Study On Constructional Mechanical Responses Of Highway Tunnel With Deeply-lying And Large Cross Section

Based on the key project of the National Natural Science Foundation"The Stability and Reliability Engineering of the Tunnel and the Underground Space Structure"and the key project of Chongqing technologies R&D program"Key Technology Research and Demonstration Project of Large-span Tunnel Construction", the paper focuses on the study of mechanical responses and the instability mechanism of tunnel with deep-lying and large cross section with the methods of theories analysis, model test of equivalent material, numerical simulation and field measurement. The main research is as follows:The methods of researching tunnel construction mechanics and the stability of tunnel surrounding rock and the current method of constructing tunnel with lager cross section are systematically studied, and the distributing regularity of initial earth stress field of rock and the basic mechanical characteristics of tunnel with lager cross section are discussed.Consulting the typical demonstration projects, based on the indoor rock mechanics testing, ratio experimental of similar materials, and through the physical model experiment of large section tunnel excavation process by the large-scale geotechnical engineering model test machine, the paper gets the distribution state of the second stress field and the failure character of the surrounding rock of the deep-lying and large section buried heights stress rock tunnel construction.The paper analyzes the mechanical responses of the tunnel with deep-lying and large cross section when adopting five different construction methods of full-scale excavation, top and bottom branch excavation, top and bottom-three-step branch excavation, left-right branch excavation and left-right-four-step branch excavation. By analyzing their moving regularity of the stress field, emergency field, displacement field in different steps, the paper finds out the most suitable construction methods.According to the comprehensive analysis of the types of surrounding rock pressure and the influence factors, the paper analyses the divide standard of the deep-lying and low-lying tunnel, investigates the unity of surrounding rock pressure formula in nature, and then following the example of typical tunnel, studies the mechanical responses of deep-lying and large cross section tunnel shotcrete and bolt support by field actual research.