基坑开挖数值分析中MMC模型参数的试验

Experimental study of MMC model parameters in numerical analysis of foundation pit excavation

为了得到修正摩尔库伦模型精确的数值模拟参数,以某深基坑工程实例为依托,取深基坑各土层的土样进行不同围压下的三轴剪切试验、卸载-再加载试验以及固结试验,从应力-应变关系曲线中获得割线模量、卸荷弹模等数值模拟参数,将这些模型参数与压缩模量进行对比分析,得出:试验粉土在不同围压下,发生的都是软化型破坏.细砂在200 kPa的围压下,有效偏应力-应变曲线无峰值点,呈现硬化型破坏.在土体还未发生破坏前,卸载再加载基本不影响土体的应力-应变曲线形式,所求得偏应力峰值点前后的卸载再加载模量近乎大小相等.试验粉土的切线模量、割线模量和压缩模量大致相等.随着参考应力的增加,土体的卸荷弹模与压缩模量的比值呈二次函数型增加.通过数值模拟验证了参数的准确性,试验研究是参数精确化的重要途径.

In order to get accurate numerical simulation parameters of the modified Mohr coulomb model,based on a deep foundation pit engineering example,each soil layer of soil samples of a deep foundation pit was taken to carry out the triaxial shear test,unloaded-load test again and consolidation test,respectively,under different confining pressure.The secant modulus and unloading elastic modulus were obtained from the stress-strain relation curve,following the comparison between the model parameters and compression modulus.It can be concluded that:under different confining pressures,the silty soil in the test is softened.Under the confining pressure of 200 kPa,there was no peak point in the effective deviation-strain curve of fine sand,showing hardening failure.Before the soil is damaged,the stress-strain curve form of the soil is hardly affected by the process of unloading and reloading,with nearly the same unloading and reloading modulus before and after the obtained deviant stress peak point.The tangent modulus,secant modulus,and compression modulus of the test silty soil are approximately equal.With the increase of the reference stress,the ratio of the unloading modulus to the compression modulus increases in a quadratic function.The accuracy of the parameters is verified by numerical simulation,so experimental research is an important way of parametric precision.