| Large deformation and instability caused by failure-fragmentation are easy to occur in deep coal mine roadway after excavation due to the prominent contradiction between high ground stress and low surrounding rock strength.To realize stability control of deep roadway surrounding rock,it is necessary to reveal the large deformation instability process of deep roadway surrounding rock and its interaction mechanism with reinforcement.For this reason,in this study,the combined finite-discrete element method(FDEM)serves for the simulation study the process of fracture initiation,fragmentation,and deformation of surrounding rock and effects of various reinforcement methods in the deep coal mine roadway.At present,FDEM shows many problems,including low computational efficiency,many computational parameters and unclear values,and little rock reinforcement models and insufficient research on the action mechanism algorithm of rock bolt reinforcement,which cannot effectively simulate the effect of prestressed bolt reinforcement.Given this,a series of experimental and modeling studies were conducted in this paper.Firstly,efficient computing of FDEM in CUDA platform through the GPU parallel algorithm is realized.Secondly,aiming at the parameter value problem of FDEM calculation,a fast calibration method of FDEM calculation parameters is proposed through statistical analysis of the relationship between macro and meso parameters in FDEM rock failure constitutive model.Then,FDEM bolt reinforcement model based on physical material element modeling is established by studying the composition of bolt bonding force,action law of rib structure,and parameter value.Based on the analysis of surrounding rock grouting reinforcement mechanism,FDEM simulation method for surrounding rock grouting reinforcement is put forward.On this basis,relying on deep roadway engineering in the Pingmei mining area,the engineering application research of FDEM method is carried out,and the comprehensive simulation of the process of prestressed bolt-grouting reinforcement combined support in the deep roadway of the coal mine is realized.The specific research contents and main conclusions are as follows:(1)Aiming at the computational efficiency of FDEM,the realization strategy of the GPU parallel algorithm was studied,and the multi-GPU parallel program based on the CUDA platform of NVIDIA was realized.The calculation efficiency is significantly improved,which provides a basis for the simulation of underground roadway excavation and support.(2)In view of the accurate parameter value of FDEM,the relationship between parameters of mesoscopic and macroscopic in FDEM constitutive model of calculation rock failure was discussed based on laboratory rock mechanical parameters test and statistical analysis of test results with different strengths.The results show that there is a statistical power function relationship between the parameters of mesoscopic fracture and the macroscopic tensile strength,the ratio of compressive strength to tensile strength is a function of the internal friction angle,the ratio of penalty parameters of tangential to normal is only related to Poisson's ratio,the size effect of rock mechanical parameters is mainly reflected in the strength parameters,and there are size-independent parameters.All the law reflects the strong correlation between the parameters above.On this basis,a fast calibration method for FDEM calculation parameters is proposed,and the accuracy and efficiency of the method are verified by calibration simulation and experiment.The calibration result shows that the method can serve as a reliable and accurate basis for FDEM to simulate the rock mechanics characters.(3)A rock bolt reinforcement model based on the physical material element modeling is established in FDEM.Based on the rebar bolt structure,bond force and radial stress are analyzed theoretically.The action law of the rib in the bolt model and the parameters of the grout based on the joint element is studied.The theoretical analysis of the force of the refined bolt structure,axial pullout test simulations of different strength rock and grout combination,and physical laboratory axial pullout test were carried out,the parameters of the model were obtained and verified by the obtained bond load-slip relation law.Results showed that radial stress increased by a power law.Then,the model is implemented in FDEM and verified by axial pullout test simulation.The action law of the model can well represent the active law of bonding load-slip curve and loading rate,and reflect the action characteristics of the bolt.(4)In situ stress application and tunnel excavation methods are implemented in parallel FDEM.On this basis,the surrounding rock fracture process is simulated;Grouting reinforcement effect model based on cohesive element re-cohesion is implemented in FDEM.Cohesion law of different grout material was studied by UCS and wedge splitting test;and parameters of?T and fracture energy G?funder splitting was obtained.The effects of different grouting material,grouting technology,and grouting range were studied by deformation and fracture of surrounding rock.Results show high strength grouting can effectively reduce the fracture range of surrounding rock.(5)Combined with the coal mine tunnel,lining element support model is implemented in parallel FDEM.On this basis,the surrounding rock fracture process is simulated under diverse reinforcement conditions,including high strength and low strength shotcrete lining,steel arch,and U-shaped yieldable steel rib.The deformation and failure process of surrounding rock after roadway excavation and the supporting effect of various supporting methods are analyzed.It is believed that the large deformation of surrounding rock failure mainly occurs in the weak part of the stress release channel.Based on the analysis,the principle of“Equal reactive force reinforcement of the full section”was put forward to eliminate the stress release channel and maintain the overall stability of the excavation space.The simulation approach of the prestressed bolt is realized.The reinforcement effect of rock bolt and grouting was studied by comparing damage range and deformation of roadway surrounding rock.Results show that prestressed bolt reduces the tensile fracture and mixed fracture near-surface of surrounding rock,which is beneficial to the stability of the roadway;the proposed bolt model can effectively decrease the surrounding rock damage range and deformation of the roadway. |
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