Patent Application
20160265184
The subject matter disclosed herein relates to soil improvement systems and methods. Particularly, the subject matter disclosed herein relates to systems and methods for isolation of structural foundations from soil improvement elements and distributing stress from high stiffness elements to lower stiffness covering materials.
Techniques for soil or ground improvement include soil mixing, jet grouting, stone columns, vibro concrete columns, controlled modulus columns, and aggregate pier techniques. Soil mixing and jet grouting involve the enhancement of in situ soil with cement binders. Vibro stone column techniques were developed in the 1940s in Germany. Vibro concrete columns were a later extension of traditional stone columns. Controlled modulus columns were developed in France in the 1980s. Aggregate pier techniques were developed by Nathaniel S. Fox and his coworkers in the early 1990s as described by U.S. Pat. No. 5,249,892, titled “Short Aggregate Piers and Method and Apparatus for Producing Same,” and issued Oct. 5, 1993. Fox's technique involves the steps of drilling a hole in the ground, filling the hole incrementally with loose lifts of aggregate, and compacting the aggregate with a tamper head.
Fox also developed the “Impact Pier” technique which includes the steps of driving a hollow steel pipe in the ground, filling the pipe with aggregate stone, extracting the pipe in increments, and then advancing the pipe back downwards to compact the placed lift of aggregate in the ground. Advancements of the Impact technique include the use of grout or concrete, sometimes in a closed, pressurized system to construct a rigid cemented aggregate element. These aggregate or cemented-aggregate elements provide vertical support for foundations. Shortcomings exist between the interface of the rigid elements and the foundation.
These more rigid soil improvement systems including vibro concrete columns, grouted or concreted aggregate piers, controlled modulus columns, and others require an aggregate transfer pad constructed following element construction between the tops of the rigid element and the bottom of foundations. Accordingly, it is desired to provide improved techniques to enhance this critical interface and to provide other soil improvement techniques and systems.
The presently disclosed subject matter provides a system and methods for reducing the shear load transferred from a structural foundation of a building to a ground improvement element. Particularly, the subject matter disclosed herein relates to systems and methods for isolation of structural foundations from soil improvement elements and distributing stress from high stiffness elements to lower stiffness covering materials.
Accordingly, in some aspects, the presently disclosed subject matter provides a shear load transfer reduction system including one or more ground improvement elements for supporting applied load. The system also includes one or more shear break elements positioned above the ground improvement elements. The shear break elements are configured to have low interface shear strength.
In other aspects, the presently disclosed subject matter provides a method for reducing shear (horizontal) load transfer. The method includes placing one or more ground improvement elements into the ground. The method also includes positioning one or more shear break elements having a low interface shear strength above the ground improvement elements. The method further comprises positioning a structural foundation above the shear break elements.
In other aspects, the presently disclosed subject matter provides a method for reducing stress concentration in the aggregate transfer pad constructed following element construction between the tops of the rigid element and the bottom of foundations.
The present disclosure can be better understood by referring to the following figures. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the present disclosure. In the figures, like reference numerals designate corresponding parts throughout the different views.
The presently disclosed subject matter is described herein with specificity to meet statutory requirements. However, the description itself is not intended to limit the scope of this patent. Rather, the inventor has contemplated that the claimed subject matter might also be embodied in other ways, to include different steps, materials or elements similar to the ones described in this document, in conjunction with other present or future technologies. Moreover, although the term “step” may be used herein to connote different aspects of methods employed, the term should not be interpreted as implying any particular order among or between various steps herein disclosed unless and except when the order of individual steps is explicitly described.
The presently disclosed subject matter provides systems and methods for isolating friction, such as isolating the friction between ground improvement elements (also termed ground improvement inclusions or vertical inclusions) and building foundations built on top of the ground improvement elements. The presently disclosed subject matter reduces the shear loads transferred to soil improvement elements by the structures built above the elements. Specifically, the subject matter is provided to reduce the transfer of shear and lateral stresses from the structural elements to the tops of the ground improvement elements. The ground improvement elements considered in this application include any stiff vertical inclusion installed to treat the ground and support applied loads. The systems used comprise materials exhibiting low coefficients of friction to reduce the shear stress transfer.
Materials comprising the presently disclosed shear break elements 102 exhibiting “low interface shear strength” as used herein refer to materials with low friction angles and low values of interface cohesion. Non-limiting examples include, but are not limited to, high density polyethylene (HDPE), poly(vinyl chloride) (PVC), polypropylene, polished metal, ceramic materials, fiberglass, composite materials with low friction angle, smooth aggregate with low friction angle, particulates with low friction angles, and the like. In some embodiments, at least one shear break element 102 comprises a plastic material. In other embodiments, at least one shear break element 102 comprises material selected from the group consisting of high density polyethylene (HDPE), poly(vinyl chloride) (PVC), and polypropylene.
In some embodiments, the presently disclosed system may include a granular bedding material 106 placed in between the ground improvement element 104 and one or more shear break elements 102. In other embodiments, the bedding material 106 may include, but is not limited to, sand, aggregate, other soil materials, slag, and the like. In other embodiments, the bedding material 106 may be include sand, aggregate, slag, the like, and combinations thereof.
The number of shear break elements 102 in the presently disclosed system 100 can vary from 1 to more than 1, such as 2, 3, 4, 5, or more. In some embodiments, two shear break elements 102 are placed on top of the ground improvement element 104.
In some embodiments, the presently disclosed subject matter includes an example method for constructing the presently disclosed system 100 to reduce the shear load transferred from a structural foundation of a building to a ground improvement element 104. The method includes placing the ground improvement element 104 into the ground. The method also includes placing one or more shear break elements 102 exhibiting a low interface shear strength for a high axial stiffness on top of the ground improvement element 104. The method also includes building the structural foundation of the building on top of the at least one shear break element 102.
In other embodiments, an example method may include excavating the area around the ground improvement element 104 to expose the ground improvement element 104 and the soil around the ground improvement element 104 prior to placing the shear break elements 102 on top of the ground improvement element 104.
In other embodiments, example methods include filling in the excavated area with a solid material 112 before building the structural foundation of the building on top of the shear break elements 102.
In further embodiments, the solid material 112 may include, but is not limited to, aggregate, sand, slag, earthen materials, the like, and combinations thereof. In other examples, the solid material 112 may include aggregate.
In some embodiments, bedding material 106 may be placed between the ground improvement element 104 and shear break elements 102. In other embodiments, a viscous lubricant 110 may be placed on top of at least one shear break element 102. In still other embodiments, two shear break elements 102 may be placed on top of the ground improvement element 104.
In some embodiments, the system includes two or more separate sections 108 of a material exhibiting a low coefficient of friction. In other embodiments, the sections are of sufficient thickness to avoid cracking or extensive deformation when subjected to the applied stresses over the ground improvement inclusion. While circular in shape is the preferred embodiment, alternate shapes including square, oval, and rectangular are also envisioned. In still other embodiments, shapes may extend at least to the edge of ground improvement inclusion in some or all directions. In further embodiments, the shapes may extend beyond the edge of the ground improvement elements 104.
In some embodiments, an excavation may be made following construction of the ground improvement inclusion and prior to placement of footing 114 concrete. The excavation may expose both soil and ground improvement inclusions. In other embodiments, one shear break element may be placed over the top of each of the inclusions. In an example, a thin layer of bedding material 106 may be placed over the top of the inclusion prior to shear break element 102 placement to create a more level surface and cushion. Also, a layer of viscous lubricant 110 may be placed between two shear break elements. In still other embodiments, a second shear break element 102 of similar shape and size is placed over top of the first. In further embodiments, the remainder of the footing excavation is filled with aggregate extending at least above the height of the top of the first plate. In still other embodiments, the concrete footing 114 may subsequently be constructed over the top of the backfilled excavation.
In some embodiments, the presently disclosed system and methods allow reduction of the lateral load resistance (or reduction of the shear loads transferred to ground improvement elements 104) by any amount. It may be desired to reduce the lateral load resistance by at least between about 10% to about 80%. In other embodiments, the reduction of the shear loads transferred to ground improvement elements by the structures built above the elements 104 may be at least about 50%.
This system and method will allow for horizontal movement 116 of the foundation when subjected to horizontal loads 116 without direct transfer of lateral and shear stresses to the ground improvement inclusions thereby maintaining their integrity and support characteristics under a dynamic event.
In some embodiments, the system extends beyond the edge of the ground improvement elements 104 with oversized sections of a material exhibiting sufficient stiffness to reduce stress concentration in the aggregate transfer pad.
In an example, a ground improvement inclusion measuring between 14-inches and 20-inches in diameter is considered. The ground improvement inclusion is constructed from either aggregate contained within a cementitious grout or concrete. The inclusion is constructed such that the top bears within 3 inches of the planned footing bottom. The solid shear break elements 102 are constructed from high density polyethylene (HDPE) and are cylindrical. Each element measures 21 to 30 inches in diameter and between ¼-inch and ½-inch in thickness. A lubricating layer 110 of hydraulic oil or automotive grease is used to further reduce the frictional resistance at the shear break interface. A bedding layer 106 of fine sand is placed over the top of the inclusion followed by the placement of the first shear break plate. The lubricant 110 may be applied followed by the placement of the second plate of similar size over the lubricant 110.
The system and method are evaluated through a series of comparative load tests with a control group and the proposed system and method. The control features a 14-inch diameter concrete inclusion surrounded by soil. A concrete footing 114 is placed over top. A second control features the 14-inch diameter concrete inclusion surrounded by soil, followed by placement of a 9-inch thick aggregate layer over the entire area. A setup for testing of this system and method includes a 14-inch diameter concrete inclusion surrounded by soil, followed by the system described herein. In all test cases, a concrete footing 114 of consistent size was used.
The test was performed by applying a constant vertical load by use of a hydraulic jack and a reaction frame. A horizontal load 116 is applied and lateral deflections are measured. The validity of the shear break device is confirmed by the reduction of the lateral load resistance between the two controls and the test case by at least 30%.
Although the foregoing subject matter has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be understood by those skilled in the art that certain changes and modifications can be practiced within the scope of the appended claims.
This application claims priority to U.S. Provisional Patent Application No. 62/132,488, filed Mar. 12, 2015, and titled SOIL IMPROVEMENT FOUNDATION ISOLATION AND LOAD SPREADING SYSTEMS AND METHODS, the content of which is hereby incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62132488 | Mar 2015 | US |
