RESEARCH ON THE DEFORMATION CHARACTERISTICS OF THE SURROUNDING ROCK ABOUT HIPPARION RED CLAY UNDER THE ACTION OF WATER-FORCE COUPLING

Tunnel located in hipparion red clay region encountered many engineering geological problems in the construction process. In order to make sure construction safe and smooth traffic, a series of experiments and methods was carried out in the tunnel construction, such as laboratory test, field test and permeability test in situ, et al. Taking the surrounding rock section of the typical hipparion red clay in Shilou tunnel below the underground water level as an example, several aspects about the surrounding rock of hipparion red clay will be analyzed, including volume moisture content, pore water pressure, stress of surrounding rock (soil pressure), vault subsidence and horizontal convergence through the field monitoring. Based on this, a series of works will be done:the reliable situ shear strength parameters of surrounding rock will be obtained by shear tests, three dimensional finite element numerical model of tunnel will be built, the deformation law of the hipparion red clay surrounding rock will be investigated respectively for the water-force coupling effect and without considering it, the variation of the pore water pressure during excavation, the influence degree about the displacement field and stress field of water-stress coupling on red clayrock will be analyzed, and the mechanism of the surrounding rock deformation will be proposed. The results show that:(1) The site monitoring vault settlement is greater than horizontal convergence, and the stress level of surrounding rock is higher on the whole, which can be described by using three different stages, the growth period ( < 20 days), the adjustment period (20~60 days), the stable period (>60 days).Water content of the lower stage is higher than the top, the pore water pressure has experienced the process from negative to positive. (2) The cohesion determined by situ shear test C is 64.0kPa, the angle of internal φ is 27.7°. (3) Numerical analysis shows that, the change of pore water pressure is very obvious after the tunnel excavation, which is caused by the change of the underground water flow velocity field, the hydraulic gradient near lining surface, and the soil hydrodynamic seepage pressure are larger; considering the water-stress coupling, the surrounding rock shear stress, maximum shear strain, crown settlement, horizontal convergence, floor heave are all larger. (4) Groundwater appears seepage influenced by the excavation and support, and passing through the crown, side wall, ending in the tunnel bottom; rock joints appears the further expansion affected by the excavation and groundwater seepage, and becoming the good migration pathway of groundwater; the decrease of the surrounding rock pore water pressure enlarges the effective stress, and the mechanical strength is plunge as the soil tending to the saturated state. In turn, high effective stress, low strength of surrounding rock and through joint fracture together change the groundwater seepage field state. (5) In order to guarantee the whole stability of the surrounding rock, timely discharging water of the tunnel bottom and making construction of inverted arch are suggested.