Research On Rock Deformation Localization And Its Damage Quantitative Characterization Method

With the rapid development of my country's infrastructure construction,it is increasingly urgent to accurately evaluate the safety and reliability of geotechnical engineering construction.Among them,basic research on the deformation damage and instability failure of rocks under external loads is particularly important.To this end,this paper intends to use the self-developed 3D-DIC non-contact rock surface three-dimensional observation system to pass the triaxial load tests,load rate dependence tests,seepage-generalized stress relaxation tests and other test conditions on the circumference of cylindrical rock specimens.The systematic analysis of the evolution process of the surface deformation field during the loading process has found that the deformation of the rock during the deformation and damage process under the external load has an obvious concentration phenomenon,that is,the localization of the rock deformation.Based on this,the characterization of the rock deformation and damage is further proposed.The degree and spatial distribution of the deformation localization factor and the calculation method of the damage factor are expected to provide scientific guidance for the localization of rock deformation and the in-depth understanding of the damage and degradation mechanism of rock.The main research work and research results obtained are as follows:1)Triaxial load tests(different confining pressures,different water contents),load rate dependence tests,seepage-generalized stress relaxation tests and other different test conditions,the deformation of the rock under load changed from uniform to non-uniform mode,strain(or deformation)was finally concentrated in one or more narrow areas,that was,the deformation localization zone,and finally instability failure occured along the direction of this narrow zone.2)Based on the evolution process of the strain field cloud diagrams such as axial strain,radial strain,and shear strain,and a comprehensive statistical analysis of the corresponding characteristic statistics(variance S~2),it was proposed that radial strain was more appropriate as a strain parameter to describe rock damage,and the strain measurement points in the first 5%of the deformation amount were used as observation points to describe the deformation localization process of the rock.3)This paper proposed the localization factor L_f and the damage factor D_f to reflect the spatial distribution of damage and the degree of damage on the rock surface during the localization of rock deformation.The localization factor L_f decreased slowly at the pre-peak stage,and then suddenly droped sharply at a certain stage after the peak;the damage factor D_f changed slowly at the beginning of loading,and exhibited a"sudden"increase after the peak.The damage factor constructed based on the numerical value of the larger strain point was a quantitative description of the radial strain field,which could describe the damage degree information of the rock surface.At the same time,the localization factor grasped the damage evolution law from the time and passed the larger strain point.The spatial distribution reflected the spatial characteristics.Combining these two curves could grasp the key information of rock structure characteristics,damage distribution,evolution trend,etc.as a whole.4)The two-factor characterization method was extended and applied to several test conditions,and the results showed that the damage two-factor method could effectively characterize the rock damage evolution process quantitatively.The results of rock triaxial load tests(different confining pressures and different water-bearing conditions)showed that the higher the confining pressure,the stronger the toughness of the rock material;the higher the water content,the more the damage factor curves would change from a"sudden increase"to a"steady"increase.The characteristics of sculpting failure were becoming more and more obvious.The test results of the load rate dependence showed that as the load rate increased,the rock undergoed brittle failure in a shorter time,and there was also a change in the shape of the structural surface.The experimental results of the generalized stress relaxation characteristics of rock under the coupling of seepage and stress showed that the development rate of localized deformation of rock increased rapidly before the formation of macroscopic cracks under different rheological direction coefficients;In addition,the presence of osmotic water pressure would stimulate the generation of shear cracks and accelerated the fracture of rocks.