TIME-DRAWDOWN BEHAVIOR OF CONSTRUCTION DEWATERING SYSTEMS IN FINE SOILS

In the design of a construction dewatering system in a fine-grained soil it is necessary to consider not only the steady state flow rate that must be pumped, but also the time it will take to achieve a given drawdown. This may be weeks because the soil will usually remain saturated, and the mechanism of pore-water pressure reduction is consolidation rather than dewatering per se. If the response time is not taken into account in programming an excavation, the cost implications could be considerable. In this Paper approximate methods based on the assumption that the isochrones are parabolic are developed for the estimation of time-drawdown relationships for dewatering systems in fine soils. The parabolic isochrone analyses are compared with exact solutions where these exist, and with field data from five case studies. The parabolic isochrone approximation is shown to be suitable for flow to lines of wells, and to rings of wells, provided that the distance of influence remains small compared with the radius of the ring.