预留缝宽度对大理岩直剪试验结果的影响

在岩石直剪试验过程中，上下剪切盒（夹具）之间往往需预留一定宽度的缝隙，但预留缝隙的宽度值没有明确的规定。本文采用相同直径、不同高度的大理岩试样进行直剪试验，研究了上下剪切盒预留缝宽度对岩石抗剪强度和破坏特征的影响。试验结果表明：同一法向应力下，随着试验预留缝宽度的增加，试样剪切断裂面的正视图由一条近似直线逐渐变成三段近似直线构成的折线，剪切断裂面由水平曲面逐渐变为倾斜曲面，主导试样破坏的应力由剪应力逐渐变为拉应力；在同一法向应力下，试验预留缝宽度越大，测得的峰值抗剪强度值越小；随着预留缝宽度的增加，直剪试验获得的试样黏聚力整体上呈增加趋势，但变化不大，较为平稳，而内摩擦角则逐渐减小，且变化明显，幅度较大。试验预留缝宽度的取值对试验获得的抗剪强度、黏聚力、内摩擦角均存在影响，因此目前情况下在岩石直剪试验中应尽量减小预留缝宽度，而预留缝宽度的定量取值尚需开展进一步的研究。

Influence of Width of Reserved Gap on Marble Direct Shear Test Results

In the process of rock direct shear test, a gap with a certain width is usually reserved between upper and lower shear boxes (clamps), but the width value of the reserved gap is not clearly specified. In this paper, marble samples with the same diameter and different heights were used for direct shear tests, and the influence of the width of the reserved gap of the upper and lower shear boxes on the shear strength and failure characteristics of the rock was studied. The test results show that under the same normal stress, with the increase of the width of the test reserved gap, the front view of the shear fracture surface of the sample gradually changes from an approximate straight line to a broken line formed by three approximate straight lines, and the shear fracture surface gradually changes from a horizontal curved surface to an inclined curved surface, and the stress that dominates the failure of the sample gradually changes from shear stress to tensile stress. Under the same normal stress, the larger the width of the test reserved gap, the smaller the measured peak shear strength value; With the increase of the width of the reserved gap, the cohesion of the samples obtained by direct shear test shows an increasing trend on the whole, but the change is small and relatively stable, while the angle of internal friction gradually decreases and changes obviously with a larger amplitude. The value of the width of the reserved gap in the test has influence on the shear strength, cohesion and internal friction angle obtained in the test. Therefore, the width of the reserved gap should be reduced as much as possible in the rock direct shear test at present, while the quantitative value of the width of the reserved gap needs further research.