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Practice shows that a large number of tunnels, the tunnel fault fracture zone and its impact zone, shallow section of the tectonic movement zone and strongly weathered zone above the tunnel section and the loose sand accumulation body body segment positions, such as tunnel excavation, rock loose off, a large amount of plastic deformation in a short, easy to loose body takes the form of spalling damage, tunnel face instability, dome collapses and other engineering disasters. However, the existing studies, can not be broken rock zone on the loose mechanical behavior of tunnel construction process to make a perfectly reasonable explanation. Therefore, it is necessary for such a tunnel excavation and support process modeling, analysis of its impact on the stability of surrounding rock and used to guide the construction. In this paper, DU Ji Huai Expressway Tunnel night K34 200 ~ K34 250 segments, segment dispersion on shallow rocks in the construction process of deformation and mechanical behavior of the correlation analysis, design and construction of the tunnel for the class to provide a theoretical reference. The main research work and conclusions are as follows: (1) introduces the concept of rock and dispersion characteristics of granular rock tunnel failure modes and stability characteristics were analyzed, summarized and characteristics of tunnel construction methods used and analyzed rock and supporting structure interaction mechanism. (2) on a small pipe grouting model experiments, the results show that small duct grouting support can significantly improve the mechanical properties of granular rock, rock to improve self-supporting capacity, reduce settlement deformation of surrounding rock vault. (3) using engineering software FLAC3D rock excavation and support for different process numerical simulation to study different construction methods dispersion stability of surrounding rock. Through the numerical analysis of the results shows that dispersion large section tunnel excavation method, great disturbance on rock, rock is not conducive to stability, especially within the tunnel face greater air displacement will occur, vaults and difficult to control surface subsidence ; using a small cross-section segments law excavation, rock is relatively stable, vaults and small surface subsidence, but the supporting structure borne rock deformation pressure increases, and the construction technology cumbersome, slow progress, project cost high; using Positive steps aside core indigenous excavation, can reduce the disturbance of rock, especially in the core of soil under the effect of the stress state of the working face of significant improvement within the space rock tunnel face displacement has been effectively controlled, reducing the vault and surface subsidence, rock stability improved. On support measures, since the poor dispersion stability of surrounding rock, if not for advance support was excavated rock in initial support facilities to do or be effective before they have produced a large area of ??plastic yield, resulting in around Convergence dome and the surrounding rock is too large or the overall instability destruction; using forepoling after dispersion rock mechanical properties significantly improved, rock strength increases, improving the overall stability of surrounding rock. Meanwhile, in the lead role in supporting the range, the formation of a stable structure with a certain role in carrying compressive arch, effectively improve the dispersion from rock bearing capacity and stability. (4) test section of the tunnel excavation monitoring results revealed that the core with positive step aside indigenous excavation, crown settlement amount is small, and short excavation step method, a large amount of crown settlement . However, due to the length of the core soil limits the level of convergence ratio ultrashort cave excavation big step method, and numerical simulation results.
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