Columns' Stability Analysis Of Cave No.9 And No.10 In Yungang Grottoes

The Cave 9 and 10 are the most distinctive among the many caves in Yungang Grottoes.The cave 9 and cave 10 is a set of double-cave in the caves,each of the caves has two pillars in the front Hall.Pillars are octagonal cylinders ang engraved with ten layers of the shrines.Unfortunately,outside of the pillars and the bases have been weathered now and can not display the splendid scene.With the loss of years,the vertical columns of four vertical columns have gradually become more and more weathered,and its strength is gradually weakened.Once the four columns are damaged and destabilized,the overall stability of Cave 9 and 10 will be destroyed.Therefore,in order to find out the stability of the weak spots in 9th and 10th caves and the current stability of caves,and to provide a scientific reference for the next reinforcement of caves,we use the finite element software Abaqus to analyse the stability of columns.The simulation includes column's stability during the excavation of the grottoes,the column's stability after the weathering and the column's stability when the temperature changes.Grotto cutting is divided into five stages,named octagonal column stage,antechamber stage,window hole stage,door hole stage,and rear room stage.This section is to calculate the changes of the stress,the displacement fields,and the stability of the four columns in the antechamber.The second part is calculating the four columns' stability after weathered.Firstly,calculati the overall stability of caves under self-weight,and then we will import the calculation of the whole model into the sub-model.At the same time,the column is divided into finer grids,and reset the boundary conditions,divided into layers based on the degree of weathering.Finally,every layer was gived different physical and mechanical properties,and we submit assignments for calculation.The third part is that simulating the influence of temperature on column stability through the sub-model technology.The method is similar to the second part's.In this part,we select the monthly average temperature in 2016 as the temperature load to calculate the impact of high temperature and low temperature on the stress field and displacement field of the column.After simulating and calculating,we will find some results as follows:1.During the excavation,the displacement of the mountain is increasing,and reaching a maximum of 3.228 mm.With the cutting carried out,the tendency of slope to the south is exacerbating.The compressive stress on top of columns is increased from 0.3Mpa in the octagonal to 0.62Mpa in rearing room.2.The compressive stress on the top of the anterior chamber and the posterior chamber are decreasing,replaced by tensile stress,which is harmful to the stabiity of caves' top.3.The influence from excavation on shear stress of Y-direction is far less than the influence on compressive stress of Z-direction,therefore,columns are likely to instability by pressure.4.In all simulations,the top or bottom of the four columns are the places where the maximum stress concentration occurs,which indicating that columns are always the weakest part in caves.Reinforcing columns is the most important task.5.Under the pressure from upper part,the maximum Mises stress of columns is 3.014Mpa.And this value increases to 4.465 Mpa at high temperature coupling,the value is 1.950Mpa at low temperature coupling,which shows that high temperature has a greater impact on the stability of the column.