| With the increase of mining depth,the creep effect of rock becomes more obvious,and many geological disasters are especially prominent.At present,there are few researches about creep based on continuous-discontinuous methods.It is great significance to study rock creep by continuous-discontinuous methods.In order to accurately describe the processes of creep cracking of rock,the Burgers creep constitutive model was introduced into the combined Lagrangiandiscrete element method(a kind of continuous-discontinuous methods).The fictitious crack model was modified based on the relation between the creep failure and the conventional failure of rock,and the continuous-discontinuous method with creep was developed.The continuousdiscontinuous method with shear creep,which was established by introducing the creep shear crack model into the original continuous-discontinuous method,was validated through simulating the creep experiment of the red sandstone specimen in uniaxial compression.In this method,cracks not only include creep shear cracks,but also conventional tensile cracks and conventional shear cracks.The processes of creep tensile cracking of single beam and laminated beams in three-point bending was explored,the influence of the superposition order of single beams was studied,Cracking processes of the surrounding rock of the soft rock roadway with or without bolt supports were modeled.The rock specimen in uniaxial compression enters the accelerated creep stage after creep shear cracking occurs.The two conjugated shear bands formed by creep shear cracking and flake tensile cracking zones formed by conventional tensile cracking develop near the two corners of the lower end of the rock specimen,which are related to the strong constraint of the lower end of the rock specimen.During the processes of creep tensile cracking of two kinds of laminated beams with different superposition order of single beams in three-point bending,the lower single beam cracks earlier than the upper single beam;the curves of displacement-timestep curves can be divided into three stages.The occurrence of the stage 2 is mainly related to the rapid development of the tensile cracking of the lower single beam,and the occurrence of the stage 3 is mainly related to the rapid development of the tensile cracking of the upper single beam.Without bolt supports,creep shear cracking occurs near the tip of V-shaped notches.The number of creep shear crack segments is much smaller than of conventional shear crack segments,and both of them show a slow growth trend,which should be related to the creep shear cracking zone entering the strain-softening stage.At this time,V-shaped notches at two sides of the roadway are difficult to maintain stability.With bolt supports,the range of the creep shear cracking zone decreases.When 400 days after the tunnel excavation completed,The average displacements of the left and right sides of the roadway decrease 87.02 % and 89.26 % respectively.The average displacements of the floor and roof of the roadway decrease 34.54 % and 85.72 % respectively.There are 63 figures,14 tables and 127 references in this thesis. |
