瀑布沟大坝防渗墙应力分布特性及机理探讨

Discussion on mechanism and stress distribution features of diaphragm walls of Pubugou Hydropower Station during construction period

瀑布沟水电站大坝为砾石土心墙堆石坝,坝基为深厚河床覆盖层,最大深度达到75.36 m。坝基覆盖层防渗采用两道各厚1.2 m的全封闭式混凝土防渗墙。为了探讨防渗墙的应力分布特性,首先,根据瀑布沟水电站大坝施工期应变监测成果,综合分析墙体应变变化分布特征;其次,基于混凝土徐变和应力松弛理论,应用松弛法将混凝土应变转换为应力;最后,综合各相关影响因素对防渗墙应力分布机理进行探讨。结果表明：偏应变所占比例基本上在5%以内,施工期防渗墙未出现较大偏心受压的情况;防渗墙最大压应力发生在墙体中部,其量值为顶部和底部的7~9倍;影响防渗墙应力分布的主要原因是墙体和河床覆盖层不均匀沉降（变形不协调）而产生的负摩阻力。分析指出：在防渗墙的结构设计中应重点考虑负摩阻力的影响。

The dam of Pubugou Hydropower Station is a gravelly soil core rockfill dam,and its foundation is in a deep riverbed overburden layer with the maximum depth of 75.36m.The seepage works of the dam foundation overburden layer are two fully enclosed concrete diaphragm walls with 1.2m thick each.We discuss the stress distribution features.Firstly,according to the monitoring result of the strain of the station during construction period,we analyze the distribution features of the strain of the wall comprehensively.Secondly,based on concrete creep and stress relaxation theory,the strain of concrete is converted to stress using relaxation method.Finally,the distribution mechanism of diaphragm wall stress is discussed with consideration of all relevant factors.The conclusions are：（1） the proportion of deviator strain is basically within 5% and large eccentric compression does not appear in the diaphragm walls during construction.（2） The maximum compressive stress is in the central section of the diaphragm wall,and the measured values are 6 to 8 times larger than those in the top and bottom of the wall.（3） The important influential factor of the stress distribution of diaphragm wall is the negative friction formed by uneven settlement（uncoordinated deformation）of wall and the riverbed overburden layer,which should be emphasized in the structural design of the diaphragm wall.