Patent Description:
The present invention relates to open-end extensible shells and related methods for constructing a support pier.

Buildings, walls, industrial facilities, and transportation-related structures typically consist of shallow foundations, such as spread footings, or deep foundations, such as driven pilings or drilled shafts. Shallow foundations are much less costly to construct than deep foundations. Thus, deep foundations are generally used only if shallow foundations cannot provide adequate bearing capacity to support building weight with tolerable settlements.

Recently, ground improvement techniques such as jet grouting, soil mixing, stone columns, and aggregate columns have been used to improve soil sufficiently to allow for the use of shallow foundations. Cement-based systems such as grouting or mixing methods can carry heavy loads but remain relatively costly. Stone columns and aggregate columns are generally more cost effective but can be limited by the load bearing capacity of the columns in soft clay soil.

Additionally, it is known in the art to use metal shells for the driving and forming of concrete piles. One set of examples includes <CIT> and <CIT>, which disclose the driving of a tapered, tubular metal shell into the ground and subsequent filling of the shell with concrete in order to form a pile. Another example is <CIT> which discloses the installation of shells in the earth for subsequent filling with concrete for the forming of a concrete pile. A disadvantage of these prior art shells is that their sole purpose is for providing a temporary form for the insertion of cementitious material for the forming of a hardened pile for structural load support. The prior art shells are not extensible and thus do not exhibit properties that allow them to engage the surrounding soil through lateral deformations. Further, because they relate to the use of ferrous materials, which are subject to corrosion, their function is complete once the concrete infill hardens. Thus, the prior art shells are not suitable for containing less expensive granular infill materials such as sand or aggregate, because the prior art shells cannot laterally contain the inserted materials during the life of the pier. The prior art shells are also not permeable and are thus ill-suited to drain cohesive soils.

Accordingly, it is desirable to provide improved techniques for constructing a shallow support pier in soil or the ground using extensible shells formed of relatively permanent material of a substantially non-corrosive or non-degradable nature for the containment of compacted aggregate therein. <CIT> describes an extensible shell and method for constructing a support pier. The shell can be flexible such that the shell expands when granular construction material is compacted in the interior of the shell. <CIT>, <CIT> and <CIT> describe also other shells of the prior art.

According to a first aspect of the present invention, there is provided an extensible shell as described in the claims. According to a second aspect of the present invention, there is provided a method for constructing a support pier in ground as described in the claims.

Extensible shells and related methods for constructing a support pier in ground are disclosed. An extensible shell defines an interior for holding granular construction material and defines an opening for receiving the granular construction material into the interior. The shell is flexible such that the shell expands laterally outward when granular construction material is compacted in the interior of the shell.

According to the invention the shell includes a first end that defines the opening. The shell may be shaped to taper downward from the first end to an opposing second end of the shell.

According to another aspect, the second end of the shell may define a substantially flat, blunt surface.

According to yet another aspect, a cross-section of the shell may form one of a substantially hexagonal shape and a substantially octagonal shape along a length of the shell extending between the first and second ends.

According to a further aspect, a cross-section of the first end of the shell is sized larger than a cross-section of the second end.

According to a still further aspect, the shell is comprised of plastic.

According to another aspect, the shell may define a plurality of apertures extending between an interior of the shell to an exterior of the shell.

According to yet another aspect not part of the invention, the shell may be substantially cylindrical in shape. According to an aspect of the invention, the shell may be substantially conical in shape.

According to the invention, the method includes positioning the shell in the ground and filling at least a portion of the interior of the shell with the granular construction material. The granular construction material is compacted in the interior of the shell to form a pier.

According to another aspect, a method may include forming a cavity in the ground. The cavity may be partially backfilled with aggregate construction material. Next, the shell may be positioned with the cavity and at least a portion of the interior of the shell filled with granular construction material. The granular construction material may then be compacted in the interior of the shell to form a pier. The compaction may be performed with a primary mandrel. Additional compacting may be performed with a second mandrel that has a larger cross-sectional area than the primary mandrel.

According to a further aspect, the extensible shell may comprise a plurality of slots extending between an interior of the shell to an exterior of the shell, the slots being generally transverse to a centerline along the length of the shell. The slots may be discontinuous around a circumference of the shell thereby maintaining portions of continuous material connectivity along the length of the shell. The slots may have a width in the range of <NUM>/<NUM> inch (<NUM>) to <NUM>/<NUM> inch (<NUM>) and may be spaced at a distance of <NUM> inches (<NUM>) from one another.

According to the invention, the disclosure is directed to an extensible shell for constructing a support pier in ground, the extensible shell defining an interior for holding granular construction material and said extensible shell defining a first end having a first opening for receiving granular construction material into the interior and a second end having a second opening, wherein the shell is flexible such that the shell expands laterally outward when granular construction material is compacted in the interior of the shell.

In another aspect, the first end defines the first opening with the shell shaped to taper from the first end to opposing second end of the shell, with the second end comprising a second opening.

According to the invention, a method for constructing a support pier in ground is provided according to independent claim <NUM>.

In a further aspect, the disclosure is directed to a method for constructing a support pier in ground, with the method comprising: forming a cavity in the ground; partially backfilling the cavity with an aggregate construction material; positioning an extensible shell into the cavity, with the shell having a first end with a first opening and a second end having a second opening, with the shell defining an interior for holding granular construction material and defining an opening for receiving the granular construction material into the interior, wherein the shell is flexible such that the shell expands when granular construction material is compacted in the interior of the shell; filling at least a portion of the interior of the shell with the granular construction material; and compacting the granular construction material in the interior of the shell to form a support pier.

This brief description is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description of the invention. This brief description of the invention is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Further, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

The present invention is directed to an extensible shell and related methods for constructing a support "shell pier" in ground. According to the invention the shell has an interior into which granular construction material can be loaded and compacted. The shell can be positioned in a cavity formed in the ground (the cavity being formed through a variety of methods as described in more detail below, including driving the shell from grade to form the cavity). After positioning in the ground, granular construction material can be loaded into the interior through an opening of the shell. The granular construction material may be subsequently compacted. The shell is extensible (or flexible) such that walls of the shell expand when the granular construction material is compacted in the interior of the shell. Therefore, since the shell maintains the compacted granular construction material in a contained manner (i.e., the material cannot expand laterally beyond the shell walls into the in-situ soil) the ground surrounding the shell is reinforced and improved for supporting shallow foundations and other structures. The present invention can be advantageous, for example, because it allows for much higher load carrying capacity due to its ability to limit the granular construction material from bulging laterally outward during loading. The shell is typically made of relatively permanent, substantially non-corrosive and/or non-degradable material such that the lateral bulging of the material is limited for the life of the pier.

<FIG> illustrate different views of an extensible shell <NUM>. <FIG> depicts a perspective view of the extensible shell <NUM>, which includes an enclosed end <NUM>. The surface of the enclosed end <NUM> can define a substantially flat, blunt bottom surface <NUM>, which can be hexagonal in shape. In the alternative, the enclosed end <NUM> may have any other suitable shape or size. Further, the bottom of the shell may be open, or may be blunt as in the case of a cylindrical shell, may be pointed as the bottom of a conical shell, or may be truncated to form a blunt shape at the bottom of conical or articulated section such as, for example, a frustum, or frustoconical configuration. It is therefore understood, for the purposes of this disclosure, that the term conical includes frustoconical configurations. The length of the shell may range from about <NUM> to about <NUM> long; such as from about <NUM> to about <NUM> long. The surfaces of the shell (inside and/or outside) may be smooth or contain a varying degree of roughness for interaction with surrounding surfaces.

Opposing the enclosed end <NUM> is another end, open end <NUM>, which defines an opening <NUM> for receiving granular construction material into an interior (not shown in <FIG>) defined by the shell <NUM>. As will be described in further detail herein below, the open end <NUM> is positioned substantial vertical to and above from the enclosed end <NUM> during construction of the pier.

<FIG>, <FIG> depict a top view, bottom view, a side view, and a cross-sectional side view of the extensible shell <NUM>, respectively. As shown in <FIG>, the extensible shell <NUM> defines a substantially hollow interior <NUM> extending between the open end <NUM> (with opening <NUM>) and the enclosed end <NUM>.

<FIG> shows that a cross-section of the open end <NUM> may be sized larger than the bottom surface <NUM> of the enclosed end <NUM>. <FIG> shows section line A-A arrows indicating the direction of the cross-sectional side view of the extensible shell <NUM> depicted in <FIG>.

The shape of the exterior of the shell <NUM> may be articulated to form a plurality of panels that form a hexagonal shape in cross-section as viewed from the top or bottom of the shell. Alternatively, the shape may be octagonal, cylindrical, conical, or any other suitable shape.

The extensible shell <NUM> is often shaped to taper downward from the open end <NUM> to the enclosed end <NUM>. In one example not part of the invention, the shell <NUM> tapers at a <NUM> degree angle, although the shell may taper at any other suitable angle.

The extensible shell <NUM> may be made of plastic, aluminum, or any metallic or non-metallic material of suitable extensibility, and preferably substantially non-corrosive and/or non-degradable material. The shell <NUM> may be relatively thin-walled. The thickness of the wall of the shell <NUM> may range, for example, from about <NUM> to about <NUM>. The example shell <NUM> of <FIG> has a thickness of about <NUM> inches (approximately <NUM>), although the shell may have any other suitable thickness. This thickness distance is the distance that uniformly separates the interior <NUM> and the exterior of the shell. The material of the shell and its thickness may be configured such that the shell has suitable integrity to hold construction material in its interior <NUM> and to expand laterally at least some distance when the construction material is compacted in the interior <NUM>.

<FIG> illustrate steps in an exemplary method of constructing a pier in ground using an extensible shell <NUM>. In this example, side partial cross-section views illustrate the use of the extensible shell <NUM> for constructing a pier <NUM> in the ground (see <FIG>). Other methods are described with reference to <FIG> and the Examples below. The method of <FIG> includes forming a pre-formed elongate vertical cavity <NUM> or hole in a ground surface <NUM>, as shown in <FIG>. The ground may be comprised of primarily soft cohesive soil such as soft clay and silt, or also loose sand, fill materials, or the like. The cavity <NUM> may be formed with a suitable drilling device having, for example, a drill head or auger for forming a cavity or hole, or may be formed by other methods for forming a cavity such as by inserting and removing a driving mandrel to the desired pre-formed cavity depth. In some examples not part of the invention, the cavity may not be formed at all prior to shell insertion, such as described below with reference to <FIG>.

After the partial cavity <NUM> has been formed, the extensible shell <NUM> may be positioned within the cavity <NUM>, as shown in <FIG>, for ultimate driving to the desired depth. Particularly, an extractable mandrel <NUM> may be used for driving the extensible shell <NUM> into the cavity <NUM> and ground <NUM>. A tamper head <NUM> of the mandrel <NUM> may be positioned against a bottom surface <NUM> of the interior <NUM> and used to drive the shell <NUM> to the desired penetration depth, as shown in <FIG>. The cavity <NUM> is at that point formed of a size and dimension such that the exterior surface of the extensible shell <NUM> fits tightly against the walls of the cavity <NUM>.

After the extensible shell <NUM> has been driven into (while forming) the fully enlarged cavity <NUM>, the mandrel <NUM> is removed, leaving behind the shell <NUM> in the cavity <NUM> and with the interior <NUM> being empty. The shell <NUM> may then be filled with a granular construction material <NUM>, such as sand, aggregate, admixture-stabilized sand or aggregate, recycled materials, crushed glass, or other suitable materials as shown in <FIG>. The granular construction material <NUM> may be compacted within the shell using the mandrel <NUM>. The compaction increases the strength and stiffness of the internal granular construction material <NUM> and pushes the granular construction material <NUM> outward against the walls of the shell <NUM>, which pre-strains the shell <NUM> and increases the coupling of the shell <NUM> with the in-situ soil. Significant increases in the load carrying capacity of the pier <NUM> can be achieved as a result of the restraint offered by the shell <NUM>.

<FIG> illustrate steps in another exemplary method of constructing a pier in ground using an extensible shell. Referring to <FIG>, an aggregate construction material <NUM> (e.g., sand) is placed in the interior <NUM> of the shell <NUM> to a predetermined level above the bottom surface <NUM> of the shell <NUM>. Next, the tamper head <NUM> of the extractable mandrel <NUM> is fitted to the interior <NUM> of the extensible shell <NUM>, and against the top of the aggregate construction material <NUM>. The mandrel <NUM> may then be moved towards the ground <NUM> in a direction indicated by arrow <NUM> for driving the shell <NUM> into the ground <NUM>. Driving may be facilitated using a small pre-formed cavity (e.g., the cavity <NUM> shown in <FIG>), or not, depending on site conditions.

Referring to <FIG>, the mandrel <NUM> is shown driving the shell <NUM> into the ground <NUM> in the direction <NUM> such that the shell <NUM> is at a predetermined depth below grade. Next, the mandrel <NUM> may be removed. At <FIG>, the shell <NUM> is substantially filled with additional aggregate construction material <NUM> (e.g., sand) through opening <NUM>, and the mandrel <NUM> is positioned as shown. Next, vertical compaction force and/or vibratory energy is applied to the mandrel <NUM> for compacting the materials <NUM> and <NUM>. The shell <NUM> may be driven by this force to a further depth below grade. The addition of construction material <NUM> and subsequent compaction can be repeated several times until the final pier is constructed. Alternatively, the shell may be "topped off" with additional construction material after only one compaction cycle.

A second mandrel <NUM> may be used to compact the upper portion of the material <NUM> in the direction <NUM>, as shown in <FIG>. The second mandrel <NUM> may have a larger cross-sectional area than the primary mandrel <NUM> to provide increased confinement during compaction.

The shell <NUM> may define apertures <NUM> that extend between the interior <NUM> and an exterior of the shell <NUM> to the in-situ soil (see <FIG> and <FIG>). The apertures <NUM> may provide for drainage of excess pore water pressure that may exist in the in-situ soil to drain into the interior <NUM> of the shell <NUM>. Increases in pore water pressure typically decreases the strength of the soil and is one of the reasons that prior art piers are limited in their load carrying capacity in saturated cohesive soil such as clay, silt, or the like. The apertures <NUM> envisioned herein allow the excess pore water pressure in the soil to dissipate into the pier <NUM> after insertion. This allows the in-situ soil to quickly gain strength with time, a phenomena not enjoyed by concrete, steel piles, or grout elements (i.e., "hardened" elements). The drainage of excess pore water pressures allows additional settlement of the soil that may occur as a result of pore water pressure dissipation prior to the application of foundation loads.

Other examples may not define apertures, or may provide one or more apertures <NUM> on only one side of the shell <NUM>. Alternatively, the apertures <NUM> may be defined in the shell <NUM> such that they are positioned along a portion of the length of the shell <NUM>, are positioned along the full length of the shell <NUM>, or may be positioned asymmetrically in various configurations. The sizes and placements of the apertures <NUM> can vary according to the size of the shell <NUM>, the conditions of the ground (e.g., where higher water pressure is known to exist), and other relevant factors. The apertures <NUM> may range in size from about <NUM> to about <NUM>; such as from about <NUM> to about <NUM>. The top of the shell <NUM> may be enclosed and connected to vacuum pressure to further increase and accelerate drainage of excess water pressure in the surrounding soil through the apertures <NUM>.

The mandrel <NUM> may be constructed of sufficient strength, stiffness, and geometry to adequately support the shell <NUM> during driving and to be able to be retracted from the shell <NUM> after driving. The shape of the exterior of mandrel <NUM> may be substantially similar to the shape of the interior <NUM> defined by the shell <NUM>. The mandrel <NUM> may be comprised primarily of steel. Other materials are also envisioned including, but not limited to, aluminum, hard composite materials, and the like.

The mandrel <NUM> may be driven by a piling machine or other suitable equipment and technique that may apply static crowd pressure, hammering, or vibration sufficient to drive the mandrel <NUM> and extensible shell <NUM> into the surface of ground <NUM>. The machine may be comprised of an articulating, diesel, pile-driving hammer that drives the mandrel <NUM> using high energy impact forces. The hammer may be mounted on leads suspended from a crane. The hammer may be a sheet pile vibrator mounted on a rig capable of supplying a downward static force. The shell <NUM> may be placed in a pre-formed cavity <NUM> and constructed without the use of an extractable mandrel. Standard methods of driving mandrels into the ground are known in the art and therefore, can be used for driving.

The following Examples illustrate further aspects.

As an example, piers were constructed using extensible shells at a test site in Iowa. Load tests were conducted on the piers using a conventional process. The extensible shells used in the tests and the methods of their use consisted essentially of that described above and shown in the attached Figures. In this test, extensible shells formed from LEXAN® polycarbonate plastic were installed at a test site characterized by soft clay soil. This testing was designed to compare the load versus deflection characteristics of an extensible shell to aggregate piers constructed using a driven tapered pipe. Two comparison aggregate piers (of fine and coarse aggregate) were constructed to a depth of <NUM> feet (<NUM>) below the ground surface.

In this test, the extensible shell was formed by bending sheets of the plastic to form a tapered shape having a hexagonal cross-section and that tapered downward from an outside diameter of <NUM> inches (<NUM>) at the top of the shell to a diameter of <NUM> inches (<NUM>) at the bottom of the shell. A panel of the shells overlapped, and this portion was both glued and bolted together. The length of the extensible shell was <NUM> feet (<NUM>). In this embodiment, apertures were formed in the extensible shell by perforating the sides of the shell with <NUM> to <NUM> diameter "weep" holes spaced apart from each another. The bottom portion of the shell was capped with a steel shoe to facilitate driving. LEXAN® polycarbonate plastic has a tensile strength of approximately <NUM> MPa (<NUM> psi) at <NUM> percent elongation and a Young's modulus of <NUM> MPa (<NUM>,<NUM> psi). The extractable mandrel used in this test was attached to a high frequency hammer, which is often associated with driving sheet piles. The hammer is capable of providing both downward force and vibratory energy for driving the shell into the ground and for compacting aggregate construction material in the shell.

In this example, the extensible shell was driven into the ground without pre-drilling of the cavity or hole. Particularly, in this test, the two shells were installed by orientating each shell in a vertical direction, placing approximately <NUM> feet (<NUM>) of sand at the base of the shell, and then driving the shell into the ground surface with an extractable mandrel with exterior dimensions similar to those of the interior of the shell. The shell was driven to a depth of approximately <NUM> feet (<NUM>) below grade. The mandrel was removed and the shells were filled with sand. The extractable mandrel was then re-lowered within the shells and vertical compaction force in combination with vibratory energy was applied to both compact the sand to drive the shell to a depth of <NUM> feet (<NUM>) below grade. The mandrel was then extracted and the upper portion of the shell was then filled with crushed stone to a depth of <NUM> ft (<NUM>) below grade. A concrete cap was then poured above the crushed stone fill to facilitate load testing.

Radial cracks were observed to extend outward from the edge of the shell pier. These cracks form drainage galleries that are the result of high radial stresses and low tangential stresses created in the ground during pier installation. Drainage was afforded by the perforations in the shell and allowed soil water to drain into the sand and aggregate filled piers.

The shell piers were load tested using a hydraulic jack pushing against a test frame. <FIG> is a graph showing results of the load test compared with aggregate piers constructed using a similarly shaped mandrel. As shown in <FIG>, at a top of pier deflection of one inch, the piers constructed without shells supported a load of <NUM>,<NUM> pounds to <NUM>,<NUM> pounds (<NUM> kN to <NUM> kN). The shell piers constructed in this example supported a load of <NUM> kN to <NUM> kN (<NUM>,<NUM> to <NUM>,<NUM> pounds) at a top of pier deflection of one inch. The load carrying capacity of the shell piers constructed in this example provided a <NUM> to <NUM> fold improvement when compared to aggregate piers constructed without extensible shells.

In other testing, extensible shells were formed from high-density polyethylene polymer ("HDPE") and installed at the test site as described in Example I. This testing program was designed to compare the load versus deflection characteristics of this example to aggregate piers constructed using a driven tapered pipe as described in Example I. A total of six shell piers were installed as part of this example.

In this test, the extensible shell was formed by a rotomolding process. The shells defined a tapered shape having a hexagonal cross-section and that tapered downward from an outside diameter of <NUM> (<NUM> inches) at the top of the shell to a diameter of <NUM> (<NUM> inches) at the bottom of the shell. The bottom of the extensible shell was integrally constructed as part of the shell walls as a result of the rotomolding process. The mandrel in this embodiment was attached to the same hammer as described in Example I.

The installation process in this Example was somewhat different from that in Example I and included pre-drilling a <NUM> inch (<NUM>) diameter cavity to a depth of <NUM> feet (<NUM>) to <NUM> feet (<NUM>) below the ground surface (rather than driving the shell initially from top grade). The shell was then placed vertically in the pre-drilled cavity. The extractable mandrel was then inserted into the shell, and the shell was driven to a depth <NUM> feet (<NUM>) to <NUM> feet (<NUM>) below grade. The extensible shell was then filled with aggregate construction material and compacted in four lifts; with each lift about <NUM> cubic feet (<NUM> cubic meters) in volume. The aggregate consisted of sand in five of the piers and consisted of crushed stone in one of the piers. Each lift was compacted with the downward pressure and vibratory energy of the extractable mandrel.

After placement and compaction of sand within the extensible shells, the top of the shells were situated at about <NUM> feet (<NUM>) to <NUM> feet (<NUM>) below the ground surface. Crushed stone was then placed and compacted above the extensible shell to a depth of <NUM> foot (<NUM>) below the ground surface. A concrete cap was then poured above the crushed stone fill to facilitate load testing.

The shell piers were load tested using a hydraulic jack pushing against a test frame. <FIG> is a graph showing results of the load test compared with the aggregate piers described in Example I. As shown in <FIG>, at a top of pier deflection of one inch, the piers constructed without shells supported a load of <NUM>,<NUM> pounds to <NUM>,<NUM> pounds (<NUM> kN to <NUM> kN). The shell piers constructed in this example supported loads ranging from <NUM>,<NUM> pounds (<NUM> kN) to <NUM>,<NUM> pounds (<NUM> kN) at the top of pier deflections of one inch. The load carrying capacity of the shell piers constructed in accordance with this example provided a <NUM> to <NUM> fold improvement when compared to aggregate piers constructed without extensible shells.

In another test, an extensible shell of the same embodiment described in Example II was installed at the test site as described in Example I. This testing program was designed to compare the load versus deflection characteristics of this example to aggregate piers constructed using a driven tapered pipe as described in Example I. The mandrel, hammer, and extensible shell used for testing were the same as used in Example II.

In this example, the installation process included pre-drilling a <NUM> inch (<NUM>) diameter cavity to a depth of <NUM> feet (<NUM>) below the ground surface. The extractable mandrel was then inserted into the pre-drilled cavity, to create a cavity with a total depth of <NUM> feet (<NUM>) below the ground surface. This cavity was then backfilled to the ground surface with sand. The extensible shell was then driven vertically through the sand filled cavity with the extractable mandrel to a depth of <NUM> feet (<NUM>) below the ground surface, so that the top of the shell was situated <NUM> inches above the ground surface. The extensible shell was then filled with sand in four lifts, with each lift about <NUM> cubic feet (<NUM> cubic meters) in volume. Each lift was compacted with the downward pressure and vibratory energy of the mandrel. A concrete cap encompassing the top of the shell was then cast over the shell to facilitate load testing.

The shell pier was load tested using a hydraulic jack pushing against a test frame. <FIG> is a graph showing results of the load test compared with the aggregate piers described in Example I. As shown in <FIG>, at a top of pier deflection of one inch, the piers constructed without shells supported a load of <NUM>,<NUM> pounds to <NUM>,<NUM> pounds (<NUM> kN to <NUM> kN). The pier constructed in this example supported a load of <NUM>,<NUM> pounds (<NUM> kN) with a top of pier deflection of one inch. The load carrying capacity of the shell pier constructed in accordance with this example provided a <NUM> to <NUM> fold improvement when compared to aggregate piers constructed without extensible shells.

In yet another test, an example was installed at a project site characterized by <NUM> feet (<NUM>) of loose sand soil over <NUM> feet (<NUM>) of soft clay soil over dense sand soil. The example at the project site was used to support structural loads, such as those associated with building foundations and heavily loaded floor slabs. The mandrel, hammer, and extensible shell used for testing were the same as used in Examples II and III.

In this example, the installation process included pre-drilling a <NUM> inch (<NUM>) diameter pre-drill to a depth of <NUM> feet (<NUM>) below the ground surface. Approximately <NUM> cubic feet (<NUM> cubic meters) of sand was then placed in the pre-drilled cavity. This resulted in the pre-drilled cavity being about half-full.

The extensible shell was then placed vertically in the partially backfilled pre-drilled cavity. The extractable mandrel was then inserted into the shell, and the shell was driven to a depth <NUM> feet (<NUM>) below grade. The extensible shell was then filled with sand in four lifts; with each lift about <NUM> cubic feet (<NUM> cubic meters) in volume. Each lift was compacted with the downward pressure and vibratory energy of the mandrel.

After placement and compaction of sand within the extensible shell, a lift of crushed stone about <NUM> cubic feet (<NUM> cubic meters) in volume was placed and compacted within the extensible shell. Crushed stone was then placed and compacted above the extensible shell until the crushed stone backfill was level with the ground surface.

At one shell location, a <NUM> inch (<NUM>) diameter concrete cap was placed over the shell to facilitate load testing. At a second shell location, a <NUM> foot (<NUM>) wide by <NUM> foot (<NUM>) wide concrete cap was placed over the shell to facilitate loading and to measure the load deflection characteristics of the composite of native matrix soil and extensible shell (to simulate a floor slab).

The shell piers were load tested using a hydraulic jack pushing against a test frame, with the results of the load testing being shown in <FIG>. The shell pier tested with the <NUM> inch diameter concrete cap supported a load of <NUM>,<NUM> pounds (<NUM> kN) at a deflection of <NUM> inches (<NUM>). The shell pier tested with a <NUM> foot wide by <NUM> foot wide concrete cap supported a load of <NUM>,<NUM> pounds (<NUM> kN) at a deflection of <NUM> inches (<NUM>).

With reference to <FIG>, an alternative example is shown and which includes an extensible shell <NUM> with one or more slits or slots <NUM> that extend between an interior of the shell to an exterior of the shell. The slots <NUM> may be placed over the entire length of the shell <NUM> or only partially located along the length and have varying spacing, such as, for example, slots being spaced every <NUM> inches (<NUM>) starting generally <NUM> foot (<NUM>) from the top and bottom. The slots <NUM> may be of varying widths, such as, for example, <NUM>/<NUM> inch (<NUM>) to <NUM>/<NUM> inch (<NUM>) wide. The slots <NUM> typically run generally transverse to a centerline along the length of the shell and may form a minor or major part of the circumference of the shell <NUM>. In one embodiment, such as shown in <FIG>, the slots <NUM> are discontinuous around the circumference leaving three spines <NUM> to maintain portions of continuous material connectivity along the length of the shell <NUM>. The shell <NUM> of this embodiment may be of any suitable size or shape as described above with reference to shell <NUM>.

As an example, a slotted extensible shell of this embodiment was installed at a test site in Iowa to compare the load versus deflection characteristics of this embodiment of the extensible shell to aggregate piers constructed using a driven tapered pipe. The test site was characterized by soft clay soil and the two comparison aggregate piers (of fine and coarse aggregate) were constructed to a depth of <NUM> feet below the ground surface.

For this test of the extensible shell, the shell was formed from High Density Polyethylene polymer and was formed by the rotomolding process. The shell formed a tapered shape that was hexagonal in cross section and tapered downward from an outside diameter of <NUM> inches (<NUM>) at the top of the shell to a diameter of <NUM> inches (<NUM>) at the bottom of the shell. The bottom of this embodiment of the extensible shell was integrally constructed as part of the shell walls as a result of the rotomolding process. In this example (similar to that shown in <FIG>), <NUM>/<NUM> inch (<NUM>) wide slots were cut in a circumferential orientation around the extensible shell. The extensible shell was left as a single continuous piece, by not removing material from three of the six corners or spines. The extractable mandrel used in this test was attached to a high frequency hammer, which is often associated with driving sheet piles. The hammer is capable of providing both downward force and vibratory energy for driving the shell into the ground and for compacting aggregate construction material in the shell.

In this example, the installation process included a <NUM> inch (<NUM>) diameter pre-drill to a depth of <NUM> feet (<NUM>) below the ground surface. The shell was then placed vertically in the pre-drilled hole and then the shell was driven with an extractable mandrel with exterior dimensions similar to those of the interior of the shell. The shell was driven to a depth of <NUM> feet (<NUM>) below grade. The mandrel was removed and the extensible shell was then filled with aggregate in four lifts; with each lift about <NUM> cubic feet (<NUM> cubic meters) in volume. Each lift was compacted with the downward pressure and vibratory energy of the extractable mandrel.

After placement and compaction of aggregate within the extensible shell, the top of the shell was situated at about <NUM> feet (<NUM>) below the ground surface. The aggregate backfill was then leveled with the top of the shell, and a concrete cap was then poured above the shell to facilitate load testing.

The slotted shell pier was load tested using a hydraulic jack pushing against a test frame. <FIG> is a graph showing results of the load test compared with the aggregate piers described above. As shown in <FIG>, at a top of pier deflection of one inch, the piers constructed without slotted shells supported a load of <NUM>,<NUM> pounds to <NUM>,<NUM> pounds (<NUM> kN to <NUM> kN). The pier constructed in this example supported a load of <NUM>,<NUM> pounds (<NUM> kN) at a top of pier deflection of one inch. The load carrying capacity of the pier constructed in accordance with this example provided a <NUM> to <NUM> fold improvement when compared to aggregate piers constructed without extensible shells.

With reference to <FIG>, an embodiment not part of the present invention is shown and which includes an open-end extensible shell that can be used to form piers. Namely, <FIG> shows a perspective view of an example of an open-end extensible shell <NUM>. <FIG> shows a cross-sectional view of open-end extensible shell <NUM> taken along line A-A for <FIG>. In this example, open-end extensible shell <NUM> is a hollow tubular member that has a first open end <NUM> and a second open end <NUM>. Open-end extensible shell <NUM> can be used in any orientation with respect to driving into the ground. However, for illustration purposes, first open end <NUM> is hereafter referred to as advancing open end <NUM>, wherein advancing open end <NUM> means the bottom end of open-end extensible shell <NUM> that is advanced into the ground first. Further, second open end <NUM> is hereafter referred to as trailing open end <NUM>, wherein trailing open end <NUM> means the top end of open-end extensible shell <NUM> that is mated to driving equipment, such as a mandrel.

Open-end extensible shell <NUM> can be any length and any width or diameter. Without limitation, the length of open-end extensible shell <NUM> can be from about <NUM> (<NUM> ft) to about <NUM> (<NUM> ft) in one example, or can be about <NUM> (<NUM> ft) in another example. Without limitation, the width or diameter of open-end extensible shell <NUM> can be from about <NUM> (<NUM> in) to about <NUM> (<NUM> in) in one example, or can be about <NUM> (<NUM> in) in another example. In one example, open-end extensible shell <NUM> can be formed of plastic, such as high-density polyethylene polymer (HDPE) plastic. In another example, open-end extensible shell <NUM> can be formed of metal, such as steel or aluminum.

Open-end extensible shell <NUM> is not limited to a straight tubular shape. According to the invention, <FIG> illustrate various views of an example of an open-end extensible shell <NUM> that has a hexagon-shaped cross-section and a tapered tip; namely, advancing open end <NUM> is tapered. Namely, <FIG> show perspective views of the advancing open end <NUM>-portion of open-end extensible shell <NUM>, which is hexagonal and includes a taper <NUM>. <FIG> shows a cross-sectional view of open-end extensible shell <NUM> taken along line B-B for <FIG>. In one example, the width or diameter of open-end extensible shell <NUM> is tapered from about <NUM> (<NUM> in) to about <NUM> (<NUM> in).

<FIG> show an example of a process of installing open-end extensible shell <NUM> into the ground (e.g., ground <NUM>). In this example, a closed pipe mandrel <NUM> that has a shoulder collar <NUM> is used to drive open-end extensible shell <NUM> into ground <NUM>. Closed pipe mandrel <NUM> is inserted into open-end extensible shell <NUM> until shoulder collar <NUM> contacts trailing open end <NUM> of open-end extensible shell <NUM>. In this way, driving force is transferred from closed pipe mandrel <NUM> to open-end extensible shell <NUM>. In <FIG>, the advancing end of closed pipe mandrel <NUM> extends beyond advancing open end <NUM> of open-end extensible shell <NUM>. In one example, the end of closed pipe mandrel <NUM> extends about <NUM> (<NUM> ft) beyond advancing open end <NUM> of open-end extensible shell <NUM>.

However, the position of shoulder collar <NUM> can be adjustable along the length of closed pipe mandrel <NUM>. Namely, shoulder collar <NUM> can be adjustable such that a range of depths and relative positions of open-end extensible shell <NUM> and closed pipe mandrel <NUM> can be achieved without the need to change mandrels. For example, <FIG> shows the position of shoulder collar <NUM> set such that the advancing end of closed pipe mandrel <NUM> substantially aligns with advancing open end <NUM> of open-end extensible shell <NUM>.

<FIG> shows a flow diagram of an example of a method <NUM> of using open-end extensible shell <NUM> to form a support pier. Method <NUM> may include, but is not limited to, the following steps.

At a step <NUM>, open-end extensible shell <NUM> is driven into the ground using a mandrel. For example and referring again to <FIG>, open-end extensible shell <NUM> is driven into ground <NUM> using closed pipe mandrel <NUM>.

At a step <NUM>, the mandrel (e.g., closed pipe mandrel <NUM>) is withdrawn from open-end extensible shell <NUM>, leaving open-end extensible shell <NUM> in the ground. For example, <FIG> shows open-end extensible shell <NUM> in ground <NUM> after closed pipe mandrel <NUM> is withdrawn, creating a shell cavity <NUM>. Namely, shell cavity <NUM> is a portion of ground <NUM> that is void of material.

At a step <NUM>, shell cavity <NUM> is backfilled with sand, aggregate, cementitious grout, and/or any other material. For example, <FIG> shows shell cavity <NUM> of open-end extensible shell <NUM> backfilled with a volume of material <NUM>.

At a step <NUM>, the mandrel (e.g., closed pipe mandrel <NUM>) is reinserted into open-end extensible shell <NUM>. Then, material <NUM> is packed to below advancing open end <NUM> of open-end extensible shell <NUM>. For example, <FIG> shows a "bulb" of material <NUM> is formed in ground <NUM> below advancing open end <NUM> of open-end extensible shell <NUM>.

At a step <NUM>, the mandrel (e.g., closed pipe mandrel <NUM>) is withdrawn from open-end extensible shell <NUM>, again as shown in <FIG>.

At a step <NUM>, the remaining portion of shell cavity <NUM> is backfilled with material <NUM> (e.g., sand, aggregate, cementitious grout, and/or any other material).

At a step <NUM>, the mandrel (e.g., closed pipe mandrel <NUM>) is reinserted into open-end extensible shell <NUM>. Then, material <NUM> is packed into shell cavity <NUM> of open-end extensible shell <NUM>.

At a decision step <NUM>, it is determined whether the construction of the support pier is complete. If the construction of the support pier is complete, then method <NUM> ends. However, if the construction of the support pier is not complete, then method <NUM> returns to <NUM>.

A benefit of using open-end extensible shell <NUM> and method <NUM> is that it provides increased stiffness for the shell support layer and increased overall length of the extensible shell system in the upper zone (open-end extensible shell <NUM> plus "bulb" depth).

As an example, support piers were constructed using extensible shells in accordance with embodiments of the present invention at a test site in Iowa. Load tests were conducted on the piers using a conventional process. The extensible shells used in the tests and the methods of their use consisted essentially of that described above and shown in <FIG>. In this test, extensible shells formed of high-density polyethylene polymer (HDPE) plastic were installed at a test site characterized by soft clay soil. This testing was designed to compare the load versus deflection characteristics of an extensible shell in accordance with the present invention to aggregate piers constructed with a driven tapered pipe. Two comparison aggregate piers were constructed to a depth of <NUM> feet below the ground surface.

In this test, the extensible shell was formed by a rotomolding process. The shells defined a tapered shape having a hexagonal cross-section (e.g., as shown in <FIG>) and that tapered downward from an outside diameter of <NUM> (<NUM>. 4inches) at the top of the shell to a diameter of <NUM> (<NUM> inches) at the bottom of the shell. In this embodiment of the invention the extensible shell has a total length of <NUM> (<NUM> feet), and both the top and the bottom ends of the shell are open such that and extractable tapered mandrel commonly used for constructing aggregate piers could fully pass through the extensible shell.

The extractable mandrel used in this test was attached to a high frequency hammer, which is often associated with driving sheet piles. The hammer is capable of providing both downward force and vibratory energy for driving the shell into the ground and for compacting aggregate construction material in the shell. The "open bottom" extensible shell pier and the aggregate pier were constructed with a similar mandrel and high frequency hammer.

In this example, a <NUM> (<NUM> in) diameter and <NUM> (<NUM> in) deep pre-drill hole was formed at the ground surface prior to driving the extensible shell. The purpose of the pre-drill is to facilitate the placement of a concrete cap for the load test. The extensible shell, and Tapered Mandrel were then driven into the ground such that the tip of the tapered mandrel was at a depth of about <NUM> (<NUM> ft) below the ground surface, the bottom of the extensible shell was at a depth of about <NUM> (<NUM> ft) below the ground surface, and the top of the shell was at a depth of about <NUM> (<NUM> in) below the ground surface.

The tapered mandrel used in this example is hollow such that such that the mandrel can be filled with aggregate, and allowed to flow out the bottom of the mandrel. An aggregate pier is constructed with this mandrel by raising and lowering the mandrel pre-determined distances to construct the aggregate pier. In this example, an aggregate pier was constructed below and within the extensible shell using a similar process.

Claim 1:
An extensible shell (<NUM>) for constructing a support pier in ground, the extensible shell being continuous and defining an interior for holding granular construction material (<NUM>) and defining a first end (<NUM>) having a first opening and a second end (<NUM>) having a second opening for receiving the granular construction material (<NUM>) into the interior, wherein the shell is flexible such that the shell expands laterally outward in ground when granular construction material is compacted in the interior of the shell, characterized by the shell (<NUM>) has a hexagon-shaped cross-section and a tapered tip (<NUM>) at the first end.