Investigation Of The Micro/Meso-scopic Mechanism Of Creep Rheological Deformation Of Rocks

From the last few decades,due to the increasing trend of rocks excavation projects such as mines,tunnels,slopes,and dams,research on the stability and safety of these rock structures in civil and mining projects has become more and more important.As the depth of mines(especially coal mines and other deep underground projects)continues to increase,it is particularly critical to ensure the long-term stability of the rock excavation because most of these structures are to be sustained for long time,rock creep is an important influencing factor.Researchers have carried out many experiments and numerical simulation studies in this field.However,due to the heterogenous nature of rocks,their composition and structure vary at every inch,also,less attention has been paid to the creep microscopic deformation of rocks.Existing research cannot establish a good design method for rock structure,so relevant research is urgently needed to solve the problem of long-term stability during rock excavation.Long-term loading tests are carried out using sandstone from the Kouzidong Coal Mine in China.Based on the relationship between rock creep deformation and microscopic characteristics at a micro level,the microscopic fracture and deformation mechanisms of rock creep is systematically studied,and the following main innovative results are achieved:(1)Transmission electron microscope(TEM)is used to study the deformation of the sandstone lattice.In-depth analysis of the deformation and movement of the sandstone lattice after long-term creep and rheological load is carried out.The sandstone sample from the same location is scanned by TEM,and based on the Fast Fourier Transform(FFT)method and the profile plot method,the lattice spacing of the sandstone is analyzed and calculated.The study found that the lattice spacing increases with the increase of the applied constant load,and the lattice movement will be affected by the applied load and time,thus revealing that the lattice dislocation is the root cause of rock creep deformation.(2)Long-term constant uniaxial loading tests are carried out on sandstone from Kouzidong Coal Mine.The maximum creep strain of sample 1 is 0.03124,and the maximum creep strain of sample 2 is 0.03526.Analyzing the deformation of the rock before and after the creep load by scanning electron microscope(SEM),it is found that the rock has obvious mesoscopic deformation and damage after creep.The analysis shows that the degree and strength of rock deformation increases with the increase of the applied load.A novel equipment is designed to analyze long-term loading of small rock samples.(3)Transient and stable creep stages of rock are analyzed through long-term creep tests.In the process of rock creep,the creep strain first increases rapidly,and then the growth rate slows down until it remains stable.In the stable creep stage,the creep strain basically tends to be constant.Based on the 3D XRM scanning test,the grains movement and dislocation of the rock after creep are observed.With the increase of the constant uniaxial load on the second sample,the sample developed macroscopic cracks.(4)The numerical manifold method(NMM)is used to describe the instantaneous microscopic deformation,the microscopic deformation model of rock creep is proposed and verified,and the influencing factors of rock deformation are obtained.Micro crack growth law is used for short-term and long-term microscopic deformation.The research results will provide guidelines for the design of long-term stability of rock structures such as mines,tunnels,slopes,dams and chambers.