Study On Construction Methods And Stability Of Shallow Buried Bias Tunnel With Small Span

It is very important to choose reasonable construction methods and process to ensure stability of surrounding rock of tunnel due to the special form,the broken,loose and heavy weathering surrounding rock of tunnel entrance of shallow buried bias tunnel with small span.This thesis is based on Toupao tunnel of Yan Qing to Chongli highway,through numerical simulation analysis,uses four construction methods: ring cut method,single side drift method,double side drift method,bench cut method,and the excavation sequence of deep buried side and shallow buried side are taken into account for the stability research.Finding that using double side drift method,excavating deep buried side firstly is best for the stability of the tunnel.On this basis,the stability of the tunnel was analyzed by subdividing the spacing between tunnel faces into four conditions: 12 m,16m,20 m and 24 m within the range of 1～2 times the hole diameter suggested by the specification,the main conclusions are as follows:1.After tunnel excavating,vault settlement and bottom hunch-up of deep buried side reach the maximum value,horizontal displacement of shallow buried side is the maximum;And the vault settlement of the other side can be relief whether the deep buried side or the shallow buried side of tunnel is excavated firstly.The increase rate of the displacement of surrounding rock increases at first and then decreases during the excavation of tunnel face,the displacement value increases in the beginning and becomes flat,finally remains stable.2.The surrounding rock of the tunnel is in compression situation after excavation,and parts of secondary lining appears tensile stress;the vertical stress of deep buried side of tunnel was the largest,the stress concentration was obvious in the arch loins and the arch feet;the vertical stress of shallow buried side tunnel is inclined with the direction of bias.The influence on vertical stress of surrounding rock is the smallest,the supporting performance of lining is the best,the volume of plastic zone is the smallest,the axial force of anchor is the smallest,and the stability of tunnel is the best when using the double side drift method.3.Choosing double side drift method with the excavation of deep buried side first and keeping the distance between two tunnel faces about 24m(2 times the diameter of the tunnel)can get the best control result on the displacement of upper slope of the tunnel,the displacement and stress of surrounding rock of the tunnel,the displacement and stress of initial lining,the volume of plastic zone and the axial force of anchor.