A Study On The Earth Pressure Against Rigid And Flexible Retaining Wall

The calculation of earth pressure against retaining wall is one of the classical subjects in the civil engineering. It has been more than two centuries since Coulomb's theory and Rankine's theory were presented. However they are still in general use in present-day engineering practice even though the existence of some defects. Large numbers of engineering practices show that the lateral earth pressures on the retaining wall especially the flexible ones often deviates from the present theoretical prediction. Some numerical and theoretical studies on the earth pressure against the rigid and flexible retaining wall undergoing different types of movement were conducted in this paper.Firstly, FEM software ABAQUS was chosen to analyze rigid retaining wall. The coincidence between the numerical results and the former tests results about the active earth pressure against rigid retaining wall subjected to RB, RT and T movement prove that the numerical model mentioned above is reasonable. The development of the plastic zone in the soil mass is different as the wall movement varies. The displacement that is required for the shearing resistance of the soil to mobilize fully varies along the wall. And this divergence is also affected by the mode of the movement.Secondly, the numerical model is used to analyze the influence of thickness of flexible wall on earth pressure distribution, the coefficient of earth pressure and the application point of the resultant force. However, most of the distribution of the earth pressure behind the flexible wall is of "R-shape" when the flexible wall experiencing "drum-shape "movement. Besides, the friction between the flexible wall and the soil is active during "drum-shape" movement, which decreases the deformation of the wall, lowers the application point of the resultant force and makes the development of the plastic in soil mass slow down.Thirdly, according to another numerical model, the distribution of the earth pressure behind the rigid wall undergoing "bi-line" movement is almost the same as that of the flexible wall. Therefore rigid wall subjected to "bi-line" movement isthought to be an effective substitutive model for flexible wall with "drum-shape" movement.Fourthly, two equations for calculating the active earth pressure against flexible wall have been obtained. On the basis of the numerical result that a complete sliding surface exist in the soil behind the flexible retaining wall, a formula for calculating the earth pressure under limiting state was derived by considering the equilibrium of the force on the element of the soil wedge. The earth pressure distribution of R-shape behind flexible retaining wall is certified once again by the theoretical result and the total active force equal to that calculated by Coulomb theory. The second method for calculating the earth pressure under unlimited state was obtained by considering the effect of the mobilized shearing resistance of the soil.Finally, numerical models were built to analyze the passive earth pressure behind the rigid retaining wall undergoing RB, RT and T movement. Numerical results show that friction between the wall and the soils is a great factor in the calculation of passive earth pressure. Another model was about the combined earth pressure behind the rigid wall experiencing rotation about an axis close to the toe of the wall. It is found that the earth pressure distribution in the active zone is quite similar to that one behind the rigid retaining wall under RB rotation.