Study On The Mechanical Properties Of Underwater Tunnel Considering Fluid-Structure Interaction

In recent years, our country has constructed a large number of underwater tunnels in the construction of railway and highway engineering, by the end of 2013, China has built more than ten thousand kilometers of various underwater tunnels. In the construction of underwater tunnel, the thickness of the minimum covering layer has an important influence on the construction of the method、engineering cost and the stability of the tunnel. This paper takes crossing yellow tunnel engineering from Ying Men beach to Ma beach of Lanzhou city track traffic line 1 as the background, through numerical calculating and empirical formula estimating combined with the engineering practice to identify the minimum thickness of covering layer of the project, on this basis, simulation analyzing the distribution rule and characteristic of the stress field, displacement field and seepage field. The main research results are as follows:(1) Using the subsea tunnel empirical formula of Japan, Norway experience curve and domestic top water coal mining experience formula to respectively calculate the minimum thickness of covering layer of crossing yellow tunnel in the Lanzhou city track traffic line 1; A finite element analysis model is established and simulation analyzing the distribution characteristics of tunnel seepage field under the condition of the overlay thickness respectively as 18.1m, 19.1m, 20.1m, 21.1m, 22.1m, 23.1m and 24.1m. On this basis, determining that the minimum covering layer thickness of crossing Yellow tunnel is 22.1m combined with engineering practice.(2) Establishing the finite element analysis model of fluid-structure interaction, simulation analyzing the distribution rule of tunnel seepage field、displacement field and stress field. The research results indicates that:(1) In seepage field: Before the excavation of the tunnel, the pore water pressure from top to bottom increasing successively and the distribution is layered, after digging the pore water pressure from top to bottom increasing in turn and the distribution is funnel shaped and along with the increase of excavation footage, the pore water pressure decreases.(2) In displacement field: the increment of the horizontal displacement and vertical displacement gradually decreases and tends to be stable with the tunnel excavation footage continues to advance. Overall, the key points of the horizontal displacement and vertical displacement values are relatively small.(3) In stress field: Before the tunnel excavation, the vertical effective stress and horizontal effective stress appear symmetrical distribution in the direction of right and left; After the excavation of tunnel, the maximum vertical effective stress value surrounding rock mass is symmetric distribution in the crown above; At the crown and the arch waist on both sides level of effective stress value is the largest, with the increase of the tunnel excavation footage, maximum value distribution decreases gradually.(3) Selecting shield segment structure in the vault, the arch waist on both sides and the arch bottom these 4 key points, analyzing the mechanical characteristics of the tunnel, the research results shows that:(1) The vertical displacement of each key point decreases along with the increase of excavation footage; The vertical displacement at the key point of the vault is maximum, and it is minimum at the key point of the arch waist on both sides;(2) The horizontal displacement of each key point decreases along with the increase of the excavation footage; The horizontal displacement at the key point of the arch waist is maximum and appears symmetrical distribution, and it is minimum at the key point of the arch bottom;(3) The vertical effective stress of each key point increases along with the increase of excavation footage. The maximum effective stress is in the arch, and the minimum is in the arch waist on both sides;(4) The horizontal effective stress of each key point increases along with the increase of excavation footage, the maximum is in the arch waist, the minimum is in the arch bottom; Overall, the displacement and stress values of all the key points are small.