Active Earth Pressure on Retaining Walls with Unsaturated Soil Backfill

The active earth pressure coefficients and its distribution against the face of an inclined wall retaining an unsaturated soil backfill, has been established using the limit equilibrium approach. The analysis is performed with the help of a simple Coulomb-type mechanism. For different vertical unsaturated steady state flow conditions, and the location of water table, the variation of soil suction stress that occurs within the vadose zone of the backfill soil mass has been taken into account in the analysis. The influence of different parameters such as inclination of wall, roughness and adhesion of soil-wall interface, ground surcharge pressure, properties of backfill soil and its flow conditions (infiltration, no-flow and evaporation conditions) on the active earth pressure, has been examined in detail. The depth of tensile crack has also been established. The active earth pressure in unsaturated sand is not affected with the variation in the flow conditions for given angle of internal friction of sand; whereas, significant variation in the magnitudes of active earth pressure in unsaturated clay has been observed with the change of rate and type of unsaturated flow. The height of wall and the location of ground water table are found to be the two prime factors that affect substantially the active pressure in unsaturated sand. On the other hand, for a given location of water table the magnitude of the active pressure in unsaturated clay is merely affected by the change in the wall height. The solutions from the present analysis are compared with the available theoretical results that are reported in literature for some special cases.