Excavation slope stability related to pore-water pressure variations during piling
High excess pore-water pressures were measured within a confined stratum of loose silt underlying an excavation slope during pile-driving operations at the slope toe.The range of observed pore-water pressure increase with distance is generally in excess of previously published data. This is attributed to a combination of factors including superposition of increments of excess pore-water pressures generated during driving of individual piles within a group, redistribution of excess pore-water pressures with time, the effect of soil displacement in a confined loose silt layer, and the greater disturbance associated with driving batter piles as opposed to vertical piles. A further contributing factor was considered to be the increase in pore-water pressures due to small straining within the silt layer.Because of uncertainty regarding the accuracy of pore-water pressure predictions and the presence of deformation-sensitive services at the slope crest, the observational approach was adopted during construction.Based on the results of stability analyses using observed pore-water pressures in the field, the construction procedures were modified to maintain an adequate factor of safety and to minimize slope deformation. It was recognized that the method of analysis may have been conservative because changes in total stresses along potential failure surfaces were not taken into account.