Discontinuous deformation of surrounding rock for small-space tunnel with super-large section in jointed rock mass

Due to insufficiency of the existing specifications and lack of experience in design and construction, the stability of the surrounding rock, deformation characteristics and optimization of supporting schemes of middle rock pillar for small-space tunnels in jointed rock mass are still a tough problem encountered during the construction of tunnels with super-large section. Based on the Daling tunnel of ring expressway in Jinan, the actual distribution information and the related probability distribution model for joints and fractures are obtained. Then lots of random numbers that obey the probabilistical distribution models for these evaluation indexes can be produced by the Monte Carlo method, and the corresponding random rating-values of these evaluation indexes are also gained. The distribution probability affiliated with different rock mass levels can be attained through the inductive statistics, and the robust evaluation of the surrounding rock classification is carried out. Moreover, an improved discontinuous deformation analysis method is adopted to simulate the deformation failure mechanism and fracture evolution process of the surrounding rock in Daling tunnel with small space. Taking the crack propagation zone as the estimate basis for the stability of the middle rock pillar, the comparative analysis of surrounding rock stability with or without anchor supports is carried out. The results reveal that the excavation of the following tunnel hole has an influence on the crack extension and deformation of the advanced tunnel hole (but less obvious), and the anchor bolting can significantly restrict the crack extension and penetration of the surrounding rock, especially for the middle rock pillar. Under the anchor supports, the crack extension situation and deformation failure characteristics of the advanced tunnel hole with secondary disturbance are almost indistinguishable from those of single-hole excavation only, and there is little difference of the controlling effect on