Patent Application
20150040649
The invention relates to testing of geostructural constructions incorporating geosynthetic materials such as geotextiles and geogrids placed between lifts of compacted earth, and more particularly, to a system/device and method for testing geostructural constructions, including a load frame device that simulates a full scale construction using geosynthetic materials.
Geosynthetic material is used in a number of earthen supported constructions. Geosynthetic material generally refers to synthetic engineered products used in civil engineering projects including soil stabilization structures, corrosion barriers, retaining walls, abutments, and other earthworks requiring reinforcement. It has been found that geosynthetic material can offer a cost-effective and structurally sound alternative to many traditional concrete and block construction methods.
General types of geosynthetic materials include geotextiles or geotextile fabrics, geogrids, geomembranes, geosynthetic liners, geosynthetic erosion control products, and other specially designed geosynthetics. There are number of applications where geosynthetic materials may be employed, and the use of geosynthetic material applications is not limited to any particular field within civil engineering construction. Some of the more common functions that can be achieved with the use of geosynthetic material include erosion control, moisture control, drainage control, soil filtration and separation, soil reinforcement, and soil stabilization. One particular advantage provided by geosynthetic materials is that the materials provide substantial benefits in increasing both the tensile and shear strength of earthen supported structures. While concrete and block constructions may provide significant compressive strength, it is well known that these constructions can be woefully inadequate in terms of tensile and shear strength requirements.
Geosynthetic materials are commonly made from polymeric formulations, and another advantage of geosynthetic materials is that formulations can be adapted to achieve required strength specifications, and to otherwise be formulated for specific uses. With the wide range of polymeric materials available, geosynthetic uses continue to increase across many different types of construction applications.
One example of a reference that discloses a fiber-based geosynthetic material includes the U.S. Pat. No. 6,171,984. The reference also generally discloses geosynthetic composites with combinations of geosynthetic material including geotextiles fabrics and geomembranes.
U.S. Pat. No. 8,215,869 discloses a reinforced soil arch including alternating and interacting layers of compacted mineral soil and geosynthetic reinforcement material placed over and adjacent to the archway.
U.S. Pat. No. 6,890,127 discloses subsurface supports that may be used to support bridges and culverts, and more particularly, subsurface supports in the form of platforms that prevent scour type erosion that may develop from a body of moving water, such as a river or stream. The construction of the platforms includes the use of stabilizing sheet material, such as wire mesh, geosynthetic sheets, or combinations thereof.
U.S. Pat. No. 7,384,217 discloses a system and method for promoting vegetation growth on a steeply sloping surface. The system includes anchors secured to the sloping surface, an inner mesh layer in contact with the slope, a geosynthetic layer placed over the inner mesh layer, and seeded compost material placed in a gap or space between the geosynthetic layer and the inner mesh layer. And outer mesh layer is placed over the geosynthetic layer to stabilize the geosynthetic layer. Vegetation grows in the compost material, and roots of the vegetation penetrate the inner mesh layer into the slope for long term stabilization of the sloping surface to prevent erosion.
U.S. Pat. No. 6,808,339 discloses a modular retaining wall having tiers of headers which extend into compacted backfill material, and tiers of stretchers that extend between headers to form a front face of the wall. Layers of geosynthetic mesh reinforcement reinforce the load bearing capability of the backfill. Load forces in the backfill are sustained by forward ends of the layers of geosynthetic mesh reinforcement that extend upward in front of the backfill and then backward into the backfill instead of being sustained by the stretchers.
It is apparent from the wide variation in use of geosynthetic material disclosed in these references that geosynthetics can be used in multiple different types of constructions. Despite the increasing expansion in the use of geosynthetic material, there are still limitations in use of these materials. In the case of using geosynthetic material for larger scale construction projects, there is still a need to conduct on-site testing to confirm that the geosynthetic material in combination with the compacted earth formations achieve the necessary strength requirements for the particular project. Unlike concrete that may be tested in predictable and accurate small scale testing, such as slump testing, there is yet to be developed a uniform set of standards for determining how to employ geotextiles materials across various loading conditions.
Some efforts have been made to provide uniform guidance regarding employment of geotextile material. One example is the Geosynthetic Reinforced Soil Integrated Bridge System Interim Implementation Guide, published by the US Department of Transportation, Federal Highway Administration (June 2012). This reference generally discloses construction examples and preferred specifications for different types of constructions. This reference also discloses quality control and quality assurance measures, to include field testing and laboratory testing, and some guidance regarding stability analyses that may be conducted to confirm design specifications. However, this reference fails to disclose a testing method or procedure that can be used across many different types of construction projects to confirm actual performance of geosynthetically confined soils.
Because of the inherent number of variables with respect to use of geosynthetically confined soils, it has been difficult to develop a reliable and defensible mathematical equation that represents or predicts the behavior of soil and geosynthetic materials used in various constructions. For example, it is well known that the optimal compaction for soil greatly varies depending upon the type of soils encountered at a particular job site and therefore, designing and confirming a successful design using geosynthetics often requires trial and error testing at the jobsite in which soil and aggregate compaction is continually measured, and each lift of soil/aggregate must be tested multiple times to confirm optimal compaction. Further, the spacing of geotextile layers and a determination as to the number of layers used in a particular cross-section is not an established design sequence. Therefore, intense quality control is required at jobsite to ensure each lift of soil/aggregate material is properly compacted. Further, efforts have to be made to ensure that the soil/aggregate used at the jobsite is tested for optimal moisture content to ensure the type of soil and aggregate present can achieve its maximum dry density while the project is being constructed. Proctor compaction testing is yet another aspect of the construction process that can result with introduction of further variables for complicating design and implementation of a particular geostructural construction.
Therefore, it is apparent that a testing protocol or testing method is needed to enhance predictability of geostructural constructions, to not only reduce the potential for non-complying constructions, but also to reduce overall jobsite effort required for testing and quality control. There is also a need to provide a testing protocol and/or method that is easily transportable, and that can be quickly and efficiently conducted. There is yet a further need for a testing protocol/method in which deficiencies encountered regarding tested parameters can be retested and verified, thus preventing project delays and additional costs.
According to the present invention, a system and method are provided for determining optimal design conditions for structures incorporating geosynthetically confined soils. In one aspect of the invention, it includes a testing apparatus or assembly that simulates a particular geostructural construction without having to construct a full-scale or near full-scale model. The testing apparatus or assembly can be referred to as a demonstration load frame that replicates a portion or section of the geostructural construction. The load frame includes an enclosure made from materials such as concrete block or rigid panels that enclose a plurality of layers of geosynthetic materials and lifts of representative soil and aggregate from the jobsite for the geostructural construction site at issue. The size of the load frame is such that the layers of geosynthetic material and soil/aggregate are not overly confined or limited by walls of the enclosure, which might otherwise serve to falsely compact the layers as compared to the actual construction design in which lateral containment may not be present. In this respect, the load frame can be constructed with walls of the enclosure forming a square or rectangular shape, with a minimum distance between opposing walls of the enclosure preferably greater than approximately three feet which enables soil/aggregate to more naturally compact as compared to a smaller testing cylinder that may overly constrain the soil/aggregate and geosynthetic material.
In order to adequately simulate compaction efforts at a jobsite, the method of the present invention has the capability to provide not only compressive forces to optimally compact the strata or layers of soil/aggregate and geosynthetic material, but also vibratory energy to provide a preferred method for compaction to achieve optimal simulation of compaction employed in a construction project. As used hereinafter, the term “fill” is intended to mean the combination of soil and aggregate used to simulate the soil and aggregate for the jobsite of the actual construction project for which testing is conducted. Preferably, the fill used in the load frame is the same as the soil/aggregate to be used in the project. In one preferred embodiment of the load frame, it is constructed in successive layers in which a layer of geosynthetic material and a corresponding layer or lift of fill is laid down within an enclosure of concrete blocks or rigid panels. The fill is compacted, and then another layer of geosynthetic material and another lift of fill is added and compacted within the enclosure. One row of blocks can be added for each layer of geosynthetic material and lift of fill so that the peripheral edges of the geosynthetic material can be held between the rows of blocks. An adequate number of layers of geosynthetic material and lifts of fill are constructed to simulate the particular construction project.
Compaction of the layers of fill in the load frame can be completed in different methods to best simulate optimal compaction specifications for the project. According to one method of compaction of the invention as mentioned, the fill can be compacted within the load frame upon construction of each successive layer of geosynthetic material and corresponding lift of fill. According to another method of compaction, compaction can be conducted after the load frame has been constructed with multiple layers of geosynthetic material and fill resulting in a compaction effort conducted to simultaneously compact multiple layers.
The type of energy supplied to the load frame in order to achieve compaction includes static compaction forces and vibratory compaction forces. In one embodiment, compaction is achieved by use of hydraulic jacks that apply force to connected upper and lower load plates. The controlled and gradual application of compressive force is used to compact the layers of geosynthetic material and corresponding lifts of fill. In addition to this static application of force, a mechanical vibrator can be used in conjunction with the hydraulic jacks in order to vibrate contents within the load frame. One advantage of also providing vibratory compaction is that it more closely simulates actual compaction efforts at the jobsite. As an alternative to use of hydraulic jacks, static compression force can be supplied by other means, such as by an inflatable airbag.
According to another embodiment of the load frame, instead of using stacked rows of blocks, the load frame may be constructed with removable panels. According to one method of construction of the load frame with removable panels, three sides of a four sided load frame can be assembled with one side remaining open to allow placement of layers of geosynthetic material and fill. Having one open side eases compaction efforts if the method of compaction employs a separate compaction steps for each layer/lift since the open side provides easier access to the layers of fill. The fourth side of the load frame can be installed, and final compaction can then be completed with compressive and/or vibratory force applied to the upper and lower load plates.
Once compaction is completed, the walls of the load frame may be removed in order to inspect the layers of geosynthetic material and corresponding lifts. Compaction and density testing can then be conducted, or other test protocols can be conducted in order to confirm design specifications for the project. Having the capability to view the geosynthetic material and lifts of fill in cross-section also provides an excellent manner in which to inspect the compaction results, and to modify design parameters as necessary.
In another aspect of the method of the present invention, additional compaction could be performed after the walls of the load frame are removed in order to further stimulate loading conditions, and to confirm design parameters. For example, if a project had specific loading conditions that needed to be replicated, such as continual impact loading conditions, additional compaction efforts could be conducted with the walls of the load frame removed in order to further study the performance of the simulated construction achieved with the geosynthetic layers and lifts of fill.
Considering the above aspects and features of the invention, it can be considered a device for testing design specifications for a construction project incorporating geosynthetically confined soils, comprising: (i) a load frame having a plurality of walls; (ii) a plurality of layers of geosynthetic material placed within an open space between said plurality of walls; (iii) a plurality of layers of fill material located between said plurality of layers of geosynthetic material; (iv) an upper load plate covering the open space; (v) at least one force applying member communicating with said upper load plate for applying a force to compact the fill material; and wherein force is applied by said force applying member to compact the fill material.
In another aspect of the invention, it can be considered a device for testing design specifications for a construction project incorporating geosynthetically confined soils comprising: (i) a load frame having a plurality of walls; (ii) a plurality of layers of geosynthetic material placed within an open space between said plurality of walls; (iii) a plurality of layers of fill material located between said plurality of layers of geosynthetic material; (iv) an upper load plate covering the open space; (v) at least one force applying member communicating with said upper load plate for applying a force to compact the fill material; (vi) a lower load plate placed beneath a most lower layer of said plurality of layers of fill material; (vii) at least one retention bar interconnecting said upper load plate and said lower load plate; and wherein force is applied by said force applying member to compact the fill material, and said upper and lower load plates secure said layers of fill material and geosynthetic materials enabling the force applied to compact the fill material.
In yet another aspect of the invention, it can be considered a method to test design specifications for constructions incorporating geosynthetically confined soils, comprising: (i) constructing a load frame having a plurality of walls to enclose a quantity of fill material and geosynthetic material; (ii) installing at least one layer of geosynthetic material within an open space between said plurality of walls; (iii) loading at least one layer of fill material within the open space between said plurality of walls and in contact with said layer of geosynthetic material (iv) covering the layer of geosynthetic material and layer of fill material; (v) applying force to compact said layer of fill material; and (vi) conducting a compaction test to determine whether the layer of fill material is compacted to design specifications for the project.
Other features and advantages of the invention will become apparent from review the following detailed description, taken in conjunction with the drawings.
Referring to
Referring specifically to
Lower force distributing plates 24 are mounted over the respective lower ends of the retention bars 26, and the retention bars are locked in place against the lower surface of the lower load plate 22 by respective lower securing nuts 28. As shown in
The upper ends of the retention bars 26 extending through the jacks 36 and are locked in place by respective upper securing nuts 28 threaded over the upper ends and tightened against the jacks 36 as shown. Each of the jacks 36 includes a moveable cylinder 41 that is selectively raised or lowered by hydraulic fluid, and the upper edge of each of the cylinders 41 contacts a blocking bushing or washer 39 that is locked in place by the corresponding upper securing nut 28.
Hydraulic lines 38 provide fluid to the hydraulic jacks 36 by a hydraulic fluid source and hydraulic pump, shown schematically as a combined element 50. The pump is activated to force fluid through the lines 38 and into the jacks 36, resulting in a compressive force applied to the interior of the load frame by downward displacement of the upper load plate 20.
Referring also to
In the construction of the load frame 10, each individual lift of fill 16 can be initially and partially compacted, such as by hand tools and/or handheld equipment such as a vibratory tamper. Final compaction is then achieved by activation of the hydraulic jacks 36 in which compaction very closely replicates the actual compaction effort to be conducted at the project. Additional compaction effort can be supplemented with the mechanical vibrator 34. In some cases, it may not be necessary to provide any initial manual compaction, and all of the compaction is therefore achieved by compressive force of the jacks 36, and supplemented as needed with the mechanical vibrator 34. The device 10 therefore achieves full-scale replication of project compaction without having to construct a much larger and labor-intensive model or prototype of the geostructural construction.
Referring to
Upon completion of compaction, desired soil density tests can be conducted to determine density characteristics and whether the selected combination of fill and geosynthetic material used within the load frame achieved project specifications. As understood by those skilled in the art, soil density testing can be conducted by a nuclear densometer, by other types of soil density gauges, or by a manual drive cylinder method in accordance with ASTM D2937-10.
After the blocks 14 have been removed, it is also possible to conduct further loading in order to stimulate both static and live loading conditions for the project. For example, after the desired compaction has been achieved, it may be desirable to provide cyclical loading over time to replicate loading conditions at the project, and to further determine whether the selected combination of fill and geosynthetic material performs as expected. The cyclical loading can be conducted by selected cycles of activation and deactivation of the hydraulic cylinders 36 and selected activation and deactivation of the mechanical vibrator 34. Cyclical test loading sequences allow an inspector to view the performance of the fill and geosynthetic material, and to look for potential problems such as non-uniform shifting or displacement of fill or deformation of the geosynthetic layers which may indicate potential sheer stress failures or other types of potential failures.
In another aspect of the invention, use of the load frame allows engineers to quickly and efficiently experiment with different types of soil, aggregate, and geosynthetic materials that may optimize construction of each project. For example, there may be a need to provide a layer of coarser aggregate for drainage purposes along a particular section of the sub grade of a project, but with a goal of also avoiding unacceptable compaction at that area. The load frame of the present invention is ideal for testing various combinations of fill and geosynthetic materials, and in this example, compaction can be quickly evaluated for the area employing the coarser aggregate. In the event introduction of the coarser aggregate did not meet specifications, another test could be performed by assembling another test sample of fill and geosynthetics in the load frame.
Referring to
Referring to
In yet another aspect of the invention, it is also contemplated that compaction force can be provided in combination by a plurality of hydraulic jacks 36 and by an inflatable airbag 28. In this combination, it is contemplated that the jacks 36 could be used to provide the primary compaction force and the airbag 28 could be used to supplement required compressive force, as well as to provide simulation of cyclical live loading conditions. Inflation and deflation of the airbag can be achieved relatively quickly which makes it ideal for simulating some live loading conditions. The mechanical vibrator 34 can also be used to further supplement required compaction.
Referring to
As also shown in
In the construction of the load frame with the desired number of layers or lifts of fill material and layers of geosynthetic material, one method is to construct each separate layer or lift of fill material and corresponding layer(s) of geosynthetic material, and to then apply the loading apparatus for each lift to compact the lift. Another method is to construct multiple lifts and corresponding layer(s) of geosynthetic material, and then apply the loading apparatus. Depending upon the type of soil and aggregate and the depths of the lifts of fill material, sequential construction or multiple lift construction can be adopted to best replicate field practices to be used at the jobsite, and to best test and validate design parameters.
Although the load frame of the invention is described for use with evaluating geosynthetically confined soils, the load frame is also useful for conducting compaction evaluation and testing for granular fill material by itself. Therefore, for those projects in which it is only necessary to evaluate fill material, the load frame provides a solution for quickly and efficiently evaluating soil and aggregate characteristics to test and confirm design specification parameters.
The invention has been described with respect to various preferred embodiments. However, it shall be understood that modifications can be made to the invention within the scope of the claims appended hereto.
