Bio-inspired deep foundation pile and anchorage system

An expanding anchor and/or pile system wherein an outer shell of the pile/anchor is split lengthwise into at least two pieces and can be placed or driven into a hole in the earth in a retracted state and can subsequently be expanded such that the two or more pieces are forced outwardly—away from one another, thus causing them to exert a lateral force against the sides of the hole and thereby resulting in greater axial load carrying capacity in tension or compression of the anchor/pile.

BACKGROUND OF THE INVENTION

As used throughout this application, the term “anchor/pile” is intended to include an anchor and/or a pile“. Embodiments of the present invention relate to foundation piles and anchorage systems. More particularly, embodiments of the present invention relate to foundation piles and anchorage systems which feature a pile/anchor which can be expanded laterally once installed to increase the holding power and/or load carrying capacity of the anchor/pile.

Deep foundation systems transfer loads, for example the load of a building or bridge, far down into the earth. One commonly employed deep foundation system is a vertical structural element called a “pile”. Conventional pile foundations include drilled shafts or bored piles, and steel, wood or precast concrete driven piles. The vertical load capacity of these conventional pile systems under downward and/or upward loading from structures and the pullout capacity of ground anchors can be increased by incorporating unique features to these load-carrying systems that are found in some biological organisms. What is needed are deep foundation pile systems and anchorage systems that incorporate some of these biologically inspired characteristics to achieve greater load-carrying capacity.

The earthworm and the razor clam are two animals that provide biological examples of strategies of how an elongated object or body might be anchored and vary the earth pressure surrounding it. The razor clam has an elongated shape and has a hinged bivalve shell that is split longitudinally (along its axis of length). The bivalve shell provides the razor clam the ability to anchor itself in the surrounding sand by opening (radially or laterally expanding) its shell while pushing the front part (called the foot) of its soft body forward. The bivalve shell also provides the razor clam the ability to release itself from the surrounding sand by closing (radially or laterally contracting) its shell.

The earthworm, like many invertebrates, has a hydrostatic skeleton (also called a hydroskeleton). The hydroskeleton of invertebrates is composed of incompressible fluid and surrounding tissues that contain the fluid. When an external load is applied to the hydroskeleton, the hydroskeleton transfers that load to the internal fluid and converts it into hydrostatic pressure, which has equal magnitude in all directions at any given point. This hydrostatic pressure eventually becomes internal stress on the interior of the supporting walls (tissues) of the hydrostatic skeleton. Earthworms can use their hydrostatic structure to anchor their body laterally while pushing forward to advance into the soil. When the earthworm and razor clam expand laterally, the lateral earth pressure in the surrounding soil increases and provides anchorage. Additionally, earthworms havesetae, which are bristle or hair-like structures on the outside surface of their body. When the earthworm expands part of its body laterally, thesesetaeare extended by the worm's protractor muscles into the surrounding soil to anchor the worm's body. Thesetaeembedded into the surrounding soil also contribute to anchorage.

What is needed are deep foundation piles and anchorage systems that mimic aspects of the characteristics of the earthworm and razor clam to provide a greater lateral earth pressure and/or anchorage that lead to greater shaft resistance (also called “skin resistance” or “frictional resistance”) in the case of piles and greater pullout resistance in the case of piles and anchoring systems.

BRIEF SUMMARY OF EMBODIMENTS OF THE PRESENT INVENTION

Embodiments of the present invention relate to an earth anchor/pile system having a multiple-part shell formed from a plurality of elongated members, the plurality of elongated members configured to move away from one another to provide an expanded configuration of the earth anchor/pile system, the plurality of elongated members configured to move toward one another to provide a contracted configuration of the earth anchor/pile system, and the earth anchor/pile system securable in the expanded configuration. The earth anchor/pile system can also include a nearly incompressible core disposed within at least a lower portion of the multiple-part shell and can include a driving shoe disposed at an end portion of the multiple-part shell. The multiple-part shell can include a two-part shell and the plurality of elongated members can be a plurality of curved elongated members. The multiple-part shell can include an at least substantially circular shape when in a contracted configuration. The earth anchor/pile system can also include a filler material disposed within at least an upper portion of the multiple-part shell. In one embodiment, the top slab can be formed above the multiple-part shell. A plurality of tension members can extend from above the top slab and connect to one or more of the plurality of elongated members. Preferably, the earth anchor/pile system is configured to expand when the plurality of elongated members are placed in tension and forcing the top slab closer to a bottom end portion of the plurality of elongated members causes the plurality of elongated members to move away from one another, thus expanding the earth anchor/pile system

In one embodiment, the earth anchor/pile system can also include a plurality of mechanical expansion devices disposed within the multi-part shell and configured such that actuation of the plurality of mechanical expansion devices forces the elongated members to move away from each other or closer to each other. The earth anchor/pile system can also include a plurality of projections that project at least substantially laterally away from an outside surface of the multiple-part shell. Optionally the plurality of mechanical expansion devices can include a jackscrew and be configured such that rotation of the jackscrew in a first direction causes the plurality of mechanical expansion devices to extend and such that rotation of the jackscrew in a second direction causes the plurality of mechanical expansion devices to retract.

The earth anchor/pile system can be securable in the expanded configuration by disposing filler material within an inner portion of the multiple-part shell when the multiple-part shell is in the extended configuration. Optionally, the filler material can include a cement material with or without steel reinforcement. The plurality of projections can include metal spikes and/or metal elongated members. The plurality of projections can be disposed on a surface of the plurality of elongated members and/or can be incorporated or otherwise formed on the plurality of elongated members. The plurality of elongated members can optionally be two elongated members. The plurality of elongated members can include one or more openings through which one or more elongated holding members can project.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention relate to an anchor and/or pile system. Discussions related to the structure, and/or installation of either the anchor or the pile system are equally applicable for the other as it is understood that the same installed structure can function as a pile when a downward-force is applied to it and can function as an anchor when an upward force is applied to that same installed structure. As used throughout this application, the term “superstructure” is intended to include any structure of any shape and dimension that pile system10supports or serves as the foundation of, including but not limited to buildings, bridges, photovoltaic solar panels, oil rigs, any other structure, apparatus or device, combinations thereof, and the like.

Referring now to the figures, particularlyFIGS. 1A-3B, embodiments of pile system10, also occasionally referred to as a bio-inspired radially expansive pile (′BREP″) of the present invention preferably comprise a two-part shell (or longitudinally split pipe)12that forms the outer shell of pile system10and nearly incompressible core30inside the shell of pile system10. Like the split shell of a razor clam (also called a “bivalve shell”), two-part shell12provides an outer shell for pile system10and keeps pile system10together but allows pile system10to expand because its two separate halves can separate from each other. After pile system10is placed into the ground, nearly incompressible core30, located inside two-part shell12, is compressed along the longitudinal direction so that nearly incompressible core30expands in the lateral (radial) direction. Lateral expansion of nearly incompressible core30increases the lateral earth pressure on two-part shell12and the shaft resistance of pile system10. Preferably, two-part shell12is a longitudinally split steel pipe (or in other words, two steel half-pipes). Other embodiments of two-part shell12can be formed of materials other than steel, including but not limited to plastic, wood, other metals or metal alloys, and combinations thereof. Some embodiments of two-part shell12comprise more than two halves, but are split multiple times, for example in thirds, fourths, or smaller increments. Thus, discussions herein related to “two-part shell12” are intended to be applicable to embodiments of the present invention wherein more than two parts form shell12.

FIGS. 1A-3Billustrate a bio-inspired radially expansive pile system10according to an embodiment of the present invention.FIG. 1Aillustrates a radially expansive pile system10prior to it being installed into the earth,FIG. 2Aillustrates it after it is installed in the ground; and the right side ofFIG. 3Ais a more detailed view of it after installation and expansion with reference number43illustrating the outward force exerted by the expansion of pile system10.

Referring toFIG. 1A, pile system10preferably comprises a series of lateral belts20that limit the lateral deflection or expansion of pile system10and prevent separation of the two halves of two-part shell12during transportation, handling, installation and service. Preferably, lateral belts20are formed of steel, but can optionally be formed of any material adequate to maintain its hold around two-part shell12during transportation, handling, installation and service, including plastic, leather, rubber, synthetic materials, combinations thereof, and the like. Optionally, the material can be determined based on the intended expansion forces of pile system10, the environment in which pile system10is installed, and the intended length of time lateral belts20are needed to stay intact. Optionally, lateral belts20need not have a belt-and-buckle like configuration but can instead comprise another configuration that can also keep two-part shell12from expanding excessively. In one embodiment, belts20can include some interlocking rings or some other structure that allows for some limited amount of movement.

Embodiments of pile system10may comprise other components to keep it together during installation. Preferably, pile system10comprises a driving shoe22and driving cap24as is respectively illustrated inFIGS. 1C and 1D. Driving cap24not only prevents damage to pile system10while it is driven into the earth during installation, but also maintains the relative positions of the two halves of two-part shell12. In addition, each one of the two halves of two-part shell12comprises a half-circle plate35that is welded or attached to the bottom of the half shell. Half-circle plates35preferably at least substantially abut one another when two-part shell12is in a contracted configuration. Most preferably each of two half-circle plates35comprises a notch at a center portion thereof such that when abutted together to form a circle, an opening is formed in a center thereof and through which a stud of driving shoe passes such that each half-circle can rest at least substantially within a circular gap formed within driving shoe22, thus holding driving shoe22in place with respect to two-part shell12.

Pile system10is driven into the earth for installation. At this stage, its interior is preferably empty as illustrated inFIG. 1A. After the pile system10is driven, its interior is partially filled of nearly incompressible core material30. Nearly incompressible core material30preferably fills a portion of two-part shell12, which can include about the lower two-thirds of two-part shell12or less. The remaining interior of pile10is preferably filled with filler material34which can include, for example, reinforced concrete and which can optionally include top slab36. Nearly incompressible core30is preferably loaded in compression along the vertical axis of the pile to expand it radially. The compression of the core30can optionally be accomplished using tension rods32which can be pulled by one or more hydraulic jacks41to push down filler material34, thus compressing nearly incompressible core30. Alternatively, of course, other structures, devices and apparatuses can be used to pull tension rods32. After the compression is accomplished, the compression of the core30is preferably locked using bolts and nuts37that also connect the two-part shell12with the top slab36. Optionally, the other end of tension rod32and/or any connecting cables can optionally be attached to a point below—for example to one or more members or components of two-part shell12. As best illustrated inFIGS. 1E and 1F, one manner in which tension rods32can connect to two-part shell12is via ring38(which can optionally be a D-shaped ring), attached to a side of two-part shell12. Most preferably, one or more tubes or pipes are disposed within top slab36through which tension rods32translate. A bottom end of tension rods32preferably each extend through a respective one or more of rings38and preferably have a knob, nut, or some other type of enlarged area formed or disposed on an end portion thereof which cannot pass through ring38. Thus, when lifting mechanism, which can be hydraulic jack41pulls up on tension rod32, the enlarged area on the end of rod32engages ring38and thus forces filler material34downward with respect to two-part shell12, thus expanding pile system10.

Preferably, nearly incompressible core30is formed from a nearly incompressible and flexible material, including but not limited to natural or synthetic rubber, compressed recycled rubber, polypropylene, dense granular material which can include soil, and/or a fluid confined inside a chamber or membrane. In this way, pile system10employs the benefits that give hydrostatic skeletons of invertebrates their advantages. Pile system10can provide greater pile capacity compared with a conventional pile foundation of same external dimensions because the radial expansion of nearly incompressible core30that fills certain spaces within two-part shell12causes the lateral earth pressure to increase in the surrounding soil, which provides greater shaft resistance. Embodiments of pile system10can employ various types of core material30that are nearly or substantially incompressible yet are preferably flexible, and/or combinations of different materials thereof. In some embodiments, various separate sections of different core material30can be provided within pile system10, which can optionally have different characteristics to accomplish different amounts of flexibility, expansion, rigidity, temperature tolerance, etc.

Embodiments of the present invention can provide a deep foundation pile that can expand variably and that can employ the characteristics of hydrostatic skeletons of invertebrates that enhance the technology of pile foundations. Preferably, pile system10is at least partially filled with incompressible core30along at least a portion of the system's longitudinal axis. Additionally, by filling pile system10in variable amounts and with varying materials, the lateral expansion of two-part shell12can be designed or varied, thereby controlling the magnitude of lateral earth pressure in the surrounding soil against two-part shell12. The radial expansion of nearly incompressible core30pushes two-part shell12apart against the surrounding soil. The reaction of the soil increases the confining earth pressure applied on the outer surface of two-part shell12. After pile system10is completed and the load from the superstructure is applied on it, the greater confinement allows greater shaft resistance and consequently greater load capacity of the pile foundation.

Pile system10can also coordinate with other components so that it can support superstructures as their foundation. To accomplish this, as is best illustrated inFIGS. 2A and 3A; a portion of space within two-part shell12is preferably filled with filler material34, which can optionally include reinforced concrete or another filling material that can be used to support loads. As illustrated inFIGS. 2A and 3A, the upper about one-third of two-part shell12is filled with filler material34. In some embodiments, filler material34can fill all remaining space within two-part shell12that is not filled with incompressible core30. The amount or proportion of filler material34used in pile system10preferably varies depending on the desired expansion of the particular pile system10, type and characteristics of the surrounding soil, the load from the superstructure, and any other desired factors. Additionally, pile system10preferably comprises a top slab36(also called “pile cap”) that serves as the cap of pile system10. Top slab36, and other various elements such as base plate39, supports other objects such as a column of the superstructure. Optionally, base plate39, which can be formed from metal, including but not limited to steel or stainless steel can be disposed atop slab36. In one embodiment, rebar dowels40(seeFIG. 3B) can be embedded within filler material and can extend up through top slab36, and if provided, up through base plate39to wait for superstructure construction.

Pile system10can also provide greater shaft resistance when pile system10is loaded in tension. Pile system10preferably comprises mechanisms to transfer a pullout force (or tensile load) to two-part shell12. Preferably, top slab36, and if provided base plate39, are connected to two-part shell12through bolts and nuts37. In this way, when pile system10is loaded in tension, bolts and nuts37transfer the force to two-part shell12. Optionally, other pull-out apparatuses, structures, devices, and combinations thereof can be provided in pile system10other than bolts and nuts, including but not limited to, for example rods and pins, cables, combinations thereof, and the like.

Embodiments of the present invention also comprise bio-inspired mechanisms for anchoring deep foundation piles and other systems.FIGS. 4A-6illustrate a bio-inspired “setaeanchored” pile system100according to an embodiment of the present invention.FIG. 4Aillustrates thesetaeanchored pile system100prior to the anchoring system being expanded.FIG. 5illustrates thesetaeanchored pile system100after thesetaeanchored pile system has been expanded in the earth; andFIG. 6illustrates a more-detailed view of it after expansion.

Most preferably, expansive pile system100is disposed within an opening in the ground. This embodiment of the present invention can expand radially or laterally like the shell or body of a razor clam and earthworm that anchor themselves in the earth and generate traction to advance the tip of theft body forward. Referring now toFIGS. 4A-6, embodiments ofsetaeanchored pile system100, also occasionally referred to as a bio-inspiredsetaeanchored pile (“BSAP”), preferably comprise shell130that is most preferably a two-part shell which forms the outer shell ofsetaeanchored pile system100. Like the bivalve shell of a razor clam, two-part shell130preferably provides an outer shell forsetaeanchored pile system100that can expand laterally because its two halves can separate from each other during expansion of pile system100. As with pile system10, two-part shell130of pile system100can also be formed from more than two parts. Thus, discussions herein which relate to the two-part shell130are intended to also be applicable to shells130formed from more than two parts.

Another objective of this embodiment of the present invention is to enhance the load-carrying capacity of a pile or soil anchor by employing the natural characteristics ofsetae, the bristle or hair-like objects that extend from earthworms to anchor their body while burrowing. Referring toFIGS. 4A-6, embodiments ofsetaeanchored pile system100preferably comprise mechanical expansion devices110and projections (also called “bristles”)120. Preferably, mechanical expansion devices110are capable of expanding and contracting, for example with a jackscrew and/or in a manner similar to that of a scissor jack. Expansion devices110are preferably attached, which can optionally include by welding, bolting or some other manner of fastening or forming, to the inside surface of two-part shell130, so that each of the halves of two-part shell130moves outwards as mechanical expansion devices110are opened. When mechanical expansion devices110are opened, two-part shell130preferably expands radially (or at least substantially laterally) against the surrounding soil and increases the lateral earth pressure. In some embodiments, mechanical expansion devices110are devices with an apparatus other than a jackscrew, including but not limited to, hydraulically driven jacks.

Preferably, projections120are radially (or at least substantially laterally) directed structures that can be welded, attached or otherwise formed on the outer surface of two-part shell130, as perhaps best illustrated inFIG. 6. When mechanical expansion devices110are expanded laterally, they force the parts of two-part shell130away from one another, thus expanding two-part shell130radially (or at least substantially laterally) against the surrounding soil, and projections120on the outside of two-part shell130penetrate the surrounding soil like thesetaethat extend from earthworms to anchor their body while burrowing. Projections120can optionally have a shape as illustrated inFIG. 6, which is a pointed, triangular shape. Alternatively, the shape of projections120can have any of various forms depending on factors such as the environment of pile system100. As a non-limiting example, projections120can include any of the following shapes: rectangular, half-cone-like, wedge-like, plate-like, spiky, ribs, any combination thereof and the like.

Embodiments ofsetaeanchored pile system100can optionally include a remote opening mechanism for remotely opening/expanding and closing/contracting mechanical expansion devices110. Because mechanical expansion devices110can be deep within two-part shell130, each mechanical expansion device110of the series of mechanical expansion devices110within two-part shell130preferably coordinate with a system to open and close all of them, most preferably simultaneously. In one embodiment, center rod140, which is most preferably formed from a metal material, is preferably connected to each mechanical expansion device110and serves to open and close them remotely from the ground surface. Other embodiments ofsetaeanchored pile system100can optionally be actuated by ropes, wires, cables, hydraulics, poles, combinations thereof, and the like.

Setaeanchored pile system100can be particularly useful in combination with bored piles. For example, a borehole is dug and supported with bentonite slurry or drilling mud unless the walls of the borehole can remain open and stable without aid. Then, as illustrated inFIG. 4, two-part shell130, including an assembly of a series of mechanical expansion devices110within it, is lowered into the borehole while mechanical expansion devices110are in a closed/contracted configuration. Subsequently, the mechanical expansion devices110are progressively opened/expanded until the two halves of two-part shell130are in contact with and putting a desired lateral pressure on the borehole walls, and the projections are preferably fully inserted into the surrounding soil, as illustrated inFIGS. 5 and 6. As mechanical expansion devices110push two-part shell130outwards, toward the surrounding soil, the lateral earth pressure on two-part shell130increases to provide much more anchorage which leads to greater shaft resistance forsetaeanchored pile system100when loads from a superstructure are applied. This also inserts projections120into the surrounding soil to form another anchorage mechanism. After mechanical expansion devices110are expanded laterally to the desired amount of expansion, two-part shell130can optionally be filled with filler material34and rebar or other members or components can be embedded therein to engage a subsequently installed superstructure. A top slab36can be formed at a top-portion ofsetaeanchored pile system100. If desired, base plate39can also be added atop top slab36and rebar dowels40can be embedded within filler material and can extend up through top slab36, and if provided, up through base plate39to wait for superstructure construction.

Referring now toFIGS. 7A and 7B, in one embodiment, expansive pile200containing two-part shell210can feature openings212in one or both of two-part shell210, through which elongated holding members214are extended. In one embodiment, elongated holding members214can comprise rods, bolts, pipes, or any other structure which can be caused to project out of openings212and into the surrounding soil. In one embodiment, elongated holding members214can comprise a threaded end which engages with one or more nuts216, which can optionally comprise a pair of spherical nuts. In one embodiment, nut cap218can be positioned inside of two-part shell210such that filler material34does not contact elongated holding members214, or nuts216. Most preferably, expansive pile200is disposed within an opening in the ground. Then, two-part shell210is preferably expanded and then elongated holding members214are expanded or pushed into the soil. Optionally, however, two-part shell210can expand simultaneously with or can expand after elongated holding members are extended out of openings212. As with the preceding embodiments of piles/anchors, expansive pile200can expand in a manner similar to that of pile system10or100and the teachings of two-part shell12and/or130are equally applicable to two-part shell210. Thus, two-part shell210can comprise a multi-part shell comprising more than two-parts.

Expansive pile200is occasionally referred to herein as a bio-inspired root anchored pile (“BRAP”) and incorporates inspiration from the anchorage approach of the Laminariales and lateral roots. The extension of elongated holding members214can be accomplished via any known method for extending an elongated member and is preferably accomplished from within an interior of two-part shell210. In one embodiment, elongated holding members214can be rotated so as to cause the end portion of them to be forced out away from nuts216for example, by unscrewing them.

Like in the anchorage of lateral roots of plants, downward or upward forces on pile200preferably cause elongated holding members214to slightly rotate up or down, respectively, to mobilize the surrounding soil and provide resistance against the axial loading. Elongated holding members214do not need to have a large cross-sectional area to provide shear resistance against vertical loading. Instead, a hinge-type connection, which can optionally be provided with a spherical nut, at the interior end of elongated holding members214allows elongated holding members214to rotate partially and mobilize their tensile strength. Nut caps218can optionally be individually applied around each opening or can optionally be formed by an elongated continuous opening that extends down the length of pile200(for example, by welding half of a smaller diameter pipe (i.e. a section of a smaller-diameter pipe that has been split lengthwise) down the inside of each part of two-part shell210). In one embodiment, after the shell and anchor bolts are installed, the shell inner space can be filled with concrete and steel reinforcement as needed for any structural requirements and can be topped with pile cap36and, if desired, a base plate39. Features of this pile system can be used as enhancements to conventional large diameter drilled shafts.

Referring now toFIG. 12, an embodiment of soil anchor500(occasionally referred to herein as a bio-inspired expansive soil anchor (“BESA”)) is illustrated. Soil anchor500is installed and expanded as described for pile system10. The teaching for similar or corresponding components of pile system10are thus applicable to soil anchor500. As illustrated inFIG. 12, the following reference numbers and their associated descriptions follow:

502—Potential failure surface

504—Pipe with a longitudinal cut (note: this one is not two-part—it has only one cut, so it holds the nearly incompressible core but still allows expansion)

510—Steel pipe with circular plates (disks) at two ends of the pipes

514—Hydraulic jack to pull the rod

521—Length reduction due to core compression

FIG. 13illustrates an embodiment of soil anchor600(occasionally referred to herein as a bio-inspiredsetaesoil anchor (“BSSA”). Soil anchor600is installed and expanded as described for anchored pile system100. The teaching for similar or corresponding components of pile system100are thus applicable to soil anchor600. As illustrated inFIG. 13, the following reference numbers and their associated descriptions follow:

602—Potential failure surface

INDUSTRIAL APPLICABILITY

A numerical modeling example of the laterally expansive pile subjected to downward axial loading is described. The numerical analysis was performed using the finite element (FE) software ABAQUS® 2017 (ABAQUS is a registered trademark of Dassualt Systemes Simulia Corp.). For this example, a laterally expansive pile, according to an embodiment of the present invention, was compared to a conventional cylindrical pile with the same dimensions (i.e., length=10 m, outer diameter=0.3 m) in terms of the lateral confining pressure developed along the pile shaft and the load capacity. The expansive pile was comprised of a two-part cylindrical steel shell (thickness=8 mm) and a nearly incompressible core (length=6 m). The conventional pile was a close-ended steel pipe pile. The steel of the piles and the nearly incompressible core were considered linear elastic. The Young's modulus and Poisson's ratio were found to be 210 GPa and 0.3 for the steel and 0.1 GPa and 0.48 for the nearly incompressible core, respectively. The Poisson's ratio of the steel and the nearly incompressible core are assumed to be 0.3 and 0.48, respectively. The adopted values of these parameters are within the typical ranges for the materials considered.

In this case, the piles were assumed to be installed in a sand deposit with properties as those of the Erksak 330/0.7 sand, which is composed mostly of quartz particles with a trace of silt. A unified critical state constitutive model referred to as clay and sand model (“CASM”) was used to describe the sand mechanical behavior during pile loading. The CASM material parameters of the sand were: Compression index λ=0.0135; specific volume at mean normal stress of 1 kPa Γ=1.8167, Poisson's ratio v=0.3; reloading index κ=0.005; slope of the critical state line M=1.2; initial state parameter ξR=0.075; and stress state coefficient n=4.0. The pile models were analyzed for two sand densities: medium dense sand with initial specific volume vo=1.667 and very dense sand with vo=1.59.

Taking advantage of the problem symmetry shown inFIG. 8A, the model was only of a quarter of the problem. Boundary conditions and other details of the FE model of the laterally expansive pile are shown inFIG. 8B. InFIG. 8B, the reference numbers describe aspects of the model as follows:

300—Split steel pipe, only a quarter of a full shell is modeled due to the symmetry;

302—Nearly incompressible core, only a quarter of a cylinder is modeled due to the symmetry;

304—Boundary Conditions (“BC”): Rollers on entire plane, no displacement in X direction, rollers on split steel pipe section are deactivated in step2(plane symmetry);

306—BC: Rollers on entire plane, no displacement in Y direction (plane of symmetry);

310—BC: Allowed only to move vertically in Z direction;

312—Rigid Disk and Reference Point (“RP”). Axial load in Z direction is applied on this reference point (“RP”) in a separate step (step3) after end of expansion;

324—Rigid disk and RP allowed only to move vertically in Z direction;

328—Lateral expansion of split shell due to the expansion of incompressible core;

330—Compression of nearly incompressible core in a separate step (step2);

334—Compression of nearly incompressible core in a separate step (step2); and

The FE analysis included three steps. The first step was the geostatic step, in which the self-weight of the materials including the soil overburden pressure and the initial lateral soil confining pressure were applied. In the second step, the pile shell was expanded laterally by the axial compression of the pile core (static loading).

FIG. 9illustrates schematically the expansion (progressing from non-expanded, on the left to expanded on the right) of the nearly incompressible core and the deformation of the split steel pipe section in the second step of the FE analysis. InFIG. 9, the reference numbers describe aspects of the schematic representation as follows:

400—Boundary Condition (“BC”); Free end (rollers are deactivated in step2);

402—Nearly incompressible core before compression in the Z direction;

404—BC; Rollers on split steel pipe in Y direction;

406—Translation in X direction due to the expansion;

408—Lateral expansion of nearly incompressible core due to the compression in the Z direction;

410—Rotation of the free end of the split steel pipe due to expansion; and

412—Expansion in Y direction.

In the second step, the roller supports on the split steel shell section were deactivated in the X-direction to allow lateral movement (expansion) of the pile, but the roller supports in the Y direction stayed active so that the pile did not move in the Y direction even though the pile was able to expand in the Y direction because the steel section was able to dilate as a result of the core compression. The third step of the analysis consisted of the vertical (axial) downward loading of the expanded pile. The vertical pile loading was applied with a prescribed vertical downward displacement.

FIGS. 10A and 10Bcompare the lateral confining pressure on a section of the pile developed in the laterally expansive pile and the conventional cylindrical pile in medium dense and very dense sand, respectively. The lateral expansion of the pile (prior to vertical loading) lead to a significant increase in the lateral confining pressure along the expanded section of the pile compared to the conventional cylindrical pile. To quantify this enhancement, a parameter herein referred to as a confining force (Fc), defined as the area within the lateral confining pressure curve, is introduced. For the medium dense sand, Fc of the laterally expansive pile was 78% greater than Fc of the conventional pile. For the very dense sand, Fc of the laterally expansive pile was 84% greater. As illustrated inFIGS. 10A and 10B, the greatest increase in lateral confining pressure occurred along the expanded core, which in this example was located at the bottom 6 m of the laterally expansive pile (The length of the nearly incompressible core was 6 m in this case). The lateral confining pressure in the lowest 6 m of the expanded pile was almost more than twice that of the conventional pile along the same region along the pile shaft.FIGS. 10A and 10Balso show the lateral confining pressure curves along the expansive pile at two stages of the applied vertical load. One stage was when the vertical pile displacement was 25 mm, that can be considered as a serviceability limit for the pile. The other stage was when the vertical pile displacement was twice the serviceability limit. These two confining pressure curves indicate that the improvement in the lateral confining pressure obtained at the end of pile expansion is maintained even after the vertical load was applied.

FIGS. 11A and 11Bcompare the load carrying capacity of the laterally expansive pile and the conventional cylindrical pile. There is a remarkable enhancement in downward capacity in the laterally expansive pile.FIGS. 11A and 11Bshow the load-displacement curves in the medium dense sand and the very dense sand, respectively. Using the tangent failure criterion method, the ultimate load capacity of the laterally expansive pile in the medium dense sand was 970 kN. The laterally expansive pile had 1.98 times greater (98% greater) ultimate load capacity than the conventional cylindrical pile. The ultimate load capacity of the laterally expansive pile in the very dense sand was 1200 kN, which was 2.18 times greater (118% greater) than the capacity of the conventional cylindrical pile in the very dense sand. Table 1 summarizes the FE analysis results.

TABLE 1Summary of FE analysis resultsConventional cylindricalpileBREPConfiningUltimateConfiningUltimateforcecapacityforcecapacityEnhancementDensity(kN)(kN)(kN)(kN)with BREPaMedium83049014809701.98Very905550167012002.18DenseaRatio of BREP ultimate capacity to ultimate capacity of the conventional pile.

The preceding examples can be repeated with similar success by substituting the generically or specifically described components and/or operating conditions of embodiments of the present invention for those used in the preceding examples.

Note that in the specification and claims, “about” or “approximately” means within twenty percent (20%) of the numerical amount cited. Embodiments of the present invention can include every combination of features that are disclosed herein independently from each other. Although the invention has been described in detail with particular reference to the disclosed embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims an such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference. Unless specifically stated as being “essential” above, none of the various components or the interrelationship thereof are essential to the operation of the invention. Rather, desirable results can be achieved by substituting various components and/or reconfiguration of their relationships with one another.