| In the excavation of large and long tunnels,it is preferred to select TBM(Tunnel Boring Machine)method with high construction speed,high efficiency,perfect tunnel cross-section,slight impact on the surrounding environment,and safe and environmentally friendly operation.However,unfortunately,the TBM method is not omnipotent.The biggest problem is the adaptability.In a tunnel of ten or even tens of kilometers,the geological conditions of the surrounding rock is ever-changing.When the surrounding rock conditions change,it is not as flexible as the drilling and blasting method.This has caused TBM jamming accidents to occur frequently,resulting in huge economic losses and extended construction periods.In this paper,the FDEM numerical simulation method was used to study the jamming process and safety prevention and control tunnelling through deep soft ground.The main research contents are as follows:(1)This paper systematically summarized the development of FDEM from the present until now and its application in the field of rock mechanics.The former included algorithm improvement,mesh sensitivity analysis and parameter calibration.The latter was mainly for underground engineering excavation and surrounding rock stability control simulation,rock slope stability analysis,rock hydraulic fracturing simulation,rock fracture acoustic emission simulation and rock test simulation in laboratory.And putting forward its shortcomings had certain guiding significance for the development of FDEM in the future.(2)Taking the experiment and actual engineering as the reference scale,the maximum mesh size and maximum loading rate of different samples were studied.The selection method of mesh size during actual tunnel excavation was studied.When the core material softening method was used to simulate the two-dimensional tunnel excavation,the softening of the core material needs to be softened after the model was in quasi-static(the model kinetic energy was less than a certain value,called critical kinetic energy,CKE).The selection method of CKE was studied.At the same time,it was analyzed how many numbers the softening time steps of the core material should be taken and what kind of softening curve should be used.(3)In practical engineering,the timeliness of rock strength can not be ignored,because the surrounding rock or support of the tunnel is stable in a short period of time,and then after a period of time,cracking may occur.According to the assumption that the degree of deterioration of the long-term strength of the rock(the ratio of the instantaneous strength)does not change with the confining pressure,a formula for deteriorating the rock cohesion and internal friction angle with time were proposed.The effects of uniaxial compressive strength deterioration,tensile strength deterioration and elastic modulus deterioration on the surrounding rock fracture process after tunnel excavation were studied and verified by practical engineering.(4)When the dual support effect of the excavation face and the TBM coexist,the mesh overlay method can be used to simulate the TBM jamming process.The core material and the TBM do not contact each other,and the contact with the surrounding rock is calculated separately.This method can directly reflect the nonuniform radial gap between the TBM and the surrounding rock.According to this simulation method,the whole process of the jamming in the continuous tunneling and shutdown state of the ABH water conveyance tunnel was studied.(5)Surrounding rock modification and equipment modification are commonly methods used to prevent TBM jamming.The former usually includes pre-grouting and pipe roof/small pipe/rockbolt(which belongs to three-dimensional problem),while the latter generally has increasing the expansion gap,injecting lubricants,and increasing TBM rated thrust,etc.The preventive implementation effect of TBM jamming under pre-grouting and increased expansion gap were studied.It also studied the whole process of getting rid of the TBM jamming. |
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