Study On Capillary Migration Law Of Soluble Salt In Sandstone Cultural Relics And Its Induced Surface Deterioration Mechanism

Sandstone cultural relics have been exposed to the natural environment for a long time,resulting in various deterioration under the influence of environmental and human factors.Among them,surface salt damage is one of the most common and typical deterioration.Capillary action is the main way for soluble salt to enter the interior of sandstone cultural relics,and it will cause soluble salt to migrate,enrich and crystallize inside the sandstone,thereby causing damage to the structure of the sandstone and seriously affecting the ornamental and research value of the cultural relics.Therefore,studying the capillary migration law of soluble salt solution in sandstone cultural relics and the mechanism of induced surface degradation has important theoretical and practical significance for grasping the law of surface salt weathering of sandstone cultural relics and carrying out deterioration control.In this thesis,relying on the National Natural Science Foundation of China project "Research on the mechanism of rock mass damage induced by soluble salt phase change in sandstone cultural relics"(52179096),the capillary migration law of soluble salt solution in sandstone and its influencing factors are studied through laboratory simulation experiments;The distribution and evolution law of water and salt in sandstone under capillary action were analyzed;The calculation model of capillary rise of soluble salt solution in sandstone considering pore saturation was proposed;Then,the deterioration characteristics and evolution law of soluble salt recrystallization on sandstone surface structure under the action of circulating capillarity are studied;Finally,according to the research results,the mechanism and evolution model of the sandstone surface degradation induced by soluble salt under capillary action under different degradation types are proposed.The main research contents and results of this thesis are as follows:(1)Based on the self-designed capillary water absorption continuous measurement device and high-density resistivity test system,indoor soluble salt capillary migration and repeated crystallization deterioration experiments were carried out on sandstone in Dazu,Chongqing.The results show that the capillary water absorption process of sandstone can be divided into a near-linear stage,a transition stage and a stable stage,and low ambient humidity,soluble salt composition and loose pore structure can promote the rate and mass of capillary water absorption of sandstone.The capillary migration law of soluble salt solution in sandstone is summarized by analyzing the capillary water absorption curve and profile resistivity distribution characteristics of sandstone under different factors.(2)Through the change of sandstone section resistivity,the evolution law of watersalt distribution and pore saturation in sandstone during the capillary migration of soluble salt solution is analyzed.The results show that the increase of sandstone surface pore saturation and soluble salt enrichment is faster,and the rising rate of wetting front is greater than that of saturated area,and there is a certain range of unsaturated area between them.Therefore,a modified Terzaghi capillary rise model considering saturation is proposed to fit the capillary rise process of solution in the test,and its effectiveness is verified by comparison with the commonly used calculation model.(3)The analysis of the micro-meso characteristics of sandstone surface deterioration and the capillary water absorption and resistivity characteristics after deterioration shows that the deterioration of sandstone by soluble salt under capillary action is gradual in time and space.The crystallization deterioration of salt will affect the capillary migration and distribution of soluble salt in sandstone,and make the surface deterioration area develop in height and depth.Based on the above research,the action mechanism and spatiotemporal evolution conceptual model of deterioration modes such as granular disintegration,hollowing and roughening of sandstone surface caused by soluble salt under capillary action are summarized.