Piling

Abstract

A pile comprising a hollow steel bottom portion of convex polygonal cross-section having at least four substantially equal sides. This bottom portion is driven into the ground and is then filled with concrete.

Description

FIELD OF THE INVENTION AND DETAILED DESCRIPTION OF THE INVENTION

[0002] This invention relates to piling

[0003] The entire disclosure (including its drawings, FIGS. 1-15) of said U.S. Pat. No. 6,309,143 B1 is hereby incorporated herein by reference.

[0004] Also incorporated herein by reference are the entire disclosures of U.S. Pat. No. 3,422,630 (to G. Marier) and U.S. Pat. No. 2,983,104 (to T. C. Bruns).

[0005] FIG. 16 is a cross-sectional view in elevation of a pile in which the straight upper portion is a pre-cast pre-stressed concrete pile section which is joined to the tapered lower portion by a commercially available splice (“Sure-Lock”, like that of the above-mentioned Marier patent) conventionally employed for joining pre-cast pile sections.

[0006] FIG. 17 is a plan view looking down on the tapered lower portion after half of the splice has been positioned thereon.

[0007] FIG. 18 is a plan view of the female portion of a known modification of the same type of splice, showing the positions of four straight keys.

[0008] FIG. 19 is a cross-sectional view in elevation of a pile in which the straight upper portion comprises a pipe section connected to a pre-stressed concrete pile section.

[0009] FIG. 20 is a cross-sectional view in elevation of a pile like that of FIG. 16 except that it has a different commercially available splice (like that of the above-mentioned Bruns patent) conventionally employed for joining pre-cast pile sections.

[0010] FIG. 21 is a plan view of concrete pile section showing its relationship to a Bruns-type splice element thereon.

[0011] FIG. 22 is a schematic side view of the framework of a building supported by piles whose tapered sections are embedded in cohesive soil.

[0012] In the driving of the pile shown in FIG. 16, the hollow tapered bottom portion 56 (such as that illustrated in FIGS. 1-15) is driven into the ground by pile-driving hammer blows applied to the top 57 of that bottom portion. Then, when said top is at a convenient height (say about three feet above the ground level) the hollow bottom portion 56 is filled to the top with wet concrete and one half of the splice (either the female half 58 as shown, or the male half) is placed on said top 57 with the anchoring reinforcing bars 59 of that half extending into the wet concrete. After this concrete filling 65 has set, the concrete pile section 61 carrying the other half 62 of the splice is positioned so as to fit the two halves of the splice together in mating relationship and locking rods or keys 70 (31 in FIG. 1 of the Marier patent) are driven, into the keyway 69 (27 in FIG. 4 of the Marier patent) formed by the mating of those halves, to make a firm connection. Full details of the construction of the splice, and its relationship to a concrete pile section, are found in the above-mentioned Marier patent. In FIG. 16 the female half, at the bottom of the concrete section, may have a skirt (such as 9 of Marier's FIG. 1).

[0013] After the sections have been firmly spliced together the pile is driven further into the ground by blows applied to the splice half at the top of the concrete pile section 61. Then when the top 64 of the concrete pile section is at a convenient height an additional concrete pile section may be spliced thereto and the driving continued. Usually the length of a pre-stressed concrete pile section is about 60 feet. Depending on the length of piling required, still more concrete pile sections may be added.

[0014] The concrete pile sections are usually not as strong as the tapered bottom section and their cross-sectional areas will generally be larger than the cross-sectional area of the top of the tapered bottom portion. In the embodiment shown in FIGS. 16 and 17 the splice half 58 that rests on the top of the tapered portion has a square base 66 whose corner portions 67 extend horizontally beyond the perimeter of the top 57 of that tapered portion. The splice half 62 on the preformed concrete section has a corresponding square base 68 which rests on base 66 and transmits the pile driving blows thereto. The square bases 66,68 have the same dimensions as that of the square end of the uniformly square concrete pile section. Splices in which the bases are of other shapes, e.g. octagonal, hexagonal or round, are commercially available and may be used in place of the square splices.

[0015] In one embodiment, the anchoring reinforcing bars 59 are threaded all along their lengths and are screwed into corresponding threaded spaced holes in the bases 66,68.

[0016] In FIG. 17 the top 57 of the tapered portion is polygonal as shown, for instance, in FIG. 6. It may also be circularized as shown in FIG. 12.

[0017] The keys and keyways need not be arcuate. They may be straight as shown at 71 in FIG. 18

[0018] In the driving of the pile shown in FIG. 19 the combination (such as shown in FIG. 12, or FIG. 3 or FIG. 4) of the tapered bottom 50 and the straight pipe 3 is first driven until the top of the pipe portion is at a convenient height, say 3 feet, above the ground, the pile is then filled with wet concrete and a splice half is placed on top of the pipe in the same manner as described above, with the reinforcing bars 59 extending into the wet concrete. Then after the concrete has set, the concrete pile section 61 is spliced onto the top of the pipe, in the manner described above in connection with FIG. 16 and driving is continued.

[0019] The splice shown in FIG. 20 is of the type described in the above-identified Bruns patent. It comprises a generally cylindrical steel connector 81 of circular cross-section having an integral impact plate 82 between circular cup sections 83, 84. The upper cup section 83 is dimensioned to make a drive fit with a pipe sleeve 86 (20 in the Bruns patent) on the preformed concrete section 72, while the lower cup section 84 is dimensioned to make a drive fit with the circularized top 51 of the tapered portion 50 or with the circular top of the pipe portion of any of the piles of FIGS. 1-15. In the driving of the pile shown in FIG. 20 the tapered portion is first driven into the ground until its top 51 is at a convenient height. Then it is filled with wet concrete, the connector 81 is driven onto the circularized top of the tapered portion so that the impact plate 82 rests on the top 51 and on the wet concrete, the concrete 65 is allowed to harden, the preformed concrete pile section 72 with is placed on the tapered section with the pipe sleeve 86 drive fitted in the connector cup section 83 and resting on impact plate 82, and pile driving is continued. Alternatively, the connector 81 (which may be pre-attached to the concrete pile section 72) is not applied to the top 51 until after the concrete filling 65 in the tapered portion has hardened. The Bruns connector 81 may be similarly employed to join a preformed concrete pile section to the top of the combination of tapered bottom and straight pipe, the only difference being that such a combination is preferably driven until the top of the pipe portion is at the convenient height, then the combination is filled with wet concrete and the connector is fitted onto the top of the pipe in the manner described above.

[0020] In one example of the practice of the invention the pile has a 25 foot (about 9 m) tapered lower section of ¼ inch (about 6 mm) thick steel with a bottom diameter of 8 inches (about 200 mm) and a top diameter of 16 inches (about 400 mm) and a 60 foot (about 21 m) long pre-stressed pre-cast concrete straight upper section having a 16 inch (about 400 mm) square cross-section. This may be used to produce an allowable capacity of about 120 tons (about 1100 kN) when driven through 15 feet (about 5 m) of miscellaneous fill and 30 feet (about 11 m) of organic silt and into 35 feet (about 13 m) of medium sand having an “N” value of about 15.

[0021] In another example the pile has a 20 foot (about 7 m) long tapered lower section of ⅜ inch (about 9 mm) thick steel with a bottom diameter of 10 inches (about 250 mm) and a top diameter of 18 inches (about 450 mm), an intermediate 40 foot (about 14 m) long section of 18 inch diameter straight steel pipe having a wall thickness of ⅜ inch butt-welded to the lower section, the top of the pipe being connected to a 65 foot long pre-stressed pre-cast concrete straight upper section having a uniform 18 inch square cross-section. This may be used to produce an allowable capacity of about 225 tons (about 2000 kN) when driven through 10 feet (about 3 m) of garbage fill, about 70 feet (about 22 m) of soft silt and clay, 35 feet (about 13 m) of loose sand and gravel to end-bearing on bedrock.

[0022] It has been found that the piles of this invention can provide a surprisingly high load-carrying capacity even if the pile driving is stopped when the tapered body is largely embedded in cohesive soil (such as clay or cohesive silt) rather than in granular soil. At that stage the energy needed for further driving (as measured by resistance of the pile to movement under the blows of the pile-driving hammer) is relatively small but the actual load-carrying capacity, as measured by load tests, can be much higher than that expected for such a small driving energy. This discovery makes it unnecessary, for instance and in many cases, to continue driving through the cohesive soil down into an underlying layer of granular soil. Examples 1,2 and 3 below illustrate the driving into cohesive soil. It will be understood that, after the driving described in each of these Examples, a supported structure (such as a conventional pile cap and a building supported thereon, or the base slab of a fuel tank) is placed on the pile while the tapered body is still largely embedded in the cohesive soil layer.

EXAMPLE 1

[0023] A pile consisting of a 25 foot long steel tapered bottom section having a bottom diameter of 8 inches and a top diameter of 18 inches, and welded to a 40 foot long cylindrical pipe having an 18 inch diameter, driven through 25 feet of fill and organic peat and penetrating into 35 feet of clay (stable) having an “N” value of 10 can develop 120 tons or more of allowable capacity at a driving resistance of 12 blows per linear foot of penetration under the blows of a hammer delivering 30,000 foot-pounds of energy.

EXAMPLE 2

[0024] A pile as in example 1 except that the pipe is 110 feet long driven through 70 feet of fill and organic clay (which, because of its organic content, will deteriorate with time and is therefore unstable for pile-support), then 10 feet of sand having and “N” value of 12 and then 40 feet into a layer of clayey silt (stable) having an average “N” value of 8 can develop 140 tons or more of allowable capacity at a driving resistance of 22 blows per foot of penetration under the blows of a hammer delivering 45,000 foot-pounds of energy.

EXAMPLE 3

[0025] A pile having a 15 foot long steel tapered bottom with an 8 inch bottom diameter, 14 inch top diameter, welded to a 14 inch diameter cylindrical steel pipe 55 feet long driven through 20 feet of fill, than 15 feet of organic soils, and then into 30 feet of silt and silty sand having an average “N” value of 15 can develop and allowable capacity of 80 tons at a driving resistance of 24 blows per foot under the blows of a hammer delivering 22,000 foot-pounds of energy.

[0026] In FIG. 22 piles of this invention have their tapered bottom portions 50 entirely embedded in clay soil. The piles are arranged in groups or clusters under the conventional pile caps 91 which are placed on the piles after the latter have been driven. The pile caps in turn are used to support the columns 92 of a building 93. The depth of the clay substrate is much greater than the depth to which the piles have penetrated into that substrate. Especially good results can be obtained when the clay substrate is of the kind known as over-consolidated clay.

[0027] It is understood that the foregoing detailed description is given merely by way of illustration and that variations may be made without departing from the spirit of the invention. The Abstract is given merely for the convenience of technical researchers and is not to be given any weight with respect to the scope of the invention.

Claims

1. A pile comprising a hollow uniformly tapered steel body constructed and arranged to be the lower, soil-penetrating portion of a driven pile, said tapered body having a cross-section, taken perpendicular to a longitudinal axis, which is a convex polygon having 8 to 24 sides, said sides being substantially equal in length, said body being about 3 to 13 meters long, having a lower diameter which is about 200 mm to 400 mm and a larger upper diameter which about 300 mm to 600 mm and being of steel about 5 to 13 mm thick formed from a unitary sheet folded into said tapered polygon shape and having its longitudinally extending free edges welded together, said body having a closure at its bottom to substantially prevent ingress of the soil into said body during the driving of the pile.

2. A pile as in claim 1, said polygon being a substantially regular polygon.

3. A pile as in claim 2, the very top of said body being formed to a circular cross-section such that said top can engage with, match and be butt-welded to the end of a straight pipe of corresponding circular cross-section.

4. A driven pile in place in the ground, said pile having at its lower end the body of claim 1 filled with concrete.

5. A pile as in claim 3 having a pre-stressed pre-cast concrete pile section of larger cross-sectional area than said top spliced to said top.

6. A pile as in claim 3 having a pipe of circular cross-section substantially the same as said circular cross-section of said hollow body butt-welded to said very top, said pipe having a top portion which is spliced to a pre-stressed pre-cast pile section of larger cross-sectional area than that of said pipe circular cross-section.

7. A pile comprising a bottom portion which is a hollow uniformly tapered steel body having a cross-section, taken perpendicular to a longitudinal axis, which is a convex polygon having at least 4 sides, said sides being substantially equal, said hollow body being filled with concrete, the top of said hollow body carrying a first connector constructed and arranged to firmly couple said bottom portion to a pre-cast concrete pile section resting on said bottom portion in axial alignment with said bottom portion, said first connector having anchoring rods secured thereto and extending downwardly into, and bonded to, said concrete filling.

8. A pile as in claim 6 and including a pre-cast pile section resting on said bottom portion and having at its lower end a second connector which is coupled to said first connector, said connectors including a male cap presenting an axially extending projection of less diameter than that of said top and a female cap presenting an axially extending depression for receiving said projection, said projection and depression having opposed grooves forming therebetween a locking passage and a rod in said passage locking said male and female caps together.

9. A pile having a uniformly tapered hollow steel bottom portion having a cross-section, taken perpendicular to a longitudinal axis, which is a convex polygon having at least four sides, said sides being substantially equal in length and, resting on said tapered portion, a straight steel pipe having a cross-section, taken perpendicular to a longitudinal axis, which is circular, the very top end of said tapered bottom portion being formed to a circular cross-section of substantially the same diameter as, and matching with, the cross-section of said pipe and the bottom end of said pipe being butt-welded to said top of the hollow tapered bottom portion so that the load transfer from said pipe to said bottom portion is made by continuous bearing of said pipe and said bottom portion, said pile being filled with concrete, the top of said pipe carrying a first connector constructed and arranged to firmly couple said straight portion to a pre-cast concrete pile section resting on the top of said pipe in axial alignment with said straight pipe, said first connector having anchoring rods secured thereto and extending downwardly into, and bonded to, said concrete filling in said pipe.

10. A pile as in claim 8 and including a pre-cast pile section resting on said pipe and having at its lower end a second connector which is coupled to said first connector, said connectors including a male cap presenting an axially extending projection of less diameter than the top of said pipe and a female cap presenting an axially extending depression for receiving said projection, said projection and depression having opposed grooves forming therebetween a locking passage and a rod in said passage locking said male and female caps together.

11. Process which comprises driving the body of claim 1 into the ground by hammer blows transmitted to said very top of circular cross-section and filling said body with concrete.

12. Process as in claim 11 and including the step of attaching to said top a straight precast concrete pile section and continuing the driving of the resulting composite pile into the ground.

13. Process as in claim 12 in which said uniformly tapered steel body is filled with wet concrete after being driven into the ground, applying to the top of said body a first connector constructed and arranged to firmly couple said body to said pre-cast concrete pile section, said first connector having downwardly directed anchoring rods secured thereto so that said rods become embedded in the wet concrete, and allowing said wet concrete to harden in anchoring contact with said rods before said continuing of said driving.

14. Process as in claim 11 in which a straight steel pipe of circular cross-section substantially the same as said circular cross-section of said hollow body is butt-welded to said very top, the resulting composite pile is driven into the ground and filled with wet concrete and a first connector constructed and arranged to firmly couple said pipe to a straight pre-cast concrete pile section is applied to the top of said pipe, said first connector having downwardly directed anchoring rods secured thereto so that said rods become embedded in the wet concrete, and said wet concrete is allowed to harden in anchoring contact with said rods.

15. A pile as in claim 1 in place in the ground, said pile having been driven only until said tapered body is largely embedded in, and supported by, cohesive soil.

16. A pile as in claim 15 in which said cohesive soil is over-consolidated clay.

17. A structure supported by piles, said supporting piles comprising a pile as set forth in claim 15.

18. A structure as in claim 17 in which said cohesive soil is over-consolidated clay.

19. Process which comprises driving a pile as set forth in claim 1 into the ground until said tapered body is largely embedded in cohesive soil, stopping said driving, and than building a structure supported by said pile while said tapered body is so embedded.