| This paper takes Santai dangerous rock mass in Wudongde reservoir area as the research object.The geological environment and formation mechanism of Santai dangerous rock mass are analyzed on the basis of geological survey and geological data analysis.In view of the special dry-hot valley environment in the Wudongde reservoir area,considering the water-rock interaction zoning of the bank slope rock mass in the hydro-fluctuation belt,long-term immersion,dry-wet cycle and thermal-wet cycle tests were carried out respectively.The physical and mechanical properties deterioration law and damage deterioration mechanism of dolomite under different water-rock interactions were analyzed.The main results are as follows:(1)Comprehensively considering topography and fracture development characteristics of Santai dangerous rock mass,it is generalized into three secondary dangerous rock mass.The failure mode of the secondary dangerous rock mass is creep-cracking failure.The monitoring data shows that the stability of Santai dangerous rock mass is good at the present stage.Since the impoundment of the reservoir,the opening degree of cracks in the dangerous rock mass has been increasing slowly.During the operation of the reservoir,the repeated fluctuation of the reservoir water level leads to the deterioration of the physical and mechanical properties of the rock mass and the increase of the opening degree between the fissures,which has a direct impact on the long-term safety and stability of the dangerous rock mass.(2)During the process of water-rock interaction,the mechanical parameters such as compressive strength,tensile strength,shear strength,elastic modulus and deformation modulus of dolomite deteriorate obviously.The overall deterioration trend is ’fast first and then slow ’,and the deterioration value of the first five cycles accounts for more than 70% of the total deterioration value of the 12 cycles.The axial cracks of compressive failure increase continuously,and the sample gradually changes from complete to broken.The tensile fracture surface of the specimen gradually transitions from ’ linear ’ to ’ broken line ’ and ’ arc line ’distribution.Based on the variation of the macroscopic mechanical properties of and the failure modes of the samples under different water-rock interactions,the deterioration effects of different water-rock interactions are significantly different.The deterioration effect of the thermal-wet cycle is the strongest,followed by the dry-wet cycle,and the long-term immersion effect is the weakest.(3)The change law of the microstructure of the sample under different water-rock interaction was analyzed by microcosmic photos.With the advancement of water-rock interaction,the microstructure of the sample gradually changed from flat and dense to loose and porous,and the structural integrity was greatly reduced.The damage and deterioration mechanism of dolomite under water-rock interaction was revealed by analyzing the variation of microstructure,longitudinal wave velocity,density,porosity and ion concentration of soaking solution.Immersion pressure leads the water solution to go into the sample,then the soluble minerals and calcareous cement dissolved and migrated with the water.Decompression and airdry leads the secondary minerals,ions and debris generated by the hydration reaction to leak out rapidly with the aqueous solution.The deposition of insoluble silicates make the pores in the sample further develop.Compared with the relatively stable water chemical reaction state under long-term immersion,the hydration reaction under the action of drying-wetting cycle and thermal-wet cycle is more severe during the process of vacuum drying and pressure soaking,which results in stronger damage and deterioration effect of the two.(4)The cumulative damage caused by water-rock interaction is divided into two parts:damage caused by increased pore development and damage caused by softening of rock skeleton.In view of the shortcomings of the previous damage analysis,which is difficult to reflect the nonlinear characteristics of the compaction section of the stress-strain curve.Combined with the characteristics of the uniaxial compression stress-strain curve of dolomite in the process of water-rock interaction.The positive and negative damage variables are defined respectively.And the statistical damage constitutive model of dolomite under water-rock interaction is established based on Weibull distribution theory.The cumulative damage of water-rock interaction is quantitatively characterized by positive and negative damage variables.The comparative analysis of the cumulative damage amount of different water-rock interactions shows that the degradation effect of thermal-wet cycle is in turn greater than dry-wet cycle and long-term immersion.(5)The size effect of rock mass and structural plane is analyzed by numerical simulation.Combined with the test results of physical and mechanical parameters of dolomite samples under water-rock interaction,the macroscopic equivalent mechanical parameters of rock mass and structural plane are calculated respectively.With the help of Geo-studio software,the longterm stability of Santai dangerous rock mass in the process of reservoir impoundment operation is analyzed.The results show that after 5 cycles of water-rock interaction,the secondary dangerous rock mass(1)is in an unstable state.In order to prevent the sliding failure of the dangerous rock mass during the operation period of the reservoir,the system anchor cable is used to reinforce the secondary dangerous rock mass(1).The stability safety factor of the dangerous rock mass after reinforcement meets the requirements of the specification. |
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