In the context of stress field determination for a long tunnel, hydro-fracturing in-situ stress Measurement was conducted in two boreholes drilled in or near faults zones, respectively. Those results obtained in fault zone of cataclasite rock are found in poor consistence with the regional tectonic stress, while other results obtained in the hole near fault zone are found close to the regional stress.
A large number of stress measurement results show that, due to the disturbance superimposition of diagenesis and tectonic movements, the in-situ stress distribution in or near fault zone is very complex. Since large faults are found in many engineering sites, the study on the characteristics of in-situ stress in fault zone is not only an important issue to geoscientists, but also a practical problem faced by geotechnique engineers [1∼3]. In this paper, some results of stress determination by using the hydro-fracturing method for a long tunnel is presented, the stress characteristics and the effect of faults are analyzed on focus of their representative significance of the regional tectonic stress.
A railway tunnel of 12.97 km long is located in middlelow mountainous areas of Fujian Province, in Southeast China. Although no active faults exist in the tunnel site, some large faults are found in ground surface. Four faults are found in the central section of the tunnel with length of 2.5 km, see figure 1∼2. Their depth and thickness of influence zone are of important task of geology survey. The fault zones are found mainly oriented towards Northeast∼Southwest (named as compression or sheared fault zones) and NW∼SE (tensile fault zones). F3, the visible width is between 20 and 60 m, oriented at EW and dipped at about 80° eastward.