Research On Stability Influence Of The Rock Around Hidden Cave In Road And Bridge Engineering At The Karst Area

Disaster caused by the cave is one of the primary matter for the road project at Karst area. At the Karst area, rock strength of wall rock of tunnel and bedrock of the road and bridge could be weakened by the effect of the environment and load. The weakening of the rock could make the project failure. The influence of the cave on the project during the failure process is a complex and challenged problem. Because the scale of research object is great, the routine physical experiment need much resource and manpower, the experimental result can be disturbed by many reasons, the experiment also would be unsuccessful sometimes. The rock considered as the homogeneous medium and calculation model need too much predigest when we used the academic calculation. But the inhomogeneous is a important character of the rock, the calculation result may be different with the real fact. The strength reduce method is used widely for stability analysis in rock project now. The analysis result accord with the reality. It is cheaper and more effective too. Because the distance and diameter are variable, the rule got by them is unsure. So the distance diameter ratio (DDR) is used to replace the distance as one of estimate standard of the stability analysis in this thesis. The result will be more impersonal. The rock is considered as the homogeneous medium in the past stability analysis, but the inhomogeneous is a very important character for the rock. Inhomogeneous of rock is considered in thesis to make the result more fit for the fact. The tension rule is considered in the stability model too. The results got in the thesis is a integrative safety factor consider the shear stress, compressive stress and tension stress.The stability research of the cave is focused on idiographic project for most researcher. Some research on how to deal with the cave. Only a little people research on the influence rule of the cave, near the rock project. The rule is important for the people to consult in other project. Based on the research in past, the thesis sum up the influence factor and analysis method of stability of the road project at Karst area first. The rationale, strength rule, constitutive law and failure criterion of the RFPA-SRM is introduced then. At last, RFPA-SRM is used to analyse the stability influence rule of the cave near the road project. To make the result reflect truer, inhomogeneous of the rock is considered in the model. The content of the thesis as follows:(1)Influence rule of the cave on stability of the wall rock of tunnel and bedrock of the road and bridge with different homogeneousness of the rock is studied in the thesis; (2)analyse the stability variety rule of road project when the section shape of the cave is different(circle, ellipse in horizontal, ellipse in vertical); (3)analyse the stability variety rule of road project when the diameter and location of the cave is different(for the road and bridge, location means the distant between floor and cave, for the tunnel, location means the distant between tunnel and cave); (4)based on the problem caused by the cave in chong-zun highway building process, studied the influence of the cave on stress and deformation of the wall rock in true project.By the research on the influence of the cave, the results shows that:1. Influence of the rock inhomogeneousness is obvious for the stability of road project. For rock of the bad lithology or high weathering, the safety factor of the rock is more impressible to the inhomogeneous of the rock. The stability and the safety factor of the project increase with the homogeneousness of the rock increase when other conditions are the same. It's very significative for the stability estimate to inspect the strain cove of the road and feebleness stress zone. For the tunnel, stability of the tunnel roof change less when the rock homogeneousness change.2. The stability of road project is different when the section shape is changed. For the stability of the project, the influence of cave with the section of ellipse in horizontal (long axis apeak the max. principal stress way) is the most, influence of the circle is the least. change of the cave's span is more influential than the change of the cave's depth. The bedrock of the road and bridge upon the cave will be damaged easily when the span is greater than the distance between cave and bedrock surface. The failure of the roadbed is caused by the big tension, the failure of the bridge bedrock is caused by the big compressive stress.3. The change of the cave's diameter and distance diameter ratio (DDR) is very influential for the stability of tunnel. The safety factor increase with the increase of the cave's diameter and DDR. For the stability of the tunnel, influence of the cave's location is not changeless. When the diameter of the cave less than the tunnel's span, tunnel failure at first. The damage transfers gradually to the rock near the cave when the diameter of the cave increase. Specially to the cave under the tunnel, there are little damage in the rock around tunnel while cave failure when the diameter of cave bigger than the tunnel's.4. For the road and bridge, the bedrock's safety factor and stability increase with the increase of cave's DDR when the diameter is changeless, the safety factor and stability of bedrock decrease with the increase of cave's diameter when DDR is changeless.5. For the wall rock of tunnel, distance between cave and tunnel is more influential to the stability of wall rock than diameter of the cave. For the bedrock of road and bridge, diameter of cave is more influential to the stability of bedrock than distance between cave and the bedrock surface.