Critical Unsaturated Soil Properties for Soil Covers

Abstract

Monolithic soil covers are becoming more widely accepted as viable alternatives to standard resistive barriers for covers at mining facilities in arid and semi-arid regions. Design procedures and available models have been documented as have the results of monitoring data from soil covers that have been in operation for a number of years. The primary soil response associated with the design and performance of a soil cover is the Soil Water Characteristic Curve (SWCC). The SWCC test is a relatively expensive and time consuming test to perform. The next logical step in advancing the state-of-practice of soil covers from the conceptual stage to implementation on a routine basis is to develop a detailed understanding of the unsaturated soil properties, specifically the aspects of the SWCC that are critical to the performance of a soil cover; i.e. air entry pressure, storage function etc. Ideally, these properties can be reliably correlated to simple index tests; grain-size-distribution and Atterberg limits, in-place density in such a manner that a few SWCC tests can be performed for a site and the index tests used to delineate acceptable soils. The results can also be used to develop construction quality assurance and construction quality control (CQA/CQC) procedures. This paper presents the results of a parametric modeling study performed on typical cover soils. Variations in SWCC properties are utilized in the model and their impact on cover performance assessed. Changes to the SWCC as a result of changes in index properties are estimated based on trends published in the literature. Conclusions are drawn with respect to correlating index properties, cover performance and SWCC results.