| Summary: | 碩士 === 淡江大學 === 土木工程學系碩士班 === 97 === The stone column technique is a low cost, time saving, and flexible construction method for ground improvement. When the stone columns are installed in soft clay soils, the lateral confinement offered by the surrounding soil may not adequate to form the stone column due to not be able to develop the required load-bearing capacity. In such soil, the required lateral confinement can be induced by encapsulating the column with tensile geotextile material.
The purpose of this study is to investigate the mechanical behavior of geotextile encasement on the sand columns using the finite difference analysis. The results from the numerical analysis studies are presented to quantify the effect of confinement and mechanism for improvement in load capacity due to encasement. Based on the results obtained from this study, the following conclusions are made:
1. The sand that would be used in the model was tested by triaxial tests to develop its stress-strain volume relationship, which provide the basis for numerical analysis. The strain hardening - softening volume dilation model of the sand in present study proved that it could suitable simulates the dilative behavior on pre-peak deviatoric stress.
2. Volumetric strain reduction percentage increase with the increase in the geotextile stiffness after 10% axial strain. Due to the Poisson effect, the volumetric strain reduction tendency is not obvious before 10% axial strain.
3. At a specific axial strain, the radial strain reduction effect is higher for stiffer geotextiles to specimen subjected to low chamber pressure. However the radial strain reduction effect degrades with higher chamber pressure.
4. The confinement stress increment in the reinforcement obviously underestimates 35% ~ 50% against the theoretical solutions.
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