| The development of social economy is inseparable from the support of the transportation industry,and with the continuous development of transportation infrastructure construction,the expansion and construction of road tunnels in my country are entering a period of rapid development.As a systematic construction project involving the excavation and support of rock and soil,there are many construction steps during the subsection of the tunnel,and the surrounding rock of the shallow section of the tunnel is complicated by the construction conditions during the construction period.Therefore,the study on the deformation law of tunnel surrounding rock during construction is very important to ensure the safety and efficiency of tunnel construction.Relying on the tunnel project in Liuzhou,this paper studies the surrounding rock deformation characteristics of tunnels during the construction period under bias conditions through field monitoring,theoretical analysis and numerical simulation,and systematically analyzes the excavation during partial excavation.The main work carried out and the main results obtained are the effects of sequence,footage,distance between each face and step length on the stability of the tunnel,as follows:(1)The influence of the excavation sequence on the surrounding rock of the tunnel during the construction process was studied when the tunnel was excavated in sections under the condition of shallow buried bias.Through the establishment of a two-dimensional numerical model,the deformation laws of the tunnel surrounding rock and the initial support under the two excavation sequences of "shallow first and then deep" and "deep first and shallow" are studied.When excavating the deep-buried side pilot tunnel first,the vertical displacement of the surrounding rock of the tunnel is smaller than when the shallow side is excavated first,and the horizontal displacement is greater;the surrounding rock of the side pilot tunnel excavated first in a single tunnel is more disturbed.The displacement is relatively larger;the upper surrounding rock deformation of the double-hole tunnel is larger on the side of the advance tunnel.(2)The method of determining the excavation footage was studied.Based on the road tunnel design specification,the failure model in the silo theory is simplified.Taking the stability of the top of the unsupported section of the excavation site and the surrounding rock on the face of the excavation site as the control condition,the calculation formula of the shallow tunnel excavation footage is deduced,and the influence of various factors on the calculation of the construction footage is analyzed.This formula is used to analyze the reasonable value of the excavation footage of the Antai Road Project in Liuzhou.(3)The influence of different face spacing and step length on surrounding rock is studied.It is found that when the length of the steps of each pilot hole is longer,the surface settlement is smaller;the surface settlement increases significantly after the excavation of the steps on the rear side pilot hole and the middle pilot hole;the distance between the tunnel faces of each part is larger The settlement at the top of each pilot tunnel is smaller;the final results of the uplift deformation values at the bottom of the supporting structure arch under various working conditions are not much different.(4)Through the analysis of the monitoring data of the top settlement of the pilot tunnel during the construction period of the shallow buried section of the tunnel and the horizontal convergence of the arch waist,the deformation law of the surrounding rock of the typical section during the construction process is studied,and the final deformation prediction value is obtained by fitting;During local surrounding rock blasting and excavation,the vibration velocity of the initial support of each part is monitored,and it is believed that the tunnel support structure is safer during the partial blasting and excavation. |
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