基坑离心模型试验开挖方法研究与应用

Research and application of a new excavation method in centrifuge model tests on foundation pit engineering

针对离心模型试验中停机开挖、排液法、微型机器人开挖3种传统方法缺点进行分析,设计研制一种新型开挖模拟装置,对土体实际卸荷过程有更准确的模拟,并应用于一组砂土地基基坑开挖离心模型试验验证了可行性。与传统方法相比,能实现非停机开挖,较准确模拟土体侧压力,原理简单、造价低。试验中布置多种类型传感器形成立体测量,试验数据与数值分析结果形成对比分析。结果表明:悬臂式支挡结构的砂土地基基坑开挖地表沉降曲线呈悬臂型;引起挡墙最大弯矩位置随开挖逐渐下移,下移速率递减;开挖土体卸荷,引起主动区土压力减小,浅层开挖对深层土压力影响很小,深层开挖时,浅层土压力的变化不明显。最后对试验中存在的问题和有待改进之处作了讨论,对后续和同类试验提供指导和参考。

Three common excavation methods in centrifuge model tests were reviewed,including the excavation at 1 g,the drainage of appropriate liquid to simulate excavation and the excavation in-flight using a micro robot. A new excavation device was designed and developed on the basis of the understanding of the excavation processes. It was confirmed to be feasible in a centrifuge model test on foundation pit engineering in sand ground. Compared with the traditional methods,this method can be used to realize the excavation in-flight,to simulate more correctly the lateral earth pressure,and to simplify the excavation process. In the test,the multiple types of sensors were arranged to form a three-dimensional measurement. The test results were compared with the numerical simulations. It was found that the test results were always smaller than those from simulations. The surface settlement profile caused by excavations was a spandrel type. The position of the maximum induced bending moment of the retaining wall moved down along with excavations,but the moving rate decreased gradually. The upper excavation had little impact on the deep earth pressure. Similarly,the changes of the shallow earth pressure were not obvious when the lower soil was excavated.