煤矿区现场地勘岩芯直接用作抗压强度实验岩芯的几何效应研究

Experimental Study on Geometry Effects about Geological Exploration Core Directly Used for Mechanical Experiment in Coal Mining Area

对现场所取岩芯进行力学分析是确定和评价其工程性质的重要途径和手段;但对于一些整体性和强度较差以及裂隙或层理发育的岩层,将现场钻取的岩芯加工成符合规范的标准岩芯,首先加工难度大;更主要的是二次加工对岩芯扰动大,导致力学实验结果偏差较大。为此,将现场地勘岩芯直接应用于力学实验岩芯,通过抗压强度测试中的尺寸效应和形状效应研究,得出以下结论:1高径比为二比一的非标岩芯测试抗压强度的尺寸效应表明,强度与岩芯直径或体积之间的相关性明显。随几何尺寸的增大近似呈线性递减规律,且强度与直径之间的关系以及强度与体积之间的关系相似度高,这表明用非标岩芯做抗压强度试验是可行的,只需对非标试件所得结果进行修正,即可得到标准试件下的当量强度。2抗压强度的形状效应表明,不同高径比时岩石抗压强度的离散性较大,但也表现出一定的分布规律,总体上随高径比的增大而呈减小趋势,与体积的增大也呈减小趋势。因此,鉴于抗压强度形状效应的离散性,试验中尽可能采用高径比为二的岩芯进行试验,这样所得的结果线性换算后可比性高一些。

Mechanical analyses are important approach to identify and evaluate its engineering properties and means for core field engineering. But as for some poor integrity and poor strength,or crack and bedding rock formations,if the original core is processed into the standard core that is up to specification,first,the processing is difficult,and more important the disturbance is large,these lead to a large deviation about the experimental results.Therefore,the geological cores applied directly to the core mechanics experiment. Through the compressive strength size effect in the test,and the study on the effect of splitting tensile strength test method of shape,the principal conclusions of this analysis are as follows： 1 Based on non-standard core testing compressive strength subjected to the ratio of height to diameter as two to one,the size effects show the correlation between strength and core diameter or volume is obvious. With the increase of the law of diminishing size is approximately linear,and the relation between the strength and the diameter and strength and volume of high similarity. These indicate that the non-standard core for compressive strength tests are feasible,only a result to correct the non-standard test can be obtained under the condition of equivalent strength standard test; 2 Based on the different ratio of height to diameter of Brazil disk subjected to split method for indirect testing tensile strength,the shape effects show that,the discreteness is obvious with the splitting method of indirect measurement of the tensile strength and the disc size. But it also shows a certain distribution,overall,with the ratio of height to diameter increases and decreases,and the increase of volume also showed a trend of decrease. Therefore,due to the discrete nature of tensile strength and shape effect,is used in the test specification size strength test as much as possible. If there are difficult to get the standard core,the non-standard also can be used for test,but the error must be corrected.