Hydraulic conductivity of a glacial clay till liner

Abstract

The study of water flow through soils is an important aspect of soil mechanics. Past experience with glacial clay till deposits investigated in central and southern Saskatchewan has demonstrated that in situ saturated hydraulic conductivities vary from about 10⁻⁶ to 10⁻⁹ cm/s. In some applications and regulatory references, an accepted practice in the past is to assume that the field hydraulic conductivity value for a soil liner will be one order of magnitude (i.e. ten times) greater than the confirmed laboratory hydraulic conductivity value for a remoulded sample composed of the same soil. In fact, experience has shown that measured as-built field hydraulic conductivity values for a soil liner can be several orders of magnitude greater than the laboratory value if the liners are poorly constructed and, therefore, would not be compliant with regulatory criteria. The reliability of artificially applying any correction factor to a laboratory value to obtain an assumed field value is, therefore, questionable. This paper describes field and laboratory investigations that were conducted to characterize the general properties and the hydraulic conductivity of a glacial clay till soil liner. For this example case study, laboratory measurements of the hydraulic conductivity for remoulded soil samples were undertaken using a flexible wall permeameter (FWP). Air-entry permeameter (AEP) tests were performed on a soil test pad prior to construction and then on the completed soil liner immediately after construction to measure the as-built hydraulic conductivity. Both the FWP and AEP tests resulted in comparable hydraulic conductivity values that were in the order of 10⁻⁸–10⁻⁹ cm/s. A preceding and preliminary empirical approach was also found to be reasonable for purposes of determining soil suitability and estimating the “achievable” hydraulic conductivity value. The preliminary estimate was determined to be conservatively greater than the values determined by both the FWP and AEP test methods.