Research On Lateral Earth Pressure Of Retaining Structure In Foundation Pit

With the Chinese economy growing at a fast pace, utilizing underground space has become a new focus for municipal development, it fundamentally relates with excavation of the foundation pit. Due to the limitation of the surrounding environment, current excavation design has gradually shifted from strength control to deformation control. In applying deformation control, it is vitally important to accurately determine the soil pressure being applied to the retaining structure, which is also closely dependent on the deformation of the adjacent soil. Obviously, the deformation characteristics of soil are also influenced by factors such as stress path. In this thesis, four subjects were discussed.1. Based on a preliminary analysis, it is estimated that the soil layer at outer of the retaining structure could produce lateral loading and unloading stress paths. Therefore, a series of experiments were performed with different lateral loading and unloading stress paths. Based on D-C model, formulas to calculate tangent elastic modulus were developed for lateral loading and unloading conditions.2. A good agreement was observed between experimental data and results from finite element analyses using the previously mentioned tangent modulus model. A study on the relationship between soil pressure and retaining structure deformation was also conducted using finite element method. It was found that, if the horizontal displacement on the retaining structure dose not exceed H/100 (H is the length of retaining structure), there exists a linear relationship between the soil pressure and the structural displacement. In active zone. Additionally, the influence on retaining structure displacement of separate unloading of lateral and vertical pressures was also studied.3. Taking into account the relationship between soil pressure and displacements, a modification was made to the isobeam method for designing retaining structures. Retaining structures can designed according to not only strength using moment but also the practicl need of distortion .A computer program was also developed and examples were presented to illustrate the difference in numerical results with and without the proposed modification.4. Disadvantages have been summarized for two numerical methods, in which water and soil pressures are computed either jointly or separately. Using void ratio eto calculate the interacting area between soil and water, a modification to the effective stress theory was introduced for clay. Using this modified theory and a separate estimate of hydrostatic pressure and steady seepage influence, improvement was also made to the numerical method for calculating water and soil pressure on retaining structures. Some examples were presented to illustrate the difference in numerical results with and without the proposed modification.