Theoretical Study On Large Deformation Of Roadway And Rock-support Interaction

For mining operation in soft and fractured orebody,large deformtion is the main failure mode of roadway and stope.With the mine goes deeper,the squeezing potential is increasingly obvious under high in-situ stress.Accounting for these adverse mining conditions,the hazard of large deformation occurs easily if the installed support measure is inappropriate.Therefore,the deformation mechanism and the related control technology should be analyzed based on large deformation theory.On these basis,within the framework of finite strain hypoelasticplasticity,this doctoral thesis provides a theoretical analysis with respect to some practical problems,such as large deformation for circular roadway,the process of squeezing rocksupport interaction,re-profiling of a squeezing roadway,the effectiveness of advancing a pilot tunnel,and the calculation of the supporting time and yielding deformation.Centered on this topic,the following works are conducted:(1)Accounting that only the hydrostatic stress field in the cross section of roadway is considered in the conventional plane strain analysis,the plastic zone is devided into three tpyes according to the magnitude of stress components,and then the finite strain closed-form solutions for elastic-perfectly brittle plastic rock mass are derived to take into account the effects of the arbitrary axial in-situ stress and axial plastic flow on the squeezing behavior.The deviation of results by adopting small strain method in conventional plane strain analysis without considering actual axial in-situ stress and axial plastic flow are clarified under large deformation.The obtained theoretical formulas are verified by making a comparison with the numerical simulation results.(2)A numerical procedure for the strain-softening rock mass subjected to large deformation is proposed,based on which,the plastic internal variable is redefined in order to clarify the influence mechanism of axial in-situ stress and axial plastic flow for different postpeak constitutive models,and then the relationship between roadway instability and large deformation is investigated.Moreover,the validity and applicability of small strain method under different squeezing potential conditions is discussed.(3)In problems involving the violation of the roadway clearance and the repetitive reprofiling works in squeezing rock mass,a rigorous mechanical model and numerical procedure is established considering the strain-softening behavior in post-peak stage,and the accumulated strength degradation of surrounding rock subjected to repetitive excavation disturbances is quantified.Then some practical questions are addressed with respect to the required minimum rigid support pressure and over-excavation size to achieve the desired profile as well as the reprofiling efficiency.In addition,the effectiveness of advancing a pilot tunnel to release high stress and deformtion is investigated under different squeezing potential and geometrical conditions.(4)The expression for describing the actual longitudial displacement profile considering large deformation is obtained by finite strain method,which is verified by numerical simulation and analytic solutions.The method for calculating the fictitious support pressure acting on deformed roadway is then presented,and the coupled mechanical model of squeezing rocksupport interaction is established by taking account of the spatial effect of excavation face and strain-softening behavior of rock mass,based on which,the mechanical analysis of the whole process of squeezing rock-support interaction during the advance of roadway is realized.Afterwards,take the widely used U-shaped yielding steel set in mining engineering as an example,the effects of some factors including supporting time and support properties on the mechanical response of roadway and steel set are investigated,which provides some practical design ideas for choosing and quantitatively calculating the supporting time and yielding deformation of steel set in squeezing rock mass.