Study On The Deformation Mechanism Of Deep Foundation Pit In The Unsaturated Soil

The distribution of unsaturated soil is very broad in our country, however, plenty ofresearching results just staying in laboratory, because various research of unsaturated soil isunable to overcome premature actual application of engineering at present. Aiming at theproblems of deep excavation in the unsaturated soil in construction of high and high-risebuilding, this paper research on how strength parameters of soil mass, deformation of deepexcavation in the unsaturated soil and stability of pit are affected by change of soil water content."Water content→parameters of shear strength→deformation of pit→stability analysis"asthoughts of this paper, and it has these characteristic:1. For being easy to use of actual application, it search for law between change of soil watercontent (saturation) and shear strength parameters (cohesion) of unsaturated soil withunconsolidation and undrainage triaxial test, and adopt regression power model to fit the curve oftest results. After analysis of test results, here is a certain water content (w=16.60%) in variouswater contents. If a soil water content beyond the water content, strength parameters (cohesion)of soil appear a distinct tendency.2. On above basis, in the unsaturated soil construction deformation is numerically simulatedwith PLAXIS finite element program. As the results show that the settlement of the soil at pit topand the horizontal displacement of retaining wall gradually increase, but the uplift deformationof the soil at pit bottom is opposite. Considering the settlement of the soil at pit top and thehorizontal displacement of retaining wall, an estimated function of uplift is initially established.3. According to Code for Design of Building Foundation, the safety coefficients offoundation pit stability are calculated under different water content. The analyses of calculationshow that the safety coefficients decrease with water content increasing. When the water contentbeyond a certain water content (w=16.60%), the safety coefficients of anti-overturning stabilityobviously decrease.4. The uplift deformation values of soil at pit bottom are calculated under different watercontent, with Tong Chi University's empirical formula. Comparing with numerical results, the results of the empirical formula are obviously larger. But both results are relatively stable, andthe deformation of uplift has same tendency.In summary, the change of soil water content affects the soil strength and deformation of pit.In some cases the deformation or safety coefficients will increase or decrease sharply. Thus,researching on the deformation of foundation pit affected by the change of soil water content, ithas very important engineering significance; it provides a reliably scientific theory with theconstruction, design, and evaluation management of deep excavation in the unsaturated soil.