Study On Design Theory And Key Technology Of Composite Foundation Considering The Deterioration Of Cement Soil Pile

In the construction of highway, cement soil mixing pile is a common method to reinforcement the weak foundation, using the special equipment to stir powdery or slurry cement and foundation soil in situ. In addition, "specifications for design of highway subgrade (JTG D30-2004)" provisions:when there is a larger head difference on both sides of the coastal embankment, cutoff wall (usually the thickness of 300-400mm) can be set up to reinforcement the weak foundation. However, in coastal and inland areas, such as blowing filling made land, the mineralization degree of the groundwater is very high, some even greater than 50g/L-1, which will lead to deterioration of cement soil. Present rules are not considered the deterioration of cement soil as an effect when design the composite foundation, although the "building foundation design specification (JGJ79-2011)" provisions:when using the cement soil mixing method to reinforce the foundation, the using method must decided by field experiments, the specification does not given. So there is a lack of forecasting method of the full life cycle bearing capacity of cement soil piles in salt groundwater, and the influence of cement soil pile degradation on the settlement of composite foundation.Taking the Yellow River delta silt as an example, this paper studies the key scientific issues surrounding the deterioration effect of the cement soil piles around Binhai cement soil. Based on investigation and analysis the quality of underground water and soil mechanics nature of the Yellow River Delta region, and use of the comprehensive means of test, theoretical and numerical analysis, taking deterioration into account, the cement pile composite foundation design theory and key technologies are studied:taking the mixing piles from the Yellow River saltwater environments soil as an example, bearing capacity of composite foundation in long- term is researched and proposed a prediction method to calculate bearing capacity of composite foundation in long-term, compare with other people’s results, the formula that we proposed has a good performance; taking Dongying port expressway composite foundation as an example, the effect of different pile diameter to the deposition characteristics are studied by means of numerical simulation. The result shows that the bigger of pile diameter pile the smaller of foundation sedimentation, and the effect of degradation is mainly in the soil pile reinforcement area; based on Darcy’s law the evolution of the early deterioration of soil cement layer permeability of China Jiaozhou Bay is studied. Found that the deterioration of the depth of development with age increasing showing increased rate gradually decreases the trend and the permeability of cement soil degradation layer decreases with the increase of age increases.