Study On Inrush Of Excavation Induced By Dynamic Confined Water Considering Nonlinearity Of Soil

Groundwater has always been one of the main causes in foundation pit accidents.It can cause serious consequences if the confined water is treated inappropriately during excavation,such as excessive deformation of side wall,uplift of bottom and inrush accidents.The accident can have adverse impacts on surrounding environment,such as excessive settlement of outside ground surface,adjacent structures and underground pipelines.Therefore,the method of determining inrush stability and the study of failure mechanism have been the focus of engineering and scientific research.The inrush accident is generally analyzed from the perspective of overall lifting or plastic failure due to the buoyancy of confined water at present,but the soil at the pit bottom isn’t strictly impervious.It is also found in practice that infiltration failure often occurs when the confined water breaks through the soil layer at the bottom of the pit.The permeability of aquitard is seldom considered in current study of inrush.And most studies assume that the confined water level is stable or gradually rising.However,the confined water level in coastal area is fluctuated due to the influence of tidal waves.In this paper,semi-analytical,finite difference and numerical simulation methods were used to study the inrush problem of foundation pit induced by dynamic confined water.The main innovations and research work are as follows:1.The seepage consolidation theory was used to deal with the inrush problem.Then the semi-analytical solution of excess pore water pressure considering soil nonlinearity and large strain effect were deduced.Later,the effects of nonlinearity,large strain of soil and dynamic confined water parameters on the excess pore pressure and exit gradient were analyzed.It was found that the exit gradient will be smaller without considering the nonlinearity of the soil.The nonlinearity should be fully considered in analysis of stability or precipitation.Then,the solution was applied to the analysis of engineering examples.2.Numerical solutions of the excess pore pressure and exit gradient were obtained by the finite difference method which considering the soil nonlinearity and the non-Darcy seepage law simultaneously.The effects of non-Darcy seepage parameters and confined water change factors on exit gradient were studied.It was found that the exit gradient decreases with the increase of the non-Darcy parameters.3.Finite-difference method was used to obtain the exit gradient of the double-layered aquitards considering the soil nonlinearity.And it was verified with the semi-analytical solution of single layer soil.Then the effects of initial compression and permeability coefficients were analyzed.It was found that the exit gradient increases with the decrease of the permeability coefficient of upper soil.4.The infiltration failure theory was compared with overall lifting and plastic failure theory to explore the influence of width-thickness ratio of aquitard on the type of inrush.It was found that infiltration failure will occur when the width-thickness ratio is relatively small,so it is necessary to check the infiltration stability in deep shaft excavation.5.Weak surface of infiltration was taken account into the three-dimensional numerical analysis model.The influence of weak surface and local deep pit at the bottom were studied.It was found that large hydraulic gradient will be formed at the weak surface and it will cause infiltration failure.The maximum hydraulic gradient in the aquitard increases linearly with the depth of weak surface.Finally,the influence of water fluctuation was analyzed.