![]() ![]() Non-Darcy flow was observed within the range of 0–10 m around the bottom of the cut-off wall. The optimal depth of the pumping wells was 1–5 m above the bottom of the cut-off wall, and the optimal horizontal distance between the cut-off wall and the pumping wells was 25% of the pit width. The layout of the pumping wells in horizontal direction influenced water level distribution and flow rate. The insertion depth ratio of the cut-off wall most effectively influenced the drawdown. Tests were performed for the combinations of cut-off wall and partially penetrating pumping wells. A camera was used to collect flow information. Industrial solid dye and paraffin oil were used as tracers. High-purity fused silica and mixed paraffin oil were used as skeleton and fluid to simulate the confined aquifer and groundwater. In this study, transparent soil was introduced to model the coupling mechanism in the physical model test. However, the coupling mechanism is not intuitively well understood because of the limitations of existing experimental methods. ![]() The coupling effect of the cut-off wall and pumping well is used to control the drawdown outside the foundation pit. When a foundation pit is located in a built-up area and the underlying confined aquifer is not cut off, the drawdown must be minimized outside the pit to avoid land subsidence in buildings and pipelines. Cut-off wall is often used as waterproof curtain to partially cut off the dewatered aquifer. Water level is decreased during foundation pit excavation to avoid water inrush under confined water pressure. Key words : consolidation, excavation, finite element, seepage, transient unconfined flow. Comparisons between the field measurements and the calculated results are given in this paper. This method is used here for back-analysis of a full-scale excavation that has been comprehensively documented. The authors have previously developed a fully coupled numerical method that allows the computation of the displacements and pore pressures in a soil taking account of the drawdown of the water table which may accompany excavation. Ground settlements and water-surface levels were monitored during the excavation period, as the settlement of the surrounding area was of concern. A case history of excavation adjacent to closely constructed blocks of buildings is discussed in this study. These settlements may be crucial if the excavation is carried out in a congested area. In the vicinity of an excavation in a saturated soil, ground settlements are often caused by the combined effects of stress release and drawdown of the water table. ![]()
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