The Analysis On Parameter Optimization Of Tunnel Bolt

As an important part of the tunnel initial support structure, bolt support can not only restrain the deformation of rock in the reinforced area and enhance its intensity, but also provide the supporting anchor force along the surrounding rock, which makes the rock in trip-direction compression condition and its stability being improved. However, studies on the bolt support theory are still not mature enough at present. In engineering practice, engineering experience analogy method is the main approach. Generally speaking, there are two problems in the rockbolt support design. One is that parameters of bolt support design are too large which might result in unnecessary waste of resources. The other is that parameters are too small which can not reach the expected effect of bolt support and lead to the unsafe structure. Therefore, it is necessary to make an optimized analysis on the rockbolt parameters in tunnel primary support.By collecting relevant data, the article makes in-depth exploration on the bolting mechanics mechanism, design method of tunnel and the finite element software ANSYS. Meanwhile, based on the project of Daxia Tunnel from Minhe(the border region of Gansu Province and Qinghai Province) to Xiaoxia(Ping’an), ANSYS has been employed in the numerical simulation of bolt support in 3th or 4th level of surrounding rock area. The main research contents and conclusions are as follows:①Considering the surrounding rock in 3th level is relatively stable, 4 working conditions have been selected. They are respectively no bolt, bolt setted in side wall and arch ring, bolt setted only in arch ring and bolt setted only in side wall. The results didn’t show significance under the above four working conditions, suggesting that the bolting effect is not obvious. Therefore, the author recommends canceling the bolting. Moreover, directly sprayed concrete method should be applied to make primary support; in the poorer parts of surrounding rock bolt is adopted to improve the local reinforcement.②In 4th level of surrounding rock, two parameters have been studied, one related to the length of the bolt with 2.0m、2.5m、3.0m、3.5m and 4.0m and the other related to space in the ring direction with 0.8m、1.0m and 1.2m.At last the comparative analysis has been conducted on the displacement and stress of surrounding rock, axial stress of bolt and the primary support stress. According to the findings in this research, the bolt support parameter of Daxia Tunnel has been optimized. Thus, it is suggested that bolt with the length of 2.5m should be chosen and the optimized ring spacing should be 1.0m.With the optimized analysis on the bolt support parameter of Daxia Tunnel, this thesis is aimed at providing experiences and references for similar projects on tunnel engineering design, construction and bolt support research in the future.