Seepage and stability analyses for flood embankment design

ABSTRACT: This paper provides a case study on the geotechnical design of a flood barrier system to reduce the risk of flooding for EPCOR’s Water Treatment Plants (WTP), located on the lower terrace of the North Saskatchewan River (NSR) in Edmonton. Earthen embankments were adopted as the main flood barrier in the site. The flood barrier was designed following the US Army Corps of Engineers (USACE) design guidelines for various loading scenarios and conditions. Coupled seepage and stability analyses were performed to evaluate the potential seepage and stability of the proposed flood embankments using GeoStudio SEEP/W and SLOPE/W programs. Based on the analysis results, the thickness and uniformity of the “impervious” blanket layer (native clay or clay fill) beneath the flood embankments is critical to seepage flow and heaving during the flood event. While the amount of seepage flow is insignificant, the uplift pressure at the downstream toe of the flood embankment could cause concerns of internal erosion and/or heaving. The USACE method treats flood as a steady state condition. In reality, due to the transient nature of the flood event, the majority of the embankment fill and foundation soil will remain unsaturated during the 1:500-year flood event. Such results and conclusions bring some discussions on the design criteria for similar flood embankments design. The case study also provides more value for future applications with similar conditions for economical design.