A Study On Construction And Deformation Control Technologies Of A Phyllite Tunnel After Strong Earthquakes

After strong earthquakes,the geological conditions have been greatly changed,which make the construction of transportation system more complicated,bringing all sorts of new problems to the reconstruction of stricken areas.On Phyllite tunnel, this shows more.The question how to effectively control the rock deformation of Phyllite tunnel during and after the construction means a lot.The control of the surrounding rock deformation is researched and analysed in this paper based on the project of Huangpigou Tunnel of Provincial Highway Line S302through theoretical analysis, numerical simulation (FLAC3D), Advanced geological prediction and monitoring and measuring.Some achievments obtained are as follows:(1) The project is located in Phyllite areas,which is one kind of soft rocks with characteristic of developed joints and bad rock properties,causing much difficulty to excavation and supportment.After5.12earthquake, extrusion dislocation produced a large number of faults and fractures between rocks,making efflorescence deeper;tectonism between the rock is reduced caused by tectonic stress, structural variation between the layers fragile, Surrounding rock performance worse.Meanwhile, groundwater easily went into cracks and faults,making water-softening phenomenon of phyllite more serious, and so on the construction difficulty is more.(2) The simulation results of rock deformation and displacement of settlement conducted by using the finite element software (FLAC3D) show that:By the function of pregrouting with small ductle, concrete shotcrete, anchorstock and steel centering,the rock deformation can be reduced effectively.Conpared to fullface tunnelling method, steps excavation method and timely support to the top bench can reduce more.(3) Through monitoring and measuring on the spot,the phyllite property will be greatly weakened because of water-softening and water-mudding,and the original supporting stable system may be broken, and the surrounding rock deformation may suddenly increase, making composite lining crack and even total dstroyed.So,in the Phyllite tunneling,support mearsures should be strengthened,rather steel arching than Grille arching,and pregrouting with small ductle is also very effective.