Research On The Mechanical Behaviors Of The Support Structures Of LongXi Tunnel

There are much mountain in our country, as the fast development of highway, all kinds of long, complicated geologic condition tunnels appear largely. During tunnel construction, due to design, construction, complicated geologic condition and other reasons, all of those led to the distortion and breakage of the support structure and even led the support structure inrush to design's delimitation, large distortion and fall of surrounding rock and so on. Those tunnel disaster caused unsafety construction and graveness economy losing. So truly taking of the mechanical behaviors of the support structure during tunnel construction, to provide a scientific basis for dynamic design, has become a problem must be solved for long, complicated geologic condition tunnels.Taking under-construction LongXi tunnel as investigated subject, this paper adopts some advanced research methods like theory analysis, elastic-plastic displacement back-analysis, numerical simulation and calculation of support based on load structure method, the paper studied systematically the mechanical behaviors of primary support based on the result of monitoring measurement and ground stress test during construction of the deep imbedded and long tunnel in high ground stress areas and got such main research findings:1.The paper had carried out back analysis for mechanical parameters of surrounding rock at the grade V and grade IV rock section with elastic-plastic displacement back-analysis method and got the mechanical parameters, those were helpful for the numerical simulation and dynamic design.The result of back analysis showed that the elastic modulus of grade V is 1.5MPa and the elastic modulus of grade IV is 10MPa.2. According to numerical simulation of construction based on the practical on-site construction and the result of field test and back-analysis. The paper studied deeply the mechanical behaviors of primary support during construction of typical sections (the entrance section, the grade V and IV rock section in high ground stress areas, the exit section) of the deep imbedded and long tunnel in high ground stress areas with the the numerical simulation based on the result of monitoring measurement and ground stress test.The result showed that first main stress and moment of support structure was controlled by initial ground stress.The maximum first main stress appeared at side wall of support structure in the dead-weight stress field;the position of maximum first main stress was same to the acting position of the maximum principal stress(σ₁) of tectonic stress. The distribution of axial force of anchor was effected by initial ground stress.The position of maximum axial force of anchor was same to the acting position of the maximum principal stress(σ₁) of tectonic stress.3. The paper had carried on the calculation of primary support based on load structure method with practical support parameter and stratum pressure during construction of typical sections (the entrance section, the grade V and IV rock section in high ground stress areas, the exit section) of the deep imbedded and long tunnel in high ground stress areas.The result showed that the position of maximum internal force and deformation was same to the acting position of the maximum principal stress(σ₁) of tectonic stress.4.From the result of comprehense calculation, geological conditions and construction process at LongXi tunnel, the paper had analysed comprehensely the effect of stratum pressure on the mechanical behaviors of of primary support with the structure internal force and deformation, and then evaluate the safety of support structure and made the support parameter better.