Micro-meso-macroscale correlation mechanism of red-bed soft rocks failure within static water based on energy analysis

The purpose of the present study is to fundamentally investigate the micro-meso-macroscale correlation mechanism of red-bed soft rocks failure within static water,based on energy analysis.Through a series of experimental studies,changes in the micro-meso-macroscale characteristics of the rocks were characterised by measuring ion concentrations in and pH of water,the pore structure and crack propagation.Based on the experimental measurements,theoretical modelling of micro-meso-macroscale energy conservation was carried out to determine the micro-meso-macroscale correlation mechanism of red-bed soft rocks failure.The results show that the microscale dominant effect of red-bed soft rocks is determined as chemical effects.The failure mechanism of red-bed soft rocks under static water saturation involves chemical,physical and mechanical dominant effects at the micro-meso-macroscale.It was demonstrated that the dominant chemical effect of clay minerals and water comprises a series of chemical energy changes in the microscale water-rock interface.This can induce the energy changes in both mesophysical and macromechanical levels.During the first month after the water saturation,there was a significant decrease in Na+and K+concentrations in aqueous solution,whereas there was little change in Ca2+and Mg2+concentrations.The scanning electron microscope(SEM)images indicated an obvious change in microstructure of the red-bed soft rocks after 3 months of water saturation.A decrease in pore number and increase in total pore surface area could be seen after 6 months of water saturation.Furthermore,the theoretical results suggest that chemical effects at the microscale dominate the softening process of the rocks.During the water-rock interaction,nearly 80%of the energy dissipation results from the microscale change,and the meso-macroscale change accounts for the remaining 20%.As a uniform measure of material evolution,energy can correlate the micro-meso-macro dominant effect of red-bed soft rocks softening appropriately.