考虑应力路径的土体微观孔隙及宏观变形特征试验研究

Experimental research on micro-pore and macro-deformation characteristics of soils considering stress paths

为了明确工程建设中岩土体遭受复杂应力路径从而呈现出不同变形破坏模式的机制,以银西高铁早胜三号隧道典型古土壤围岩为研究对象,利用多应力路径三轴仪对试验土样进行不同应力路径的三轴剪切试验,同时通过低场扫描核磁共振得到试验土体的孔径分布特征。宏细观结合,明确不同应力路径条件下土体变形破坏机制。试验结果表明:轴向加载及侧向卸载两种应力路径条件下,土体应力–应变曲线均表现为应变硬化型。初始围压直接影响土体应力-应变曲线的变化趋势。根据归一化曲线,2种应力路径条件下土体应力–应变关系均符合双曲线模型;同时,土体的p-q(平均剪应力–广义剪应力)曲线均呈现出良好的线性关系,相同应力路径下,曲线变化趋势一致,空间位置表现出两两平行的关系。而初始固结围压直接决定了p-q曲线的位置。从土体剪切强度来看,初始围压对提高土体强度起到了重要作用。当轴向加载时,土体黏聚力、内摩擦角均大于相同条件侧向卸载时的量值,尤其在黏聚力方面表现的更为明显;最后,土体初始围压与变形呈现出良好的相关关系。初始围压越小,相同偏应力条件下,土体产生得变形越大。T2谱峰值强度较大,驰豫时间范围较大。同时,试验土样中小孔隙含量较少,而大孔径含量较多。相同初始围压条件时,土体经历侧向卸载时,T2谱峰值较大、驰豫时间较长,即土体中大孔隙含量较多。相同偏应力条件下,变形更大。另外,试样虽然达到相同轴向应变条件,但不同应力路径、不同初始围压会使得土体蕴含着不同的孔隙信息。

To confirm the mechanisms of different deformation and failure patterns of rock and soil masses in engineering constructions under complicated stress paths,taking the typical pale soil and surrounding rock in Zaosheng channel No.3 of Yinchuan-Xi’an high-speed rail as the objects,triaxial shear test was done on soil samples under different stress paths using multi-stress path triaxial apparatus,and the pore size distribution characteristics of soils were acquired by low-field scanning MRI.Macroscopic and microscopic methods were integrated to make sure the soil mass deformation and failure mechanisms under different stress paths.The test results show that,under the conditions of both axial-loading and side-discharging stress paths,the stress-strain curves of the soil present a strain-hardening pattern,and that the initial confining pressure directly affects the variation trend of the stress-strain curve of the soil.Based on the normalization curve,the stress-strain relationships of the soil under the two kinds of stress path conditions conform to the hyperbola model,The p-q(average shear stress-generalized shear stress)curve of the soil shows a good linear relationship,and under the same stress path,the variation trends of the curves are tend to be identical with a parallel correlation in spatial position.However,the initial solidification confining pressure directly decides the position of p-q curve.The initial confining pressure plays a significant role on the improvement of the shearing strength of the soil.The cohesion and internal friction angle of the soil under axial loading are both larger than those under side-discharge in the same condition,especially for the cohesion.The initial confining pressure and the deformation of the soil have a good correlativity.Under the same deviatoric stress,the smaller the initial confining pressure is,the larger the deformation of the soil mass would be.The larger the peak strength of T2 is,the larger the scope of the relaxation time would be.It is observed that the content of small and medium pores of the soil is low while that of large pores is high.Under side-discharging with the same initial confining pressure,the peak strength of T2 is high and the relaxation time is long,which indicates that the content of medium and large pores in the soil mass is high.Under the same deviatoric stress,the deformation due to side-discharging would be larger.In addition,for the same axial strain condition,the samples show different pore information with different stress paths and initial confining pressures.