2种岩石直接拉压作用下的力学性能试验研究

 利用Instron1342液压伺服机对2种典型硬岩和软岩试样进行单轴试验，包括单轴压缩试验和直接拉伸试验，研究这两种岩石在直接拉压作用下的力学性能，对比2种岩石的单轴抗压强度和单轴拉伸强度。试验过程中监测岩石试样的轴向应变和水平应变，并记录岩石试样的声发射特征，得到2种岩石在单轴拉压下的应力–应变曲线和声发射计数率曲线，对比2种岩石在单轴拉压下的声发射变化规律。试验发现，直接拉伸下2种岩石在加载初期较大范围内基本无声发射事件发生，直到破坏前声发射事件数才突然增大。讨论2种岩石在不同加载模式下的弹性模量和泊松比变化关系，发现单轴压缩下，硬岩的弹性模量随载荷变化先增大而后趋于稳定，当载荷超过单轴抗压强度的80%时又变小；而单轴拉伸下，硬岩的弹性模量初始较大，随后随着载荷增大而逐渐减小。单轴压缩下2种岩石的泊松比为0.2～0.3，而单轴拉伸下岩石的泊松比很小，几乎可以忽略。比较2种岩石的破坏角、内摩擦角以及黏聚力，讨论2种岩石在直接拉压作用下的不同破坏模式。利用三维表面形貌扫描仪对直接拉伸试样的破坏断面进行三维扫描，得到破坏面细观结构图和裂纹面表面粗糙度曲线。

EXPERIMENTAL STUDIES OF MECHANICAL PROPERTIES OF TWO ROCKS UNDER DIRECT COMPRESSION AND TENSION

Uniaxial tests are carried out on two types of hard and soft rocks by using Instron 1342 hydro-servo- controlled machine,including uniaxial compression tests and direct tensile tests. The mechanical properties of these two rocks are obtained. The uniaxial compression strength(UCS) and the uniaxial tensile strength of the two rocks are compared. Both the axial strain and the lateral strain of the specimens are logged during the tests;and the acoustic emission(AE) of the specimens is monitored by the AE sensor. The stress-strain curves and the AE counts rate curves of the two rocks are obtained under direct compression and tension. The AE characteristics of the two rocks are studied. It is found that under direct tension there are almost none of AE events during the loading process until close to the final failure. The variations of elastic modulus and the Poisson's ratio with the applied loads are compared between the two rocks. It shows that under compression,the initial elastic modulus of hard rock is relatively small at the beginning stage and then increases to a stable value when the stress is within its 80% of UCS;and then it decreases until the final failure. By contrast,under tension,the elastic modulus of hard rock is relatively large at the beginning stage and then decreases with loading. The Poisson's ratios of the two rocks are both ranged from 0.2 to 0.3 under compression;but it becomes very small and can be neglected under tension. The fracture angles,the internal friction angles and the cohesions of the two rocks are compared;and the failure modes of the rock specimens are discussed. Finally,the tensile fractures of typical rock specimens are measured by a 3D surface measurement machine. The microstructure and the roughness profile of the tensile fractures are obtained.