Seepage Studies Of Tunnel In Water-enriched Region Based On Fluid-solid Coupling Theory And Complex Analysis

With the continuous development and improvement of her highway networks, China hasbeen seeing a lot of deep mountain tunnels lain in water-enriched regions (WER) since theend of the last century. However, it’s still a challenging technical problem for civil engineersat home and abroad to build tunnel in WER. Particularly, under the current stringentenvironmentally-friendly prerequisite, the conventional philosophy drain firstly should beupdated with stop firstly, drain slightly, which is beneficial to the solution of environmentalproblems.It is of significant application value to investigate the distribution of seepage pressure insurrounding rock, grouted rim, primary support, second lining of deep tunnel, and the effectof seepage state change on lining and surrounding rock, based on percolation mechanics,plastoelasticity and complex function theory. The main researches have been conducted asfollows:(1) The formulas of the seepage flow in corresponding period and the hydraulic pressuredistribution law in secondary lining, primary support, reinforced rim, and surrounding rockshave been conducted, based on polar coordinate seepage analytic principle. The calculationresult of Fang Dou Shan extra long tunnel shows that reinforcement rim and primary supportcan obviously decrease the hydraulic seepage pressure acting on secondary lining, and thegroundwater discharge under drainage conditions; the water forces acting on secondary liningand the seepage discharge decrease sharply at the beginning, by reducing the permeabilitycoefficient and increasing the thickness of reinforcement rim, but when the reinforcementparameters reach to certain values, the groundwater pressure and seepage discharge keepstable regardless of whether the changes of reinforcement parameters are taken; the groundwater pressure behind second lining and primary support increase with the reduction of waterdischarge.(2) Based on structural mechanics method and the Roark’s Formul, the pressure actingon lining is firstly calculated by back-analysis on the field monitored data of vertical crown displacement. According to the example solutions, seepage pressure accounted for50.9%ofall pressure acting on lining.(3) Under axisymmetric conditions, based on the stress component functions with theconsideration of groundwater and the distribution law of water pressure, the stress anddisplacement of elastic and plastic zone in surrounding rocks and lining, the radius of plasticregion and support resisting force are derived. The calculation result shows: the radius ofplastic region, support resisting force and the stress in lining increased significantly due togroundwater seepage pressure.(4) Based on the Fluid-Solid coupling theory, the saturation ling, water head distributionand the velocity change in the designated path are obtained by iterative calculation. Thedistributions laws of stress and displacement in surrounding rock and lining are obtained byfurther coupling calculation. It provides important reference for understanding the effect ofwater-enriched enviroment change on the mechanical property of lining and surrounding rock.According to the accurate seepage field results, seepage-stress coupled analysis are alsoimplemented by changing thermal elements into structural elements, and applying seepageforce to the elements which below the saturation line. The example calculation results shows:the stress and placement distributions in lining and surrounding rocks are changed because ofthe seepage; the larger positions of stress and placement in lining and surrounding rocks, andthe change of maximum principal stress due to water level variation are the regions betweenarch springing and haunch at right side.(5) The mapping function formulas of not supporting and already supporting non-circulartunnels have derived by using the compound-shape optimization method which based onLaurent series. The example calculation results shows: when n=4, the map shape have perfecttally with cavern outline for not supporting tunnel; for already supporting tunnels, theaccuracy reduced when n=4, but it improved when n=8, so the mapping accuracy can beadvanced by increasing the value of n.(6) The formulas of complex stress functions φ(ζ) and ψ(ζ) have been firstly derivedunder the condition that there is a radial uniform water pressure acting at infinity. The stresscondition of any point in surrounding rock can be calculated by complex stress functions. According to the example, the stress of designated points around the tunnel has been obtained.The results shows: the stress at arch springing has the greatest value; vaults second; betweenarch springing and tunnel bottom the lowest. Additional, as a multiply connected domain, thestress calculation of the tunnel with lining and reinforcement rim needs further investigationbecause it is very difficult.