Study On Construction Mechanical Behavior Of Zhongliangshan In-situ Expansion Tunnel

Since the 21st century,transportation construction in our country has made rapid development,especially the construction of highway,the scale of construction is constantly expanding.In some densely populated big cities or huge traffic highway,the transport capacity of the tunnel has become the bottleneck of restricting the traffic.Because of the increasingly serious traffic problems,reconstruction of existing tunnels so as to meet the needs of transportation,has gradually become a hotspot in research of tunnel engineering.Based on the reconstruction project of Zhongliangshan Tunnel in Chongqing,with two-lane tunnel expand into four-lane tunnel as the background,this paper uses the method of theoretical analysis and numerical simulation,focusing on the tunnel reconstruction and expansion type,the excavation methods of in-situ expansion tunnel,the mechanical response of surrounding rock and supporting structure in construction process,the reasonable blasting method for in-situ expansion tunnel,etc.The main research contents and results are as follows:This paper briefly introduces the basic principle of the approaching construction and put forward six types about how to expand twin bore four-lane tunnel into eight-lane tunnel,and then select the suitable expansion plan according to the actual condition of the project by comparing:expanding the left existing tunnel into four-lane tunnel and build a two-lane tunnel on the right side of the right existing tunnel.In order to select the reasonable excavation method of the in-situ expansion tunnel,this paper studied the stress and deformation law of surrounding rock and supporting structure under different construction methods,different sequence and different excavation height.The research results show that the stress of surrounding rock and supporting structure is the most favorable when using the method of benching tunnelling,vertical excavation construction and the first heading excavation height is 0.6H,so this method is the most suitable method for the excavation of the tunnel in Zhongliangshan.According to the selection of reasonable excavation method,this paper simulated a three-dimensional construction process of the tunnels and then studied the stress and deformation law of surrounding rock and supporting structure in the process of tunnel construction,the influence of tunnel excavation on existing tunnel.The research results show that the displacement of the left side of the tunnel caused by the tunnel excavation is obviously larger than that of the right side and the whole tunnel showed obvious bias state.The risk coefficient of the surrounding rock of the tunnel arch foot and arch waist is l,that is,the surrounding rock has yielded,construction unit should pay attention to this.Both the displacement and the stress increment of the existing tunnel due to tunnel expansion does not exceed its maximum thresholds,so the tunnel excavation has little influence on existing tunnel.Two kinds of blasting methods were simulated by the finite element software of dynamic analysis in this paper,then analyses the propagation and attenuation law of blasting vibration velocity and stress,discusses and compares their advantages and disadvantages,the conclusion is that temporary reinforcement measures should be taken on existing tunnel at first,and then use the second scheme,that is,the method simultaneous blasting of surrounding rock and tunnel lining is the most suitable blasting method for this project.