Study On The Damage Mechanism Of The Microstructure Of The Gravel Conglomerate In The Maijishan Grottoes By Freeze-thaw Cycles

The lithology of the Maijishan Grottoes is glutenite with poor bonding.The annual average temperature in the grotto area is 8.0?,the extreme maximum temperature is38.3?,and the extreme minimum temperature is-19.2?.The temperature difference is large,Therefore,the seepage area of the cliff body in the cave area is obviously affected by the freezing and thawing cycle and other weathering effects.The cliff body of the Maijishan Grottoes has peeled off and powdered.The present paper is based on the document of the State Administration of Cultural Heritage of China that"about Maijishan grottoes reinforcement and ooze water management of the second phase of the project approval"(cultural relics undertaking(2015)No.718).By studying the physical and mechanical properties and microstructure characteristics of the Maijishan Grottoes under the influence of freezing and thawing,the microstructure damage mechanism of the glutenite under the influence of freezing and thawing is analyzed;It provides a reference basis for the analysis of the degree of rock freeze-thaw damage by calculating the frost heave homogenized stress of glutenite and comparing it with the fatigue strength of gluteniteThe specific work of this research includes:(1)Perform conventional physical and mechanical tests on the glutenite of Maijishan Grottoes,including density test,water absorption test,tensile test,uniaxial compression test and mineral composition analysis test,etc.;The block density and particle density of glutenite are 2.40 g/cm~3 and 2.66 g/cm~3,respectively.The large difference between the two indicates that there are more pores in the rock and the whole is looser;the water absorption rate of the rock is 2.19%,and the water absorption is strong;the rock is uniaxially compressive The strength is 11.59MPa and the tensile strength is 1.06MPa,indicating that the overall strength of the rock is low,and the degree of internal particle cementation is poor.When exposed to external force or weathering,the rock is prone to damage and destruction;sandy conglomerate minerals are quartz and feldspar.Mainly,there are more clay minerals,indicating that the rock is dominated by argillaceous cementation,which also limits the strength and weathering type of the rock.(2)Conduct indoor freeze-thaw tests,conduct wave speed,CT non-destructive testing,tensile strength,water absorption and other tests on the rocks that have undergone the freeze-thaw test,and analyze the effects of freezing and thawing on the physical and mechanical properties of the rock and the characteristics of the microscopic pore structure;The physical and mechanical properties of glutenite,including quality,longitudinal wave velocity,tensile strength,water absorption,etc.,all show a deteriorating trend under freeze-thaw action,and begin to stabilize after 10freeze-thaw cycles,and the rock becomes brittle under the action of freeze-thaw evolution.Through microscopic analysis,affected by the effects of freezing ice,thermal stress of rock components,pore water migration and pore water frost heave,the small pore pores expand and fail during the process of rock freezing and thawing,and interconnect to form large pore pores,showing macroscopic physics Deterioration of mechanical properties.At the same time,for different parts of the same sample,due to moisture migration and blockage of migration paths,the lower the freeze-thaw temperature,the lower the rock moisture loss rate,and the deeper the freeze-thaw damage depth.(3)Applying the theory of thermodynamic equilibrium and the idea of homogenization,the homogenized stress of rock frost heave is proposed,and it is compared with the fatigue strength of the rock to provide a reference for the analysis of rock freeze-thaw damage.Establish the relationship between frost heave homogenization stress and environmental temperature,rock saturation,rock structure characteristics,etc.The main factors affecting rock pore water crystallization homogenization stress include:(1)The pore structure characteristics of the rock,including its porosity(n)and rock The surface area(S)of the pores.For rocks with the same porosity,the smaller the pores in the rock,the larger the surface area.The pore water crystallization will cause less homogenization stress on the rock with small pore structure,so usually small pores The rock has good frost resistance.(2)The saturation of the rock.The proportion of saturated pores in the rock is related to the rock saturation.The higher the saturation,the greater the number of pores in the saturated state.With the temperature difference constant,the saturation increases,and the number of pores that produce pore water crystallization pressure increases.The macroscopic manifestation is an increase in rock homogenization stress.(3)Ambient temperature.The temperature difference is related to the crystallization pressure produced by the crystallization of a single pore water.The greater the temperature difference,the greater the crystallization pressure of a single pore.Under the condition of constant saturation,the temperature difference increases,the crystallization pressure generated by the crystallization of a single pore increases,and the macroscopic manifestation is that the homogenization stress of the rock increases.