Principle,Realization And Application Of Bolt Element Based On Continuum-Discontinuum Method

With the rapid development of deep coal resources mining,the increase of mining depth will be accompanied by complex geological environment and strong mining influence,which is manifested as high in-situ stresses,intensified deformations of the surrounding rock of the roadway and aggravated instability of strata.This will lead to the increase of the difficulty of roadway supports.In order to improve the combined Lagrangian-discrete element method(a kind of continuum-discontinuum method),a kind of bolt element was introduced into the method,which can synthetically reflect axial and shear deformations.The essence of the bolt element is that in each overlay the position of a bolt node in the subelement remains unchanged.A quadrilateral rock element was divided into two triangular subelements in two ways.Each is called an overlay.The bolt pull-out and shear numerical tests were carrying out by the continuum-discontinuum method after introducing the bolt element.In the pull-out numerical test,axial forces of bolt elements within a certain distance away from the drawing end rise in an oscillation mode as the displacement increases of the drawing end,which was explained from the view of the action of the surrounding rock on the bolt.The distribution of the axial force of the bolt was compared with the theoretical solution based on Mindlin’s solution of the displacement to check the correctness.In the shear numerical test,the stress concentration occurs in the surrounding rock near the bolt element closest to the shear surface.This is due to the shear deformation of the bolt element,which produces forces on the surrounding rock.The deformation-cracking-motion processes of the surrounding rock of the roadway with or without bolt supports under the static load were obtained through the continuum-discontinuum method after introducing the bolt element.Under the condition of bolt supports,the stress distribution of the surrounding rock of the roadway,the number of crack sections,the roof subsidence and the displacement of both sides have been improved to varying degrees,and the surrounding rock of the roadway has reached the equilibrium state earlier.The supporting mechanism of the bolt was explained from the view that the surrounding rock confining pressure increases within the length of the bolt.The results with bolt supports are more realistic than those of the traditional continuous method,which is due to the fact that obvious cracks between the rock elements in the failure zone near the roadway occur,causing a certain expansion of the surrounding rock.In a certain range of in-situ stresses,the greater the in-situ stress is,the better the supporting effect is.The deformation-cracking-motion processes of the surrounding rock of the roadway with or without bolt supports under the impact load were obtained through the continuum-discontinuum method after introducing the bolt element.When the initial compressive stress wave reaches the monitored node near the upper surface of the roadway,the maximum principal stress of the monitored node shows a down-up-down trend at the beginning,which is caused by superpositions of the initial compressive and tensile stress waves at different times.Under the condition of bolt supports,the stress of the surrounding rock of the roadway,the number of crack sections,the roof subsidence and the displacement of both sides have been improved to varying degrees,which is due to the fact that bolt and the surrounding rock bear the impact load together,and the bolt improves the bearing capacity of the surrounding rock by increasing the surrounding rock confining pressure.The bolt element has a good effect in preventing deformations of the surrounding rock of the roadway,controlling developments of cracks,and improving stress distributions.The bolt element is a virtual element,which dose not require the separate time step,leading to the high calculation efficiency.The mesh generation process of the solid element is not affected.There are 48 figures,2 tables and 114 references in this thesis.