Theory And Numerical Simulation Of Consolidation-Creep Of Saturated Soft Clay Considering Non-Darcy Effect

Land subsidence has been one of the environmental geological disasters that seriously affect people's life because of its wide impact range,long impact time and irreversible characteristics.With the development of economy and the acceleration of urbanization,the contradiction between groundwater exploitation and land subsidence control has become more and more prominent in the economically developed coastal and riverside soft soil areas.Therefore,it is of great theoretical and practical significance to study the consolidation creep theory in soft soil under different conditions in China.However,due to the limitation of eight basic assumptions,the traditional Taizaghi consolidation theory does not fully consider the nonlinear characteristics of seepage process and deformation process,so it cannot accurately explain the ground subsidence process at low seepage velocity,especially in soft clay areas.Therefore,aiming at the problem of consolidation creep of soft clay,the elastic-viscoplastic EVP model was introduced to establish a fluid-solid coupling model considering non-Darcy flow effect and time-varying permeability coefficient.The influence mechanism of non-Darcy effect on consolidation creep process of saturated soft clay was studied by numerical simulation.The main work and results are as follows:(1)According to the creep consolidation law of soft clay,the elastic viscoplastic(EVP)model was introduced to describe the deformation of soil skeleton on the basis of the traditional one-dimensional seepage consolidation theory,and Hansbo's law was obtained.The one-dimensional creep consolidation equation with variable permeability coefficient was derived considering the non-Darcy flow effect and was solved by the central difference method.Compared with the numerical results in literature,it is found that the equation can obtain good fitting results.Then,the influence of Hansbo's law seepage parameters of low-velocity non-Darcy flow on creep consolidation is further discussed.The analysis shows that the viscosity effect of soil is the main cause of "Manderle-like effect".The low-velocity non-Darcy flow will further enhance this effect.Hansbo seepage will delay the creep consolidation process of foundation.With the increase of Hansbo seepage parameters,"Mandel effect" becomes more and more obvious.The low-velocity non-Darcy effect will become more significant as the excess pore pressure dissipates and the seepage gradient decreases.Compared with the constant permeability coefficient,it is assumed that the variable permeability coefficient will delay the dissipation of excess pore water pressure and enhance the "Manderle-like effect".(2)Considering large deformation of soft clay foundation under creep consolidation process of non-Darcy seepage,the effects of introducing Hansbo seepage model,based on the large deformation elastic viscoplastic EVP model to one dimensional nonlinear creep consolidation of soft clay is deduced equation.The central finite difference numerical format is given,and the Darcy seepage under the law of the numerical results are compared with the literature,and a good fitting result is obtained.By comparing with the EVP model under the small deformation hypothesis,the dissipation of excess pore water pressure under the small deformation hypothesis is slower than that under the large deformation hypothesis.Soil thickness has an effect on the significance of non-Darcy flow effect.(3)For the problem of creep consolidation of soft soil caused by pumping,the law of water level decline of confined aquifer is characterized by exponential function.The low-speed non-Darcy Hansbo seepage and EVP model of variable permeability coefficient are introduced into the creep consolidation analysis of soil,and the dissipation of excess pore water pressure in soil accelerates with the increase of B value.The "Manderle-like effect" will become more significant with the decrease of B value and the increase of Hansbo seepage parameters.At the bottom of the soft soil layer,the effect of low-speed non-Darcy flow is not obvious because the drainage condition is better due to its proximity to the pumping boundary.Compared with the constant permeability coefficient,it is assumed that the variable permeability coefficient will delay the dissipation of excess pore water pressure and enhance the "Manderle-like effect" in the consolidation creep of soft soil caused by pumping.(4)In the radial creep consolidation drainage of sand well,the dissipation rate of excess pore water pressure will be accelerated by the increase of well diameter and overburden under Darcy's seepage law.The "Manderal-like effect" gradually increased at the distal end,but did not appear at the proximal end due to smooth drainage conditions.Compared with Darcy flow,Hansbo flow can delay the dissipation rate of excess pore water pressure in sand well foundation under non-Darcy flow condition.The effect of non-Darcy flow becomes more significant with the increase of parameters of Hansbo flow law.Compared with the constant permeability coefficient,it is assumed that the variable permeability coefficient will delay the dissipation of excess pore water pressure and enhance the "manderle-like effect" in radial consolidation creep drainage of sand well.(5)Aiming at the drainage problem of double-layer saturated soft clay under load,using the EVP constitutive model in Chapter 2,the problem of consolidation and creep of double-layer saturated soft clay with variable permeability considering the non-Darcy effect is discussed,combined with the continuous conditions between layers.Construct the central difference method format and solve it.The results show that the non-Darcy seepage effect of the upper and lower soil layers delays the dissipation of the excess pore water pressure of the double-layer foundation,increases the value of the excess pore water pressure,prolongs the time to reach the maximum excess pore water pressure,and delays the drop rate of the vertical strain value.Which is consistent with the creep law of singlelayer consolidation.By comparing the non-Darcy flow effect of the upper and lower soil layers,it is found that the non-Darcy flow effect of the lower soil layer is close to the impervious boundary,which will delay the dissipation rate of excess pore water pressure.As time goes by,the final settlement tends to be the same.