| In the process of construction of deep excavation engineering located in soil areas with higher ground water levels, great water head formed between inside and outside of foundation pit make the water of the surrounding of excavation area into turbulent flow when lower ground water level of pit and the surrounding areas greatly, and it will impact the internal forces and deformation of the support structure and stability of deep foundation. We should study the interaction between the seepage and the stress of soil if we want to analyze regularity for change of the seepage and the stress of soil caused by excavation of deep foundation pit and dewatering correctly, this is seepage and consolidation coupling.In this paper, the development status of deep foundation, and the calculation of water pressure, as well as how to resist the rebound of foundation bottom at present are summarized, seepage consolidation coupled equations in the situation of two-dimension and three-dimension is derived. Combined with practical work using pile-anchor retaining structure, numerical analysis model in the situation of two-dimension for deep excavation has been done based on the modified Cam-clay model, one is based on the total stress theory without considering seepage and consolidation coupling, the other is based on effective stress theory with considering seepage and consolidation coupling by use of the finite element software ABAQUS, and the internal force and deformation of supporting structure, and rebound of foundation bottom, as well as axial force of anchor and the settlement outside of foundation pit soils are analyzed and discussed. By the comparison of the results of two cases, it shows that:the positive bending moment of the pile considering seepage and consolidation coupling increase and negative moment decrease compared with without considering seepage and consolidation coupling; horizontal displacement of the pile considering seepage and consolidation coupling increase substantially compared with without considering seepage and consolidation coupling; the rebound of bottom of considering seepage and consolidation coupling is greater than the result without considering seepage and consolidation coupling and the magnitude is 1.5 times to 2 times; the axial force of anchor after excavation considering seepage and consolidation coupling increase minor compared with without considering seepage and consolidation coupling; the magnitude and range of the settlement outside of foundation pit soils after excavation considering seepage and consolidation coupling is larger than the result without considering seepage and consolidation coupling.The impact of curtain for cutting off water, change of permeability coefficient and dissipation of excess pore water pressure on the internal force and deformation of supporting structure, and rebound of foundation bottom are analyzed and discussed in the situation of considering seepage and consolidation coupling. The results shows that:curtain for cutting off water increase the distance of flow, decrease the velocity of water flow in the soil, weaken effect on the bottom of the foundation pit; the increase of permeability coefficient make the positive bending moment and deformation of pile decrease minor, negative bending moment increase small, quicken the dissipation of excess pore water pressure, but the rebound of bottom increase greatly; dissipation of excess pore water pressure make the moment of pile and deformation increase to varying degrees, so is the axial force of anchor.By contrast of the result based on the effective stress method considering seepage and consolidation coupling with the results based on the total stress method without considering seepage and consolidation coupling, and the permeability coefficient how to influence dissipation of the excess pore water pressure, as well as the dissipation of excess pore water pressure how to affect the process of excavation, we can know that:the results based on the effective stress method considering seepage and consolidation coupling greater than the results based on the total stress method without considering seepage and consolidation coupling, due to significant seepage and pore water connectivity level increases and the negative excess pore water pressure formed in and around the bottom of the pit after excavation make the volume of soil expand, so as to cause the decrease of soil shear strength during dissipation of excess pore water pressure when excavation in the areas which the groundwater level is high and soil moisture is rich, as well as the permeability coefficient is low, although we take the dewatering measure. This moment, the method water and soil pressure together counted is unsafe and choose the method water and soil pressure separate counted is appropriate. So we can not ignore the impact of seepage on the supporting structure during excavation when we design and construct deep foundation pit in these areas.
|
PDF Full Text Request