Mesomechanical Characteristics And Water Weakening Law Of Mudstone

Mudstone mainly composed of clay minerals is a special rock mass,which has rock characteristics when it is dry and is same as mud after hydration.Mudstone is widely existed in rock and soil engineering and the water swelling and weakening characteristics significantly affect the stability of engineering structure.This heterogeneous body is composed of clay minerals and detrital minerals so the properties of mineral components determine the mechanical properties of mudstone.From the aspect of mineral components and mesoscopic scale,this paper investigated the mesomechanical characteristics and the water weakening law of mudstone.The quantifying of mineral components in mudstone,the testing of mesomechanical properties of mineral components,the simulations of the influence of mineral components on mechanical properties and the analysis of the water weakening rules of characteristic clay mineral components were carried out successively.From argillaceous engineering to mudstone body,then to the mudstone mineral composition,this research finally based on the characteristics clay minerals.The the analysis of components and mosescopic structure of mudstone was based on the mudstone excavated from the roof of-690 m track in Donghuantuo Mining Company.The quantifying results show that this heterogeneous rock mass is composed of clay minerals and detrital minerals.The clay mineral content is as high as 87.77% and high clay mineral content leads to soft mechanical properties of mudstone and poor stability of surrounding rock.At the same time,there are tiny pores and fissures between the mineral particles of mudstone.The testing of mesomechanical properties of mineral components was conducted by nanoindentation techniques.Mesomechanical properties refer to the characteristics of mineral particles.The results confirmed that the hardness,elastic modulus and fracture toughness of different mineral particle components of mudstone are different.The mechanical parameters of nanoindentation are related to mineral components.Mixtures of Gaussians were proposed to characterize the distribution of mechanical parameters of mudstone.The proportions of Gaussians are the volume ratio of clay minerals and detrital minerals.The mean values and standard deviations are calculated from the mechanical properties of clay minerals and detrital minerals.Based on mixtures of Gaussians of mudstone elastic modulus,considering the influence of mudstone porosity on macroscopic mechanical parameters,the elastic model scale is upgraded.The simulations of the influence of mineral components on mechanical properties were simulated by mud-like materials and PFC2 D and the physical and numerical simulation considered the mesoscopic structure of detrital mineral particles and clay mineral particles in mudstone.The simulation results show that the water weakening index of mudstone increases first and then stabilizes with the increase of clay mineral content;the mechanical strength of mudstone decreases with the increase of clay minerals,which stabilizes later too.According to the mudstone water weakening index and uniaxial compressive strength,the critical clay mineral(montmorillonite)content of mudstone was determined to be 28.81 vol.%.The analysis of the water weakening rules of characteristic clay mineral components took water swelling montmorillonite as subject.The density of montmorillonite compacted specimens decreases linearly with the increase of water content.Considering the van der Waals force and electrostatic force of the interaction between montmorillonite particles,the water weakening model of montmorillonite particles was established.The uniaxial compressive strength of the specimen decreases and then stabilizes with the increase of water content.The critical water content of montmorillonite is about 60%.When the water content increases to 60%,the uniaxial compressive strength of montmorillonite particles is 0.04 MPa,which has fluid characteristics.