考虑防渗墙顶端土体剪切滑移效应的墙与土接触模型及其验证研究

The stress of seepage prevention system of high earth core rockfill dam on deep overburden layer is very complex, and its stress and deformation state are related to the safety of the dam. The engineering practice of high earth core rockfill dam indicates that the calculated stress of cut-off wall is much higer than that of measured values, and the main reason is that the contact deformation characteristics between concrete cut-off wall top and clay core is quite unclear, and the shear slip effect of soil on top of cut-off wall is not considered in the calculation. This study will adopts the model test, theory analysis, numerical calculation and centrifugal test method comprehensively to do research on the contact interaction affect between concrete cut-off top and clay core; reveals the development law of resistance on top of cut-off wall with deformation under layered filling conditions of dam by means of model test; scans the entire test process by CT system; discusses the deformation characteristics of clay core from the visual perspective; be based on that clarifies the contact deformation mechanism of concrete cutoff wall top and clay core; conducts and summarizes wall top resistance - contact deformation curve; proposes the contact model between cut-off wall and soil considering the shear slip effect of soil on top of cut-off wall and realizes it by means of writing FEM program; carries out centrifugal model test of high earth core rockfill dam on deep overburden and conducts numerical modeling to testify the reliability of contact model. This study will provide a scientific basis for the optimization design of cut-off wall, which has important theoretical and engineering significance.

深厚覆盖层上高心墙坝防渗体系的受力十分复杂，其应力变形状态关系到整个大坝的安全。高心墙坝的工程实践表明，防渗墙应力计算值远高于实测值，主要原因在于对混凝土防渗墙顶端与粘土心墙的接触变形机理不甚了解，计算模型中没有考虑防渗墙顶端土体的剪切滑移效应所致。本项目拟综合运用模型试验、理论分析、数值计算与离心试验等方法，对混凝土防渗墙顶端与粘土心墙的接触作用进行研究。采用模型试验揭示坝体分层填筑条件下防渗墙顶端阻力-接触变形的发展规律，试验全程采用CT机扫描，可视化阐述粘土心墙的变形性状，在此基础上阐明混凝土防渗墙顶端与粘土心墙的接触变形机理；归纳总结防渗墙顶端阻力-接触变形曲线，提出考虑墙顶端土体剪切滑移效应的墙与土接触模型及参数取值方法，并编写有限元程序；进行深厚覆盖层高心墙坝的离心试验并数值模拟全程，验证接触模型的可靠性。本项目将为防渗墙的设计优化提供科学依据，具有重要的理论和工程意义。

深厚覆盖层上高心墙坝的工程实践表明，防渗墙应力计算值远高于实测值，主要原因在于计算模型中没有考虑防渗墙顶端土体的剪切滑移效应所致。本项目综合运用模型试验、理论分析、数值计算与离心试验等方法，对混凝土防渗墙顶端与心墙的接触作用进行研究，主要工作内容如下：.（1）通过施加上覆压力模拟坝体分层填筑，进行了防渗墙刺入普通粘土与高塑性粘土的物理模型试验，防渗墙顶端土压力与接触变形的关系呈现双曲线形状，上覆压力越大，刺入相同位移量时防渗墙的顶端压力越大；防渗墙的厚度对试验曲线的影响较大，长度与高度的影响不显著。.（2）采用CT试验可视化防渗墙顶端土体的变形性状，可将防渗墙顶端与粘土心墙的接触变形分为剪切滑移、冲切破坏、阻力稳定这三个阶段。当防渗墙顶端分别为普通粘土与高塑性粘土时，防渗墙顶端压力-接触变形曲线分别呈“缓变型”与 “突进型”。.（3）对试验数据进行了归一化处理及数学描述，提出了考虑防渗墙顶端土体剪切滑移效应的墙与土双曲线接触模型，模型中五个参数表示与法向应力有关的接触面力学性能，并且所有参数均可根据物理模型试验获得，理论拟合曲线能够较好地模拟试验曲线，并编写相应的有限元程序实现了所提出的接触模型。.（4）考虑防渗墙顶部为粘土和高塑性粘土两种工况，采用逐级增大离心机加速度的方式模拟土石坝的填筑过程，通过离心模型试验获得了自重作用下防渗墙顶部土体的变形和土压力分布规律，防渗墙对心墙产生了十分明显的“顶托”作用，使得墙顶端局部土体产生剪切位移。.（5）采用提出的墙与土接触模型数值模拟了离心模型试验，由于提出的接触模型允许一定程度的网格嵌入，较大程度地模拟了试验中防渗墙“刺入”粘土心墙现象，与采用传统的接触模型相比，计算得到的防渗墙顶端应力集中程度较小，防渗墙顶端土压力、防渗墙自身应力分布规律均与实际情况相符，验证了提出的接触模型的正确性与有效性。