Evaluation of the effectiveness of an alternative to control groundwater inflow during a deep excavation into confined aquifers

Abstract

This paper presents a case study of groundwater control for a deep excavation into confined aquifers in Fuzhou, China. Field pumping tests were first carried out prior to the excavation to investigate the groundwater conditions at the site and as well as to evaluate the feasibility of previous designed dewatering systems (34 m diaphragm walls together with pumping wells). The results showed that under the condition of previous dewatering systems it would have been extremely difficult to safely lower the water level inside the excavation. A co-working scenario of partially penetrating curtains and horizontal waterproof curtain with jet grouting was then proposed to control groundwater inflows. Additional water-tightness assessment tests (WAT) were then performed that allowed to confirm the efficiency of the proposed method. From the feedbacks of WAT, this proposed scenario not only successfully lowered the water lever inside the excavation below the excavation bottom (maximum drawdown up to 14.9 m), but also it minimized the drawdown outside the excavation (less than 0.2 m). Furthermore, an approach was proposed to approximately estimate the hydraulic conductivity of the jet-grouting at the real site from the result of WAT. The hydraulic conductivity of jet-grouted soil is three orders of magnitude lower than that of the original sediments.