平面应变条件下含孔洞土样受内压作用的变形破坏过程

在不同加载速率下，利用自主研制的平面应变模型加载及观测系统对平面应变条件下含孔洞土样进行双轴压缩实验。垂压由试验机施加，土样受到的内压和侧压作用由气囊施加。在对土样施加内压和侧压后、进行位移控制加载前，操控数码相机对喷涂了散斑的土样表面图像进行拍摄，以记录土样在位移控制加载过程中的全部变形过程。利用数字图像相关方法获得土样的位移场，利用能较好滤掉位移场噪声的局部位移最小二乘拟合方法获得最大剪切应变的分布及演变规律。为了定量获得最大剪切应变且分析方便，根据清晰剪切带位置，布置曲折测线并在其两侧布置平直测线。研究发现：当加载速率较低且纵向应变达到一定值时，拉破坏导致土样的孔洞顶部和底部发展出高角度应变局部化带，而当加载速率较高时，未出现上述现象；当纵向应变较高时，在孔洞表面附近，随着向孔洞表面的逐渐靠近，大多数剪切带内测线上的最大剪切应变逐渐增加，而大多数带外测线上的最大剪切应变则逐渐下降；当纵向应变较高时，在离孔洞表面较远处，随着向孔洞表面的逐渐靠近，大多数剪切带内测线上的最大剪切应变逐渐增加，而大多数带外测线上的最大剪切应变则变化复杂。

Experimental measurements of deformation and failure processes of plane strain clay specimens with holes and subjected to internal pressures

Biaxial compressive tests of cuboid low liquid-limit clay specimens with holes under plane strain for different loading rates were conducted by use of designed loading and measuring system. The vertical pressures were applied by the testing machine, and the internal and lateral pressures were applied by gasbags. To obtain the full deformation process of clay specimens with holes during the displacement-controlled loading process, a digital camera is used to record speckle images of clay specimens with holes after internal and lateral pressures were applied and before the displacement-controlled loading was conducted. Displacements can be abfained by use of the digital image correlation method. Distributions and evolution of the maximum shear strains were measured by use of least-square fitting of local displacements that can better eliminate noises in displacements. To obtain quantitative maximum shear strains, curve monitored lines were arranged according to positions of clear shear bands, and two straight monitored lines were arranged at both sides of each curve monitored line. The following results were obtained:when the longitudinal strain reaches a certain value, high-angle strain localization bands from the top and bottom of the hole for lower loading rates developed, due to tensile failure. While there are no high-angle strain localization bands for higher loading rates, when the longitudinal strain shear strains of most monitored lines outside shear bands have decreasing tendencies as they approach the hole surface. When the longitudinal strain is higher and monitored lines are far away from the hole surface, the maximum shear strains of most monitored lines in shear bands have decreasing tendencies as they approach the hole surface. The change of the maximum shear strains of monitored lines outside shear bands are complex as they approach the hole surface.