Rapid drawdown in homogeneous earth dam considering transient flow and suction

Abstract

The present work intends to demonstrate the advantages of considering transient flow regime in the stability analysis of the upstreamslope for the rapid drawdown situation of a homogeneous earth dam. Upstream slope stability evaluations were carried out,considering pore pressure and suction from transient flow analysis while simulating rapid drawdown of the reservoir. The evaluationscomprised different geometries of the upstream slope (from 1V:1.1H to 1V:2.5H) and heights varying from 10 m to 50 m, as well asseveral low permeability materials (SM, SM-SC, SC, ML, ML-CL, CL, MH and CH). In addition, equations relating the safety factor tosuch slopes or dam height were adjusted to the analysis data, in order to define the minimum slope for a certain dam height or themaximum height for a given upstream slope. The results have shown that, considering the transient flow condition, including suction,within the slope stability analysis of the rapid drawdown situation, increases the safety factor in relation to the simplified analysisthat is usually adopted. This also results in much steeper slopes (for a safety factor of 1,1) than the ones recommended by the U.S.Bureau of Reclamation (USBR), suggesting the importance of performing transient flow analysis for rapid drawdown situations andconsidering its results instability analysis.