Experimental Study On The Effect Of Hydro-chemical Action On The Shear Mechanical Characteristics Of Limestone Fractures

Fractures as the main factor affecting the overall strength of rock mass engineering,a slightly change in its shear properties may lead to the instability or failure of rock mass engineering.Once groundwater or rainwater seeps into the interior of rock mass along this fractures,it will accelerate the deterioration process of the overall strength and shorten the service life of rock mass engineering.Therefore,it is necessary to carry out the experimental study on the influence of hydrochemical action on the shear mechanical characteristics of fractures.This paper selected the limestone as the research object which was widely existed in nature,the limestone fractures was obtained by splitting method,and then the limestone fracture are soaked in Na₂SO₄ solution with different pH values,according to different soaking time,the soaked limestone fractures are taken out in batches for testing.Firstly,3D morphology of rock surface before and after soaking was obtained by OKIO-300 rock surface three-dimensional laser scanner.Through comparative analysis,it can be concluded that the hydrochemical action reduced the fluctuation and roughness of limestone fracture,that is,the hydrochemical action makes limestone fracture surface smoother.Secondly,direct shear tests were conducted under different constant normal load by using RDS-200 rock direct shear system.The results show that both decrease percentage of limestone fractures cohesion and internal fraction angle were increase with the increase of soaking time,the decrease percentage of cohesion have a good logarithmic relationship with soaking time,and the decrease percentage of internal friction angle have a good exponential relationship with soaking time.By analyzing the relationship between the deterioration degree of limestone fracture shear parameters and the concentration of mineral ions in the solution,it can be concluded that both the decrease percentage of limestone fracture cohesion and internal fraction angle had certain exponential relationship with the concentration of mineral ions precipitated in the solution.Based on the regression analysis of C,?decrease percentage change with immersion time,an empirical formula for the degradation of the shear strength of limestone fracture based on the Mohr-Coulomb strength criterion was proposed.