Research On Water Pressure On Lining And The Stress Characteristics Of Lining Structure Of Subsea Tunnel

Water inflow and water pressure at the lining back of the subsea tunnel is the main problem that the designer of subsea tunnel cares for. Based on thorough analysis of existing research achievements, using model test combined with theoretical analysis, spot test and measure and numerical calculation, the distribution of water pressure at lining back and the stress characteristics of lining structure of subsea tunnel are systematic studied in this thesis. The main research work is as follows:(1)Based on groundwater mechanics and complex variable methods, the analytical model of the subsea tunnel seepage field is established and the analytical formula for water inflow and water pressure distribution of subsea tunnel in uniform rock are derived. Using the F4 entire strong weathering bursa of Xiamen subsea tunnel as engineering background, the seepage field of subsea tunnel is analyzed. The result shows that the permeability coefficient and thickness of the grouted ring and primary support have great influence on the water pressure at lining back and water inflow. In case of the drainage system blocking up, the water pressure on primary support increases with the actual water inflow decreasing in the construction period. In case of controlled drainage, by strengthening some measures such as grouting, the water pressure on primary support can be reduced to 1/3 of the full hydrostatic pore pressure.(2) Invent the model test framework and loading system which can add rock-mass pressure and water pressure at the same time is invented. Based on similar theory of model test, similar criterion is derived. The model test of subsea tunnel in stress field and seepage field is carried out on the test framework whose prototype is Xiamen subsea tunnel. The similarity scale of the model and prototype is 1:38.8. In the model test the Brag optical fiber sensors are firstly adopted(3)The model test result shows that in case of entire plugging the lining must support the full hydrostatic pore pressure and the water pressure can not be discounted. In case of limited drainage, the drainage system has a great influence on water pressure at lining back. Water pressure at lining back has an inverse liner proportion to the controlling water inflow of the subsea tunnel. The effect of water pressure discount is more obvious when the test point is closer to the drainage hole. In seepage field together with stress field, the stress of the liner structure decreases with the drainage increases. The most unfavorable part of the tunnel structure is the inner surface of the invert.. The water pressure is the main load that the tunnel structure sustains. (4) The lining water pressure distribution and the strain of the lining have been studied with different proof-drainage patterns:half covered waterproof board and whole covered waterproof board through model test. The research reveals that the lining water pressure does not be influenced much when covered waterproof board changed from fully covered to half covered. In circumstance of drainage, when the half covered waterproof board style is adopted, the stress distribution of the stress on the lining will be more equitable and even, and the stress concentration on near the invert will be improved. In consideration of that the water pressure is the main load that the tunnel structure sustains, the water proof style of half covered waterproof board should be widely adopted in subsea tunnel.(5)By model test and numerical calculation method the seepage field of Xiamen subsea tunnel is studied. Stress-seepage coupled numerical analysis is carried out to the F4 entire strong weathering bursa of Xiamen subsea tunnel. The emphasis of research is put on the security of the primary support in the construction period. The result shows that by strengthening some measures such as grouting, the primary support has a high security coefficient.(6)The waterproof and drainage system of Xiamen subsea tunnel is recommended Xiamen subsea tunnel adopt the principle of controlled drainage to deal with groundwater. The waterproof layer is half-pack style. The primary support supports the load in the construction period which is 1/3 of the full hydrostatic pore pressure and all the surrounding rock-mass pressure. The water inflow controlling criteria of Xiamen subsea tunnel is put forward. The water inflow in soft rock section in Xiamen Subsea Tunnel Should be less than 0.25m3/m. The surrounding rock-mass pressure, water pressure behind the primary support and the stress of steel arching supporter is measured on the construction spot. The changing law of water pressure and rock pressure along with excavation in the construction period is obtained. Backfill grouting at the back of primary suppot and waterproof grouting are the important measure to reduce the water pressure on the lining in subsea tunnel.The above research has expounded the problem of water pressure at lining back by the large. Part of the research achievement has been directly applied in Xiamen subsea tunnel project.