Device, method, and system for reducing earth pressures on subterranean structures

Abstract

The present inventive subject matter pertains to a device, system, and method that provides a buffer support for buried structures in response to lateral and vertical earth pressures of backfill material. The device having shaped form is able to provide timely response so as to reduce earth pressures of the backfill material exerted onto the buried structure. These behavioral features further enabling an effective geofoam device to be produced in thin proportion that conforms with industry standards.

Claims

1. A system for reducing earth pressure on buried portions of a rigid stationary structure by utilizing a geofoam device as follows: said geofoam device comprising a solid sheet of synthetic plastic cellular foam material having a first planar side and a second non-planar side, said first planar side having a flat planar surface and said second non-planar side providing a plurality of peaks and valleys, each said peak having a tapered cross-sectional shape starting at a base and terminating at a narrowed tip, each said valley defined by the space between two adjacent peaks, said first planar side having a depth of at least 1.0 inch, said second non-planar side having a depth of at least 0.5 inch between the base and tip of each peak of said plurality of peaks, wherein the total thickness of said solid sheet of synthetic plastic cellular foam material between the depths of its said first planar side and second non-planar side is at least 1.5 inches thick, whereby said second non-planar side of said geofoam device is positionable to be in contact with the surface of the buried portion of said rigid stationary structure such that the tips of the plurality of peaks of said second non-planar side are compressible and deformable against said buried surface, the flat planar surface of said first planar side of said geofoam device is further positionable to be facing towards backfill earth material, such that the force from the of pressure of said backfill earth material in its unsettled state against said first planar side causing said first planar side to be deformable and compressable within Zone 1 stress-strain behavior and causing said second nonplanar side to be deformable and compressable within Zone 1 and Zone 2 stress-strain behavior against said buried portion of said rigid stationary structure wherein zone 1 is an elastic zone and zone 2 is a compressive creep zone.

2. Said system for reducing earth pressure on buried portions of a rigid stationary structure by utilizing a geofoam device as described in claim 1 wherein the tips of said plurality of peaks of said second nonplanar side are further deformable and compressable towards a “strain hardening” range (Zone 3 stress-strain behavior range) subsequent to compressing past Zone 1 and Zone 2 stress-strain behavioral ranges.

3. A system for reducing earth pressure on buried portions of a rigid stationary structure by utilizing a geofoam device as follows: said geofoam device comprising a solid sheet of synthetic plastic cellular foam material having a first planar side and a second non-planar side, said first planar side having a flat planar surface and said second non-planar side providing a plurality of peaks and valleys, each said peak having a tapered cross-sectional shape starting at a base and terminating at a narrowed tip, each said valley defined by the space between two adjacent peaks, said first planar side having a depth of at least 1.0 inch, said second non-planar side having a depth of at least 0.5 inch between the base and tip of each peak of said plurality of peaks, wherein the total thickness of said solid sheet of synthetic plastic cellular foam material between the depths of its said first planar side and second non-planar side is at least 1.5 inches thick, wherein the initial stress-strain condition of the lateral earth pressure in its “at rest” state acting against said first planar side of said geofoam device causing said first planar side to be immediately deformable in recoverable manner and subsequently deformable with gradual resistive compression at the tips and mid-height range to the base of said plurality of peaks and portions of said second non-planar side, whereby the degree of lateral earth pressure of a backfill material that is acting against said geofoam device is reducible from its initial higher pressure “at rest” state to a lower pressure “active” state.

4. A method for reducing earth pressure on buried portions of a rigid stationary structure by utilizing a geofoam device as follows: said geofoam device comprising a solid sheet of synthetic plastic cellular foam material having a first planar side and a second non-planar side, said first planar side having a flat planar surface and said second non-planar side providing a plurality of peaks and valleys, each said peak having a tapered cross-sectional shape starting at a base and terminating at a narrowed tip, each said valley defined by the space between two adjacent peaks, said first planar side having a depth of at least 1.0 inch, said second non-planar side having a depth of at least 0.5 inch between the base and tip of each peak of said plurality of peaks, wherein the total thickness of said solid sheet of synthetic plastic cellular foam material between the depths of its said first planar side and second non-planar side is at least 1.5 inches thick, whereby the initial stress-strain condition of the earth pressure in the higher pressure “at rest” state is reduced to a lower pressure “active” state without impact of a differential load upon said rigid stationary structure, said method comprising the steps of first placing said geofoam device adjacently to the surface of said rigid stationary structure that is to be buried wherein said second nonplanar side is in contact with that surface and said first planar side faces towards the area where backfill earth material will be placed, secondly backfilling earth material against said first planar side of said device, thirdly wherein said second nonplanar side of said device deforming and compressing within its elastic range (Zone 1) and its compressive creep range (Zone 2) beginning at the tips towards mid-height range and towards the base of said second nonplanar side in response to the unsettled earth pressures.

5. Said method of claim 4 wherein the tips of said plurality of peaks of said second nonplanar side further deforming and compressing towards a “strain hardening” range (Zone 3 stress-strain behavior range), subsequent to compressing past Zone 1 and Zone 2 stress-strain behavioral ranges in response to said unsettled earth pressures.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1. Illustration of prior art device.

(2) FIG. 2. Graphical illustration of flat board foam stress-strain time dependent characteristics of EPS 15.

(3) FIG. 3. Graphical illustration of lateral earth pressure profile for a backfilled wall.

(4) FIG. 4. Illustration of cross-sectional sketch of Invention, described as Shape C.

(5) FIG. 5. A schematic cross-sectional illustration of the invention (Shaped EPS foam) placed against a buried wall.

(6) FIG. 6. Isometric Illustration of invention with zones 1, 2 and 3, described as Shape C.

(7) FIG. 7. Graphical illustration of stress-controlled compression test of Shape C

(8) FIG. 8. first photographic illustration of the invention.

(9) FIG. 9. A second photographic illustration of the invention.

(10) FIG. 10. A third photographic illustration of the invention.

(11) FIG. 11. A schematic cross-sectional illustration of shaped EPS Foam placed against a deeply buried wall.

(12) FIG. 12. Illustration of cross-sectional sketch of Invention, described as Shape E

(13) FIG. 13. A first and second alternate embodiment of the invention.

(14) FIG. 14. A schematic cross-section sketch of shaped EPS foam placed above a rigid structure within deep excavation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(15) FIG. 1 provides illustrative example of prior art geofoam device comprising large planar (rectangular) blocks of geofoam material 100. Said prior art geofoam block 100s are buried adjacent to underground structures 101 to an extensive degree of multiple feet which has the effect of very minimal elastic cushion against lateral and vertical earth pressures.

(16) The inventive solution herein introduces a device, method, and system for reduction of soil pressure against a structure by controlled deformation adaptable to a variety of diverse micro-environments. The invention, according to an embodiment of FIG. 4, comprises a plurality of peaks 400 and valleys 401 rising from a base 403 on a nonplanar surface of expanded polystyrene (EPS) foam board that have proportions suitable for specific applications. The particular proportion and positioning of said plurality of peaks 400 and valleys 401 in combination with the time-dependent complex stress-strain properties of the EPS material throughout a large range of strains provide a relative and deformation effect interacting with the stress-strain properties of the soil adjacent to a structure as described by graphical illustration according to FIG. 7.

(17) As illustrated according to FIG. 5, the particular stress-strain compressive properties of the foam device of this invention 500 must be able to manage the lateral pressure from adjacent disturbed soil 501 between its “At Rest” state through its transition to its “Active” status, serving as a sufficient compressive barrier to avoid transfer of excess soil pressure onto the buried structure 502 rearward therefrom. See FIG. 5. Similarly, as shown in FIG. 14, the device 1401 should be able to activate an effect identified as soil “arching” 1402 in backfill material over buried structures 1403, which limits vertical stress exerted by deep amounts of overburden placed above the structure 1403. See FIG. 14. In either case, the application of this invention is to reliably minimize exercise of the resistive strength of the subterranean structure as well as protect it from excessive loads that may be caused by a wide range of micro-environmental factors.

(18) To start, the invention (as illustrated in FIGS. 4 and 6) broadly relates to a plurality of peaks 400, 600 and valleys 401, 601 on compressible plastic synthetic foam material, preferably EPS foam or other type of material having similar complex stress-strain properties as described herein. The valley space 401, 601 broadly comprising an area of open space between peak elements 400, 600 that begins at the base 403, 602 of and adjacent peak element and rising therefrom. See, FIGS. 4 and 6. The compressible matter is herein discussed without limitation with respect to EPS foam. The peak 400, 600 and valley 401, 601 elements may have either a two-dimensional (adjacent to two valleys) or three dimensional (surrounded by valley space and creating a peak island) with symmetric or asymmetric cross-sectional shape. The cross-sectional shape may comprise further any rounded or geometric shape or combinations thereof. Each peak having a tapered shape that terminates at a narrowed tip end. The peak 400, 600 and valley 401, 601 elements provide a pattern of non-uniform stress distribution along the device to take advantage of the full range of the material's complex stress-strain properties. This is visually shown in FIG. 6, highlighting localized behavior along different segments of the device, performing between Zones 1 603, II 604, and III 605.

(19) The peak elements additionally experience beyond Zone I both intermediate (Zone II) and advanced (Zone III) stress and strain to provide the desired amount of total compression needed to reduce the lateral earth pressure to a minimum possible “Active” condition using no more thickness of foam than is otherwise desired to provide thermal insulation. The peak and valley elements comprising a partial aspect of the device. The remaining portion (the planar side) comprising in fact a continuum of uninterrupted foam (planar sheet of foam material) located below the base of said peaks of the nonplanar side. This planar side portion of the device will continue to engage in the elastic range (Zone 1) in a manner similar to prior art (flat foam blocks). By effect, the device enables a concurrent combination of multiple range elastic and compression effect responding to changing soil pressure over its long-term application. The progression of this effect is illustrated in photographic images of deformation over time at constant pressure in FIGS. 8, 9, and 10. As discussed herein, the compression effect within Zone 1 and Zone 2 is experienced within the peaks but not below its base. The subject invention can also effectively and more efficiently reduce the vertical earth load on the top of buried structures by developing “arching” effects among the soil profile of the overburden as illustrated in FIG. 14.

(20) Typical ranges of horizontal load exerted by backfill materials placed against walls, including residual stress from compaction of backfill during its placement compaction stresses are depicted in FIG. 3. See FIG. 3, Lateral Earth Pressure Profile for Backfilled Wall. See Chen, T., & Fang, Y., Earth Pressure due to Vibratory Compaction, Reston, Va.: Journal of Geotechnical and Geoenvironmental Engineering (2008, March).

(21) The first step in developing the details of any specific application of the invention is simply to select the foam density (in this case EPS foam) of which the stress at about 1% compressive strain sustains a stress commensurate with the maximum value of application's “At Rest” lateral earth pressure profile. The next step is to presume a thickness of the continuum portion (the planar side portion) of the cross section sufficient to provide most of the desired amount of thermal insulation to the structure. Because many building codes require a minimum R-Value of 10 in temperate climate regions and the R-Value of common densities of EPS is about 4/inch of thickness, a continuum thickness of about two inches accommodates most applications because the projections and air space of the peak and valley elements provides similar amount of insulation value per inch of cross section. The final specific application design step is to develop appropriate proportions and dimensions of the projections and recesses in at least one surface of the foam board that will provide the required short and long-term stress-strain interaction with the adjacent backfill material.

(22) Because thorough time dependent stress-strain computational analysis of the above described methodology that has non-uniform cross sectional geometry is inordinately complex, quite simple analysis based on the three zone relationship of foam for stress-strain after a large amount of elapsed time (which avoids the time-dependency of computations) allows sufficient estimation of prospective particular foam density and shapes for specific application provided it is accompanied by verification from actual testing in the laboratory. FIG. 4 depicts proportions of peaks 400 and valley 401 elements in the face of EPS 15 (0.9 pcf foam density) foam board appropriate for the range of stresses exerted by the most common range wall backfill depths. See FIG. 4, Cross-Section of Shape C (EPS 15). This is labeled as Shape C (see FIG. 4) because it is this third of several trial proportions, preceded by prior trial shapes A and B (not shown within the illustrations) in the course of developing this invention. Lab testing of shape “A” revealed that it had too long a wave length that caused the Zone II stresses to extend into a substantial portion of the continuum, which would cause excessive long-term compressive creep. Trial “B” verified appropriate wave length, but had insufficient height of peak projections for the amount of immediate and long-term compressive strain needed to sustain reduction of lateral earth pressure to the “Active” condition. Shape C has cross sectional proportions that were verified by lab testing to be effective for common residential and commercial basement walls applications, as confirmed by the long-term laboratory test results plotted in FIG. 7. See FIG. 7, Shape C Stress Controlled Compression Tests of EPS 15 Foam.

(23) Because the three stress-strain zones within the invention's cross section shown in FIG. 6 operate in physical series with each other at all times, the creep occurring over time in Zone 2 is partially compensated by some elastic rebound within the relatively thick Zone I. And increasing amounts of “strain hardening” (Zone 3) occurs as a progressive creep accumulates over time in the narrowest portions of areas of Zone 2, limiting additional compression there over time. The combined effect of these actions results in an overall performance of the invention's cross section that is uniquely effective in minimizing lateral earth pressure by virtue of soil-structure interaction stress and strain compatibility in mobilizing the reduction of lateral earth pressure from the “At Rest” to the “Active” condition.

(24) Although the lab test results plotted in FIG. 7 include loading times only for the initial months of lab testing that has progressed to date, the longer term performance can be estimated from this test data because of the linear relationship of stress (in stain controlled test) or strain (in stress controlled tests) as plotted vs the logarithm of time that is characteristic of the invention beyond the first day of load application.

(25) While the peak and valley elements in the surface of the foam board could be formed during manufacture of the foam material, it's commonly most economical to cut (“hot wire”) them because these relatively thin, shaped sheets are being cut from large blocks of foam that are commonly four feet thick, about four feet wide, and sixteen to eighteen feet long. In order to prevent the relatively high stress-strain performance of the foam material's cross-sectional shape from extending into the continuum of the material in order to maintain a relatively uniform, low stress-strain field within that continuum, the peak elements must have a base width that is substantially less than the thickness of the continuum. And the height of the projections must be sufficient to provide much of the total compressive deformation that is required to mobilize reduction of earth pressure. Because compacted clay as well as granular soils have their own time-dependent stress-strain properties the design of the invention's projections and recesses must also take those properties into consideration to provide long term backfill interaction compatibility with the invention. This may include accommodation of ground frost heave, expansive soil swell, seismic acceleration of soil, as well as soil arching effects in vertical load applications.

(26) FIG. 4 depicts the specific portions developed by the inventor for use of EPS grade 15 that are effective in providing sufficient strain in buried wall backfill materials to mobilize reduction from the “At Rest” to the lessor “Active” earth pressure for common wall heights ranging from eight to twelve feet. It turns out that a two-dimensional pattern of peaks and valleys provides soil-structure stress-strain compatibility with common backfill materials. The principles exercised by the invention provide the basis to develop other specific shapes, which can include three-dimensional valleys and peaks (see FIG. 13, 1301, 1302), as may be required to provide compatibility with the soil-structure interaction characteristics of additional specific applications. See FIG. 6, Isometric Sketch of invention shape C.

(27) The following photographs of FIGS. 8, 9, and 10 are of the ongoing stress-controlled lab compressive lab tests being performed to verify long term performance of the invention. Results of these tests to date are the data from which FIG. 7 was generated. FIG. 8 depicts the shape C of an EPS 15 sample before appreciable load is applied. FIG. 9 shows the distribution of compression across the sample's cross section at a common range of final (“Active” lateral earth pressure) long term stress in common applications. FIG. 10 shows the amount of compression the same sample experiences under the initial, short term load beginning with the “At Rest” lateral earth pressure condition as backfill is placed but the “Active” earth pressure is not yet mobilized. In actuality, the maximum amount of compression that EPS shape C will initially compress is in between what is shown in FIGS. 9 and 10.

(28) In FIG. 8, lines 801 spaced 0.2 inches apart were drawn onto this cross-sectional view of EPS 15 shape C prior to installing the sample in the stress-controlled compression apparatus used in the long-term lab testing performed in the course of developing this invention. The flat surface of the planar (toward the top as installed in this test apparatus) side of the sample 802 measures 4.5 inches square, to which this initial load of just 61 psf is applied. The width of contact stress at the tips 803 of the peaks (toward the bottom in the apparatus) is just 4 mm at this light load, so the tips (at about 600 psf contact stress) are not loaded much beyond the elastic limit at even this location. As such, very little compression of the tips has occurred as can be seen here.

(29) In FIG. 9, the sample is loaded to 242 psf at the flat surface of the planar side 901, which is toward the lower range “Active” lateral earth pressure with a depth of wall backfill of about eight feet. The tips 902 of the peaks are quite compressed as is evident from the curvature of the original straight lines that had been drawn on the sample. At this load the contact stress of the tips 902, now 9 mm wide, is about 1,020 psf. So the tips 902 are stressed into Zone 2 (compressive creep with time) range of behavior, while the wider base of the peaks 903 is still within the Zone 1 (elastic) range of stress.

(30) In FIG. 10, the sample is loaded to 485 psf on the flat surface 1001 of the planar side of shape C of EPS 15. This is equivalent to the “At Rest” lateral earth pressure with a depth of wall backfill of about eight feet. The tips 1002 of the projections are now very compressed into the range of “strain hardening” (Zone 3). The mid-height portion of the projections 1003 is stressed to about 1,200 psf (Zone 2), while the rest of the test sample comprising the continuum is still within the elastic (Zone 1) stress range 1004.

(31) A preferred embodiment according to FIG. 5 utilizes the invention as a board of EPS foam 500 placed with its shaped face 503 against the vertical outside face of a structural wall 502 to form an appropriately compressive layer between the wall and the backfill material 501 that reduces the lateral earth pressure profile exerted against the wall from the “At Rest” to the “Active” condition. Use of the invention in this manner as shown in FIG. 5 is preferable to the present common practice of using flat sheets of XPS foam insulation board that are inherently too rigid to activate any substantial reduction of lateral earth pressure. See FIG. 5, Schematic cross section sketch of the invention (Shaped EPS foam) placed against a buried wall.

(32) For applications, as illustrated in FIG. 11, that require a backfill depth of more than ten or twelve feet, the next efficient step to reduce lateral earth pressure is to install horizontal layers 1101 of very high modulus tensile reinforcement within the backfill as it is placed in compacted lifts. This is a well-established geotechnical practice. In this case, the invention 1102 can also be used to additional advantage to minimize the lateral earth pressure caused by each “cell” 1103 (the vertical space between each layer of tensile reinforcement) of the backfill as depicted in FIG. 11. See FIG. 11, Schematic cross section sketch of shaped EPS Foam placed against a deeply buried wall.

(33) Another embodiment as illustrated in FIG. 14 utilizes the invention 1401 as a board of EPS foam placed with its shaped face 1401 against the top of a deeply buried structure 1403 in order to activate “arching” effects 1402 within aggregate backfill placed above the structure and thereby greatly reducing the vertical pressure exerted by the backfill placed over the structure. Use of the invention in this manner is preferable to using a substantially thicker “inclusion” of EPS board or block operating only within the foam material's Zone 1 quite limited elastic response range. See FIG. 14, Schematic cross section sketch of shaped EPS foam placed above a rigid structure within deep excavation.

(34) The present invention is best understood by reference to the detailed figures and description set forth herein.

(35) Embodiments of the invention are discussed herein with reference to the Figures. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanatory purposes as the invention extends beyond these limited embodiments. For example, it should be appreciated that those skilled in the art will, in light of the teachings of the present invention, recognize a multiplicity of alternate and suitable approaches, depending upon the needs of the particular application, to implement the functionality of any given detail described herein, beyond the particular implementation choices in the following embodiments described and shown. That is, there are numerous modifications and variations of the invention that are too numerous to be listed but that all fit within the scope of the invention. Also, singular words should be read as plural and vice versa and masculine as feminine and vice versa, where appropriate, and alternative embodiments do not necessarily imply that the two are mutually exclusive.

(36) Detailed descriptions of the preferred embodiments are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner.

(37) It is to be understood that any exact measurements, dimensions or particular construction materials indicated herein are solely provided as examples of suitable configurations and are not intended to be limiting in any way. Depending on the needs of the particular application, those skilled in the art will readily recognize, in light of the following teachings, a multiplicity of suitable alternative implementation details.