改进的粗粒土破坏准则及其初步验证

Improved Failure Criterion for Coarse-Grained Soils and Its Preliminary Verification

提出了一个改进的粗粒土破坏准则,推导的φ_b—b(b是反映大、中、小主应力σ_1、σ_2、σ_3相对大小的参数,φ_b为不同b值时的综合内摩擦角)关系表明,随着b的增大,φb先增大后减小,但减幅不大;对于任意φ_0(φ_0为b=0时的综合内摩擦角),都有φ_1>φ_0(φ_1为b=1时的综合内摩擦角),且φ_0越大,φ_b增幅越大,表明中主应力对内摩擦角的影响越显著;与Lade-Duncan准则及Mastsuok-Nakai准则相比,改进准则的φ_b—b关系与保持σ3与b为某一定值时的试验值更接近;在π平面上,改进的破坏准则介于Lade-Duncan准则及Mastsuok-Nakai准则之间,M0(M0为某一σ_3下b=0时的破坏应力比)较小时,准则的破坏轨迹形状近似于圆形,随着M0的增大,其破坏轨迹趋于一个等边三角形。某坝粗粒土真三轴p、b一定时的试验结果表明:按改进准则所得破坏轨迹较Lade-Duncan准则及Mastsuok-Nakai准则与试验值更加吻合,验证了改进破坏准则的合理性。

A new failure criterion for coarse-grained soils was presented. The φb-b （b is the parameters which reflects the relative size among the major principal stress 0-1, the principal stress 0-2 and small primary stress σ3, φb is the comprehensive inner friction angle corre- sponding to the different b） relationship of the failure criterion was deduced. The analysis indicates that the φb firstly increases then reduces with increasing of the b. But the reduced amplitude of the φb is not large, and the φ is larger when the b equals to 1 than that b equals to zero, that is to say, for any φ0（φ0 is the comprehensive inner friction angle when b equal to zero）, there is φ1〉φ0（φ1 is the comprehensive inner friction angle when b equal to 1 ）. Moreover, the more φ0, the larger the increasing amplitude of φb, which shows that the influence on angle of internal friction due to intermediate principal stress is more obvious as the φ0 grows up. Comparing with the Lade-Duncan criterion and Matsuoka-Nakai criterion, the φb-b relationship of the presented failure criterion is closer to the test values, in which both σ3 and b are constant. The failure surface of the presented failure criterion is between Lade-Duncan and Matsuoka-Nakai on the π plane. Further, the shape of the presented failure surface is similar to circle when the Mo is small, while that is close to equilateral triangle as the M0 becomes large. According to the results of the true triaxial test on coarse-grained soils from a dam hydropower station, in which p or b is invariable, failure trajectory calculated by the presented failure criterion is more consistent to the experimental values than that both Lade-Duncan criterion and Matsuoka-Nakai criterion. So, the failure criterion is reasonable.