STUDY ON FORECASTING AND EVALUATION OF OVERBREAK IN DOUBLE-ARCH TUNNELS OF HIGHWAY

The geological characteristics of discontinuity plane of Hongfeng doubled arch tunnel in Jinhua— Lishui—Wenzhou highway are investigated and analyzed to obtain the characteristic parameters.Based on discontinuity plane mapping theory and keyblock theory,the overbreak of doubled arch tunnel is forecasted by using the analytical discontinuity plane characteristic parameters.At the same time,the appearance probability and the location of overbreak block in doubled arch tunnel are forecasted.The result shows that the overbreak location of doubled arch tunnel is located mainly in the connection between tunnel and middle guide tunnel.Under the condition of good connectivity of discontinuity,a great quantity of overbreak on side wall may occur.The forecasting and in-situ excavation are contrasted,and the causes of overbreak are analyzed.The good coincidence of forecasting and excavation offers a theoretical basis for the excavation of doubled arch tunnel reasonably.