Shaking Table Test And Numerical Simulation Analysis Of Underground Loess Cave

The loess cave dwelling is a typical tradition dwelling in the Loess Plateau of Northwest China.Its proper protection and inheritance has great practical significance for solving China’s current energy and environmental issues.For hundreds of years,the loess cave dwellings have been subjected to natural weathering,rain erosion,earthquakes,and man-made damage for a long time,and their existing conditions are not optimistic.At present,scholars’ research on loess cave dwellings mainly focuses on the study of physical and mechanical properties of loess materials,structural static and dynamic finite element analysis,while a large number of existing loess cave dwellings are located in high-intensity seismic fortification areas,and the experimental study on seismic performance of loess caves have not been carried out.Based on this,the research group carried out the shaking table test of the seismic simulation of the loess cave,and analyzed the seismic performance of the loess cave,which provided an important theoretical basis for the future repair of the loess cave.The main work of the thesis is as follows:(1)The pit kiln in Sanyuan County of Shaanxi Province was selected as the prototype.The underweight test model was designed and fabricated according to the second similarity theorem and the uniform similarity law.The boundary conditions of the infinite body around the cave was simulated by the laminated shear soil container.By comparing and analyzing the acceleration response time history of each measuring point in the soil layer,it is verified that the laminated shear container can simulate the boundary conditions of loess caves,and ideally eliminates the reflection and scattering effects of seismic waves at the boundary.(2)In order to study the dynamic characteristics and dynamic response characteristics of underground loess cave test model,the white noise sweep and the loading of three different spectral characteristics of the seismic wave were carried out on the experimental model.Quantitative analysis of the acceleration response and displacement response time history of each key point of the model structure under various working conditions shows that the initial first-order natural vibration frequency of the model structure is 8.105 Hz,and the first-order initial damping ratio is 3.41%;the first-order vibration mode is translation along the vibration direction.The acceleration and displacement response of the cave vault is stronger than that of the middle leg and the leg arch,and the acceleration response is enlarged along the height direction;the acceleration response and displacement response of the legs and legs in the cave are different,and the response changes in the depth direction are different;the horizontal displacement response of each key part in the cave is similar to the forced vibration according to the motion of the excitation point.(3)Based on the experimental phenomena and experimental analysis results,the failure mechanism of the underground loess caves under lateral horizontal earthquakes is explored.The analysis results show that under the horizontal earthquake,the underground loess cave dwelling has shear deformation between the soil layers and the difference of the movement range between the middle legs and the legs in the cave,resulting in large normal stress and cracking damage at the vault of the cave.And the above-mentioned covered soil area produces large normal stress and shear stress and oblique cracking damage.In addition,the middle leg of the cavern has cracking damage due to the difference in the amplitude of the movement in the depth direction under the action of large ground motion.(4)Based on the ABAQUS finite element analysis software,the finite element numerical simulation analysis was carried out based on the shaking table test of the underground loess cave.The geotechnical tests were carried out on the undisturbed loess and the test soil samples,and the basic parameters of the loess Mohr-Coulomb constitutive model were determined.The basic principle of the infinite element artificial boundary is analyzed and the input of the external vibration load at the artificial boundary is realized.And the accuracy of the example is verified by a case study.Finally,the finite element simulation of the dynamic characteristics and dynamic response of the prototype structure of the loess cave is carried out.The numerical simulation results are compared with the shaking table test results,and the main tensile stress state of the numerical model is compared with the experimental failure phenomenon,which verifies the reliability and accuracy of the numerical model established in this paper.