平面应变条件下不同裂隙方向原状膨胀土变形破坏性状与剪切带演化特征

Deformation behavior and shear zone evolution characteristics of undisturbedexpansive soil with different fissure directions under plane strain condition

富含裂隙是膨胀土的重要特性之一,原生裂隙以及受力过程中的裂隙扩展对土的力学行为影响显著。为了调查裂隙对膨胀土的变形规律与破坏模式的影响,借助改进型真三轴仪,对不同原生裂隙主方向角的原状膨胀土(I型裂隙试样长轴垂直优势裂隙方向、II型裂隙试样长轴45°斜交优势裂隙方向、III型裂隙试样长轴平行优势裂隙方向),开展固结排水平面应变剪切试验,并利用数字图像相关(digital image correlation,简称DIC)技术分析变形规律,重点研究裂隙影响的变形局部化特征。结果表明:同一围压作用时,II型裂隙试样的峰值应力最小,应力-应变曲线呈应变软化型,其破坏类型为滑动破坏;I型裂隙试样峰值应力最大,且I型裂隙试样与III型裂隙试样的应力-应变曲线呈应变硬化型。I型裂隙试样的破坏类型为压缩剪切破坏,III型裂隙试样的破坏类型随围压不同而存在差异。同一围压作用下,I型裂隙试样产生的剪切带倾角较其他裂隙类型样品小,且基本不随围压变化。II型裂隙试样的剪切带沿原生裂隙面发育形成,其倾角大小随围压变化并无明显规律,围压影响II型裂隙土试样剪切带发育的数量。对于III型裂隙试样,围压影响剪切带发育类型,且随着围压增大,主剪切带倾角减小。利用Roscoe理论得到不同裂隙方向土样的剪切带倾角大小与试样实际破坏时剪切带的倾角较为符合。该试验为研究裂隙性膨胀土力学特征各向异性奠定了基础。

The abundance of fissures is one of the important characteristics for expansive soils.The inherent fissures and fissure propagation during the loading process have a significant impact on the mechanical behavior of the soil.In order to investigate the influence of fissures on the deformation and failure mode of expansive soil,with the help of an improved true triaxial instrument,the undisturbed expansive soils with different inclination angles of inherent fissures(type I-the long axis of the sample is perpendicular to the dominant fissure direction,type II-the long axis of the sample is 45°oblique to the dominant fissure direction,and type III-the long axis of the sample is parallel to the dominant fissure direction)were used to conduct the consolidated drained plane-strain shear test.Meanwhile,the deformation was analyzed using digital image correlation(DIC)technology,focusing on the local deformation characteristics controlled by fissures.The results show that under the same confining pressure,the peak stress of the type-II fissured soil sample is the smallest,the stress−strain curve is of strain softening type,and its failure type is sliding failure.The peak stress of the type-I fissured soil sample is the largest,and the stress−strain curve is strain hardening type.The failure type of the type-I fissured sample is compression-shear failure,and the type-III fissured sample presents different failure forms due to different confining pressures.Under the same confining pressure,the inclination angle of the shear zone produced in the type-I fissured samples is smaller than that of other fissure types and basically does not change with the confining pressure. The shear zone of thetype-II fissured sample develops along the original fracture surface, and its dip angle has no obvious regularity with the confiningpressure. The confining pressure affects the number of shear zones developed in the type-II fissured samples. For type-III fissuredsamples, the confining pressure affects the development type of the shear zone, and as the confining pressure increases, the dip angleof the main shear zone decreases. Based on Roscoe’s theory, the inclination angle of the shear zone in the samples with differentfissure directions is more in line with the inclination angle of the shear zone when the sample is actually damaged. This test lays afoundation for studying the anisotropic mechanical properties of fissured expansive soil.