Modeling Method Of Finite Element Model And Seismic Response Of Large And Complex Grottoes

With the development of The Times,cultural relic protection has gradually become a social consensus.As an important part of immovable cultural relics,grottoes has extremely important political,economic and cultural values.However,in the long process of development,due to the natural environment such as cutting,water and salt erosion,seepage and microorganisms,some of the grottoes deformed,slipped and scattered,forming dangerous rock mass,resulting in the stability of the grottoes decreased.In order to strengthen the preventive protection of the grottoes and explore the influence of self-weight and earthquake on the grottoes,this paper proposed a 3D reverse modeling method.Based on the3 D laser scanning data of a grotto,the high-precision 3D finite element model of the complex grotto was constructed from the physical entity of real space to the virtual space.On this basis,ABAQUS software was used to analyze the stress-strain distribution,displacement response and acceleration response of grotto under the effect of self-weight and earthquake.The specific research contents and results of this paper are as follows:(1)Based on 3D laser scanning data,the modeling method of fine model for large and complex grottoes was proposed.GEO SLAM handheld 3D laser scanner was used to obtain the point cloud datas of interior and exterior surfaces of the grotto.The Geomagic studio software was used to process the point cloud datas,including the generation of polygonal mesh,extraction of contour lines and coordinate points.Coordinate points were fitted by CAD software and surface domain were generated.Based on APDL language,ANSYS software was used to construct the three-dimensional solid model of the grotto by means of point,line and surface.Finally,the tetrahedral mesh was divided into the solid model by Hypermesh software.(2)The tetrahedral mesh model of the grotto in Hypermesh software was imported into ABAQUS,and parameters such as calculation range,boundary conditions,element type,material constitutive and load conditions were set to analyze the stability of the grotto under the effect of gravity.The results show that the maximum tensile stress of the grotto under the effect of gravity is 1.1MPa,which is less than the tensile strength of the rock mass and located at the top of the grotto.The maximum compressive stress is 4.5MPa,which is less than the compressive strength of the rock mass and located at the foot of the grotto.The stress concentration occurred in the arch foot of the grotto,the rock walls on both sides of the window,the pedestal of the Buddha statue and the passage,which were the relatively weak positions of the grotto.(3)The stability of the grotto under the effect of gravity was analyzed by using three-dimensional solid finite element model.Based on the above finite element model,seismic wave,viscous-spring artificial boundary and Rayleigh damping are selected to analyze the seismic performance of the grotto under the effect of frequency earthquake,moderate earthquake and rare earthquake.The results show that the peak displacements of the grotto and Buddha statue are 3.5mm,11.4mm,22.8mm and 2.2mm,7.8mm and 16.3mm,respectively.Under the effect of frequency earthquake,moderate earthquake and rare earthquake,the maximum acceleration amplification coefficients of the grotto and Buddha statue are 4.33,3.96,3.57 and 3.96,3.26,3.14,respectively.The acceleration amplification coefficients of the grotto and Buddha statue decrease with the increase of the input seismic amplitude.Under the effect of frequency earthquake,moderate earthquake and rare earthquake,the maximum tensile stress of the grotto is 0.83 MPa,1.4MPa and 1.6MPa respectively,which is less than the tensile strength of the rock mass,and no tensile failure occurs in the grotto.Under the effect of frequency earthquake,moderate earthquake and rare earthquake,the arch feet of grotto,the window and the pedestal of Buddha statues enter the plastic state,and the above positions have the risk of shear failure.(4)According to the characteristics of stress and strain distribution,displacement response and acceleration response under the effect of gravity and earthquake,combined with the current situation of the grotto,the monitoring needs of the grotto are analyzed,the vibration and stability monitoring scheme of the grotto were proposed,and the monitoring instruments and application methods for every monitoring content were given.