高应力状态下的黄土抗剪强度特性研究

STUDY OF SHEAR STRENGTH OF LOESS UNDER HIGH STRESS STATE

土体抗剪强度包络线在一定的应力范围内可近似看做直线,一般工程中直剪试验正应力和三轴试验围压常为0～400k Pa,试验可得出以黏聚力c和内摩擦角φ确定的强度。在黄土地区,人工和自然边坡可超百米,坡内应力自低到很高变化范围大,对该类高边坡需考虑强度参数随应力状态的变化。本文先通过线弹性有限元模拟一黄土高边坡应力场。以潜在滑面上关键点的应力为固结应力进行三轴压缩试验（NCTC）。为了对比分析,又进行了100k Pa、200k Pa、300k Pa、400k Pa围压下的三轴压缩试验（CTC）。结果表明,考虑黄土高边坡应力状态时,由总应力莫尔圆得到的强度包络线为曲线,直线型莫尔-库伦强度准则不适用;而有效应力莫尔圆的到的强度包络线可为直线,其有效强度参数高于CTC试验。在σ-τ应力空间中,NCTC试验总强度包络线和有效包线均位于CTC试验强度包线之上,抗剪强度高,这同固结应力高且为偏压固结有关。

The shear strength envelope is linear in some range of stress. The commonly used 0～400 k Pa vertical stress for direct shear tests and confining pressure for triaxial tests can meet many engineering soil stress state of interest. And the shear strength envelope can be linear,designated by cohesion c and internal friction angle φ. In loess area,high loess slope over 100 m is common,and the stress state of soil on the potential failure surface varies greatly from the low to the high. It is necessary to consider the shear strength parameters changing with the stress state. The research herein firstly utilizes a linear elastic finite method to figure out the stress field of a high loess slope. It then consolidates soil samples at the stress state of some key point on the potential sliding surface and performs triaxial compression tests（ NCTC）. Triaxial compression tests with 100 k Pa,200 k Pa,300 k Pa,400 k Pa confining pressure are also performed for comparison. Results show that when considering the stress state of high loess slope,the shear strength envelope yielded by the total stress Mohr circle is not linear and the linear M- C criterion is not effective. But that yielded by the effective stress Mohr circles is linear,and the strength parameters are higher than CTC tests. In σ-τ space,the shear strength envelope（ total and effective） of NCTC is higher than that of CTC,which is related to the high consolidated stress.