地铁车站端头井施工数值模拟参数的确定

Determination of parameters used in numerical simulation for construction of the end wall of a subway station

数值模拟能够有效分析深基坑开挖引起的围护结构变形和地表沉降问题,但模拟时所用主要参数目前还没有公认的确定方法。以上海市某地铁车站新建深基坑工程端头井段为例,使用有限元软件ABAQUS对施工过程进行模拟,使用正交试验方法研究了数值模拟所用土层参数的重要性,分析了不同土层参数对围护结构水平位移影响的敏感性,使用反分析方法提出了基坑开挖过程有限元数值模拟时参数的确定方法。结果表明:有限元数值模拟时对连续墙水平位移影响最大的参数为弹性模量、泊松比;数值模拟时,淤泥质黏土和淤泥质粉质黏土的模量比(弹性模量与压缩模量的比值)可取3.25~3.35,黏土和粉质黏土的模量比分别可取3.67,5.69~5.81,粉土、粉砂的模量比分别可取6.14,6.17~6.44,模量比取值从小到大对应的土层分别是黏性土、粉性土、砂性土;淤泥质土泊松比与勘察所得泊松比的比值为1.05~1.12,其他土层的泊松比与勘察结果的比值为0.90~1.05。

Numerical simulation may efficiently analyze the deformation of the envelope structure and surface settlement caused by the excavation of deep foundation pits.However,there are no common recognition for determining the parameters of the layered soil mostly used in the numerical simulation.Taking the end well section of the deep foundation pit in a subway station in Shanghai as an example,the construction process was simulated using the finite element software ABAQUS.After estimating the importance of each parameter by using orthogonal test,the sensitivity of the influence of the parameters of various soil layers on the horizontal displacement of the envelope structure was analysed.The back analysis was furthermore conducted to determine the parameters used in the finite element simulation for the pit excavation.It is shown that two parameters,i.e.,the elastic modulus and Poisson's ratio,have the greatest influence on the horizontal displacement of the continuous wall in the numerical simulation.In the finite element simulation,the modulus ratios(ratios of the elastic modulus to compressive modulus)for the sludgy clay and sludgy silty clay can be taken as 3.25~3.35,those for the clay and silty clay can be taken as 3.67 and 5.69~5.81,while those for the silt and silty sand can be taken as 6.14 and 6.17~6.44.The modulus ratios for the corresponding soil layers from small to great are cohesive soil,silty soil,and sandy soil in order.The ratio of the Poisson's ratio to survey ratio for silty soil is 1.05~1.12,while those of other soil layers are 0.90~1.05.