Microscopic Characteristics Of Schist And Its Effect On Anisotropy Of Uniaxial Compressive Strength Based On Particle Flow Simulation

The common law of foliated rocks is that they contain original weak surfaces,so they have significant physical and mechanical anisotropy,which are widely distributed in nature.Schist is one of the representatives of foliated rocks,and tunnel engineering,hydraulic engineering and slope engineering problems caused by schist anisotropy have long been common.At the mesoscopic level,the preferred orientation of flaky minerals in schist and the directional distribution of some microcracks are the essential reasons for the anisotropy of compressive strength.In this paper,focusing on the relationship between the mesoscopic characteristics of schist and the anisotropy of uniaxial compressive strength.The mesoscopic structure is divided into two types: discontinuous and continuous interbedded cases,and the research work is carried out.The research work is mainly divided into two parts,pre-modeling experiments and particle flow code simulation(PFC).The tests before modeling include uniaxial compression tests and mesoscopic test.The main research contents and research results are as follows:(1)Uniaxial compressive test,including groupings of dry state and different soaking days.The results show that,compared with the uniaxial compressive strength of the dry state after long-term soak,the discontinuous and continuous interlayer specimens generally have the largest decrease in the medium schistosity angle,and the strength of the continuous interlayer specimens anisotropy change after long-term soak more obvious than discontinuous specimens.(2)Mesoscopic test,divided into polarizing microscope test,scanning electron microscope test(SEM)and mesoscopic data extraction.The results show that,in general,the continuous interlayered samples have a higher content of flaky minerals than the discontinuous samples,and the degree of continuity and orientation of the former flaky minerals is also better.The flaky mineral clusters have various shapes,such as linear and cluster.(3)In the discontinuous structure simulation,by drawing mineral boundary lines in CAD and importing PFC,the new simulation idea of assigning values inside and outside the boundary lines basically realizes the simulation of slip,kink and fracture of flaky minerals.It is an improvement to the traditional way of using short straight lines instead of flaky minerals,and the mineral deformation is closer to the real situation.(4)In the discontinuous structure simulation,the relationship between the internal and external factors and the anisotropy of uniaxial compressive strength is studied.Intrinsic factors of flaky minerals: angle,ratio of major and minor axes,content level,degree of orientation,and degree of coplanarity.The external factor is the duration of immersion.The results show that among all the factors studied,the flaky mineral content has the highest sensitivity to the influence of the strength anisotropy of the discontinuous structure model.The degree of orientation of flaky minerals are likely to be the main reason for the uniaxial compressive strength of foliated rocks,which has various curve shapes with the change of weak face angle.(5)In the simulation of continuous interlayer structure,the influence of internal and external factors on the anisotropy of uniaxial compressive strength was studied.Intrinsic factors of flaky minerals: angle,schistosity density and flaky content level.The external factor is the duration of immersion.Long-term water immersion has the highest sensitivity to the change in strength anisotropy of the continuous interlayer structure model.The schistosity density and mineral content were positively correlated with the strength anisotropy,respectively.