Sensitivity Analysis On Selection Of Construction Method For Twin-arch Tunnel

With the rapid development of highway since 1990s, there have been increasing numbers of road tunnels in our country. Due to the limitation of separate tunnel line in some special geological and topographic condition, more and more twin-arch tunnels are adopted, which take advantage of smooth line type and small floor space bring about fruitful economic and social benefits.On the basis of Lishi twin-arch Tunnel, three 2D Elastic-Plastic Finite-Element Models of tunnels are separately established from the three aspects: rock classification ,buried depth and span by means of large-scale Finite Element Software ANSYS. Stress and displacement is attained through the whole process simulation of full section excavation, central drift benching method and three drift method. Contrastive analysis on stress and strain of characteristic nodes on vault crown, haunch and arch bottom with the three different excavation method is made to discuss sensitivity of construction method about twin-arch tunnel. The main conclusion is as following:â‘ Stress and displacement of nodes on vault crown, haunch and arch bottom is got from simulation of the whole constructed process of tunnels which go through I~V class surrounding rock. The result of contrastive analysis indicates that the lower rock class is, the more sensitive stress and placement correspond to construction method is. It can be seen that, the constructed method is more important when the surrounding rock is weak.â‘¡Stress and displacement of characteristic nodes is got form numerical Simulation of the whole constructed process of tunnels with three different excavation method which are separately buried 30m, 50m and 100m beneath the ground. The analysis indicates that, within a certain buried depth range, with the buried depth increasing, the choice of construction method is more sensitive.â‘¢Stress and displacement of characteristic nodes on vault crown, haunch and arch bottom is got through the whole construction process simulation of three different span tunnels, two-lane, three-lane and four-lane, with three different excavation method. The variations of stress and displacement can be seen from the result of contrastive analysis. From the analysis of haunch stress and vault crown displacement, to some extent, with the span and sensitivity of tunnels increasing, choice of construction method should be more cautious.