| Summary: | 博士 === 國立臺灣科技大學 === 營建工程系 === 95 === To evaluate the effect of ground improvement on the behavior of bermed excavation in clay, a 1-g model test using the extremely soft clay was proposed here. In addition, the numerical analyses using a three-dimensional explicit finite difference program (FLAC3D) are also performed for comparing the surface settlement associated with different ground improvement layouts in the field. Also, two field observation cases are compared with the numerical analysis results to evaluate the results generated from the model study. Test and analysis results had indicated that the buttress type arrangement has a better effect on controlling the bermed excavation induced surface settlement than the column type arrangement. Moreover, it has been found that it is more effective to reduce the soil movement when the improved zone has enough strength and the dimension of improvement extends beyond the passive failure zone of the retaining wall. When the safety factor of global sliding stability of bermed excavation is lager than 1.4, the reductions in ground settlement for various ground improvement layouts are only fractional. Under this condition, the ground improvement inside the berm can more effectively reduce the soil movement caused by bermed excavation. However, when the safety factor of global sliding stability is less than 1.2, the reduction of ground settlement varies in a wider range. In summary, if the berm size is large and with sufficient ground improvement, the stability of excavation is high and can reduce a lot of soil movement. In contrast, if the berm size is small and safety factor against global sliding is low, then the soil movement will be large. But with high improvement ratio in the berm, the stability of berm can be maintained. So the ground improvement can play a role in reduction the excavation induced ground movement.
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