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 .
In this study, a two-dimensional finite difference model was used to simulate the heat transfer occurred during a 17-day heat extraction test performed in an MSW landfill cell in Santee, California. The heat extraction was performed using serpentine horizontal heat exchangers installed 6 m above the base liner of the cell, and it started after the waste reached a stable temperature value of 52 °C. The model was developed based on the differential heat conduction equation and an inverse analysis was performed to estimate the thermal diffusivity of the waste. The values of in-situ thermal diffusivity obtained ranged from 7.85 10 -7 m 2 /s to 1.05 10 -6 m 2 /s and are consistent with the higher range of values presented in the literature for MSW.
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.
As municipal solid waste (MSW) in landfills can reach temperatures greater than 50°C that may be sustained for several decades due to methanogenic bacteria activity, the generated heat is an alternative energy source that can be exploited for direct heating of nearby infrastructure or for augmenting industrial processes. However, in-situ measurements of MSW thermal properties are needed to properly design heat extraction systems for landfills. In this study, the spatial and temporal evolution of the waste temperatures in a new MSW landfill cell in Santee, California were monitored over 13 months. After the temperatures reached stable values, a 17-day heat extraction thermal response test was performed on serpentine geothermal heat exchangers that were installed at three elevations in the cell during waste placement. As the serpentine segments were separated from each other to minimize thermal interference during the heat extraction test, the pipes were assumed to represent line heat sinks. The values of effective thermal conductivity estimated from infinite line source analyses ranged from 0.86 to 1.32 W/m°C , which are consistent with values on the higher range of those from laboratory tests on MSW.
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