Research On Earth Pressure Theories Of Cohesive Soil

In the past few years, with the continuous development of urbanization, the underground space has been widely used. At the same time, a mass of engineering problems have arisen, so it’s necessary to farther perfect and improve the design theories of foundation pit. To calculate the lord acted on the supporting structure for foundation pit is always the key issue in the practical engineering. Therefore it’s involved with a basic content, the earth pressure theory. This thesis investigates three elementary problems about the cohesive soil on the basis of existing achievement, the water and earth pressure on the supporting structure of foundation pit, non-limit active earth pressure, together with the over-consolidated soil pressure result from excavation.The present computation methods, estimating water and earth pressure separately or together, can only figure out the results in extreme cases, which cannot be used widely. This thesis bring forward a new method based on the truth that the hydration water of cohesive soil must take up a certain space of the total void space with the result that the transmission effect of pore water pressure will decrease. Two different kinds of shear strength parameters can be unified adopting the combined action coefficient^of water and soil. The numerical examples indicate that this new method can calculate the earth pressure from the cohesion-less soil to the cohesive soil, so the method has general applicability.The classical earth pressure theories can only calculate the pressure when the wall movement achieves the limit state. In order to match up to the practical situation, it is necessary to develop the earth pressure theories under non-limit state. However, previous researches are only involved with the cohesion-less soil. Based on the existing results for active earth pressure of cohesive soil under non-limit state, the relationship between the internal frictional angle φ, cohesion c and the wall movement is established according to Mohr circle of stress under the situation of intermediate active state. Finally, a new equation for determining active earth pressure of cohesive soil under non-limit state is derived using horizontal slices analysis method. The value of calculation has an approximate agreement with the measured value of two model tests.The passive earth pressure inside pit is a problem of over-consolidated soil owing to pit excavation. There are two basic issues, effective vertical pressure and the shear strength parameters of over-consolidated soil. This thesis put forward new formulas to compute the effective vertical pressure and the strength parameters, meanwhile, the Rankine’s earth pressure theory has been modified in order to get the passive earth pressure inside pits. The method can correct the computed result of traditional method through the example analysis.