| Tunnel expansion under construction often has the particularity of multiple construction disturbances in high frequency and short period,which will lead to complex stress superposition effect of surrounding rock in the construction process,which is more prone to surrounding rock collapse and instability of support structure,which undoubtedly puts forward higher requirements for safe and efficient expansion technology in the construction process.Therefore,based on the dongjiaping tunnel project of Jiangyu Expressway in Guizhou Province,this paper carries out the optimization research of tunnel expansion technology under construction.Based on the comparative checking calculation of field measured data and numerical simulation,this paper quantifies the differential change of support structure response in the process of tunnel expansion,which is not clear in the theoretical research.Carry out optimization analysis on the expansion scheme of the tunnel under construction through numerical simulation;The critical eigenvalue of canceling the temporary support construction of the tunnel under construction is proposed,and the temporary support parameters are further optimized;According to different complex geological conditions,explore the optimal construction process parameters of single side wall bench method construction.The main work and achievements of this paper are as follows:(1)Based on the field measurement and analytical analysis,the differential state data before and after the expansion of dongjiaping tunnel are obtained.Combined with the finite difference calculation method,the similarities and differences of the load characteristics of the surrounding rock in the excavation and expansion process of the tunnel under construction,the operating tunnel and the new tunnel are analyzed,and the load differences of the surrounding rock of the tunnel under construction are quantified based on the supporting project.The results show that the settlement of arch crown in the form of single wall expansion is 1.22 ～ 1.27 times that in the form of double wall expansion and surrounding expansion;The disturbance degree of different excavation and expansion states on tunnel stability is as follows: new tunnel >tunnel under construction > operating tunnel.(2)Combined with the numerical simulation method,the characteristics of the surrounding rock stress and the load of the initial support structure under the unilateral expansion process of the tunnel project are obtained.The theoretical work efficiency differences of different temporary support methods for tunnel expansion are determined.According to the evaluation index of vault settlement,the critical conditions for the construction of temporary support under the form of unilateral expansion of tunnel under construction are obtained.At the same time,the optimization scheme for the construction form and parameter selection of temporary support is put forward.The research results show that under the s-xva support grade and s-xvb support grade,the volume of plastic zone without temporary support is increased by 44%;In terms of displacement limiting effect on surrounding rock,the effect of bilateral arc support is 13.2% higher than that of vertical support.(3)The optimization scheme of construction technology of single side wall bench method expansion under complex geological conditions of tunnel under construction is put forward.Based on the multi factor and multi-scale analysis of excavation spacing,support spacing and step length in the construction technology,the optimal construction technology of single side wall expansion of tunnel under construction under three complex geological conditions of shallow buried bias pressure,joint development and surrounding rock transition is summarized and put forward.The research results show that the influence of single side wall bench method construction technology on surrounding rock stability disturbance of tunnel under construction: arch support spacing > excavation cycle spacing > bench excavation length. |
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