Soil Compressibility in Transient Unsaturated Seepage Analyses

Most levee underseepage and uplift analyses are based on steady-state seepage and can yield conservative results. Although computations are simpler and steady-state seepage parameters are easier to determine and readily available, transient and unsaturated seepage analyses are more representative of levee seepage conditions. Transient seepage analyses using a case study floodwall indicate that as soil compressibility of the underseepage layer decreases, rapid landside pore-water pressures increase and can approach steady-state values. The transient results for this case study also indicate that uplift factor safety during the flood event are about 25% higher than steady-state. The effect of soil compressibility can delay or accelerate the onset of uplift water pressure increase from the initial steady-state conditions.