Mechanism Of Black Rocks Deterioration And Water-rock Interaction Under Dry-wet Cycle

The comprehensive interaction of water and rock causes the change of rock properties and the happening of this change usually causes the instability failure of engineering project and threatens human life and property.The black rocks in Chengkou area of Chongqing is taken as the research object,the engineering geological characteristics of the black rocks is investigated and the basic physical properties and geochemical characteristics of the rock is analyzed.In order to study the characteristics and mechanism of rock degradation under the action of dry-wet cycle,dry-wet cycle test has been carried out on rock samples to test the water absorption,surface hardness and uniaxial compressive strength of the rock.The pore characteristics and the water solution chemical characteristics of the reaction solution were discussed in depth.The main content and views are as follows:(1)The basic physical properties and geochemical characteristics of rocks are analyzed by X-ray diffraction(XRD)and X-ray fluorescence spectroscopy(XRF).It is found that the natural water content of the black rock samples are extremely low,which indicates large density.The rock is rich in organic matter and pyrite,the main rock-forming minerals are quartz,pyrite,dolomite and clay minerals,containing a small amount of feldspar.(2)Different times of "water absorption-air drying" cycle is realized in the black rock samples by using indoor dry-wet cycle simulation test.The properties of the sample under different cycle times such as water absorption rate,surface hardness and uniaxial compressive strength were tested,the law of rock deterioration is summarized.The experimental results show that the rock properties have obviously deteriorated under the action of the dry-wet cycle.With the increasing of the times of dry-wet cycle,the water absorption rate of the rock increases,the hardness of the rock surface decreases slightly and the uniaxial compressive strength of the rock decreases constantly.The test results show that the dry-wet cycle causes damage to physical and mechanical properties of the rock.(3)The microscopic pore characteristics of the rock and the hydrochemical characteristics of the reaction solution indicate that the pore size of the rock increases continuously with the increasing of the times of dry-wet cycle.Increased contact space between water and rock will accelerate the progress of water-rock interaction and the dissolution and alteration of various mineral components in the rock.During the deterioration of the rock properties,the physical and chemical effects of water and rock proceed simultaneously.Carbonate minerals mainly exhibit physical dissolution in the neutral environment under the interaction of dry-wet cycle,which makes the pore size of the rock continuously increase.The expansion and softening of clay minerals such as illite and montmorillonite when exposed to water will also cause the stripping and shedding of the surface layer of the rock,increasing the internal pores of the rock mass and accelerating the water-rock interaction.The oxidation of pyrite and other sulfide minerals forms various weathering products,which causes adverse effects on the rock mass.