Date of Final Oral Examination (Defense)
Type of Culminating Activity
Master of Science in Civil Engineering
Bhaskar Chittoori, Ph.D., P.E.
Debakanta Mishra, Ph.D., P.E.
Arvin Farid, Ph.D., P.E.
Jairo Hernandez, Ph.D., P.E.
Transportation industries encounter substantial challenges with respect to ride quality and serviceability when they deal with expansive soils underneath roadway structures. These soils exhibit swell-shrink behavior with moisture variations, which cause surficial heaving on the pavement structure and cost billions of dollars for the maintenance of pavements. For the past four decades, a particular stretch of US-95 (Oregon line to Elephant Butte) exhibited recurrent swelling distresses due to the underlying expansive soils. Despite remedial measures that exhibited satisfactory results for most of the sections, recurrent damage still continued in few sections. Further research indicated that the problematic soils were located at a depth below 1.82 m. Conventional chemical remediation methods typically performed at a depth no greater than 0.9 to 1.2 m. To be able to address the adverse effects of this swell-shrink behavior of soil at a deeper depth, hybrid geosynthetic systems were proposed. Hybrid geosynthetic systems were successfully used to mitigate expansive soil swelling in railroad applications. Hence, this research study explored this idea of using hybrid geosynthetic reinforcement systems (geocell-geogrid combination) to mitigate differential pavement heaving resulting from underlying expansive soils.
To evaluate the use of hybrid geosynthetic systems in reducing differential heaving from expansive subgrades, a large-scale box test was developed to simulate a pavement section with a base course and expansive subgrade (asphalt overlay was ignored). The surficial heaving on the base course reinforced with geocell, geogrid and hybrid geosynthetic reinforced system (HGRS) were measured over time and compared with the unreinforced case. The large-scale box test results showed that the geosynthetic systems significantly reduced the maximum surficial heave along with the differential swelling on the pavement section. HGRS exhibited better performance than geocells and geogrids.
Numerical analysis using the finite element approach was conducted to study the response of other soil types not tested in the box. The numerical model was first calibrated using using the box test results and the calibrated model was used to change soil properties for two other soil types with different swelling charecteristics. In the numerical model, swelling behavior of expansive soils was simulated using material models that incorporate volumetric swelling and suction as a function of moisture content. The modulus of the unreinforced base was determined using laboratory tests while the modulus that for the reinforced sections was calibrated using large scale test data. The calibration of control model was performed by controlling the moisture percolation through subgrade. The improvement of reinforced models were quantified by higher modulus of reinforced base. These calibrated models were used to conduct a parametric study by varying the subgrade soil properties and their performance with respect to the modulus of reinforced base. The parametric study revealed that the expansive soils with high PI exhibited higher swelling than the expansive soils with low PI. It was observed that the reinforcing effect was higher for soils with lower swelling characteristics.
Tamim, Mir Md., "Evaluating the Effectiveness of a Hybrid Geosynthetic Reinforcement System to Mitigate Differential Heave on Flexible Pavement due to Expansive Subgrades" (2017). Boise State University Theses and Dissertations. 1367.