Molecular Dynamics Study On The Micromechanical Properties Of Clay Minerals

With the increase of mining depth,deep geological environment,such as the stress increase,water inflow increased,and ground temperautre rises,is more complex.The deep engineering disaster become increasingly serious,especially the deep soft rock engineering disasters,which bring severe challenges to the research of deep soft rock engineering probelms.Soft rock is different from general rock is due to that clay minerals is the main constituent.Clay minerals will swell and burst apart in complicated stress conditions,especially absorbing water,which result in the decrease of mechanical strength.At present,the study on the deformation of soft rock focuses on the deformation characteristics and causes,mechanical properties and engineering support technology of soft rock.However,little reasearch focuses on the micro-mechanical properties of clay minerals.In this paper,kaolinite minerals and montmorillonite are studied.Kaolinte minerals are non-expanding clay minerals,and montmorillonite is a typical representative of swelling clay minerals.Due to its special structural characteristics and wide application,the structural and mechanical properties of clay minerals have received extensive attention,but there are still many aspects of molecular dynamics research on their micromechanical properties that need to be supplemented and improved.On the basis of summarizing the research status at home and abroad,the main frame of this thesis is formed:(1)Kaolinite is one of the most important components of clay minerals.The tensile mechanical properties of kaolinite were simulated by molecular dynamics in the temperature range of kaolinite retained its crystal structure.The deformation and failure mechanism of kaolinite microstructure at different temperatures and the temperature effect of anisotropic mechanical properties were studied.Due to a large number of defects in clay minerals in nature,we consider the temperature effect of intrinsic defect kaolinite and reveal the influence of defect location,type and density on its mechanical properties.(2)The most common kaolinite minerals are kaolinite and halloysite.Based on the model of halloysite,the microstructure and anisotropic mechanical properties of 7,8.6 and 10 A hydrated kaolinite are studied.The effect of interlayer water on the mechanical properties of kaolinite is analyzed,and the interaction mechanism between water molecules and kaolinite lamella is revealed.At the same time,the temperature effects of the microstructure and mechanical properties of hydrated kaolinite were investigated,and the process of deformation and failure of the crystal under tension and compression were reduced from the microscopic point of view.(3)The water absorption and expansion of expansive clay minerals is the main cause of rock strength softening.Taking Na-montmorillonite as the research object,the process of water swelling and disintegration of montmorillonite was reduced at molecular scale.The macroscopic elastic modulus of montmorillonite was calculated by Voigt-Reuss-Hill approximation.The influence of aqueous solution of inorganic salts on the microelastic behavior of montmorillonite was studied.The optimum concentration range of four kinds of inorganic salts was determined and compared with the experiment.The mechanism of aqueous solution inhibiting the hydration of montmorillonite was analyzed.(4)A key factor affecting the degree of swelling of the clay is the type of interlayer cation.The dry montmorillonites with four different interlayer compensation cations(Na+,K+,Ca2+,Mg2+)were simulated.The interaction between interlayer cations and clay sheets was studied.The relationship between the internal characteristics and mechanical properties of montmorillonite structure and the type of interlayer compensated cations is revealed,and the structural characteristics and mechanical properties of pyrophyllite without isomorphic substitution are compared.In this paper,molecular dynamics simulations are used to investigate the micromechanics of clay minerals,the deformation and failure mechanism of clay minerals under different stress states and different conditions are explored.The relevant mechanical parameters are calculated and to obtain the critical stress and strain during the elastic-plastic transformation and failure of materials.According to the actual engineering conditions,considering the influence of temperature and water on the mechanical properties of clay minerals,as well as the actual situation of clay minerals in nature,the problems of defect and isomorphism substitution are considered.This paper aims to provide the microscopic mechanisms of large deformation of soft rocks.The microstructural information will greatly enhance the perception of how the atomic level deformation process affects the deformation and failure of clay minerals.