| The carbonate rocks in karst area show an obvious phenomena of dissolution,softening and argillization under the transformation of groundwater chemical environment.The dissolution of carbonate rocks is closely related to the external hydrochemical environmental factors.The different grain pore microstructure of the dissolution samples under different combinations of factors is the fundamental reason for the different macro physical and mechanical properties.In order to clarify the dissolution characteristics of bedding limestone,a series of standard cylindrical samples(?=0°,15°,30°,45°,60°,75° and 90°)with different dip angles were immersed in acid solution at room temperature and atmospheric pressure under different test conditions.The mass loss,dissolution zone distribution,longitudinal wave velocity and Ca2+/Mg2+concentration of bedding limestone before and after hydrochemical acid etching were obtained The influence of bedding angle,bedding dip angle(?),acid concentration(pH),water flow velocity(v)and dissolution reaction time(t)on the dissolution of limestone samples is preliminarily discussed.The relationship between the dissolution damage variables and various factors of layered limestone is established.Combined with the results of SEM and EDS,the heterogeneous dissolution process of limestone under the influence of bedding direction is revealed Process and mechanism.The specific research contents and main understandings are as follows:(1)The acid immersion corrosion tests of limestone samples under different test conditions were designed,and the state variables such as sample quality,longitudinal wave velocity,corrosion zone distribution,acid Ca2+/Mg2+concentration before and after the test were measured.(2)The relationship between the dissolution amount of rock sample and bedding dip angle,hydrochloric acid pH value,soaking time and acid flow rate was studied.It is considered that the corrosion damage of rock samples with different bedding angles in different time periods mostly presents the characteristics of 30°>75°>15°>90°>0°>45°>60°;with the increase of acid pH,the lower the concentration of dissociated H+is,the smaller the dissolution amount of rock samples decreases,showing an exponential curve decreasing trend;the time effect is obvious in the process of rock dissolution,and the longer the water rock reaction time is,the higher the dissolution degree of layered limestone is The results show that the acid flow velocity has a significant effect on the dissolution degree of rock samples,which promotes the water rock chemistry.(3)Scanning electron microscope(SEM)and energy dispersive X-ray diffraction(XRD)tests were carried out on limestone samples before and after dissolution.The results show that the differences of rock structure and mineral composition of bedding lead to the micro dissolution differentiation of limestone with bedding.The increase of immersion time and water flow rate makes the mineral dissolution degree deeper,the overall dissolution process is later,the pore connection is weakened,and the physical-chemical interaction is weakened The bigger the solution pore is,the easier it is to form with superposition effect.(4)Through multiple regression analysis by mathematical statistical method,it is found that the influence degree of each factor on the hydrochemical damage variable of rock sample is:acid pH>water rock reaction time t>acid flow velocity v>bedding angle ?,and the dissolution damage model of layered limestone is preliminarily established.The results can provide initial damage and deterioration parameters for deformation and failure analysis of dissolved rock mass. |
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