A true triaxial apparatus which is composed of three sub-devices is presented. This apparatus allows for investigations on deformation and seepage behaviors of a single rock fracture subjected to lateral stress, as well as under normal stress. The first device has three jacks which can apply loads independently in three orthogonal directions. The second device is used to supply water inflow, control seepage pressure and measure flow velocity in real time. The last device is for measuring the normal deformation of rock fractures. Four strain gauges are symmetrically embedded into the rock sample, connected with a data acquisition instrument. After the presentation of the true triaxial experimental apparatus, some tests for investigating normal deformation behaviors of rock fractures subjected to normal and lateral loads, adopting hard granite specimens with an artificial persistent fracture, are introduced. The results show that the aperture of rock fractures is influenced not only by the normal stress but also by lateral stresses. The aperture decreases with increasing the normal stress but increases as the lateral stress rises and obeys an exponential relationship with both normal stress and lateral stresses. Further studies on normal deformation behaviors of rock fractures considering mechanical and geometrical parameters and stress, and deformation and seepage coupling properties subjected to triaxial loads are in progress.


Seepage and stress fields coupling of jointed rock masses in many geotechnical situations such as water conservation, hydropower, high-lever radioactive waste disposal, oil reposition and slope engineering, has attracted concentrated attention. Since a rock fracture is the weakest part of rock masses, it is extremely important to investigate stress, deformation and seepage coupling properties of a single fracture to study the hydro-mechanical law of jointed rock mass. Many researchers (Snow 1968; Gangi 1978; Witherspoon et al. 1980; Barton et al. 1985; Tsang 1987; Liu 1987; Su et al. 1997; Chen et al. 2000) have made significant contributions to the understanding of this problem. However, most investigations have mainly focused on the aspect of seepage and normal stress coupling. Actually, rock masses always lie in a condition of 3D stresses. Accordingly, it is significant to study seepage properties of rock fractures under 3D stresses. Limited investigations in this field are documented in literature. Zhang et al. (1997) and Zeng et al. (2005) studied flow of rock fractures under different stress conditions and pointed out that the flow velocity diminishes as the normal stress increases, but rises with increasing lateral stress. Zhao et al. (1999) developed an empirical equation to calculate hydraulic conductivity subjected to triaxial stresses. These investigations were performed by general triaxial experimental tests. Although they greatly promoted studies on the seepage characteristics of rock fractures subjected to 3D stresses, much more researches are necessary to obtain robust theories, especially in the area of true triaxial hydro-mechanical properties.

In this paper, a true triaxial device (RPT-3D) designed for studying stress, deformation and seepage properties of rock fractures.

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