Study On Deformation Characteristics Of Fully Weathered Formation Tunnel With Boulders

Engineering practice shows that the excavation of tunnel in fully weathered stratum containing boulders will have a significant impact on the movement of tunnel stratum.At present,most of the research on the boulders in tunnel is focused on the detection of boulders and the prevention and treatment of engineering accidents caused by boulders,while the study on the movement and deformation mechanism of tunnel stratum caused by boulders is less.Based on the exit section of ShiNiuLing Tunnel in the second tender section of QingYuan FuQingCong Expressway,through theoretical analysis,field observation test and numerical simulation analysis,the stratum movement characteristics of the entrance section of fully weathered tunnel with boulders are studied.The main conclusions and results are as follows:(1)Testing and analysis of the movement and distribution law of weathered strata with boulders are carried out.It is found that the distribution of boulders in sensitive areas has a significant impact on the settlement of the vault of the tunnel.The settlement of the Vault near the section of boulder is larger,but the influence of boulder on the horizontal convergence value of the tunnel is smaller.When the distribution of boulders is at the waist of the tunnel,the corresponding maximum ground settlement has a certain deviation.The Peck formula method is not applicable to the prediction of the surface settlement of the section near the boulder but it has better applicability to the prediction of the surface settlement of the section far away from the boulder.(2)The numerical model of tunnel stratum excavation with boulders is established,and the influence of boulders on tunnel stratum movement and mechanical characteristics of support structure is analyzed.The calculation results show that the boulders in tunnel stratum will affect the surface subsidence.The surface subsidence of boulders stratum is obviously larger than that of non-boulders stratum,and the surface subsidence increases with the increase of the size of boulders;the maximum surface subsidence decreases with the increase of the distance between solitary stones and tunnel boundary and the increase of burial depth;when the boulders are located at the arch waist,the maximum surface subsidence point occurs in the direction Offset.(3)The analysis of the influence of boulders on the mechanical properties of tunnel support structure shows that when the boulders are above the arch top,the bending moment and shear force at the arch top increase obviously,but the axial force does not change obviously.The bending moment and shear force increase with the increase of the size of the boulder,and the influence on the bending moment and shear force of the supporting structure decreases with the increase of the distance between the solitary stone and the boundary of the tunnel,but the influence on the supporting axial force is not obvious.(4)Orthogonal analysis of the size and sensitive distribution of the boulders is carried out.Among the four factors selected by the boulders stratum model,the degree of influence on the surface settlement of the tunnel is the depth of the tunnel(the ratio of overburden to span),the size of the solitary stones,the azimuth angle of the boulders,and the distance between the boulders and the boundary of the tunnel.(5)Around the weathered boulders stratum,the distribution law of ground subsidence caused by tunnel excavation is studied based on stochastic medium theory,aiming at tunnel diameter,tunnel depth,and convergence of tunnel section and stratum influence angle.The results show that the maximum ground settlement increases with the increase of tunnel diameter,tunnel convergence value and stratum influence angle,and decreases with the increase of buried depth.(6)When boulder is located in a typical sensitive part,based on the stochastic medium theory and the non-uniform deformation mode,the ground settlement prediction model of the shallow buried and boulder stratum considering the superposition of the three deformation modes is established.The tunnel surface settlement curve and the field measurement are obtained according to the model.Have a high degree of fit.