Influence of Sample Height-to-Width Ratios on Failure Mode for Rectangular Prism Samples of Hard Rock Loaded In Uniaxial Compression
Influence of Sample Height-to-Width Ratios on Failure Mode for Rectangular Prism Samples of Hard Rock Loaded In Uniaxial Compression
复制标题
试件高宽比对单轴压缩硬岩矩形棱柱试件破坏模式的影响
DOI：
10.1007/s00603-010-0127-0
复制
发表时间：
2011-05-01
影响因子：
6.2
通讯作者：
Li, Xibing
中科院分区：
文献类型：
--
作者：
Li, Diyuan;Li, Charlie C.;Li, Xibing
地表平行剥落是地下高应力硬岩中常见的一种破坏模式。本文介绍了不同试样高宽比下硬岩板裂破坏的试验研究结果。本研究的主要目的是找出在单轴压缩条件下产生板裂破坏的条件，并在实验室中确定硬岩的板裂强度。采用五组花岗岩试件进行了单轴压缩试验。在圆柱形和巴西圆盘状试样上测量了来自挪威Iddefjord花岗岩样品的力学参数。采用矩形棱柱试样研究了失效模式的转变。通过分析外加应力、应变与声发射之间的关系，确定了试样板状裂纹的萌生和扩展过程。确定的应力阈值与其他作者报告的裂纹萌生和脆性破坏进行了比较。观察到，在单轴压缩条件下，当高宽比降至0.5时，棱镜试件的宏观破坏模式由剪切转变为裂裂。当侧向应变偏离其线性时，微σ1平行断裂开始。板裂断口与加载方向近似平行。室内试验表明，硬岩的抗剪强度（σsl）约为其单轴抗压强度的60%。这意味着当地下开挖周围的最大切向应力达到劈裂阈值附近时，开挖边界可能发生劈裂断裂。因此，制止或消除剥落破坏的最佳途径是控制开挖边界，避免大的应力集中，使最大切向应力在剥落阈值以下。
Surface-parallel slabbing is a failure mode often observed in highly stressed hard rocks in underground excavations. This paper presents the results of experimental studies on slabbing failure of hard rock with different sample height-to-width ratios. The main purpose of this study was to find out the condition to create slabbing failure under uniaxial compression and to determine the slabbing strength of hard rock in the laboratory. Uniaxial compression tests were carried out using five groups of granite specimens. The mechanical parameters of the sample rock, Iddefjord granite from Norway, were measured on the cylindrical and Brazilian disc specimens. The transition of the failure mode was studied using rectangular prism specimens. The initiation and the propagation of slabbing fractures in specimens were identified by examining the relationship among the applied stress, strain and the acoustic emission. The stress thresholds identified were compared to those reported by other authors for crack initiation and brittle failure. It is observed that the macro failure mode will be transformed from shear to slabbing when the height/width ratio is reduced to 0.5 in the prism specimens under uniaxial compression. Microσ1-parallel fractures initiate when the lateral strain departs from its linearity. Slabbing fractures are approximately parallel to the loading direction. Labotatory tests show that the slabbing strength (σsl) of hard rock is about 60% of its uniaxial compression strength. It means that if the maximum tangential stress surrounding an underground excavation reaches about the slabbing threshold, slabbing fractures may take place on the boundary of the excavation. Therefore, the best way to stop or eliminate slabbing failure is to control the excavation boundary to avoid the big stress concentration, so that the maximum tangential stress could be under the slabbing threshold.