Study On Failure Mechanism Of Mudstone Based On Digital Core Technology

In order to study the damage evolution rule and failure mechanism of mudstone under different stress conditions,the in-situ CT scanning experiment of uniaxial compression was carried out with the mudstone of Guandi Coal Mine as the main research object,and the formation and evolution process of deformation localization caused by the damage evolution and damage accumulation in the mudstone under uniaxial compression were studied from the micro perspective combining with the digital volume image correlation method(DVC)The quantitative characterization and visualization method.Computer tomographic imaging technology can detect the internal structure of rock materials without damage and with high resolution,which has become one of the important means to study the evolution process of the internal pores of rock materials.Although CT scanning technology can largely characterize the fracture evolution process in the rock failure process at the resolution scale of scanning equipment,it will still lose part of the pore information whose size is smaller than the resolution scale,which will cause some errors to the subsequent analysis;and the complex mineral components inside the rock are also another important factor in the complex failure process of rock,such as How to characterize the three-dimensional damage process and fracture evolution in rock,and how to reveal the influence and development process of complex mineral composition on crack evolution,are urgent problems to be solved,which are beneficial to the understanding and understanding of the meso failure mechanism of mudstone.This paper combines micromechanics,experimental mechanics and numerical calculation theory,with the help of high-resolution CT scanning equipment,combined with digital core technology and digital font image correlation method,and takes the three-dimensional characterization of the internal mineral composition and pore characteristics of mudstone as the main research content,as well as the evolution process of localized damage,and carries out the step-by-stepin-situ CT scanning experiment of mudstone under the condition of uniaxial compression,The parameters such as porosity,pore volume,pore coordination number and the spatial evolution process of pores and mineral composition in different loading stages of mudstone are analyzed.Finally,the above data are summarized and analyzed,and the following conclusions are drawn.(1)The composition of diagenetic minerals in the roof mudstones of Guandi mine is relatively simple,mainly including quartz,feldspar and other brittle materials and clay minerals.The high proportion of brittle minerals is the main reason for the high strength of this part of mudstones.And through the scanning electron microscope,it is found that the brittle minerals in the mudstones,such as quartz,often exist in the form of agglomerated strips,which may lead to the connection of different minerals The contact surface forms weak structural surface.(2)Through further study on the failure mode of mudstone under load,a digital core model of different loading stages is established.It is found that there will be a large number of primary intergranular pores near the mineral accumulation zone.With the increase of axial load,the connectivity of pores will gradually increase,which is shown as the increase of porosity of rock,and gradually expand cracks,and the abnormal development of internal pores When the rock reaches the critical state of failure,the number of throats and coordination number of pores increase greatly compared with the previous loading stage.(3)Based on the statistical analysis of the spatial distribution of mineral particles,it is found that there is no obvious difference in the distribution of mineral particles of different sizes.The interior of mudstone is mainly affected by a large number of small-size mineral particles,which shows that the slip between the mineral belts is mainly dominated by small-size minerals,and the final crack growth pattern is very consistent with the shape of the mineral belt,indicating that the aggregated mineral belt It is easy to form a weak plane,and the mineral belt gathered under load is easy to produce local deformation,which is related to the mechanical properties of the mineral belt and its surrounding rock matrix.It also shows that the rock is easy to producealong the junction of the two minerals when breaking.(4)When using CT image to analyze the damage,it will be affected by the scanning resolution of CT system.The scales studied by different analysis methods have their applicability.The digital core and pore network model is suitable for the analysis larger than the resolution scale.The digital font image correlation method can analyze the fracture before the CT resolution scale appears.Local deformation and evolution process caused by microcracks smaller than CT resolution scale.(5)Through the analysis of the displacement field and strain field evolution in different loading stages,it is found that the displacement value in the polymerized mineral belt is small,the deformation displacement value of the rock skeleton near the quartz mineral belt is large,and the deformation of the rock skeleton in the area is restrained by the quartz mineral with larger strength.