| Yungang Grottoes are one of China's three major grottoes, which are located in the south of Mount Zhouwhu,16km away from the west of Datong city of Shanxi province. The grottoes were dug in the 5th century AD in the Northern Wei dynasty,5 million statues existed in the Yungang Grottoes now. They are known as huge and Impressive st(?)es. Yungang Grottoes are the sculpture art treasure house of China because of long history, rich contents and fine carving, with important cultural, arti(?)ic, religious, historical value. They were announced as the first batch of national key cultural,elics protection units by the State Council in 1961. included as "World Heritage(?)t in 2001.The cave 9 and cave 10 is a set of double-Cave in the caves, with the most concentrated flavor of the hall style. Each of the caves has two pillars in the front Hall. Pillars are octagonal cylinders and 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 long period of weathering damage, the overall strength of the two pills is very weak, and the pills will directly affect the instability of the overall cave.Therefore, in order to get the present stability and deformation law of 9,10 Cave, providing the scientific basis for the reinforcement design, we use the finite difference software FLAC3D, analyzing on the stability of the rock of Cave 9 and 10, combining the strength reduction theory to calculate the stability coefficient in stable system, moreover, making the seismic effect of the stress and displacement of the pills. Through the simulation and calculation we find some Conclusions as follows:1.By the calculations of FLAC3D we find that, under the natural gravity, the maximum unbalanced force with the time step of the model is reduced to zero rapidly from 4.5Mpa and convergence, but only the 6457 time step to achieve convergence.It shows the model has the good stability under the natural Weight state. 2.The total displacement direction of model is vertical downward and tilted forward. The largest displacement occurred in the top of the 4 pillars and mountain, the largest displacement is 1.28mm.lt shows that the stability of rock here is relatively poor, deformation is large,should be reinforced to strengthen the monitoring and protection. Cave 9 and cave 10 displacement field distribution is basicly symmetric.3.Under the natural gravity, the overall principal stress increases gradually from top to bottom, the maximum principal stress direction in the Grottoes area above is mainly vertical, deflect to according with slope direction in the area near the slope;The maximum principal stress is approximately parallel with the cave wall.the minimun principal stress is approximately vertical with the cave wall near the cave wall,which gradually return to normal near the slpe body, in line with the slope stress distribution.4.Based on the strength reduction theory nrogramming with the Fish language, calculating the overall stability coefficient R. R= 1.45> 1.3. It shows that the current model is stable. However, with the further intensifion of the weathered and flaked to a certain extent, the bottom of pills will be in shear failure firstly. So we suggested make the long-term monitoring on the pills, and make the necessary bonding, supporting,reinforcement and other protective measures to prevent the further weathering.5.Under the small earthquakes, shear stress of the pills is small, the shear stress direction is negative, pointing to outside of cave. The average shear stress is 687 KPa. The max shear stress of pill 2 is largest, which is 115.8 KPa. Pills are not damaged, there is no plastic zone. So the response of displacement, velocity and acceleration are relatively small. The average displacement of 4 pillars is 2.75 cm.a(?) rage speed is 0.85cm. average acceleration is 0.10 m/s2. The upper, middle and lower part the displacement, velocity and acceleration of pills are basically the same, the difference is small.6.Under the medium earthquake, the max average shear stress is 114.5 KPa. The shear stress of pill 4 is largest.which is 111.9 KPa. The shear stress direction is negative, pointing to outside of cave. Shear failure occurs in the inside of lower part of the pills. The displacement, velocity and acceleration of pills are larger. The average displacement of 4 pillars is 7.34cm, average speed is 2.31cm, average acceleration is 2.38 m/s2. The upper part the displacement, velocity and acceleration of pills are smaller than middle and lower part the displacement, velocity and acceleration of pills.7.Under the large earthquake, the max average shear stress is 327.1 KPa. The shear stress of pill 3 is largest, which is 4.7 MPa. The shear stress direction is negative, pointing to outside of cave. Shear failure occurs in the whole of lower part of the pills. The displacement, velocity and acceleration of pills are largest. The average displacement of 4 pillars is 19.71 cm, average speed of 6.55 cm, average acceleration is 4.32m/s2. The upper part the displacement, velocity and acceleration of pills are smaller than middle and lower part the displacement, velocity and acceleration of pills.8.Under small earthquake,the responses of stress, displacement, velocity and acceleration of the pillars of Caves 9 and 10 of Yungang Grottoes are small, there is no damage; Under medium and large earthquake, the responses of stress, displacement, velocity and acceleration of the pillars are larger, pills are damaged in Shear failure. It basiclly meet the requirement of "small earthquake not damage, medium earthquake repairable and large earthquake not down",but the pills are damaged under the medium and large earthquakes.So it should be taken to strengthen the monitoring and bonding, such as Bonding, supporting or anchoring and other appropriate reinforcement measures to better protect the Yungang Grottoes. |
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