Study Of Construction Mechanics Behavior Of Large And Adjacent Unban Tunnel Groups

In order to absorb the sharply-increased population and simultaneously utilize space resources of cities in a reasonable way, cities construction has witnessed a gradual change from on-the-ground to underground. To make use of underground space of cities could decentralize traffic, protect original state, reduce environment pollution, and increase space utilization efficiency. So, the use of underground space has attracted enough attention and underground space are playing strategic role in the process of city development.Based on tunnel group in Hongyan village of Chongqing city, this paper combined investigation, theoretical analysis, numerical simulation and laboratory test to study the stability of rock mass, failure mechanism, support measures and construction mechanics in terms of constructing large-span, high-density complex tunnel group in sandstone and mudstone alternated beds of Chongqing. The main research conclusions and achievements were as follows:1. According to computation principle of strengthen reduction method, fine sand and barite powder were decided as aggregate and paraffin wax as cement by lots of ratio debugging and indoor mechanics test. New strengthen-reduction geotechnical similar material (SRM material) was made. By changing its temperature, its strengthen parameters, c and ?, would reduce in the same speed. Moreover, the material could be made easily with a lower discreteness, and its mechanics parameters could be adjusted by actual demand, which is suitable to simulate rock.2. With the help of self-made intelligent temperature control system, New strengthen-reduction geotechnical similar material was made to achieve tunnel strengthen reduction method by indoor model test. A contrastive analysis of displacement development tendency along with the change of surrounding rock strength and the influence of thermal expansion of similar material to test results was made between the test and numerical simulation. It was general feasible to achieve strengthen reduction method by indoor model test, and it could meet the precision requirement in laboratory model experiment.3. By means of numerical simulation, strengthen reduction method was used to analyze progressive failure mechanism of unsupported tunnels in Hongyan village of Chongqing city and corresponding safety factor in the process of exaction. The paper has put forward that the shared rock was the weakest part in tunnel group and optimized the construction sequence of tunnel group. The lower subway station tunnel should be constructed firstly, and then the upper three-ordinate tunnel should follow.4. According to construction sequence of tunnel group, the stress state of shared rock was distributed into five stages, and detailed analysis was given. The least favorable stress state during construction was pointed out and the important measure to ensure the stability of shared rock was to support it in time so that it was in a plane stress state during construction5. Interaction mechanism between counter-pulled bolts (anchor cable) and shared rock was analyzed by establishing bolts (anchor cable)-surrounding rock coupling model.6. Based on similarity theory for model test, and with the computation principle of strengthen reduction method introduced, similarity relation between actual safety factor and model safety factor was got.7. Indoor model test was used to simulate rock mass of tunnel group in different support conditions and its failure mechanisms were got. It was put forward that the weakest part of tunnel group in different support conditions differed, and it would move along with support conditions.8. The construction process of tunnel group was really simulated by indoor model test, and evolution laws of surrounding rock stress, displacement, and the supporting structure during construction of tunnel group were got.9. Three-dimensional numerical simulation was used to simulate space relationship of tunnel group, geological conditions and surface topography. The simulation completed the part which could not simulated in the indoor model test and made an analysis of evolution law of plastic zone, stress field, displacement field and internal force of secondary lining along with construction of tunnel group, which confirmed the indoor model test to a certain degree.