Abstract:

Large deformation and steel frame contortion are easily occurred due to poor stability of weak surrounding rock after excavation. Hence, a series of items of entrance section of Gaojiaping Tunnel on ZhengzhouWanzhou Highspeed Railway constructed by mechanized fullsection blasting excavation method, i.e. surrounding rock pressure, stress of steel frame, stress of shotcreting, axial force of anchor bolt, internal displacement of surrounding rock and extrusion deformation of tunnel face, are systematically studied. The results show that: (1) The surrounding rock pressure, stress of steel frame and stress of shocreting are affected significantly by lithological conditions and construction disturbance, and they show a variation law of "sharply increasing, slowly increasing, fluctuation variation and stable convergence". (2) According to the peak position of axial force of anchor bolt, the plastic zone of surrounding rock can be initially determined to be about 3.0 m away from tunnel wall. The distributions of compressive stress, axial force and bending moment of primary support structure are analyzed by numerical simulation based on field monitoring; and the analytical results coincide with the field measurement data, which can better reflect the stress characteristics of primary support. The experimental study can provide reference for mechanical study of soft rock deformation and support system of tunnel constructed by mechanized fullsection method and establishment of rational supporting structure system.

Key words: ZhengzhouWanzhou highspeed railway tunnel, soft rock, mechanization, fullsection blasting excavation, mechanical characteristics of primary support