Analysis On The Tensile Characteristic Test And Thermo-Hydro-Mechanics Coupling Of The Freeze-thaw Rock

In order to prevent the freeze-thaw disaster scientifically and service to the construction of western development, according to the ever-increasing geotechnical engineering demands in cold regions, the freeze-thaw damage propagated mechanical character of rock is analyzed based on experimental research. On the background of rock tunnel engineering in cold regions, the multi-field coupling of surrounding problem is numerically simulated by adopting the finite element method, and the important theoretical basis is provided for the engineering construction in cold regions.The standard samples of red sandstone and shale were used to take the freeze-thaw experiments under the opening moisture saturation condition (the variation range of freeze-thaw temperature is-20℃～+20℃). The freeze damage deterioration process and freeze destruction behavior are recorded, the freeze resistance to freeze-thaw is analyzed. The splitting tensile experiments are conducted from the two types of rock on different freeze-thaw cycles (5,10,20,40,60,100times) and before freeze, the effects of lithology and freeze-thaw cycle function to the rock damage and anti-tensile character are analyzed. The results show that, the deterioration modes of freeze-thaw damage of red sandstone are spalling mode and fracture mode, while that of shale is crack mode. The resistance to freeze-thaw of red sandstone is poorer than that of shale. Both of the splitting tensile strength and elastic modulus decrease with the number of the freeze-thaw cycles increases, but the damage of red sandstone is more serious. The freeze-thaw effect of anti-compression and tensile characters for the two rocks are identical, but the anti-tensile character is more sensitive to freeze-thaw cycle, the damage deterioration more obviously. The road tunnel of Daban Mountain in Qinghai province is taken as analysis object, the single-seepage, temperature and stress fields of tunnel in cold region are studied by numerical simulation, the pore pressure, frost depth and stress distribution are analyzed. The multi-field coupling problem of rock tunnel within an open system is researched by numerical simulation, the mutual influence and varied laws of temperature, seepage and stress fields of the surrounding rock are analyzed. The results show that, tunnel walls near the ground are easier affected by the temperature changes and open ventilated convection, and the temperature, displacement and stress changes obviously. Under the three fields coupling, the frost depth of tunnel surrounding rock, displacement and stress value are increased with the time goes by. It is shown that during the rock tunnel design and construction in cold regions, the interaction among the temperature, moisture and stress fields and the effect of frost heaving force to the structure should be considered. In order to decrease tunnel disaster in cold region, the suitable heat preservation measures are taken in tunnel opening and inner wall to reduce the heat exchange between air temperature inside and outside the tunnel and surrounding rock.