软弱地层双排板桩围堰水平位移简化计算方法

Simplified calculation method of horizontal displacement of double-row sheet pile cofferdam in soft strata

为研究围堰内部基坑开挖时双排板桩的变形特性,提出了一种适用于软弱地层实际的双排板桩围堰水平位移计算方法。针对该地层围堰底端水平位移不可忽略的问题,在堰芯填土不可压缩假定下,构建了桩底为非固定端的双排板桩围堰计算模型。通过将背水侧被动区土体简化为弹性地基梁,获得降水阶段围堰水平位移微分方程。再进一步采用影像源法计算基坑开挖引起的土体位移场,推导出降水及基坑开挖引起的围堰水平位移微分方程,并利用有限差分法求解出围堰水平位移近似解。依托实际工程,将计算结果与有限元数值模拟结果、监测数据对比,结果表明:对于艾溪湖隧道工程,钢管桩水平位移的理论计算结果较数值结果偏小7~11 mm,桩顶水平位移最大处偏小15%;对于雁洲水闸工程,钢板桩实测水平位移最大值较理论计算值偏小约16.7%。总体上,对比结果均较为吻合,证明了所提简化计算方法的合理性及适用性。

In order to explore the deformation characteristics of double-row sheet pile during the excavation of foundation pit inside the cofferdam,a calculation method of horizontal displacement of double-row sheet pile cofferdam was proposed.Aiming at the problem that the horizontal displacement at the bottom of the cofferdam can’t be ignored,a calculation model of double-row sheet pile cofferdam with non-fixed pile bottom was constructed under the assumption that the filling of the cofferdam core was incompressible.By simplifying the soil in the passive zone of the backwater side as an elastic foundation beam,the differential equation for horizontal displacement of cofferdam in the dewatering stage was obtained.Furthermore,the virtual image technique was used to calculate the displacement field of soil caused by foundation pit excavation,and the differential equation of horizontal displacement of cofferdam caused by dewatering and foundation pit excavation was derived.Then,the approximate solution of horizontal displacement of cofferdam with non-fixed bottom of pile was solved by finite difference method.Finally,based on actual projects,the calculation results were compared with the finite element numerical simulation results and the monitored data.The results show that in Aixi Lake tunnel project,the theoretical calculation results of the horizontal displacement of the steel pipe pile are 7-11 mm smaller than the numerical results,and the maximum horizontal displacement of pile top is 15%smaller than the numerical results.In Yanzhou sluice project,the maximum horizontal displacement of steel sheet pile is about 16.7%smaller than the theoretical calculation value.Overall,the comparison results are in good agreement,which validates the rationality and applicability of the simplified calculation method.