Experimental design on shear degradation of schistosity plane under dry-wet cycles
[Objective]The schistosity plane,a common weak structural feature in schist formations,serves as a conduit for water transfer and storage and is an active zone for water-rock interaction within schist.However,under the cyclical conditions of rainfall and evaporation,the mechanical properties of the schistosity plane tend to deteriorate.This degradation reduces the stability of schist slopes and contributes to frequent geological hazards such as landslides and collapses.Hence,conducting experimental research on the degradation of schistosity planes under dry-wet cycles is essential.Such research aims to uncover the patterns of degradation,vital for long-term stability assessments of schist slopes,and to nurture students'ability to integrate theory with practical application.[Methods]In this study,cylindrical samples with an aspect ratio of 1∶1 were prepared and subjected to dry-wet cycle treatments.During the drying phase,the samples were exposed to a temperature of 105℃for 24 hours,while for wetting,the free water absorption method was employed,during which the samples were soaked for 24 hours.Subsequently,direct shear tests were conducted on the samples after 0,1,3,5,10,15,and 20 cycles of dry-wet treatment,with normal stress levels set at 3,6,9,12,and 15 MPa,respectively,to determine the corresponding peak shear stress.Following the Mohr-Coulomb failure criterion,cohesive force and internal friction angle of the schistosity plane were fitted.Additionally,the total deterioration degree and stage deterioration degree were calculated using respective deterioration degree formulas.Finally,the apparent changes in the schist samples were observed,and the deterioration mechanism was elucidated by correlating it with the law of shear strength.[Results]The experimental findings revealed the following:1)The degradation rate of peak shear stress,cohesion force,and internal friction angle was more rapid and pronounced in the initial stages but slowed down and became smaller in the later stages.2)Following 20 cycles of dry-wet treatment,cohesion decreased by 49.05%,the internal friction angle decreased by 15.34%,and cohesion decreased approximately 3.2 times more than the internal friction angle.3)gradually,the schistosity planes exuded yellowish-brown materials,staining the samples.This manifestation made the schistosity planes more apparent,leading to the gradual development of cracks along these planes,which extended into the rock's interior.4)The schistosity planes served as conduits for water ingress and egress,facilitating the dissolution and removal of argillaceous cement and soluble minerals between the planes.Consequently,the cementation and cementation area between the schistosity planes gradually decreased,leading to a progressive deterioration in shear resistance.[Conclusions]Through this experiment,the deterioration law of the shear strength of the schistosity plane under dry-wet cycles and the deterioration mechanism can be obtained.Furthermore,experimental teaching holds the potential to enhance students'theoretical comprehension and practical skills,fostering their innovative thinking in scientific inquiry and their capacity to integrate theory with practice.Moreover,integrating ideological and political elements into the experiment can inspire students to appreciate the beauty of science,thereby stimulating their enthusiasm for professional learning and scientific research.
mica quartz schistschistosity planedry-wet cyclesshear strengthdeterioration test
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