The application of geosynthetic products can provide an effective solution for the earth retaining systems as well as different foundation systems by reinforcing the earth materials. These products include, but not limited to, geocells, geogrids, and laminated geogrid products. Different combinations of these products have been used in the field for quicker construction and better performance. However, there are no established guidelines for designing such products. Giroud and Han (2004) provided a design methodology for geogrid reinforced pavement structures. The purpose of the current study is to expand on the existing methods by improving the study behind the theories and/or incorporating new concepts and methods of calculations.
Significance of Proposed work
This study mainly focuses on the utilization of a new combination of High-Density Poly Ethylene (HDPE) products (e.g., Fabgrid and Fabgrid+GeoCell). This study aims to develop design charts for different HDPE products/combinations for different stiffnesses of foundation materials. The outcome of this research will comprise charts that can help in the safe and reliable design of the geotechnical structures.
There are two major objectives in this study.
Part I: Performing repeated load tests on geosynthetic reinforced base layers built on different weak subgrades and then use the test data to calibrate parameters that can be used with Giroud and Han (G&H) designs
Part II: Developing various design charts and methods for IFI, Inc’s Geosynthetic Products based on the results and calibration studies from Part I
Scope of work
Physical and engineering soil testing, including grain size distribution, standard Proctor test, Atterberg’s limit, resilient modulus, shear strength, and undrained strength tests, and California Bearing Ratio (CBR) test will be performed on the base material and subgrade soils. For subgrade selection, the subgrades with different CBR values (1% and 3%) will be prepared by adjusting the moisture content. A large-scale test setup was designed and constructed at the Center for Infrastructure Renewal (CIR), Texas A&M University, to facilitate a wide range of static and repeated load tests and evaluate the performance of the geosynthetic reinforced soils. The large-scale test setup consists of a steel testing box, loading frame, and actuator, along with a data acquisition system. The steel testing box has dimensions of 6 ft x 6 ft x 5 ft (1.83 m × 1.83 m × 1.52 m). In the test box, a subgrade layer of select CBR will be prepared using selected material compacted at target dry density and moisture content.
Test results will be analyzed and calibrated to determine various parameters for both geocell, and Fabgrid reinforced soils. Test results from the repeated load tests would be used to generate 1/tanα (α = stress distribution angle) vs. log N (number of loading cycle) plots. This information could be used to calibrate the performance of the section as a function of the Aperture Stability Modulus (J) for the proposed Fabgrid. Analysis of these results would provide calibration parameters that will be useful for designing reinforced base/subbase systems using IFI geosynthetic products.
Several laboratory tests have been conducted to characterize the subgrade and base materials. California bearing ratio (CBR) tests were performed at different moisture contents for the subgrade materials to develop a correlation between CBR with moisture content. In addition to CBR tests, light-weight deflectometer (LWD) tests were also performed on CBR molds to establish a correlation between CBR with LWD-modulus for the subgrade soil.
Large-scale repeated load tests will be conducted on reinforced and unreinforced test sections. A simple algorithm will be developed to process the laboratory test results to desired outputs. The outcome of the laboratory experiments will be used for the development of design charts with different HDPE materials.
Impact on the State of Practice
The existing design guidelines were developed only with the available test data, which includes limited types of HDPE products. With the advancement of technology, a wide variety of geosynthetics products are currently available with higher aperture stability modulus. This study will evaluate the performance of new types of geosynthetic products and provide necessary guidelines for future design.