Ventilated Well Method for Efficient Dewatering of Soft Soils: Experimental Investigations

Abstract

Two of the conventional methods to improve soft soil deposits are evaporative dewatering and accelerated consolidation of the deposits using prefabricated vertical drains (PVDs). Evaporative dewatering is limited in application to densification of the surficial layers providing little to no improvement of the soft consistencies that lie at the bottom of the deposit. Development of smear zones around PVDs has been understood to affect their efficacy. To this end, this paper discusses a novel method of dewatering using controlled evaporation through ventilated wells [the ventilated well method (VWM)] that traverse the thickness of the deposit. Air, under controlled conditions, is circulated inside the perforated well, which progressively drives the moisture out of the soil skeleton. This is accompanied by development of an internal stress (suction) condition in the soil system leading to its densification. First, the paper introduces the method and discusses its underpinning physical principles and a laboratory-scale implementation of the VWM. Next, a systematic parametric study was carried out to understand the corresponding effects on the efficacy of the VWM due to varying dimensions of the well and the testing mold, rate of the air flow, and soil and pore fluid properties. Based on the laboratory-scale investigations, it is observed that the VWM performed better than surficial evaporative dewatering. The method is transferrable to the field and has a great potential in ground improvement exercises involving soft deposits such as those encountered in dredged sediments, mine tailings, and fluidized industrial waste.