Mechanism and classification criterion for large deformation of squeezing ground tunnels

Based on a practical project of Wushaoling tunnel,a squeezing ground tunnel with high geostress conditions,the essential characteristics of squeezing ground tunnels were analyzed according to the monitored data.In terms of laboratory tests and in-situ monitoring,the physical and mechanical parameters of surrounding rock were synthetically established and analyzed.The condition for the generation of plastic zone arround tunnels,the influencing factors of plastic zone and displacement of tunnels and the relationship between radius of plastic zone and displacement of tunnel were quantitatively analyzed.Based on the monitored data,theoretical calculation and experience of similar tunnels,considering relative deformation,strength stress ratio,ground stress,elastic ratio and comprehensive coefficient α as classification indexes,the classification criterion and measures to prevent large deformation of squeezing ground tunnels were worked out.