Numerical analysis of rapid drawdown: Applications in real cases

• Published in: Water Science and Engineering Vol. 9; no. 3; pp. 175 - 182
• Main Authors: Alonso, Eduardo E., Pinyol, Núria M.
• Format: Journal Article Publication
• Language: English
• Published: Elsevier B.V 01.07.2016; Department of Civil and Environmental Engineering, Universitat Politècnica de Catalunya UPC, Barcelona 08034, Spain; Elsevier
• Subjects: analysis; Coupled; Coupled flow-deformation analysis; coupling; Drawdown; Enginyeria civil; Esllavissades; flow-deformation; Geotècnia; Hydro-mechanical; Hydro-mechanical coupling; Landslide; Landslides; Mecànica de sòls; Numerical; Numerical analysis; Pore; Pore water pressure; pressure; water; Àrees temàtiques de la UPC; Landslide; Pore water pressure; Numerical analysis; Coupled flow-deformation analysis; Drawdown; Hydro-mechanical coupling
• ISSN: 1674-2370; 2405-8106; 2405-8106
• DOI: 10.1016/j.wse.2016.11.003

In this study, rapid drawdown scenarios were analyzed by means of numerical examples as well as modeling of real cases with in situmeasurements. The aim of the study was to evaluate different approaches available for calculating pore water pressure distributions during andafter a drawdown. To do that, a single slope subjected to a drawdown was first analyzed under different calculation alternatives, and numericalresults were discussed. Simple methods, such as undrained analysis and pure flow analysis, implicitly assuming a rigid soil skeleton, lead tosignificant errors in pore water pressure distributions when compared with coupled flow-deformation analysis. A similar analysis was performedfor the upstream slope of the Glen Shira Dam, Scotland, and numerical results were compared with field measurements during a controlleddrawdown. Field records indicate that classical undrained calculations are conservative but unrealistic. Then, a recent case of a major landslidetriggered by a rapid drawdown in a reservoir was interpreted. A key aspect of the case was the correct characterization of permeability of arepresentative soil profile. This was achieved by combining laboratory test results and a back analysis of pore water pressure time records duringa period of reservoir water level fluctuations. The results highlight the difficulty of predicting whether the pore water pressure is overestimated orunderestimated when using simplified approaches, and it is concluded that predicting the pore water pressure distribution in a slope after a rapiddrawdown requires a coupled flow-deformation analysis in saturated and unsaturated porous media.