Experimental And Theoretical Study On Earth Pressures Considering Limited Soils And Retaining Wall Deformation

With the development of urban construction, underground space is being widely used. Underground structures become more and more densely distributed. Some situations in which the width of the backfill near the retaining wall is limited begin to occur, such as the retaining wall adjacent to an exsiting basement or rockface, and narrow excavation of subway station etc. However, the classical Coulomb and Rankine earth pressure theory assume that the rigid retaining walls translate and reach the limited state, and the soil near the wall must be semi-infinite. So it is obviously inappropriate to calculate the earth pressure in above cases using the classical pressure theories. This paper focuses on model test and theoretical studies on the earth pressures for finite soils considering the displacement mode and magnitude of retaining wall. The main work and conclusions are as follows:1. Based on existing experiments, facilities for a1g scale model test were designed and produced to study the earth pressure problem for finite soils considering the displacement mode and magnitude of retaining wall. The particle image velocimetry(PIV) method was applied in the model test to visually observe patterns of soil deformation and development of the slip surface.2. Four T model active earth pressure tests were conducted under different n (the ratio of backfill width and wall height) and experimental results were analyzed. It was shown that the earth pressure was significantly affected by wall displacement and n in a non-linear distribution. With the increasing of the retaining wall displacement, the earth pressure gradually decreased from the rest earth pressure to the limit active earth pressure, and a sliding surface arose through the wall bottom.The limit active earth pressure was in good agreement with existing theoretical solution. With the increasing of n, the earth pressure increased and the slip surface inclination decreased gradually under the same wall displacement magnitude. While n≥ncr, the limit active earth pressure was close to Coulomb active earth pressure and the sliding surface inclination.was close to the theoretical Coulomb slip surface inclination.3. Two T model passive earth pressure tests were conducted under different n and experimental results were analyzed. It was shown that the earth pressures were in non-linear distribution and increased along the depth of the wall. With the increasing of wall displacement, the earth pressures gradually increased from the rest earth pressure. The earth pressures decreased with the increasing of n under the same wall displacement.4. Based on the experiments and existing theories, calculation models on the earth pressure of rigid retaining wall with wall movement of rotation about top and bottom for finite soils were presented. Horizontal thin-layer element method was used in which the equivalent internal friction angle between the horizontal thin layers were associated with retaining wall displacement modes and n. The differential equation of the first order was set up by the equilibrium of forces on the horizontal layer. The theoretical formulae of the unit earth pressure, the active earth pressure coefficient and the relative height of the application points of the resultant earth pressures on the retaining wall were obtained. The effects of n and wall friction angle on the active earth pressure under the two different modes were mainly discussed. It demonstrated that n, wall displacement mode and soil parameters were the major factors which had impact on the active earth pressure. The results by the method proposed here were in good agreement with those of the existed numerical analysis and experimental results. This verified the method presented here was reasonably practicable.5. Considering the relative position of maximum wall displacement point and the intersection of the slip surface and the adjacent retaining wall, theoretical analysis model on the earth pressure of a flexible retaining wall with drum deformation for finite soils were established respectively. The theoretical formulae of the unit earth pressure, the active earth pressure coefficient and the relative height of the application points of the resultant earth pressures on the retaining wall were obtained. It was shown that the earth pressure distribution about this problem was more complicated than other simple displacement modes. The results for Semi-infinite soil by the method proposed here were compared with those existed experimental data and theoretical solutions, and a better fitting than the existed theoretical solutions was achieved.