Study On Stability Of Tunnel Surrounding Rocks In Yunxi-Yunxian Fault Area

As a mountainous country, 69% of the land of China is mountains, hills and plateau, China's terrain is high in the west and low in the east, representing a progressive downward pattern from west to east. This complexity of the terrain seriously hinders the development of transportation. With continual progress of China's economic construction and constant increase of Chinese government's investment in the West, transportation has become a bottleneck for China's further growth. Therefore, Chinese government initiated a project to build national transportation arteries and also stepped up its investment in road construction. In light of this more and more mountain highway has started construction, which will undoubtedly demand better solutions to tunnel construction. China has a complex terrain and geological structure, which makes complex geological conditions, such as the fold, fault and earthquake zone, an unavoidable factor in China's tunnel construction process. Consequently, it's of good significance to make possible accurate analysis of the stability of tunnel surrounding rocks in a complex geological condition in order to ensure safe design and construction of the tunnels.ShiMan Highway, which is now under-construction and 100 kilometers long, involves 28 tunnels of various lengths and various patterns. This highway crosses through the challenging LiangYun Fracture (Yunxi-Yunxian Fault Area), where exists many weak secondary faults and fault fracture zones. Surrounding rocks here are dominated by metamorphite rocks and various interfaces of these rock bodies, such as schistosity, joint and crack, mingle with and grow into each other, which delivers a negative impact on the stability of those surrounding rocks. What's more, also present are various geological hazards, such as tunnel bias, rock weathering inequality, regional tectonic stress and rock weak expansion, which lead to frequent dramatic deformations of surrounding rocks and landslides disasters. All this obstructs safe tunnel construction.This thesis evolves around the construction practice of Shi Man Highway and takes the rocks of LiangYun controlled areas to its study. It aims to shed some light on the characteristics of structural geology and engineering geology region in the region. This thesis offers a preliminary analysis of the stability of the rocks in the region by researching into the history of structural formation and the rock engineering mechanical properties of the region. Besides, by firmly relying on rock characteristics and construction practice, it analyzes the factors affecting the stability of surrounding rocks, and also sets aside the four major factors, whose specific effects are analyzed by ways of theory and calculation. This thesis also conducts an elaborate analysis of typical tunnels, tries to verify the results of calculation through appropriate means, and also analyzes the validity of the results in practice. In light of the fact that the classification of rocks deviates a bit far from the actual conditions due to the complexity of surrounding rocks, this thesis explores appropriate rock classification methods specifically fit for the ShiMan area at the end.This thesis has main research areas and major conclusions as follows:(1)Study on the geological conditions of the area alongside the road.Analyze the geological conditions of the area by way of researching into the geological conditions of the tunnel projects alongside the road, such as lithology, topography, structural characteristics, hydrogeology, etc. Delve into the historical development of the geological structure in the area so as to analyze the characteristics of faulty activities and changes in the load. Then analyze the characteristics of the resulting load distribution and try to come up with some basic distribution rules. A preliminary evaluation of the stability of the tunnel region is thus achieved.(2)Study on the characteristics of engineering geology.Through the rock mechanics testing, the paper analyzes the basic mechanics and water physical properties of the rock, from which it deduce the deformation characteristics and failure mode of the surrounding rock. Through the expansibility tests and the expansion index, the rock can be judged of a weak expansion. Connected to the research to grading of structural planes, the rock mass discontinuity can be classified as V, it summarizes the extent and characteristics of each grade structural plane respectively and also make grading evaluations of the overall stability of the rocks.(3)Analyze the factors affecting the stability of surrounding rocks.List the factors affecting the stability of the tunnel in LiangYun Fracture and analyze their respective roles briefly. It selects and gives detailed analysis of the tunnels or sections on which one particular factor has the worst effect through exclusion.(4)Anaylze those factors which affect the stability the most respectively, such as the conditions of the stress field, the vertical load, bias load and expansive stress, by taking into consideration of the characteristics of surrounding rocks. Study the distribution characteristics of those factors in broken rocks which are affected by big fractures and also their influence characteristics in the surrounding rocks in ShiMan Highway tunnel. Select and analyze typical tunnel sections and verify the results of theorectical analysis through appropriate methods. The result's applicability is further studied. Analyze the formation of the fault so as to better analyze the characteristics of the reverse fault and its impact to the stability of the tunnel from the perspective of rock mechanics by taking into consideration of the characteristics of LiangYun Fracture reverse fault. Analyze the calculation method of the load, in particular the vertical load, of tunnel in response to the existence of broken rocks due to big fracture impact. Adopt Terzaghi Theory to calculate the vertical load and verify the result through on-site stress tests as well as its applicability in practice. Study the calculation method of bias load tunnels which are widely present in ShiMan Highway. Analyze the shortcomings of the standardized method and set forward specific measures to improve it. Use the improved method in HuoCheling tunnel and verify the result through FLAC3D. Analyze the accuracy of the result. Analyze the expansion mechanism and the features of rocks in light of the weak expansionary characteristics rocks. Take the bottom board bulging in YunLing tunnel as an example to study the effect of rock expansion in the process of deformation.(5)Study appropriate classification method in light of the fact that surrounding rocks crack and are difficult to be accurately graded. By introducing the fuzzy mathematics theory and establishing fuzzy mathematics classification model fit for the ShiMan area, it tests the model in practice and studies its applicability in the fault zone so as to explore into proper classification methods fit for the great fracture zone.In conclusion, this thesis relies on the construction of the tunnels along the ShiMan Highway, studies the characteristics of rocks in LiangYun Fault area, and combines outdoor geological prospections, indoor theorectical analysis, data compilation, experiment and research so as to achieve to study the stability of the tunnel, classify the factors which may affect the stability and calculate the impact in every circumstances. This thesisi also applies the results in practice, verifies them by various means and analyzes their possible effects. This thesis explores into classification methods fit for the fault area at the end and analyzes the applicability and accuracy. In one word, the study of the stability of the tunnel in LiangYun Fault area as well as the classification method in the thesis is closely connected with the actual project and can be verified by practice. The findings shed some light on similar engineering practices.