IN-SITU STRESS MEASUREMENT AND ROCKBURST FORECAST ANLYSIS IN XIZHOULING TUNNEL

In order to guide construction and improve the safety and economy of construction,hydro-fracturing stress measurements have been conducted for Xizhouling tunnel of Zhejiang Province.It is found that the most important stress direction is the horizontal direction in the surveyed area.Within the measured depths,the maximum horizontal stress is of 10.57~19.39MPa.This stress level can be classified as middle to high level in this deep-seated tunnel.The dominant direction of the maximum horizontal stress is about N33W.The angle between the direction of the maximum horizontal stress and the direction of the tunnel axis is relatively small for this tunnel,and favorable to the stability of the tunnel and the surrounding rock mass.Based on the in-situ stress results and four distinguished methods( i.e. , Hoek method,Turchaninov method,Russenes method and engineering rock quality classification standard)rockbursts are forecasted during tunnel construction in the deep-seated tunnel conditions.The critical buried depth of rockburst is estimated.The results show that there are high possibilities of occurring weak and moderate rockbursts in this tunnel.The critical buried depth of rockburst is about 397m.In order to avoid the disadvantage conditions,reasonable excavation method and safety precautions should be adopted during the tunnel construction.