Mechanical properties of cellular diaphragm wall in deep excavations considering nonlinear contact between wall and soil
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摘要: 格形地下连续墙(简称“格形墙”)作为一种相对新型的无内支撑式基坑围护结构,其力学性状研究滞后于工程实践。基于将双曲线接触模型嵌入到商用软件中的二次开发,开展了砂土中格形墙围护结构的受力变形特性有限元分析。墙土间的接触采用线性和非线性两种本构模型,砂土的应力应变关系采用基于UMAT子程序自定义的亚塑性本构模型模拟。与已有离心模型试验结果的对比验证了本文有限元模型的有效性。研究结果表明,考虑墙土间非线性接触特性得到的格形墙围护结构的力学性状更为准确,其内在机理为双曲线接触模型能够反映出墙体底部与土体间接触面剪应力的非均匀分布特性以及关键节点的剪应力集中现象。作用于墙体上的土压力未达到极限状态,且具有明显的空间分布特性。墙体水平位移模式为悬臂式,墙顶竖向位移模式为前墙沉降后墙隆起的整体旋转式。前后墙两中隔墙中间位置的弯矩分布规律类似。研究成果对于格形墙围护结构的设计优化具有积极作用。Abstract: Cellular diaphragm (CD) wall, as a new kind of excavation supporting structure without internal bracing system, has not been well studied, despite its successful applications in many engineering practices. By incorporating the hyperbolic contact model into a commercial finite element software through FRIC subroutine, the finite element analysis of the mechanical properties of CD wall in sand is performed. Two contact models, i.e., the Mohr-Coulomb linear and hyperbolic nonlinear models, are adopted. The stress-strain behavior of sand is simulated using the user-defined hypoplastic model through UMAT subroutine. By comparing with that of the existing centrifuge test results, the performance of the proposed numerical model is validated. The results indicate that the nonlinear contact model adopted is superior to the linear contact model in capturing the performance of the CD wall during excavation. This is because that the nonlinear contact model has an ability to account for the nonuniform distribution of interfacial shear stress between the wall bottom and the surrounding soil as well as the stress concentration phenomenon in the critical part of the wall. The lateral earth pressure on the wall has not reached its ultimate state, and an obvious spatial distribution feature of the lateral earth pressure can be observed. The mode of the horizontal displacement of the wall is cantilever, while the mode of the vertical displacement at wall top can be regarded as integral rotation with the front-wall settling and the back-wall uplifting. The distributions of the bending moment in the middle of the back- and front-walls are similar. The results obtained are helpful for the design optimization of CD wall for supporting excavation.
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图 2 离心模型试验装置及数据采集设备[14]
Figure 2. Centrifuge model testing system
表 1 数值模型参数
Table 1 Parameters required for finite element model
类别 本构模型 参数 砂土 亚塑性模型 φc = 30°,hs = 2.6 GPa,ns = 0.27,edo = 0.61,eco = 0.98,eio = 1.10,α = 0.14,β = 3,mR = 8,mT = 4,R = 2×10-5,βr = 0.1,κ = 1.0,K0 = 0.5格形墙 线性弹性模型 Edw = 27GPa,vdw = 0.167,γdw = 25 kN/m3接触面 库仑摩擦模型 μ = 0.3 接触面 双曲线接触模型 δ = 24.48°,Rf = 0.87,n = 1.0,KI = 75000, γw = 10 kN/m3,pa = 101.3 kPa,c = 0注: φc 为土体临界状态内摩擦角;hs,ns为控制正常压缩线和临界状态线形状的参数;α,β为指数;edo为零压力下的最小孔隙比;eco为零压力下的临界孔隙比;eio为零压力下的最大孔隙比;mR为控制180°应变路径逆转下的初始剪切模量的参数;mT为控制90°应变路径逆转下的初始剪切模量的参数;R为应变空间中弹性范围的大小;βr,κ为控制刚度随应变衰减速率的参数;K0为静止土压力系数;Edw为墙体弹性模量;νdw为墙体泊松比;γdw 为墙体重度;μ为墙土接触面摩擦系数;δ为墙土接触面摩擦角;Rf为破坏比;n为刚度指数;KI为无量纲刚度系数;γw 为水的重度;pa为标准大气压;c为墙土接触面黏聚力。 -
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