Abstract
Based on the engineering practice of large cross-section highway tunnel, this paper reveals the space-time coordinated evolution law of the construction mechanical characteristics and deformation distribution of the support structure in the construction by half bench CD method through field test. At the same time, the mechanical response calculation model of the supporting structure in the partial excavation is constructed, and the mechanical characteristics of the support structure in the partial excavation process are analyzed by above mechanical calculation model. Then, the mechanical and deformation distribution of the feet-reinforcement bolt in the steel frame—foot-reinforcement bolt combined support system is analyzed under different levels of surrounding rock load and different structural parameters of the feet-reinforcement bolt. The research results show that: (1) The internal force of the supporting structure changes most obviously during the excavation of Part Ⅰ, Part Ⅱ and Part Ⅲ, and the internal force of the support structure gradually tends to be stable after a slight increase in the excavation of Part Ⅳ and Part Ⅴ; (2) The horizontal deformation and vertical deformation of the support structure mainly occur in the excavation process of Part Ⅰ, Part Ⅱ and Part Ⅲ, and the excavation of Part Ⅳ and Ⅴ has little effect on the deformation response of the structure. The vertical displacement of the supporting structure is larger than the horizontal displacement, and the dynamic response of the temporary diaphragm structure during tunnel excavation is shrinkage-expansion-shrinkage-expansion; (3) The bending strain of each measuring point decreases with the increase of the distance from the loading point, and the bending strain of section 1 and section 2 is much larger than that of the other three sections; (4) With the increase of the angle, the section position with strain close to 0 gradually moves to the deeper position of the bolt, and the axial strain of each section on the bolt gradually changes from positive strain to negative strain.
Highlights
For tunnel with weak surrounding rock, in order to ensure the stability of surrounding rock and supporting structure in the construction process, it is inevitable to adopt the partial excavation methods, such as cross diaphragm method (CRD) [9, 10], the two-side pilot hole method [11] and center diaphragm method (CD) [12]
In order to accurately reflect the interaction between surrounding rock and support structure, the surrounding rock pressure used in mechanical calculation is selected according to the measured contact pressure between surrounding rock and support structure in the field test, and the parameters in the above structural calculation process are obtained from field test
The internal force values of the supporting structure calculated by the mechanical model and the field test values are compared and analyzed, and the calculation results show that the errors between the field measured value and the calculated value of the mechanical model is less than 25%, and the results show that they are in good agreement, which can prove that the mechanical calculation model in this paper has strong applicability and high reliability in engineering
Summary
The research on the construction mechanical behavior of the support structure for large cross-section tunnels using the partial excavation method mainly focuses on the traditional construction methods such as CD, CRD and the two-side pilot hole method, and there is little research on the half bench CD method which can improve the construction efficiency and save the cost of project. This paper, based on the engineering practice of large cross-section highway tunnel, aiming at the construction mechanical response of the support structure in the application of half bench CD method, reveals the space-time coordinated evolution law of the construction mechanical characteristics and deformation distribution of the support structure through field test. The mechanical and deformation distribution of the footreinforcement bolt are analyzed under different levels of surrounding rock pressure and different structural parameters of the foot-reinforcement bolt
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