Study On Mechanism Of Stratum Displacement Caused By Shallow Tunnels With Large-span Constructed In Intensely Weathered Granite With Abundant Water

With the fast development of the urban underground traffic engineering in China, a lot of new construction problems are coming: on one hand, large-span tunnels emerge in large numbers, but under the condition of the urban environment, the ground settlement should be strictly controlled; on the other hand, based on different geology conditions, different measures should be put forward during the construction. Based on the background of mining excavation of shallow tunnel Xiamen airport road (from Xianyue road to Yanwu bridge), using the methods of theory analysis, soil test, numerical simulation, the actual construction site verification, and so on, this paper aims at the mechanism and controlling of the stratum displacement caused by the large-span and small interval tunnel constructed in the intensely weathered granite with abundant water in southeast coastal areas of China, which is seldom reported in literature of domestic and foreign. It not only successfully directed the construction, but also can be applied in the following project. Through a comprehensive technology research, acquired research results are as follow:Firstly, by analyzing the stratum structure of the mining excavation of shallow tunnels' overlay earth, point out that studying on the mechanics character of the stratum is the premise for controlling the displacement; the core is to give binding force for the excavated area and give pre-binding force for the break area before the palm faces.Secondly, study on the mechanics of the intensely weathered granite. The results show that the shear strength of the specimens was low. If the water content was lower than 14%, the cohesive strength was high and the angle of internal friction was very low; as the water content increasing to the plastic limit (19%-20%), the cohesive strength was increased obviously and the angle of internal friction was changed a little; when the water content was higher than the plastic limit, the angle of internal friction reduced rapidly because the inside pore was thread together. The specimens'collapse process can be divided into three stages: slowly peeled off,piecemeal collapsed and monolithicly collapsed; and at last, analyzed the mechanism and measures of controlling the abundant water and reinforcing the intensely weathered granite.Thirdly, study on ground sinking which is caused by different ways of construction by using numerical simulation. Point out that if the small interval tunnel constructed by CRD (center cross diagram) method, compared with solely excavated the two tunnels, excavated both the lift and right sides pilot headings which were far from the rock pillar between small interval tunnels at the same time cause a little greater ground sinking, but as long as the tunnel is supported properly, the settlement can still be controlled in scope permitted, and it can also obviously speed up the construction.Fourthly, analysis the spatial effects when excavating the tunnels through 3-D finite element calculation. Full-cross-section grouting can not only control the stability of the palm faces, but also obviously reduced the ground sink, and it also confirm the results of the theory analysis.