| Buddhist caves are an essential part of cultural heritages and are also art treasures integrating architecture, sculpture and murals that have a huge significance of art, history, science and social impact. However, on the influence of long-term natural and human elements, a series of serious Geological deteriorations occur such as slope instability, rock collapse, pass-through fissure growing, detaching and collapsing, surface weathering and so on. These problems cause varying degrees of damages to the art of caves. And because a lot of caves are located in the zone of high-frequency of earthquakes, this brings some security risks to them. To reduce the existing and potential risks to the minimum has become today’s hard task, and analyzing and understanding deteriorations of unstable rock of the caves and their causes will be the bottleneck problem for solving these difficulties. Therefore, this study based on GEO-slope focus on the zone of cave No.406to415at Mogao Grottoes and finds out the characteristics of static balance and dynamic damage before and after the application of protection methods to the unstable rock. To carry out the research on stability analysis of unstable rock under static state before and after consolidation and dynamic response in seismic load contributes to find analysis methods of field tests, parameter determining, control measures selecting, stability assessment together with the method of slope control of unstable rock of cave temples and the analysis in both static and dynamic states. This provides experience to further consolidate unstable rock of the caves in a scientific and effective way.This paper carries out a systematic analysis of the basic engineering characteristic of unstable rock in zone405-415, and stability analysis of establishing nature slope, excavating cave site slope, long-term growing fissure slope on site, the slope being consolidated by retaining wall and anchor in both static and dynamic states. It also studies further analysis methods of the stability of unstable rock and control measures. It includes the following contents.(1) Dig a50meters deep well on the west of150meters far from the top of Nine-story Building at Mogao Grottoes and take samples, then analyze the samples taken from the zone of cave No.406to415in the area that is perpendicular to the rock face within15meters deep and finish relative tests. Thus, it helps to understand the basic strata condition of unstable rock in the zone of cave No.406to415. At the same time, it combines with the survey datas of consolidation project in the1960s and then gets relative parameters to provide reliable reference for stability analysis of rock body.(2)Finish the analysis of stress and strain in multiple profiles from the zone of cave No.406to415based on GEO-sigma, mainly including stress and strains analysis of natural state, rock state being excavated, the states of fissure growing and being consolidated by retaining wall and anchor. And observe and analyze the distribution and tendency of stress of unstable rock under different conditions.(3) Analyze the results based on software modules of GEO-slope and GEO-sigma, and research the static stability of rock body in the conditions of natural state, being excavated, fissure growing and being consolidated by retaining wall and anchor together with the stability analysis under acceleration. Then analyze the methods of establishing module GEO-slope and analyzing for unstable rock.(4) Come up with a more practical calculating method, that is combining test analysis with theoretical judgement to get the physics and mechanics index of soil and rock.(5) Though stability analysis in the state of natural state, being excavated, fissure growing and being consolidated together with the state of seismic load, this provides reliable theory for major failure surface, failure form, force of consolidation and effort assessment and it also give theory support to reinforcing unstable rock.(6) On the basis of analyzing and studying failure surface, the protection and consolidation method for local concentrated stress reducing and homogenizing to varying degrees in different conditions shows good efforts and meets the requirement of stability in scientific and effective.On the base of GEO-slope, the typical zone of cave No.406to415is taken as a case to establish a finite-element model of cave unstable rock with multiple profiles. Aiming at static and dynamic response analysis of unstable rock in different environments, it points out the stress concentrated area and fragile area in dynamic state, and then prove that taking improvement methods should be based on the safety parameter in natural state to calculate the required resistance. Thereby, this contributes to take reasonable consolidating measures to improve the whole stability of the rock body of Mogao Caves effectively. Therefore this study has a considerable significance of stability analysis of unstable cave rock slope, consolidation technique selection and engineering measures optimization in a scientific and effective way. |
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