单轴压缩条件下土石混合体开裂特征研究

CRACKING DEFORMATION CHARACTERISTICS FOR ROCK AND SOIL AGGREGATE UNDER UNIAXIAL COMPRESSIVE TEST

土石混合体作为一种物质成分和内部结构特征极为复杂的多相多组分散粒材料,其破坏是一个复杂的结构变化过程。应用CT试验和数值模拟方法研究土石混合体的变形破坏特征,指出开裂是土石混合体区别于其他地质体变形破坏的一个显著特征。土石混合体破坏的根本原因是块石与土体的弹性不匹配和土–石界面的差异滑动,破坏的实质是内部裂纹产生、扩展、互锁和贯通的过程。通过对土石混合体开裂机制的研究得出以下结论:(1)基于CT试验的变形特征分析表明试样、块石包裹体及其邻近土体三个感兴趣区域的CT数随应力水平的增加而不断减小,且块石包裹体的CT数变化较土体更为敏感。(2)数值模拟结果表明试样破坏过程经历了土石结合裂纹的萌生、慢裂、快裂致贯通破坏的过程。土石接触面是最薄弱的部位,荷载作用下界面差异滑动引起裂纹的产生,随后裂纹沿块石边界缓慢扩展直至扩展到土体中,受块石形状及分布的影响,裂纹会出现局部化发展和互锁现象。大量裂纹在土体中快速扩展聚集引起试样的破坏。(3)土石混合体的破坏具有渐进性的过程,破坏可分为三级:一是土–石界面的开裂,二是土体中裂纹的扩展、聚集和贯通并且最终导致试样的破坏,三是针对软弱的片岩块石的穿石破坏。

Rock and soil aggregate(RSA) is a kind of multiphase and multi-component material and its composition and internal structure characteristic is very complex. The damage process of RSA is a complex structure change process. CT tests and numerical simulation method are used to study the deformation and cracking characteristics of RSA,and it is point that cracking failure is a unique characteristic for RSA which differs from other geology bode. The primary reason cracking is the elastic mismatch between rock blocks and soil. The essence for RSA failure is a process including crack initiation,propagation,interlocking and coalescence. In this paper,some conclusions can be drawn as follows:(1) The RSA deformation features analysis based on CT tests show that the mean CT value for specimen,rock block inclusions and its adjacent soil region decease with the increase of loading,and the change is more sensitive for block inclusions.(2) The numerical simulation results show that the failure process of RSA go through with crack initiation,slow-cracking,fast cracking and coalescence. Interface between rock blocks and soil is the weakest part of RSA. The difference sliding unloading result in the crack initiation,then cracks propagate to soil along block boundary and cracks are influenced by rock blocks. The local development of crack and interlocking leading to formation of shear line with X character or wedge shape.(3) Failure of RSA is a progressive process which can be divided into three levels——rock-soil interface cracking,soil cracking and rock cracking.