Research On Optimization Of Section Form Selection And Reliability Analysis Of Support Structures Of Tunnel On High-class Highway

With the construction of the west of our country developing at top speed and the need of construction of mountainous expressway, the tunnel engineering, especially the tunnels on the mountainous expressway, will be increased. If the design of support structures of the tunnel still adopts traditional design methods, it will be difficult to give full considerations for the reasonability in economy of the sections of the support structures and for the reliability of bearing capacity and stability of the support structures. The safety coefficients are generally bigger than those of the standard. Thus the goal of "optimum design" will not be reached.Considering that the characteristics of our country's highway tunnels are always of long spans, tabular and of various geometry, by means of thorough analysis of the different problems existed in the design of support structures of the tunnels at present, this paper pays special attention to the two key problems, optimization method of form selection of structural section of the tunnel as well as the stability and bearing capacity of the support structures, in the design of the long and large tunnel on high-class highway, introduces the simplified complex-form optimum method in the structure optimization theory, discusses the optimum design model of lining section of highway tunnel with satisfying demands in building clearance, ventilation and load conditions, puts forward an optimization method of form selection of three different kinds of lining sectional forms (i.e. single-center circle, three-center tabular circle and three-center sharp circle), establishes a complete set of systematic optimum design theory and method of long and large tunnel on high-class highway, develops the corresponding computer software used on the planned Xuefeng Mountain Highway Tunnel on Shaoyang to Huaihua Expressway in Hunan Province for optimization of form selections of the structural sections, and obtains a series of relatively reasonable structural design parameters.Besides, this paper adopts the Random Finite Element Method, uses geometric and physical mechanical parameters that are relevant to liningweight of surrounding rock, coefficient of lateral pressure, height or buried depth of vertical loading, elastic resistance coefficients of surrounding rock, elastic modulus of support structure, unit weight of concrete, thickness of the structure as well as torsional strength and compression strength of concrete and etc., as random variables, applies the Monte-Carlo Method to sampling by computer, preliminarily evaluates the reliability of bearing capacity and stability of molded concrete lining of the Xuefeng Mountain Tunnel, and obtains the related displacement of the lining, mean value and variance of internal force, and computed the reliability index of lining structures.The research results and the developed computer software in this paper can provide guiding references and be used as an auxiliary tool for the follow-up design and construction of the Xuefeng Mountain Tunnel, and for the design and construction of other projects of the similar kind.