冲击荷载作用下结构性软黏土力学特性试验研究

A study of the mechanical characteristics of structured soft clay under impact loading

冲击荷载作用对土体力学特性影响较大,为了研究此特性,基于天津滨海结构性软黏土,以空心圆柱扭剪仪模拟冲击荷载作用,并在冲击荷载作用前后对土体进行不固结不排水三轴试验,对比研究不同试验条件下结构性软黏土力学特性。试验结果表明:低围压常规三轴剪切试验状态下,土体表现出弱应变软化现象,且土体抗剪强度包线不能用直线表示,而是可由两条直线近似拟合而成;冲击荷载作用时,在一定应力范围内,冲击荷载越大,土体轴向应变、孔隙压力以及主应力差峰值也越大;冲击荷载作用后三轴剪切试验各围压下土体都呈应变硬化型,主应力差峰值均大幅减小,且土体抗剪强度包线均可用直线表示,c、φ值也远小于未受冲击荷载时三轴剪切试验相应数值。最后,总结分析冲击荷载作用对软黏土强度的影响,并拟合得到强度折减与围压、冲击荷载的关系,为实际工程中承受冲击荷载的结构性软黏土强度确定提供参考。

To examine the great effect of impact loading on the soil mechanic characteristics, impact loading was simulated by hollow cylindrical torsional shear apparatus using the Tianjin coastal structural soft clay. The mechanical characteristics of the structural soft clay under different experimental conditions are comparatively analyzed from the results of non-consolidation and non-drainage triaxial tests before and after impact loadings. The experiments results show that the soil exhibits weak strain softening in the conventional triaxial shear tests under the low confining pressure, and the shear strength envelope of the soil is approximately fit by two straight lines other than one straight line. In the impact loading tests, the axial strain, pore pressure and the peak values of the principal stress difference grow with the increasing impact loading. After the impact loading, the soft clay shows strain hardening under all kinds of confining pressures in the triaxial shear tests, and the peak values of the principal stress difference reduces drastically. The shear strength envelopes of soils are straight lines, and the values of c, ~ are far less than the values of the soil which were impacted. Finally, the influence of impact loading to the strength of the soft clay was summarized and analyzed , and the relationship between the strength reduction, confining pressure and impact loading were proposed with the fitting formula. The results of tests for determining the strength of structural soft clay under the impact loading has a guiding significance in practical engineering.