made by others to eliminate that defect by reacting the upward force used to pull the casing downward on the concrete which had been poured into that casing, but acknowledged that such a method had not proven satisfactory inactual usage since the downward reactive force when applied to the unset concrete would cause that concrete to arch and distribute a substantial component of the downward force to the very casing one was trying to remove.

The Upson patent also discussed certain inherent disadvantages in using the pile-forming method employing a temporary outer casing which was withdrawn before the poured concrete had set, especially when several piles are to be driven in closely adjacent positions, stating that although the pile in such a cluster may initially be formed in good condition, as soon as the driving of a closely adjacent pile commences, the lateral walls of the first shell-less pile are subjected to severe ground stresses resulting in partial or complete distortion thereof. Experience has shown that when a plurality of piles are driven in closely adjacent positions, permanent protective shells of some sort should be provided in order to insure perfect piles in each instance.

Further research to develop a practical method of creating a cast-in-place caseless concrete pile discloses that there are three principal problems involved in forming cast-in-place caseless concrete piles. When pile holes or bore holes are driven in areas relatively close to each other for forming a plurality of piles, a problem arises with the concrete itself which is poured into pile holes or cavities which have been formed, since the vibrations of the driving of successive piles adversely affect the integrity of previously poured or preceding piles. Secondly, in addition to this vibration problem, problems of necking in, pinching in or constriction of the pile or heaving of the pile itself arise. It has been observed that there can occur necking in or pinching in or constriction of the pile diameter in two vertically spaced regions along the piles length as it is installed, one zone of necking in or pinching in Occurring near the lower tip or lower end of the pile and the other in the zone or region of the pile near the surface of the ground. This necking in or constriction of the pile in the lower or bottom tip region of the pile and in the upper or top surface region of the pile is observed when pile holes have been driven, filled with concrete, and the concrete is allowed to set'and then the pile is withdrawn and inspected.

It is now recognized that the necking in or constriction of the pile in the top or surface region does not occur at the same time as the necking in of the pile near the foot or bottom. In fact, the upper necking formation and the lower necking formation are not produced at the same time, but are in fact the result of two different physical phenomena. The necking formation near the bottom or foot of the pile is thought to be the result of forces produced during forming of that particular pile hole, while driving a mandrel with a releasable boot or driving foot into the soil to the proper depth and either filling concurrently with the mandrel driving operation or after the driving boot or foot has been driven to the proper depth. In other words, as the driving boot or foot of the pile hole forming mechanism descends into the soil, the driving forces emanating from the boot or foot are thought to cause the soil directly beneath the foot member to rotate out from under the foot member and continue to rotate until they act inwardly on the pile hole surface at some distance above the bottom of the hole. It is the rotation of the soil out from beneath the driving foot of the pile hole forming mechanism and the attempt of the soil to continue along a circular shear plane and encroach on the interface or pile hole surface above the bottom hole forming foot and mandrel assembly, due to earth transmission of forces or shock waves to a previously poured fresh pile or piles within a certain range of proximity to the location of the successive pile or pile hole. As the successive or subsequent pile or pile hole forming assembly descends into the soil, the lower end generates forces in the soil which move laterally through the soil and attempt to squeeze adjacent freshly poured piles within a certain proximity range. This phenomena is different from the earlier mentioned squeezing or necking in at the lower end portion of the pile or pile hole, because this squeezing in the upper region of one pile is caused, not by the driving of that pile or pile hole but by the driving of a succesive pile or pile hole.

Consequently, three disturbing problems which have been identified in connection with forming caseless cast-in-place concrete piles are (l) the tendency for vibration from driving successive piles or pile forming holes to disturb the concrete of earlier piles, resulting in possible creation of cold joints; (2) the tendency of the soil beneath the foot of a pile hole forming mechanism, as it is driven, to rotate upwardly and in to the pile hole cylinder being fonned; and (3) the tendency of forces generated by the driving foot or boot during formation of a successive or subsequent pile forming hole in a certain proximity to freshly poured previous piles to squeeze the freshly poured previous piles.

An object of the present invention is the provision of a method and apparatus for formation of cast-in-place caseless concrete piles involving driving of pile forming holes or bores in the soil, whereby necking in, pinching in or squeezing of the initially substantially cylindrical pile forming hole of a freshly poured pile or piles during driving of the pile hole forming mechanism for successive or subsequent piles within a certain proximity is avoided.

Another object of the present invention is the provision of a method and apparatus for installation of castin-place caseless concrete piles, as described in the immediately preceding paragraph, whereby necking in or pinching in of an initially substantially cylindrical pile forming hole or bore in the soil in the lower region of the pile hole resulting from tendency of the soil beneath the driving tip of a pile during driving to rotate upwardly and into the pile hole cylinder is avoided.

Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings illustrating a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a fragmentary perspective view, partially in section, showing a cluster of cast-in-place freshly poured concrete piles and a pile-forming bore hole in process of formation for another pile in the cluster, illustrating an application of the present invention;

FIG. 2 is a fragmentary side elevation view of a pile cluster and footing illustrating an application of the caseless piles formed by the method of the present invention; and

FIGS. 3 A-3 E are side elevational views, partially in section, illustrating in a sequential manner the steps for installing piles according to the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings, wherein like reference characters designate corresponding parts throughout the several figures, the present invention is concerned with a method of forming caseless cast-in-place concrete piles in such a way that where a plurality of such piles are required in relatively close proximity to each other, in what may be called a pile cluster, located sufficiently near to each other to produce problems of necking in or pinching described earlier herein, operation of the pile hole-forming mechanism for pile holes subsequent to the first pile hole will not damage or produce necking or construction of the previously poured piles in the cluster. One example of an application of the method of the present invention is where a plurality of caseless cast-in-place concrete' piles, for example five piles, are required to be formed in a cluster to support one or more building footings, with each pile to be located about four feet on centers. Such an application is illustrated in FIGS. 1 and 2, where the fifth pile hole, indicated by the reference character l0e, is in process of being formed by a pile hole-forming mandrel and driving foot assembly, indicated generally at 12, while other pile holes 10a, 10b, 10c, and 10d in the same pile cluster have already been formed and filled with freshly poured concrete. The five cast-inplace caseless concrete piles to be installed in this cluster, two of which, indicated as and 14b in FIG. 2, are designed to support a large rectangular poured concrete footing 16, for example, for a portion of a large building. It will be appreciated that the problems to be overcome by the method of the present invention are also applicable to a wide variety of other possible situations wherever two cast-in-place piles are required to be formed at sufficiently small distances from each other that shocks or forces created during driving of the hole for the second or subsequent pile to be formed would be transmitted with sufficient intensity to the wall of the earlier formed pile hole to produce necking or constriction in the upper region of the earlier pile hole.

A preferred example of the mechanism and method employed to form each of the pile-forming holes in putting into practice the present invention employs a driving foot or boot member 18 having a bottom plate or leading end plate 20 and an upwardly extending hollow cylindrical sleeve or pipe portion 22 forming an upwardly opening cylindrical cavity or socket to receive in telescoping relation therein the lower end portion of the driving mandrel 24. The diameter of the bottom plate or leading end plate 20 of the driving foot 18 is of slightly larger diameter than the outer diameter of the upper sleeve portion 22, as illustrated in FIGS. l-3, in the preferred embodiment, although a driving foot wherein the lower end portion is of the same diameter as the outer diameter of the upper sleeve or hollow tubular portion 22 may be employed. Also, it will be appreciated that the bottom surface of the driving foot 18 need not be a flat planiforrn surface, but can be a downwardly converging pointed cone or other desired configurations, and while the driving foot contemplated in the preferred embodiment would normally be formed of a flat circular metal bottom plate to which an annular or tubular circular pipe section is welded or similarly secured, the driving foot may be formed in other ways and of other materials as will be apparent to those skilled in the art.

The inner diameter of the upwardly opening hollow cavity or socket 22a in the sleeve portion 22 of the driving foot is sized to closely approximate the outer diameter of the lower end portion of the driving mandrel 24 to releaseably telescopically receive the lower end portion of the driving mandrel therein. In one preferred embodiment, the driving mandrel, or elongated pusher member as it is sometimes termed, is in the form of an axially elongated hollow cylindrical pipe section having an axial hollow bore or center opening 24a surrounded by a cylindrical outer wall 24b, which may be about 1 inch thick for a driving mandrel of 8 or 10 inches outer diameter, and which is provided with a plurality of openings or apertures 240, which may be, for example, circular or oval, slot-like openings, at spaced locations in the cylindrical pipe wall 24b. It will be appreciated that the cross-sectional configuration of the mandrel need not be of annular circular cross-section, but may be a rectangular tubular configuration with right angular or rounded corners, or may be of other desired cross-sectional configurations providing appropriate rigidity. The cross-sectional configuration of the drive mandrel is chosen, however, in this preferred embodiment, so that the total cross-sectional area of the material forming the mandrel wall 24b or the body of the mandrel is much less than the cross-sectional area of the pile hole or cylindrical bore being formed in the earth during driving of the driving foot so that pile forming material, such as concrete or the like, can readily flow by gravity from the zone at the top of the pile hole being formed into the area outwardly I surrounding the wall or walls of the driving mandrel and into the hollow interior thereof and can freely flow between these two zones through the openings 240 in the driving mandrel wall. The lower end of the driving mandrel 24 is suitably shaped to releaseably interfit into the socket or cavity 220 of the driving foot 18, and the upper end of the driving mandrel is suitably shaped to provide for releaseable connection of the driving mandrel to the driving head components of conventional pile driving rigs, indicated diagrammatically at 26, to permit application of impact driving forces from the pile driving rig to the upper end of the driving mandrel during forming of the pile hole, and to permit withdrawal of the driving mandrel when desired from the completed pile hole. Examples of suitable hollow cylindrical drive mandrels with apertures in the wall thereof for producing such pile forming holes in the earth are illustrated and described in United States Patents of Jerry A. Steding, US Pat. Nos. 3,851,484 and 3,851,485 granted Dec. 3, 1974. It will be appreciated however, that many other types of driving foot members and releasable driving mandrels may be employed to drive the driving foot or boot into the earth to the proper depth to form the vertical column bore or pile hole in the earth to be filled with the concrete or similar pile forming material, either concurrently with the driving of the pile hole or shortly after the pile hole has been formed.

When the concrete or similar fill material to form the pile is to be gravity fed into the pile forming opening in the earth during the driving of the driving boot, it is desired in the practice of one preferred embodiment of the invention to locate a fill hopper, such as that illustrated diagrammatically'at 28 in FIGS. 1 and 3 at grade level at the location where the pile is to be formed, the

fill hopper having inclined side walls 28a which form downwardly and inwardly convergent sloping walls extending to a bottom opening 28b in the hopper of substantially the diameter of the driving foot, controlled if desired by some kind of movable gate 280, so that the fill material such as fiowable concrete is gravity fed downwardly through the bottom opening into the pile hole being formed in the earth during driving of the driving foot. The fill material thus flows into the outer annular region 30 of the pile hole being formed, between the outer cylindrical surface of the mandrel, such as the cylindrical driving mandrel 24, and the substantially cylindrical walls of the column bore or pile opening being formed by the driving foot, and also flows inwardly through the apertures or openings 24c in the wall of the mandrel into the inner bore of the mandrel to substantially fully occupy the cross-section of the mandrel bore as well as the outer annular zone immediately outwardly of the outer mandrel surface. The examples of a suitable fill hopper construction usable in practice of this embodiment of the invention are also disclosed in the earlier Steding patent applications identified above.

The ordinary procedure for forming a caseless castin-place concrete pile is to form one pile hole for a single pile in the earth by driving the driving boot or foot with some type of mandrel structure until the foot is driven to the proper depth, thereby forming a vertical cylindrical column, cavity or hole in the earth, and either withdrawing the mandrel and filling that pile hole with concrete, or pumping fluent concrete into the hole thus formed while the mandrel is being withdrawn, usually by incorporating pressurized concrete conduits in the mandrel structure itself, or gravity feeding fluent concrete into the pile hole while the hole is being formed in the manner described previously and withdrawing the mandrel immediately upon completion of the driving of the driving foot to the proper depth. In any event, in each of these procedures, the mandrel is withdrawn from that pile hole before proceeding with driving of other pile holes in the same vicinity with the same pile driving or pile forming equipment.

In order to avoid the problems of pinching or necking in of the pile detailed earlyin this application, the method of the present invention involves the use of a plurality of identical mandrels and driving in succession the boots or foot members for a plurality of piles in a cluster or group located within a predetermined proximity to each other, and includesgthe important step of leaving the mandrel employed in driving each of the pile holes in the cluster or group in place fully inserted in its respective pile hole until all of the pile holes in the cluster or in the group in predetermined proximity to each other have been driven, so that the mandrels left in place in each previously formed pile hole protect their associated pile holes from the necking in or pinching forces previously described. Differently stated, the method of the present invention involves the forming of a plurality of caseless cast-in-place concrete piles in a cluster or group within a predetermined proximity to each other corresponding to the zone over which such pile hole distorting forces might occur, wherein a first one of the pile holes is formed by driving the driving foot or boot into the earth to the proper depth with a hollow cylindrical mandrel which is releaseably assembled with the driving foot, leaving the mandrel for such first pile hole fully inserted into the hole and proceeding in succession to form the remaining pile holes in the cluster or group .in a similar manner each with its own driving foot and mandrel, in each case leaving the mandrel fully inserted in its associated pile hole until all of the pile holes of the cluster or group are formed. The pile holes can either be filled with concrete currently with driving of the driving foot and mandrel into the pile hole, or can be filled with concrete after each pile hole is formed or after all of the pile holes in the cluster or group are formed. It will be appreciated that where the maximum time required to form the pile holes for all of the piles of the cluster or group is such that the concrete introduced into the earliest driven pile holes concurrently with or immediately after driving such earliest holes would have set to such an extent as to prevent withdrawal of their associated mandrels without damage to the associated pile after all of the pile holes are formed, then filling of the pile holes with concrete should be deferred until the last pile hole or the last few pile holes have been formed. In any event, when the pile holes forming the cluster or group have been filled with concrete, the mandrels are then promptly removed from each of the filled pile holes. The effect of leaving the mandrels in the pile holes until all of the pile holes in the cluster or group have been driven is that the mandrel then serves as a protective casing or body within the driven pile hole to protect the pile hole and the concrete within that pile hole if it has already been poured, from the destructive forces giving rise to the pinching or necking in of the piles in the upper region and in the lower region of the pile. Once the mandrel is installed in the pile hole, its structural rigidity serves to protect the pile hole and the configuration thereof, and the concrete within that pile hole after it has been introduced into the pile hole, from the forces of subsequent driving of closely adjacent pile holes as well as from forces caused during driving of that pile hole itself.

As one example, assuming it is desired to install five 12 inch diameter caseless cast-in-place concrete piles in a five pile cluster, for example, to support a footing such as the footing 16 illustrated in FIG. 2, with each pile located four feet on centers, and each pile to be approximately 35 feet long, five pile forming foot members or boots 18 and five mandrels 24 would be required. The assembled foot member and mandrel 12 for each pile hole would be driven in succession to form the respective pile holes a, 10b, 10c, 10d, and Ne, and the pile holes may either be left unfilled until the last pile hole, for example pile hole 10a, has been driven or they may be filled with concrete concurrently with the driving of each pile hole or immediately following the driving of each pile hole. In any event, the mandrels 24 are left fully inserted in each of the pile holes 10a, to We until the fifth or last pile hole has been driven, after which the mandrels are then removed, preferably after previously filling of the pile holes with concrete. This procedure insures that the pile hole or column cavity formed for each pile by the driving of the foot or boot is protected against concurrent and subsequent pinching or squeezing forces until the last boot and mandrel assembly has been installed and there are no subsequent driving forces acting on the five pile group. After the mandrels for the five pile group have been extracted, in effect uncasing the piles, what remains will be the five caseless cast-in-place concrete piles each installed in a manner protecting the pile hole from the pinching or pile constricting forces which 8 would adversely affect the load bearing capacity and integrity of the pile.

What is claimed is:

1. The method of forming plural cast-in-place caseless concrete piles in such proximity area to each other that earth transmission of forces during driving of some of the pile holes may damage the shape of other pile holes already formed in the proximity area, comprising the steps of forming a first pile hole in the earth by driving to the desired depth a first hole forming assembly including a first driving foot having a portion of cross-sectional shape and size corresponding to the desired cross-sectional shape and size of the pile hole and a first elongated driving mandrel of hollow tubular configuration releasably coupled to the driving foot and having a tube wall surrounding the hollow interior of the mandrel of slightly smaller size than the transverse size of the pile hole locating the outer surface of the tube wall sufficiently near the pile hole wall surface to protect the latter against inward distortion, temporarily leaving said first driving mandrel and driving foot in said first pile hole driven to said predetermined depth and forming a second pile hole located in said proximity area by driving a hole forming assembly of a second driving foot and a second driving mandrel of substantially the same construction as said first driving foot and mandrel to the desired depth in the earth while the first driving mandrel remains fully inserted in its respective pile hole protecting the shape of the first pile hole throughout its height against distorting forces, filling the formed pile holes with concrete, and withdrawing the driving mandrels from the pile holes before any concrete therein has set sufficiently such that mandrel withdrawal would damage the concrete, thereby leaving a cast-in-place caseless concrete pile in each pile hole.

2. The method of forming plural cast-in-place caseless concrete piles as defined in claim 1, wherein said first pile hole is filled with concrete while said first driving foot and mandrel are being driven to said predetermined depth.

3. The method of forming plural cast-in-place caseless concrete piles as defined in claim 1, wherein said first pile hole is filled with concrete while said first driving foot and mandrel are being driven to said predetermined depth by concurrently gravity feeding flowable concrete downwardly into the hollow interior of and the space outwardly surrounding said tubular mandrel progressively during driving of the mandrel.

4. The method of forming plural cast-in-place caseless concrete piles as defined in claim 1, including the steps of locating a mobile hopper having a bottom opening sized to correspond substantially to the desired pile hole diameter and downwardly convergent sloping sides converging substantially to said opening over each respective pile site where a pile hole is to be formed, vertically alining the bottom opening of said hopper with the center axis of the pile hole to be formed, feeding flowable concrete adequate to form the pile into the hopper, and driving the mandrel for each pile hole along a vertical axis downwardly through the concrete in the hopper and through the bottom opening into the earth to flow concrete from the hopper into the hollow interior and the outer surrounding regions of the mandrel concurrently with the driving thereof.

5. The method of forming plural cast-in-place case less concrete piles as defined in claim 4, wherein said 9 driving mandrel has plural radial openings in the tube wall thereof for passage of fiowable concrete between said outer surrounding region and said hollow interior of the mandrel during driving of the mandrel.

6. The method of forming plural cast-in-place caseless concrete piles as defined in claim 5, wherein said tube wall of said driving mandrel is of sufficient thinness as to occupy only a minor fraction of the total cross-sectional area of the pile hole being formed affording maximum void space for gravity flow of the flowable concrete downwardly along and within the mandrel during driving thereof.

7. The method of forming plural cast-in-place caseless concrete piles as defined in claim 1, wherein said step of filling the pile holes with concrete is performed only after all of the pile holes in said proximity area have been formed, and said mandrels are withdrawn promptly upon filling of the respective pile hole which it occupied.

8. The method of forming plural cast-in-place caseless concrete piles in a cluster in such proximity area to each other that earth transmission of forces during driving of some of the pile holes of the cluster may damage the shape of other pile holes of the cluster already formed in the proximity area, comprising the steps of forming a first pile hole in the earth by driving to the desired depth a first hole forming assembly including a first driving foot having a portion of crosssectional shape and size corresponding to the desired cross-sectional shape and size of the pile hole and a first elongated driving mandrel of hollow tubular configuration releasably coupled to the driving foot and having a tube wall surrounding the hollow interior of the mandrel of slightly smaller size than the transverse size of the pile hole locating the outer surface of the tube wall sufficiently near the pile hole wall surface to protect the latter against inward distortion, temporarily leaving said first driving mandrel and driving foot in said first pile hole driven to said predetermined depth and forming each successive pile hole in the cluster occupying said proximity area by driving a respective hole forming assembly of a driving foot and a driving mandrel for each successive pile hole having substantially the same construction as said first driving foot and mandrel to the desired depth in the earth while the driving mandrel for the first and each previously formed hole of the cluster remains fully inserted in its respective pile hole protecting the shape of previously formed pile holes throughout their height against distorting forces, filling the formed pile holes with concrete, and withdrawing the driving mandrels from all of the pile holes in the cluster before any concrete therein has set sufficiently such that mandrel withdrawal would damage the concrete, thereby leaving a cast-in-place caseless concrete pile in each pile hole.

9. The method of forming plural cast-in-place caseless concrete piles as defined in claim 8, wherein said first pile hole and each successive pile hole in the cluster is filled with concrete while its respective driving foot and mandrel are being driven to said predetermined depth by concurrently gravity feeding flowable concrete downwardly into the hollow interior of and the space outwardly surrounding said tubular mandrel progressively during driving of the mandrel.

10. The method of forming plural cast-in-place caseless concrete piles as defined in claim 8, including the steps of locating a mobile hopper having a bottom opening sized to correspond substantially to the desired pile hold diameter and downwardly convergent sloping sides converging substantially to said opening over each respective pile site where a pile hole is to be formed, vertically alining the bottom opening of said hopper with the center axis of the pile hole to be formed, feeding flowable concrete adequate to form the pile into the hopper, and driving the mandrel for each pile hole along a vertical axis downwardly through the concrete in the hopper and through the bottom opening into the earth to flow concrete from the hopper into the hollow interior and the outer surrounding regions of the mandrel concurrently with the driving thereof, each driving mandrel having plural radial openings in the tube wall thereof for passage of flowable concrete between the outer surrounding region and said hollow interior of the mandrel during driving thereof.

Claims

1. The method of forming plural cast-in-place caseless concrete piles in such proximity area to each other that earth transmission of forces during driving of some of the pile holes may damage the shape of other pile holes already formed in the proximity area, comprising the steps of forming a first pile hole in the earth by driving to the desired depth a first hole forming assembly including a first driving foot having a portion of cross-sectional shape and size corresponding to the desired cross-sectional shape and size of the pile hole and a first elongated driving mandrel of hollow tubular configuration releasably coupled to the driving foot and having a tube wall surrounding the hollow interior of the mandrel of slightly smaller size than the transverse size of the pile hole locating the outer surface of the tube wall sufficiently near the pile hole wall surface to protect the latter against inward distortion, temporarily leaving said first driving mandrel and driving foot in said first pile hole driven to said predetermined depth and forming a second pile hole located in said proximity area by driving a hole forming assembly of a second driving foot and a second driving mandrel of substantially the same construction as said first driving foot and mandrel to the desired depth in the earth while the first driving mandrel remains fully inserted in its respective pile hole protecting the shape of the first pile hole throughout its height against distorting forces, filling the formed pile holes with concrete, and withdrawing the driving mandrels from the pile holes before any concrete therein has set sufficiently such that mandrel withdrawal would damage the concrete, thereby leaving a cast-inplace caseless concrete pile in each pile hole.

5. The method of forming plural cast-in-place caseless concrete piles as defined in claim 4, wherein said driving mandrel has plural radial openings in the tube wall thereof for passage of flowable concrete between said outer surrounding region and said hollow interior of the mandrel during driving of the mandrel.

8. The method of forming plural cast-in-place caseless concrete piles in a cluster in such proximity area to each other that earth transmission of forces during driving of some of the pile holes of the cluster may damage the shape of other pile holes of the cluster already formed in the proximity area, comprising the steps of forming a first pile hole in the earth by driving to the desired depth a first hole forming assembly including a first driving foot having a portion of cross-sectional shape and size corresponding to the desired cross-sectional shape and size of the pile hole and a first elongated driving mandrel of hollow tubular configuration releasably coupled to the driving foot and having a tube wall surrounding the hollow interior of the mandrel of slightly smaller size than the transverse size of the pile hole locating the outer surface of the tube wall sufficiently near the pile hole wall surface to protect the latter against inward distortion, temporarily leaving said first driving mandrel and driving foot in said first pile hole driven to said predetermined depth and forming each successive pile hole in the cluster occupying said proximity area by driving a respective hole forming assembly of a driving foot and a driving mandrel for each successive pile hole having substantially the same construction as said first driving foot and mandrel to the desired depth in the earth while the driving mandrel for the first and each previously formed hole of the cluster remains fulLy inserted in its respective pile hole protecting the shape of previously formed pile holes throughout their height against distorting forces, filling the formed pile holes with concrete, and withdrawing the driving mandrels from all of the pile holes in the cluster before any concrete therein has set sufficiently such that mandrel withdrawal would damage the concrete, thereby leaving a cast-in-place caseless concrete pile in each pile hole.