Experimental Study On Macro- And Mesoscopic Damage Of Typical Secondary Muddy Interlayers In The Sichuan Basin Under Dry-wet Cycles

The mudded intercalation is one of the common soft interlayers in rock mass,and is the main weak surface to control the stability of rock mass.There is a kind of secondary mudded intercalation in mudded intercalation,which mostly exists in shallow surface.At the same time,it is affected by geological tectonic movement and environmental action.It is easy to cause landslides and other disasters.Especially in the harsh environment of dry-wet cycle in flood season,the problem of slope stability is more prominent.Therefore,it is of great significance to study the damage deterioration of secondary mudded intercalation under the action of dry-wet cycle for the prevention of geotechnical disasters and the evaluation of slope stability.Secondary mudded intercalations are abundant in the basins of Eastern Sichuan,especially in the hills and Longquan Mountains in central Sichuan.In this paper,the clay mudded intercalation in Jiangyou carbonate rock,the red mudstone mudded intercalation in Longquan Mountains of Janyang and the muddy siltstone intercalation in Nanjiang are taken as the research objects.The macro and meso damage evolution characteristics of mudded intercalation are studied through phase analysis and macro and meso dry-wet cycling laboratory tests.The relationship between macro and micro damage is also discussed in this paper.The main research contents and results are as follows.(1)The composition of three kinds of mudded intercalation is analyzed by X-ray diffraction test.The diffraction patterns of muddy interlayers before and after dry-wet cycling are compared.It is found that there is some chemical damage in the process of dry-wet cycling,but the effect is very small.The chemical damage is mainly caused by feldspar,clay minerals and other substances which could react with water,mainly by water dissolution and ion exchange.These chemical effects affect part of the cohesion.(2)The macro damage evolution process of three kinds of mudded intercalation is obtained by means of macro dry-wet cycling test and camera photography.The original photos were processed by the image software developed by our research group based on Matlab,and the damage characteristics such as the proportion of macroscopic damage area,the total length of cracks and the average width of cracks are extracted and quantified,and the evolution law of macroscopic damage is studied.Different types of mudded intercalation also have different macro damage development laws.Damage initiation,healing and development coexist in the process of macro damage evolution.(3)A sample nesting device and observation method suitable for the calibration of scanning area of electron microscopy are designed,and the observation effect is good.To some extent,it solves the problem that it is difficult to control the same area in the microscopic comparative study of rock and soil materials.The micro-damage evolution process of three kinds of mudded intercalations is obtained by micro-wet-dry cycling test and scanning electron microscopy observation.Micro-damage shows the change of pore.The damage characteristic parameters of pore number,pore size,pore shape and pore arrangement are quantified by PCAS software.Evolution law of pore damage is found,which proves that dry-wet cycle mainly affects cohesion but has no obvious effect on internal friction angle.(4)The relationship between macro and micro representative damage characteristic parameters and cohesion is discussed with quantitative data.The relationship between macro damage area,total fracture length and micro-pore number,pore size,fractal dimension and cohesion is obtained.At the same time,it is found that damage and cohesion are more sensitive to short-term wet-dry cycling,and the change rate slows down and stabilizes with the increase of cycling times.Finally,the damage mechanism of micro-pore directional penetration forming macro-cracks and gradually developing along the weak direction to damage stability is revealed.This paper provides a reference for the future research on water damage of muddy interlayer.