| In view of the problem that the surrounding rock of the soft rock tunnel entrance is generally weak and broken,the site at the exit end is narrow,and the tunnel cannot be supported by long pipe sheds,the double grouting small pipe is used to replace the pipe shed for advance support,so as to achieve The purpose of pre-reinforcement of surrounding rock.In this paper,combined with the example of the left line project of Huluding Tunnel,the theoretical analysis and numerical simulation are carried out to study the reinforcement mechanism,supporting effect,and the effect of supporting parameters of the double-layer advanced small pipe support technology,and to study with other advanced support methods.Perform comparative analysis.(1)After explaining the reinforcement mechanism of the double-layer small pipe,the most unfavorable state model of the small pipe in the process of tunnel excavation is established based on the Wenkel elastic foundation theory,and the deflection,rotation angle and bending moment of the small pipe are derived based on actual engineering,Shear force expression,and use MATLAB programming to get the distribution characteristics of the catheter force.(2)Based on the finite-difference numerical simulation technology to simulate the excavation process of the tunnel with or without the double-layer small pipe advance support technology,the double layer is analyzed from the three aspects of surrounding rock deformation,stability of the palm face and initial support stress Reinforcement effect of advanced support technology for small catheters.The results show that the double-layer small pipe pre-reinforcement technology can effectively control the development of the surrounding rock displacement,which has obvious constraints on the surrounding rock vault settlement and surface settlement,improves the self-stability of the palm face,inhibits the vertical displacement of the surrounding rock;The stress state of the protective structure weakens the degree of stress concentration;although the numerical result of the bending moment of the catheter is lower than the theoretical calculation result,the change trend of the two is roughly the same.(3)The main parameters of the double-layer grouting small pipe are selected for analysis.The length and diameter of the small pipe,the external and internal angles of the two layers and the cohesion of the grouting reinforcement ring are analyzed through the vault settlement of the target section and the force of the small pipe.Influence of internal friction angle,grouting range and thickness.The results show that increasing the length of the small pipe can reduce the surrounding rock settlement,but the diameter and the extrapolation angle have little effect on them,and all three have a greater influence on the force of the pipe.The optimal design parameters of the small pipe are given by comparison;In addition to the internal friction angle,the four parameters of the grouting reinforcement ring have a great influence on the settlement of the surrounding rock arches.In actual engineering,sufficient grouting is needed to ensure the reinforcement effect.(4)From the perspective of the deformation and stress of the surrounding rock and the initial support structure,the support effects of three types of advance support such as pipe roof support,single-layer small pipe support,and double-layer small pipe support are analyzed.The results show that : If the double-layer small pipe advance support is adequately grouted,the support effect is even better than the pipe shed support.The double-layer small pipe support effect is better than the other two advances in terms of wall rock displacement and stress,initial support displacement Support method,but the support effect of the double-layer small pipe and the pipe shed in the initial support stress is not much different. |
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