Abstract Partial expansion was observed in stratified subsidence during foundation pit dewatering. However, the phenomenon was suspected to be an error because the compression of layers is known to occur when subsidence occurs. A slice of the subsidence cone induced by drawdown was selected as the prototype. Model tests were performed to investigate the phenomenon. The underlying confined aquifer was generated as a movable rigid plate with a hinge at one end. The overlying layers were simulated with remolded materials collected from a construction site. Model tests performed under the conceptual model indicated that partial expansion occurred in stratified settlements under coordination deformation and consolidation conditions. During foundation pit dewatering, rapid drawdown resulted in rapid subsidence in the dewatered confined aquifer. The rapidly subsiding confined aquifer top was the bottom deformation boundary of the overlying layers. Non-coordination deformation was observed at the top and bottom of the subsiding overlying layers. The subsidence of overlying layers was larger at the bottom than at the top. The layers expanded and became thicker. The phenomenon was verified using numerical simulation method based on finite difference method. Compared with numerical simulation results, the boundary effect of the physical tests was obvious in the observation point close to the movable endpoint. The tensile stress of the overlying soil layers induced by the underlying settlement of dewatered confined aquifer contributed to the expansion phenomenon. The partial expansion of overlying soil layers was defined as inversed rebound. The inversed rebound was induced by inversed coordination deformation. Compression was induced by the consolidation in the overlying soil layers because of drainage. Partial expansion occurred when the expansion exceeded the compression. Considering the inversed rebound, traditional layer-wise summation method for calculating subsidence should be revised and improved.

中文翻译：

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基坑脱水分层沉降局部膨胀模型试验

摘要 基坑脱水过程中出现分层沉降的局部膨胀现象。然而，这种现象被怀疑是错误的，因为已知发生沉降时会发生层的压缩。选择由压降引起的沉降锥的切片作为原型。进行了模型测试以研究这种现象。下面的承压含水层是一个可移动的刚性板，一端带有铰链。覆盖层是用从建筑工地收集的改造材料模拟的。在概念模型下进行的模型试验表明，在协调变形和固结条件下，分层沉降发生了部分膨胀。在基坑脱水过程中，快速下降导致脱水承压含水层快速下沉。快速下沉的承压含水层顶部是上覆层的底部变形边界。在下沉的上覆层的顶部和底部观察到非协调变形。上覆层的下沉在底部大于顶部。这些层膨胀并变得更厚。采用基于有限差分法的数值模拟方法对该现象进行了验证。与数值模拟结果相比，物理测试的边界效应在靠近可移动端点的观测点处明显。由脱水承压含水层的下伏沉降引起的上覆土层的拉应力促成了膨胀现象。上覆土层的局部膨胀定义为反向回弹。逆回弹是由逆协调变形引起的。由于排水，上覆土层的固结引起了压缩。当膨胀超过压缩时发生部分膨胀。考虑到反向回弹，传统的计算沉降的分层求和方法应加以修正和改进。