Research On Tunnel Fracture Mechanism Based On Discrete Element Meso-Modeling

The construction and operation of the tunnel is a high-risk project due to the long period,many projects,complicated technology,many unpredictable risks and large impact on the social environment.In this paper,experiments and detailed numerical simulations were carried out on the tunnel rainfall collapsed and concrete with holes in the service tunnel lining.Global warming will cause more extreme heavy rainfall disasters.It must influence the process of engineering and can easily cause a tunnel collapse accident at a poor geological location.This seriously threatens the safety of workers and engineering property in the tunnel.Therefore,research on the tunnel roof mechanism under rainfall infiltration is an important issue.The integrity of the lining plays a vital role in the construction and operation of the tunnel.According to the statistical results of tunnel defects,cracking and falling blocks are mostly caused by insufficient thickness of the lining.Voids and large-sized bubbles constitute insufficient lining thickness.At present,less research on the cracking mechanism of concrete caused by large-sized bubbles.Therefore,this paper mainly studies the effect of large-scale hole defects on the performance of concrete structures.This will prepare the foundation for the future research on the cracking mechanism of defective linings.In this study,aimed at the accident of Kosman tunnel roof under heavy rainfall,the dynamic change law of surrounding rock fracture and seepage flow under heavy rainfall was analyzed basis on the real-time monitoring and discrete element numerical simulation.At the same time,the failure of surrounding rock was studied by means of energy.The X-ray computed tomography(X-ray CT),acoustic emission(AE)and numerical modelling techniques were applied to record the cracking process of the precast defective concrete containing expanded polystyrene(EPS)particles.Mainly include the flowing aspects:1.In the initial stage of tunnel excavation,the supporting capacity of the surrounding rock is well.The rainfall gradually increased the seepage at the top of the tunnel.As a result,the stiffness and strength of the joint were gradually reduced,and a large number of shear failure cracks appear from the surface to the arch foot,and the number and length decrease with the increase of the burial depth.The through crack becomes a seepage channel,which causes rainwater to flow into the cave from the crack in the vault.The pore water pressure and seepage field around the tunnel are funnel-shaped and gradually decrease.Increasing effective stress of surrounding rocks exacerbates roof fall accidents.2.This manuscript proposed a method for efficiently identifying aggregate boundary information by X-ray computed tomography technology(CT)and a discrete element modelling method(DEM)for equivalent random polygon aggregates.The CT slice images were processed in batches,and the numbers of edges,axial length,elongation of the aggregate were identified.This method overcomes the shortcomings of the Grain Based Model(GBM)which is impossible to establish a mesoscopic model with a large difference in grain radius.Based on aggregate statistics,this manuscript achieved the meso-model recovery to the maximum extent.The established model can give an accurate description of the CT scans,AE behavior and damage evolution of concrete.3.The X-ray computed tomography(X-ray CT),acoustic emission(AE)and numerical modelling techniques were applied to record the cracking process of the precast defective concrete containing expanded polystyrene(EPS)particles.A new method for the preparation of concrete with initial defects is proposed.These results show that internal defects have a significant influence on the mechanical behaviour of concrete.Many microcracks in concrete were evenly distributed in the early stage.The defects in concrete did not collapse with the increase of the load.Fracture surfaces were formed only at individual defects,and all cracks expanded along the ITZ.The macroscopic cracks formed after reaching the uniaxial compressive strength(UCS).The places where the macro fracture surface is more likely to occur are the closer distance between the two holes and the edge of the concrete.