In this paper, we have carried out the permeability tests for rock joints under the shear process and have discussed the influence of the joint surface roughness and the material properties on the permeable character of rock joints. Based on the experimental results, it has been found that the permeability of rock joints is strongly affected by both the aperture and the joint surface roughness. In particular, it is thought that the flow path along the rock joint is determined by the contact condition of the joint surface roughness. Based on the shear mechanical model for rock joints [1], [2], we have carried out simulations for the permeability of rock joints. In this paper, we have applied two kinds of simulation methods, namely, the discrete cubic law model and the two-dimensional flow model. The channeling flow can be expressed in consideration of the various types of joint surface roughness.
1. INTRODUCTION
In order to estimate the stability and the performance of underground structures, nuclear waste disposal facilities in particular, and CO2 geosequestrations, etc., we must grasp not only the mechanical behavior, but also the hydro-mechanical behavior in the subsurface. In jointed rock masses, both the mechanical behavior and hydro-mechanical behavior are strongly controlled by rock fractures and/or rock joints [3]. In order to grasp the permeability of single rock joints under the shear process, in consideration of the geometrical properties, permeability tests on rock joints have been carried out under the direct shear process. Moreover, by applying the shear mechanical model [1], [2] to rock joints, the shear behavior and the variation shapes of joint surface roughness on rock joints have been clarified. Using the geometry of the joint surface roughness and the aperture distributions through the shear mechanical model, two kinds of flow simulations, that is the discrete cubic law model and the two-dimensional flow model, have been applied. Comparing the experimental results with the numerical simulations, the hydro-mechanical behavior of rock joints has been discussed.
2. EXPERIMENTS
In this study, direct shear tests and permeability tests are simultaneously conducted in consideration of the joint surface roughness and the material properties under constant normal confining conditions. The shear behavior and the permeable properties of rock joints are then discussed.
2.1. Specimens
In order to investigate the influence of the joint surface roughness and the material properties, artificial specimens are employed in this research work. After choosing three kinds of natural joint surface roughness, impressions are made of them. Using the impressions, reproduced plaster specimens are then created. The artificial specimens used in this research are rectangular, and each has a length of 80 mm along the shear direction at the cross section, a width of 120 mm, and a height of 120 mm. Every specimen contains a single joint, located at the center (lengthwise) of the specimen, and is approximately aligned on the horizontal plane.
Before and after performing the tests, measurements of the joint surface roughness are taken with a roughness profiler [4]. Each kind of joint surface roughness is measured at intervals of 0.25 mm.
