Study On Creep Mechanics Model And Application Under Water-rock Coupling Action Of Deep Buried Sandstone In Wanfu Coal Mine

With the continuous development and progress of society,a large number of geotechnical engineering,such as traffic tunnels,slopes,nuclear waste treatment and mining tunnels,have been continuously constructed,and the service time of such engineering often lasts for decades or even centuries.Therefore,the safety and stability of the structure in the long-term use process have been widely concerned,and the creep property of rock has become the focus of many engineering long-term stability studies.At the present stage,the roadway（tunnel）is developing to a greater depth,and has entered the kilometer mining stage in the field of coal production.The surrounding rock of deep roadway is affected by complex geological conditions.In addition to the greater ground stress level,it is most seriously affected by groundwater.There are numerous engineering damage cases caused by groundwater in various projects.It is more and more important to study the water-rock coupling,especially the creep characteristics of rock under the water-rock coupling.However,the research on instantaneous compression properties under water-rock coupling,especially the long-term mechanical properties of rock is not enough.On the basis of previous studies,this thesis uses laboratory mechanics experiment,theoretical analysis,numerical calculation and other methods to study.Taking the sandstone of Wanfu Coal Mine as the research object,the instantaneous compression test and creep test of water-rock coupling samples under different moisture content conditions were carried out,and the nonlinear damage creep model of water-rock coupling was established.UMAT program was developed by ABAQUS,and the NPR bolt-cable coupling support was studied by numerical calculation,and the results were applied to explore practical engineering problems.The conclusions are as follows:（1）Hydraulic experiments with key water contents of 0%,0.8%,1.6%,2.4%and3.3%,uniaxial and triaxial compression mechanics experiments,and microscopic monitoring experiments（including Nuclear Magnetic Resonance experiment,Scanning Electron Microscope experiment,Mercury Injection experiment,etc.）were carried out.It is found that the mechanical parameters such as compressive strength and elastic modulus decrease negatively with water content and increase linearly with confining pressure.The failure mode is mainly shear failure.With the increase of water content,the samples become more broken due to the increase of fine tensile cracks,while the confining pressure leads to lateral deformation of the samples,so the number of branch cracks decreases and the single inclined plane shear failure is the main failure mode.（2）According to the pore size change rule corresponding to different relaxation time of T₂ NMR spectrum,the water absorption process can be divided into four stages,namely rapid water absorption stage,uniform water absorption stage,pore transformation stage and stable water absorption stage.At the same time,through the study of microscopic pore structure,it is found that the strength softening of sandstone mainly occurs in theⅠandⅡstages,and the pore transformation mainly occurs in the III stage.Compared with the lubrication of bound water film and the loss of water absorption strength of clay minerals,it lags behind and affects the final failure mode.（3）The uniaxial and triaxial creep tests of sandstone under different water content conditions were carried out,and the relationships between long-term failure strength,instantaneous strain,creep strain and steady creep rate and water content were obtained.The ratio of uniaxial compression creep stress to UCS is between 0.76-0.84,and that of triaxial compression creep stress is between 0.80-0.98.The law of instantaneous strain and uniaxial compression is similar,and the law of creep strain and creep strain rate and water content increase exponentially.Both the creep failure mode and the instantaneous compression failure mode are shear failure mode.But there are also differences,mainly in the low confining pressure rock surface stripping linear,and X conjugate crack failure mode appear with high water content.When the confining pressure increases,the microcracks decrease and the failure is a single shear crack.（4）According to the isochronous curve,the modulus E_v describing the creep viscous deformation behavior was proposed.Combined with the softening law of elastic modulus and viscous modulus,two damage factors were proposed to modify the traditional Nishihara model,and the damage creep constitutive model of water-rock coupling was obtained.The parameters of Wanfu sandstone creep test were identified,and the model parameters were obtained.The fitting curve was in good agreement with the creep test curve.Further research divides the creep isochronic curve deformation into three parts,namely viscoelastic deformation,plastic deformation and nonlinear deformation.Based on the experimental data,the accelerated creep model based on stress damage is obtained,which can also better reflect the deformation law of the complete creep curve.（5）Based on the moisture content damage creep model above,the constitutive model was developed and the experimental results were numerically calculated,which could reproduce the laboratory experimental results and verify the reliability of the modified model.The results show that the NPR anchor cable coupling support has advantages in the long-term stability support of creep failure of roadway,which can provide guidance for on-site support and construction.