Research On Damage Law And Anti-fault Measures Of Tunnel Crossing Active Fault

The southwest region of China belongs to the Tethys-Himalayan tectonic domain,where a large number of active faults are located,and the fault activity is mainly in the form of reverse punching,reverse masking or slip faults.The study of the mechanical response of tunnel structures crossing active faults under the effect of slip misalignment and the measures to resist misalignment within the influence of misalignment is one of the difficult problems in tunnel engineering.In this paper,based on an actual tunnel project,theoretical analysis and numerical simulation methods are used to establish MATLAB analytical calculation model and 3D surrounding rock-tunnel-fault fracture zone finite element model respectively to carry out relevant numerical simulation research,mainly to analyse the displacement-internal force response of the tunnel structure under the action of slip fault misalignment and the damage law,combined with the actual engineering selection of reasonable anti misalignment measures,research and analysis The main conclusions are as follows:(1)Based on the elastic foundation beam theory,the Matlab calculation model is established,and the analytical solution of the tunnel structure under staggering action is obtained by substituting the site dependent parameters,and the analytical solution of the longitudinal internal force of the tunnel lining under different working conditions is compared and analysed,and the results show that the displacement,bending moment and shear force distribution laws along the longitudinal direction of the tunnel are the same as those of the positive and negative fault staggering,thus proving that the Pasternak two-parameter elastic foundation beam theory is still applicable in the slip fault.(2)Using the CDP instantonal model in ABAQUS,a 3D finite element model of tunnelfault-perimeter rock was established under the slip-fault misalignment conditions.The larger the fault intersection angle,the greater the effect on the deformation,internal force and damage response of the tunnel structure;the change of the fault tunnel intersection angle has little effect on the deformation of the tunnel structure,mainly affecting the internal force and strain and damage distribution,the larger the fault intersection angle,the smaller the effect;the width of the fault fragmentation zone has little effect on the deformation and damage of the tunnel structure;the effect size is ranked as misalignment > fault intersection angle > fault width.In tunnels,a small fault width and a vertical crossing of the fault zone should be considered to reduce the impact of fault misalignment on the tunnel structure.(3)According to the analysis of the fault movement under different working conditions,the peak internal force and strain after deformation of the tunnel,and the peak damage factor are mainly distributed at the location of the tunnel sidewalls on both sides of the fault movement surface,and the "section + flexible joint" anti-fault method is chosen to be set up on both sides of the fault movement surface.When the second lining is articulated with segmental joints in the central zone of the fault zone,the tunnel settles in "segments" under the effect of the fault movement,indicating that the second lining with segmental design can control the deformation of the surrounding rock when the surrounding rock is deformed;when the tunnel When the tunnel is stagger-resistant,the shear impact of the tunnel with stagger-resistant construction is33% of the original;the bending moment impact is 13.3% of the original,the peak equivalent plastic strain is reduced to 7.58% of the original,the shear strain is concentrated in the flexible joints,and the plastic damage is reduced to 60.13% of the original.The overall assessment result: using the anti-stagger construction,the local bit of the second lining may be damaged under the action of fault stagger,but the overall can maintain normal work.(4)Through different section lengths,different flexible joint widths on the tunnel structure anti-stagger effect analysis can be seen,the shorter the section length,the better the anti-stagger performance,so should be combined with the actual project,under the condition of meeting the construction requirements,the section length should be selected as small as possible to ensure the anti-stagger performance.