Laboratory Investigation on Geometric Characteristics of Different Rough Fractured Specimens Under the Normal Stress

Chen, Yuedu (Taiyuan University of Technology) | Liang, Weiguo (Taiyuan University of Technology) | Lian, Haojie (Taiyuan University of Technology) | Yang, Jianfeng (Taiyuan University of Technology) | Xiao, Ning (Taiyuan University of Technology)

OnePetro 

ABSTRACT: The hydraulic and mechanical behaviors of a rough fracture largely depended on the fracture geometries formed between two rough surfaces, especially for deformable fractures under the normal stress. To investigate the variations of fracture geometric characteristics with normal stresses, a total of six fractured rock specimens, including cubic cement and cylindrical sandstone specimens with different grain sizes, were chosen to conduct the normal compression tests. The 3D scanner was used to capture the surface characteristics of the rough fracture, and the point-cloud data matching method was adopted to calculate the fracture apertures distribution variation with increasing normal stress. Then, the geometric characteristics of the fracture, including the areas of distributions of the contact and interconnected void, and the size of apertures of the interconnected voids, were determined. Test results shows that the required normal stress to achieve the maximum facture closure are different for various specimens, which are largely related to the joint compression strength and the matching degree between two surfaces. Besides, the distribution of the void and contact regions shows heterogeneous under different normal stress, and the frequency of apertures variation approximately follows a normal distribution function. With the increase of the normal stress, the contact area ratio shows a rapid increase at low stress and then tend to stable at higher level, while the variation of the interconnected void area ratio is just the opposite. Meanwhile, both the effective mechanical and mechanical aperture show rapid decrease at low stress and then tend to stable at high stress,. The gap between these two apertures are larger for high normal stress than for low normal stress, mainly due to the rapid increase of the isolated void spaces at high stresses. The test results is helpful to the knowledge of the hydro-mechanical behavior of the rough fracture.

1. INTRODUCTION

The mechanical and hydraulic behaviors of the rock mass largely depended on that of fractures or joints in them, which gained wide attention in various underground geotechnical engineering, including CO2 geological sequestration (Noiriel et al., 2013; Radilla et al., 2013), hydraulic fracturing for exploiting shale gas (Chen et al., 2015) and geothermal extraction. However, the natural joints are intrinsically heterogeneous and easily modified by natural and human activities (Pyrak-Nolte and Nolte, 2016), which in turn affect the coupled hydro-mechanical behaviors. Thus, an adequate knowledge of the geometric characteristics evolution in deformable rough fractures is necessary to understand the mechanical and hydraulic behaviors of the fractured rock mass.

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