Study On The Large Deformation Of Wall Rock On The Tunnel Through Daxiangling Niba Mountains Of Yaan-Lugu Highway

Study on various geological hazards, especially on large deformation of wall rock, which may occur in construction and operation of tunnel, is meaningful for finishing the whole project. This assay studies on the tunnel through Daxiangling Niba Mountains of Ya'an-Lugu highway. Through various methods, such as spot measuring, laboratory and field testing, theory calculation, numerical simulation, etc., this assay studies on the large deformation failure mechanism of the wall rock and its stability in deep-buried long tunnel, put forward the supporting proposal for the large deformation of wall rock, and concludes as follows:Rock joint and rock physical-mechanical characteristics are main elements affecting wall rock large deformation. Tunnel area is located in "Y" joint of Longmen mountain fault zone, Xianshui river fault zone and north-south trending tectonic belt, and influenced by multi-geologic structure, development of fault zone and structural plane. Most of rock masses in several large fault zones passed by the tunnel, are disintegrated, with hidden crack development, some part is in net, which make the rock mass with lower completeness. Rock in runnel area is of rhyolite and andesite. However, the original weak plane, such as prismatic joint and may-layer, is generally developed, which reduce the wall rock mechanical characteristics. According to laboratory rock mechanical testing, the rock uniaxial compressive strength in disintegrated belt of fault zone is lower. Tuff in contacting-interface of rhyolite and andesite is of soft rock. In deep-buried large disintegrated belt of fault zone and tuff section, large deformation is easily occurred after excavation and unloading.High in-situ stress is the important element of wall rock deformation. Testing trough borehole hydraulic fracturing technique, the gravitational stress and horizontal tectonic stress around the axle of tunnel is higher. Using FLAC3D and multiple regression method, with borehole measuring in-suit stress, the in-suit stress in tunnel area is inversion-analyzed. The results inversion-analyzed shows that in-suit stress in tunnel area is of high in-suit status, and generally conform to results measured and theory-analyzed. Max. main stress around the axle of tunnel is 30MPa-53MPa , in direction of N50°-60°W. The angle to tunnel axle is 78°, which is the max. and not good for the stability of wall rock.Based on conclusion of wall rock large deformation mechanism, the large deformation occurred in tunnel wall rock mainly distributes on "V" level wall rock and partial 'IV'" level wall rock in disintegrated belt of fault zone. Type of large deformation is of rock joint control, the deformation mechanism includes structural rheology, progressive loosing-expansion.This essay separately calculates out the vertical variables of each section in tunnel through rock mechanical theory and FLAC^3D . The result shows that the sections with large deformation are all with high in-suit stress and in 'V' level fault zone of wall rock and its influenced surroundings. However, the simulation value is less than calculating value.Finally, combining the theory-calculating result with numerical simulation analyzing result, referring to the research achievements for large deformation by the forefathers, using spray anchoring and supporting method to change the stress of wall rock, improve the strength of wall rock, and prevent the large deformation damage of tunnel wall rock. Through FLAC^3D to establish the model and analyze, comparing the results with supporting and without supporting, while supporting, the deformation on top of tunnel is 53.4% lower, which shows protection by spray anchor supporting method is a rewarding way.