While most soil-geosynthetic interaction models have focused on the characterization of failure conditions, little emphasis has been placed on models and parameters suitable for characterizing the stiffness of soil-geosynthetic systems. In the companion paper, a soil-geosynthetic interaction parameter (SG C K) was developed that captures the stiffness of a soil-geosynthetic composite under small displacements. This included validation of the suitability of the assumptions and outcomes of the model for a specific set of materials and testing conditions. This paper presents the results of a comprehensive experimental program that allows the suitability of the model to be generalized for a wider range of materials and testing conditions. An initial test series was conducted using large-scale soil-geosynthetic interaction test equipment to evaluate the repeatability of the experimental results. A comparison of the test results from this series, as well as an assessment of an extensive database on the expected variability of soil and geosynthetic properties, revealed that the coefficient of variation of the model parameters was acceptable and well within the typical range of similar geotechnical and geosynthetic properties. Results from additional test series confirmed the linearity and uniqueness of the relationship between the geosynthetic unit tension squared and corresponding displacements, which are the key features of the proposed model. These tests were conducted under various conditions using different geosynthetic and backfill materials. Results also showed that the constitutive relationships adopted in the model were adequate for the extended range of confining pressures, geosynthetic lengths, geosynthetic types, and backfill soil types adopted in the study. The consistency of the results obtained in the experimental testing program underscores the suitability of the proposed SG C K parameter as a basis for the evaluation of soil-geosynthetic interactions under small displacements.

While significant emphasis has been placed on the quantification of soil-geosynthetic properties under failure conditions, studies of properties that are suitable for characterizing this interaction under serviceability conditions have been limited. Also, most geosynthetic properties are currently defined in isolation rather than under the confinement of soil. The purpose of this study is to develop a soil-geosynthetic interaction framework that, with a single and repeatable parameter, can capture the stiffness of a soil-geosynthetic composite under small displacements. The soil-geosynthetic interaction model developed in this study involves well-established force equilibrium differential equations. However, the constitutive relationships and boundary conditions were specifically selected so that the model results in a closed-form analytical solution. Since the analytical solution involves a single parameter, its use may be particularly suitable for specification and the design of structures such as stabilized roadways. This parameter, referred to as the stiffness of the soil-geosynthetic composite, or SG C K , captures both the tensile characteristics of the geosynthetic and the shear behavior of the soilgeosynthetic interface. Experimental procedures to quantify SG C K were developed as part of this study. The results of a pilot experimental program, conducted using tailor-made soil-geosynthetic interaction equipment, are presented in the paper. These results confirm the suitability of the assumptions and outcomes of the model. A companion paper provides the results of a comprehensive experimental program with particular emphasis on the evaluation of the repeatability of the results and on the sensitivity of the assumptions and outcomes of the model to variables that impact SG C K .

Geosynthetics have recently been used for base course stabilization of roadways subjected to environmental loads associated with the presence of expansive clay subgrades. Repeated cycles of wet and dry seasons have often led to significant, non-uniform moisture changes within clay subgrades, resulting in differential settlements between the roadway edges and its centerline and, ultimately, in environmental longitudinal cracks. This paper quantifies the field performance of different sites in order to assess the effectiveness of using geosynthetics to stabilize the base course of roadways constructed on expansive clay subgrades. This includes evaluation of five full-scale field projects that had been subjected to actual traffic and environmental loads. The long-term performance of geosynthetic-stabilized and control sections was evaluated by quantifying the development and extent of longitudinal cracks and the degradation of the base course stiffness. Collectively, the performance evaluation of the multiple geosynthetic-stabilized and control sections in the five case studies demonstrates that geosynthetics can effectively mitigate roadway problems associated with expansive clay subgrades. In addition, field performance data also indicates that unconfined stiffness and tensile strength may not be sufficient for proper geosynthetic selection, pointing to the need for selecting them using properties that also quantify the soil-geosynthetic interaction.

Geosynthetic reinforcements have shown effective performances in basal reinforcement of low volume roads under traffic loads. In recent years, these reinforcements have also been used to improve roads against environmental loading. This study evaluates the performance of geosynthetic-reinforced and lime-treated low volume roads under both traffic loads and environmental conditions. Thirty two test sections were constructed in 2006 over expansive clay subgrade in Grimes County, TX. The sections involved eight different cross sections, including control (unreinforced) sections, subbase lime-treated sections, base geosynthetic-reinforced sections with three geosynthetics types, and combinations of subbase lime-treated with base geosynthetic-reinforced systems. An index of pavement performance was used to compare and rank the overall performance of the road sections. The geogrid reinforced sections were found to significantly enhance the performance of the road sections by preventing the development of longitudinal cracks in paved area. On the other hand, lime treatment showed only limited improvements to the performance of the reinforced sections.

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