Stability Analysis Of Sandstone Columniation Based On Ultrasonic Detection

Under the influence of natural environment, climatic variation and human factors, the stability of Yungang Grottoes have been faced with many risk factors: such as the deformation, fracture, dislocation and the decrease of intensity of sandstone, etc.Since the excavation of Yungang Grottoes, the research of protection work has never been stopped. Geophysical prospecting methods have been most widely used. After reading a large number of documents and reference materials, I found some limitations in the research work at the present stage. The effective combination of geophysical methods and stability analysis is still at the exploratory stage. In view of the weathering in Yungang Grottoes, although different kinds of geophysical exploration methods have been adopted, but most studied on the thickness of weathered layer or weathering conditions. These studies were not effective combined with subsequent stability analysis. This thesis will combine the result of ultrasonic detection with the stability analysis, simulate and analysis the mechanical characteristics of the columniation. It have very important guiding significance for the protection and restoration in Yungang Grottoes.The following contents have explained in this paper.First, expound the theoretical basis of ultrasonic detection, rock mechanics, and the numerical simulation theory of finite difference method. After the study, I find that the rock weathering condition have relationship with wave velocity variation. Second,through the investigation of the geological background in Yungang Grottoes, the various diseases that stone cultural relics are facing have been explained, such as wind diseases, salt alkali and dust pollution. Then determine the survey plan, and using the data of ultrasonic experiments to determine the weathering layer of the columniation.Third,the FLAC software is briefly introduced and the stability analysis was carried out in FLAC software.The results are shown below. The weathering of the bottom of the columniation is the most serious, and the surface is mostly strongly weathered. Because of the weak strength of the strong weathering rock, the rock is most easily broken when it faces extrusion from the top and bottom. In the middle of the columniation, it has serious weathering in the east and south, the other direction is moderate weathered. It will be stable when face the extrusion. At the top of the column, the strong weathering distribution is less,the rock strength is better, and when facing the pressure of the top and bottom it will be stable.The sandstone is a brittle material, the tensile strength is less than the compressive stress. From the force changes, the columniation will face both compressive stress and tensile stress. The main stress is a major role in the North West medium weathered sandstone and micro weathered rock.Overall, columniations is currently in stable state, but with the passage of time,the compressive strength of sandstone will continue to decline, the columns stability will become increasingly weak.