A Study on the Mechanical Properties, Temperature, and Stresses of Rock Near a Deep Tunnel
Dr. Yii-Wen Pan
|Keywords:||岩石力學性質;高溫高壓;隧道;地溫梯度;熱應力;三軸試驗;mechanical properties of rock;high temperature and high pressure;tunnel;geothermal gradient;thermal stress;triaxial test;FLAC|
Engineering projects of deep tunnels may involve site conditions of a large overburden. As the overburden depth increases, both the temperature and pressure tend to elevate. This research aims to (1) study the mechanical properties of rock at elevated pressure and temperature, and (2) to explore the approach for estimating the temperature and stress distribution in rock mass near an excavated tunnel before and after ventilation. The study carried out a series triaxial compression tests on specimens of slate and marble at elevated temperatures and confining pressures (5~40MPa). The results of these tests indicate that (1) these specimens exhibit brittle behavior at elevated temperature range from 25~100℃; (2) the influence of the random variation and disturbance of the sample is greater than the influence of temperature (range: 25~100℃). In general, the rock strength increases with increasing confining pressure, and decreases with increasing temperature. The thermal expansion coefficient of the specimens lies within 4~9×10-5(1/℃) . The study makes use of the numerical methods to study the temperature and stress distribution in rock mass near an excavated tunnel before and after ventilation. First, the initial distribution of temperature around a tunnel is estimated on the basis of steady-state thermal analysis. Ventilation following an excavation is then modeled by specifying temperature boundary conditions along the tunnel surface. Distribution of temperature and stress-state near the excavated tunnel is calculated and analyzed. From the result of the numerical study, the following is found. In principle, the ventilation may result in higher overall unstability of the rock-mass near the excavated tunnel. Condition of tensile failure due to thermal stress in the rock-mass near the excavation face is possible. The calculated result shows that the thermal stress in the shotcrete is not very significant.
|Appears in Collections:||Thesis|