| As a large-scale open-air stone cultural relic in western my country,the rock arts of Helan Mountain is the largest and most concentrated rock arts area in the geographic unit.Due to the longterm seasonal cold zone,and the repeated long-term effects of extreme temperature changes in nature,surface water penetration and load cycles,the surface of the petroglyphs appears to be cracked,flaked,and powdered to varying degrees,and weathering is seriously on the verge of disappearing.For this reason,this paper selects the rocks near the Helankou petroglyphs.Firstly,uses the ultrasonic nondestructive testing technology to screen the prepared rock samples by longitudinal wave velocity and group them.Then,considering the temperature-water coupling field,the vacuum-saturated rock sample is subjected to 0,10,20,30,and 40 freeze-thaw cycle tests to obtain the macroscopic deterioration characteristics of porosity and longitudinal wave velocity,and through indoor uniaxial and triaxial compression mechanical tests and acoustic emission technology are used to monitor the failure process of rock samples,and the characteristics of strength degradation of rock samples and the temporal and spatial evolution of rock sample crack propagation under acoustic emission are discussed.Finally,the damage variable based on the combination of macro and meso physical quantities is defined,and the damage constitutive model of the rock arts carrier rock in Helankou is established.The main research results of this paper are as follows:(1)Under uniaxial compression,the peak stress of rock samples decreases with the increase of the number of freeze-thaw cycles,and the elastic stage is shortened,while the plastic stage is prolonged.Due to the freeze-thaw cycles,the inter-layered cement in the rock sample migrates with water.Due to the frost heaving force,the pores between the grains begin to expand,causing the particles to peel off under the action of external load,and the failure mode gradually changes from brittle failure to plastic failure.(2)Under triaxial compression,the number of freeze-thaw cycles of a rock sample under the same confining pressure increases.The elastic phase and the plastic phase are shortened.The plateau phenomenon in the plastic rheology phase is more obvious,and peak stress and residual stress show a decreasing trend.Sample under the same number of freezing and thawing as confining pressure series extension of elastic stage and plastic stage,the increase in the number of freezing and thawing is greater than 20 times and confining pressure is greater than 20 Mpa,the peak stress and residual stress increase after the biggest change,shows that when the confining pressure is greater than 20 Mpa due to the degradation of the sample's ability to provide strong resistance to deformation.(3)There are five stages for the change of acoustic emission count and energy.The sharply active period corresponds to the moment of stress drop of the rock sample,indicating that the internal particles of the rock sample are subjected to micro-strain under load,and strain gradually accumulates at the crack to store a large amount of strain energy,and when the crack expands the strain energy is released to excite the acoustic emission count and energy.Cracks and fissures are generated in densely populated places with three-dimensional positioning points.When a certain angle is arranged inside the rock sample,the main fracture surface will be generated,and the spatial distribution of the positioning points will destroy the cracks of the rock sample.There is a good correspondence in the direction.The uniaxial failure mode is mostly tensile splitting failure accompanied by volume expansion,and the uniaxial failure mode is mostly conical shear failure.(4)Sample after freezing and thawing cycle the degradation rate of vertical wave velocity,the average pore growth rate increases with the number of freezing and thawing is exponentially increased,modulus of elasticity is exponentially decreases with increase number of freezing and thawing,wave velocity of degradation rate and the average pore growth in the number of freezing and thawing is 20 times increase,the largest impact sample the freezing and thawing at 20 times the highest sensitivity,The development of internal pores and the loss of cements are the fastest,which are the nodes of deterioration of freeze-thaw damage.(5)Analyze the physical parameters of the rock sample after freezing and thawing from the macroscopic and mesoscopic perspectives,and combine the elastic modulus with the cumulative ringing count of acoustic emission under load to obtain the damage variable with the coupling item,and establish the damage cost on this basis.The theoretical result curve of the constitutive model is in good agreement with the experimental result curve trend,indicating that the damage constitutive relationship can effectively predict the development trend of the internal damage of the rock arts carrier rock,and provid a theoretical basis for subsequent rock arts conservation and restoration work. |
PDF Full Text Request