The Study Of Construction Mechanics Of Neighborhood Tunnel With Large Span

It is well known that tunnel construction is a subject much depended on experience, and tunnels have been designed and constructed by experience for a long time. However, as to neighborhood tunnel with large span, there is little experience to be learned, as a result, many problems come into being in its design and construction. Based on Xi'an tunnel in Erguang highway construction- in-progress, the thesis firstly introduces the monitoring measurement and the role of practical methods explicitly, then analyses the displacement of the supporting structure and internal forces from monitoring, and last judges the stability of supporting structure. At the same time, the history and current situation of displacement back analysis is systematically introduced. And based on an actual project, the thesis presents its application in the tunnel project.This thesis firstly summarizes the on-site monitoring methods and the attentions, and then plots the curve through the measured data. From the analyzing of the curves of V level rock surrounding, it indicates that, the excavation of inverted arch will cause big displacement, and it is best to reduce the excavation& enclosed time. To prevent the cave-in, lateral bracing is needed when the groundwater is rich.Secondly, TongJiShuGuang software used for displacement back analysis is briefly introduced. Based on the parameters of rock and support known, as well as the measured data, the parameters of surrounding rock uncertain are back analyzed. Integrating the various steps of the monitoring data and excluding abnormal monitoring data, the parameters are accessed. Each back analysis is based on the corresponding construction step, and the displacement of other construction-step is predicted and compared with the measured displacements. Through multiple back analyses, the parameters are obtained from the average of back analysis results. Two-dimensional excavation model for neighborhood tunnel with large span is established by ANSYS, which using the rock's elastic modulus E₁ and the rock reinforcement ring elastic modulus E₂ from back analysis. The back analysis results are tested through the comparing with the normal computation. In this thesis, the ultimate inversion parameters are consistent with the analysis of the results of the displacement measured in the following step, the back analysis model and displacement back analysis method proved to be reasonable.Finally, the varying of displacement and stress of IV& V level surrounding rock is analyzed. During the excavation of IV level surrounding rock, the vault goes down, the both side walls stretches and the inverted arch rises. And finally, a "U" shaped groove is formed above the tunnel, and an arch shaped is formed between the two tunnels. As to V level surrounding rock, the displacement of surrounding rock above the tunnel is reduced effectively due to the cooperation of temporary steel arc and core soil. When excavating the upper core soil, the displacement of the surrounding rock is very big, and it is best to reinforce the rock at the tunnel crest to avoid cave-in.