Study On Damage And Deterioration Of Cretaceous Grotto Sandstone Under The Control Of Microenvironment

The change of microenvironment of rock mass in grottoes controls the weathering damage process of grottoes.It is of great significance to study the damage and deterioration of grotto sandstone caused by different weathering factors under the control of microenvironment for the protection of cultural relics in China.Sandstone is commonly found in nature,with a soft texture and easy to depict and decorate.Therefore,cultural sites using sandstone as a building material are extremely common.80% of Chinese grottoes are carved on sandstone,but due to the poor strength,porosity,and susceptibility to weathering of sandstone,the long-term protection and treatment of weathering diseases in Chinese grottoes face great challenges.In order to explore the damage and degradation characteristics of the cave sandstone under the control of the microenvironment,this paper takes the Cretaceous sandstone of the North Grotto Temple as the research object,the main weathering factors under the two microenvironment of temperature and salt damage as the research variables,and the in-situ monitoring and indoor tests as the research means,to explore the damage evolution characteristics of the two degradation modes of the North Grotto Temple sandstone under the control of the microenvironment,and points out the main controlling factors of the weathering of the North Grotto Temple,A damage deterioration aging model has been established.The research results are as follows:(1)In terms of the control mechanism of temperature on the damage and deterioration of Cretaceous cave sandstone,in the conventional meteorological temperature range,the subcritical crack propagation caused by thermal stress generated by temperature changes controls the cumulative deformation and damage and deterioration characteristics of cave sandstone.Based on the two-phase linear thermoelastic formula and the solid volume coefficient of thermal expansion of multi mineral composition,the traditional quantitative evaluation method of thermally induced cracks is improved.Combined with the monitoring means of infrared IRT and ground-based SAR technology,the practicability of this method is verified.The indoor freeze-thaw cycle degradation simulation test results show that the physical and mechanical properties of grotto sandstone show a gradual deterioration trend with the progress of freeze-thaw damage,and grotto sandstone with different bedding directions exhibits distinct damage and deterioration failure modes;(2)In terms of the control mechanism of salt damage on the damage and deterioration of sandstone in Cretaceous grottoes,the alternation of dry and wet conditions and the repeated dissolution and crystallization of salt control the development of weathering damage process of sandstone and rock salt in grottoes.This study found through detailed and microscopic analysis that during the indoor salting out cycle degradation process of sandstone,the quality,wave velocity,and strength show a trend of progressive damage and degradation,accompanied by the reciprocating cycles.In addition,through the analysis of micro mechanical effects,it was found that the alkaline environment caused by salt in the northern grotto temple area will increase the subcritical propagation rate of cracks and accelerate the salt weathering process of the grotto rock mass;(3)In terms of the research on the aging model of damage and degradation of sandstone in Cretaceous grottoes: considering the influence of microenvironment controlled failure on the stability of sandstone grottoes,according to the theory of Damage mechanics and the principle of generalized equivalent strain,a damage degradation aging model for different diseases was established,which can better reflect the damage evolution law of North Grotto Temple’s sandstone and the relationship between the strain and damage factors of grotto sandstone under different degrees of degradation.In addition,based on the AHP analytic hierarchy process,the main control factors of damage deterioration under the control of the microenvironment of North Grotto Temple’s sandstone were identified,and the practicability of the aging model was verified.