Study On The Stability Of Surrounding Rock During Excavation Of Tunnel With Multiple Weak Intercalations

Weak interlayer is the weakest place in the tunnel,which will cause tunnel collapse,support deformation and other problems,and affect the normal construction of the tunnel.The high degree of development of weak interlayer will cause life safety and property losses.At present,scholars at home and abroad have done a lot of research on the stability of surrounding rock of tunnel with weak interlayer by means of on-site monitoring measurement,experimental model and numerical simulation,but their research mainly focuses on the stability of surrounding rock of tunnel with single weak interlayer.In practical engineering,there are many weak intercalations in tunnels,which restrict the stability of surrounding rock and affect the construction.Therefore,through theoretical research,FLAC3 D numerical simulation and on-site monitoring measurement,this paper studies the influence of the number of weak intercalations,the thickness of multiple weak intercalations and the angle of multiple weak intercalations on the displacement,stress and plastic zone of surrounding rock during tunnel excavation.The main contents of this paper are as follows:(1)The stability model of surrounding rock for tunnel excavation with multiple weak intercalations is established,and the influence of the number of weak intercalations on the stability of surrounding rock in the construction process of tunnel bench method is co MPared and analyzed.The results show that: the vertical displacement of tunnel surrounding rock increases significantly,the measurement points of vault,arch waist and arch bottom increase by more than 127%,and the increase of right arch waist is the most obvious,reaching 145.8%.The increase of horizontal displacement is more obvious,the increase of each position is more than 211%,especially the increase of right arch foot is 541.4%.Due to the tunnel excavation,the maximum principal stress value of the arch waist changes significantly.The stress value increases gradually before the excavation to the cross section,and decreases suddenly after the excavation.This reduction effect is more obvious with the increase of the number of interlayer,the left arch waist decreases by 3.01 MPa,and the right arch waist decreases by 2.12 MPa.The maximum tensile stress of surrounding rock without interlayer is 1.72 k Pa,while the tensile stress reaches 0.23 MPa when the weak interlayer increases to three layers.It is found that the displacement of surrounding rock is most affected by the weak intercalation,so the displacement should be used as an index to evaluate the stability of surrounding rock of tunnels with multiple weak intercalations.(2)The influence of the angle of multiple weak intercalations on the stability of tunnel surrounding rock is revealed.When the angle of the interlayer is greater than 60 degrees,the vertical displacement increases with the increase of the angle of the interlayer;the horizontal displacement of the left arch waist is most affected by the angle of the interlayer,and reaches the maximum value of 4.78 mm at 45 degrees.For the maximum principal stress,when the interlayer angle is less than 30 °,the stress value of the right arch waist is greater than that of the left arch waist;when the interlayer angle is greater than 30 °,the stress value of the left arch waist is always greater than that of the right arch waist;for the minimum principal stress,when the interlayer angle is less than 45 °,there will be a complete tensile zone at the arch bottom,and when the interlayer angle is greater than 45 °,the tensile zone will break at the interlayer,forming a discontinuous tensile zone.When the angle of the interlayer is greater than 45 degrees,there is a plastic zone at the bottom of the arch under all working conditions,and the plastic zone of the whole tunnel contour is closed into a ring.(3)The influence of the thickness of multiple weak intercalations on the stability of tunnel surrounding rock is revealed.When the thickness of the interlayer increases from0.5m to 3m,the vertical displacement of the right and left arch waist increases by3.57 mm and 4.5mm,respectively,with the increase rate of 55.5% and 71.4%.With the increase of interlayer thickness,the more obvious the stress release from excavation to monitoring section is,and the stress release value reaches 1.01 MPa when the thickness is 3M;the larger the plastic zone area of surrounding rock increases with the increase of interlayer thickness,and the shear tensile zone appears when the interlayer thickness is1 m.(4)Combined with the actual project of Shatian tunnel,through the numerical simulation inversion and monitoring measurement,the comparative analysis of the multi weak interlayer section and the surrounding rock integrity section shows that the numerical simulation results are basically consistent with the monitoring measurement results.The vault settlement and peripheral convergence can be divided into three stages:rapid increase stage,slow increase stage,stable no longer change stage,The deformation duration of the first stage is relatively short,but the deformation amount is more than 70%.Compared with the section with good integrity of surrounding rock,the settlement displacement of the vault of the tunnel with multiple weak intercalations is larger,and the difference between the monitoring measurement results and the numerical simulation results is 5.19 mm and 4.9mm.It is suggested that the initial support should be strengthened in the construction process,and the monitoring and measurement frequency should be increased to prevent the tunnel collapse caused by excessive support deformation caused by excessive displacement...