Study On Stability Control Of Construction Of Subsea Tunnels With Large Section In Weak Strata

This dissertation combines the construction process of Xiamen Xiang'an subsea tunnel. Based on the main study course of stability control of the surrounding rock in the shallow shoal and shore, the aim is to maintain the rock self-stability and guide the construction, Contrast of the sedimentation in CRD and CD construction method in weak strata of the shallow shoal and shore; Analysis different sedimentation caused by different step distance and sequence in CRD method; Study on the displacement dividing principle and its use; Numerical simulation of the mechanism of the feet-lock bolt; Study on the effect of distortion control by radial grouting behind the initial shoring in large-section tunnel in weak surrounding rock.Setting up models and caculating for CD and CRD method according to simulating the conditions of the site strata and construction by using numerical simulation, selecting the suitable construction method for large section subsea tunnels based on analyzing and the result comparision, considering intergrational factors include the plan, economic and safety. Based on CRD method, optimizing the construction sequence and step distance, mending the excavation and shoring scheme and control the distortion to the minimum value and conquering the construction difficuilties.Using the displacement dividing principle in Xiamen Xiang'an subsea tunnel. First, selecting target value of the distortion according to numerical caculating. Second, commanding the progress of the distortion of the tunnel and comparing the distortion with the target value. Last, analyzing and finding out the reason of over-distortion and giving the control measures and making sure the adding up distortion value not exceeding the target value.Setting up the analyzing model of the mechanics of the feet-lock bolt by systemic study of the working mechanism of the feet-lock bolt, analyzing the relationship of the top arch sedimentation and the influence factor, optimizing the design and construction method of the feet-lock bolt.Studying the mutational breakage through the stiffness of the initial timbering and the weaken stiffness of the surrounding rock and by setting up the interactional mutation model of the initial timbering and the surrounding rock. And the result of the study explains the mechanism of the reinforcement of the grouting on the back of the initial timbering and giving the key point of the mutation. After the distortion exceeds the key point the surrounding rock will coming into the incompact state. the size of the key point of the distortion is decided by the inner factors—the surrounding wall and the initial timbering and had no relation to out side conditions, so the design and construction of the grouting should be based on the material conditions of the initial timbering and the surrounding rock. The distortion was controlled well tested by the monitoring data.Xiamen Xiang'an subsea tunnel is the beginning of subsea tunnel construction in China. The fruit achieved from the study of the stability control, the site working monitoring and numerical caculatiing will guide the incoming subsea tunnel building.