| dc.description.abstract | Composite rock mass is a mixture of rocks, composed of geotechnically significant blocks with a bonded matrix of finer texture or rock materials with two kinds of distinct strength and stiffiness. Because of the heterogeneity, anisotropy and complex nature, composite rock mass is a kind of difficult geotechnical material with which to deal in geotechnical engineering. The engineering properties and mechanical behaviors of composite rock mass are mainly influenced by the mechanical properties of composite materials, volumetric fraction of block, preferred block orientation and the anisotropic behaviors of deformation and strength.
The volumetric fraction of block is a general parameter for assessing the overall engineering properties of composite rock mass. By analyzing the crossing length between the block and scanline in representative volume element (RVE), this research represented the discussion on the influence of total length of scanline, diameter of block, volumetric fraction of block, the aspect ratio of block and the preferred block orientation on the volumetric fraction of block measured by scanline. Using the concept of confidence level and confidence interval offers a qualitative and quantitative description of the volumetric fraction.
Furthermore, the main purpose of this research is to investigate the failure strength, deformation properties and mechanical behaviors of composite rock mass from both theorectical and experimental approaches. The preparation technique for artificial composite rock mass which overall mechanical properties are macroscopically isotropic and transversely isotropic is developed. A series of triaxial tests are conducted to investigate the influence of the volumetric fraction, confining pressure, the orientation angle on the composite rock mass. In the experiment carried out, a procedure using a rotary scanner to obtain the “unrolled” images of rock specimens at different stress level during the uniaxial compressive tests is employed. Based on the experimental results, the failure modes of isotropic rock mass and transversely isotropic rock mass are classified.
For theoretical prediction, five micromechanical models are used to predict the Young’s modulus and Poisson’s ratio of isotropic composite rock mass with different block proportions. Comparing the theoretical predictions with test results, the feasibility of using the micromechanical models to predict the mechanical properties of isotropic composite rock mass was investigated. A new failure criterion for the transversely isotropic rocks has been developed and presented. The criterion is based on the maximum axial strain criterion, the constitutive laws of linearly elastic of anisotropic materials and the theory of single plane of weakness. The predictions of the failure strength of various types of transversely isotropic rock masses with different orientation angles and under various confining pressures agree well with experimental data. The accuracy and the versatility of the criterion are demonstrated. | en_US |