Quality Control and Quality Assurance Methods for Cutoff Walls in Dams and Levees

Abstract

Detailed performance assessments of many existing dams and levees have demonstrated a need to install cutoff walls to reduce seepage quantities and provide protection against internal erosion and piping. Cutoff walls can be constructed by removal and replacement technologies or by in-situ mixing technologies. In either case, a high level of quality control (QC) by the construction Contractor is necessary to produce an effective barrier, and sound quality assurance (QA) activities are necessary to provide the Owner with confidence that the result will perform as intended. This paper provides descriptions of different cutoff wall construction technologies and appropriate QC/QA activities to accompany each. The principal objectives of QC/QA programs are to produce and verify cutoff walls that have the specified geometry, homogeneity, integrity, permeability, strength, and deformability. QC/QA programs include component material certifications and tests, construction process observations, construction process records, observations and tests of samples from the completed cutoff wall, and tests of completed cutoff wall performance at specific locations. Appropriate application and details of these QC/QA components differ in important ways for the different types of cutoff wall. This paper provides guidance regarding QC/QA methods and data interpretation.