基于混凝土多轴强度的高土石围堰防渗墙安全性研究

RESEARCH ON HIGH EARTH-ROCK COFFERDAM IMPERVIOUS WALL SECURITY BASED ON MULTIAXIAL STRENGTH OF CONCRETE

塑性混凝土材料广泛用于水工建筑物基础的防渗处理中,尤其在高土石围堰防渗墙中得到了较大规模的应用,但其材料试验方法及结构计算中所采用的安全评判标准尚无相应的规程规范。以往常采用土石料的三轴压缩试验方法获取塑性混凝土的变形及强度参数,并采用应力水平衡量围堰塑性混凝土防渗墙的安全性。但应力水平由土体三轴压缩状态引入,其多用于适应莫尔库仑摩擦强度理论的散粒体材料安全状态的评判,对于应力状态复杂的深防渗墙混凝土材料宜通过混凝土强度理论进行安全复核。通过对高土石围堰防渗墙应力状态的分析,引入包含混凝土多轴强度的安全度准则,以白鹤滩大坝上游高土石围堰防渗墙为例,利用三维有限元分析,比较基于应力水平与安全度准则评价防渗墙安全性的差异,表明安全度准则较应力水平能更为灵敏地反映防渗墙安全性态,认为在三轴受压状态下应力水平尚能较好的反映防渗墙的安全状态,但在拉应力较明显的条件下宜采用基于混凝土多轴强度的安全度准则进行复核。

Plastic concrete was widely used in foundation impermeability treatment,especially in impervious wall of high earth rock cofferdam. There were no special guiding regulation and standard about testing method and corresponding structure calculation security evaluation criteria for this material. The triaxial compression test of rock earth material was utilized to obtain the deformation and strength parameters of plastic concrete and stress level was used to measure the safety of concrete impervious wall. But stress level was introduced in triaxial shear state of soil. It adapts for Mohr-Coulomb friction strength theory of granular material safe state. Complex stress state of deep concrete impervious wall material safety check should be carried out through the concrete strength theory. Security criterion which contains multiaxial strength of concrete was introduced. The Baihetan high earth-rock cofferdam whose impervious wall reaches 50 m is taken as an example. Comprehensive three-dimensional finite element calculation was conducted to analyze the safety state of cofferdam. The differences of safety index based on stress level and safety criterion were found. It show that the safety criterion than the stress level can be more sensitive to reflect the impervious wall security state. Stress level could reflect the safety status of the wall when the element positioned in three-dimensional compressed state. The security criterion should be used for safety check when the tensile stress region is obvious.