Evaluations of the effectiveness of seepage barrier walls and foundation grouting programs requires multifaceted analysis at the US Army Corps of Engineers. During construction, on site quality control measures are put into place to carefully monitor and ensure that seepage barriers are constructed as per specification. However, the evaluation of the design intent and long term performance of the barrier wall installation is still required. Each project is required to be assessed as part of a Post Implementation Evaluation (PIE) after construction is complete. This process examines whether the design intent of the wall was achieved and evaluates whether the project achieved potential failure mode risk reduction. After the risk evaluations are complete, monitoring is still needed to continue to verify that the wall continues to achieve the designers’ intent and continues to successfully reduce the risks at the project. A well designed monitoring program is used to verify project performance for both pre- and post-construction. For seepage barrier projects, one of the most useful instruments for performance monitoring are piezometers. These installations provide the basis for understanding of the influence of the constructed works on the groundwater beneath the dam and are used to evaluate the effectiveness of grouting program and barrier wall installations. Common methods include the use of traditional time series plots. However, use of net head dissipation calculations, correlation plots, multi-variable statistical analysis, contour plots and other analysis methods can also be used to understand the behavior of the project performance over time. Methods of analysis used to monitor the barrier wall and foundation grouting performance with key consideration using examples from Center Hill Dam and Mosul Dam are presented herein.
Subjects: seepage barrier walls, piezometer, instrumentation
Author: Georgette Hlepas, PhD, PE and Vanessa Bateman, PG
Publisher: DFI, EFFC