Benson, CH & Albright, WH 2012, 'Pedogenesis and soil hydraulic properties – a challenge for design and monitoring', in AB Fourie & M Tibbett (eds), Mine Closure 2012: Proceedings of the Seventh International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 343-350, https://doi.org/10.36487/ACG_rep/1208_31_Albright
(https://papers.acg.uwa.edu.au/p/1208_31_Albright/)
Abstract: Soil hydraulic properties are required to determine the required thickness of water balance (evapotranspiration) final covers and as input to models used to predict cover performance. Saturated and unsaturated properties are typically determined on laboratory-compacted specimens and may not reflect the in-service condition following lengthy exposure to local environmental conditions. Site-specific environmental processes – freezing and thawing, wetting and drying, root growth and death, and burrowing of worms and insects – form macroscopic features and alter the hydraulic properties of the soil and the hydrology of the cover. Few data exist regarding how hydraulic properties change over time. Test sections from the Alternative Cover Assessment Program (ACAP) were exhumed four to nine years after construction to make field measurements and take specimens for laboratory analysis. Changes in hydraulic properties occurred in all cover soils evaluated, regardless of climate, cover design, or service life. Larger changes were observed for soils with lower as-built saturated hydraulic conductivity and soils with a greater proportion of clay particles in the fines fraction. Hydraulic properties of the cover soils were similar when exhumed, regardless of the as-built condition. Because changes in the engineering properties of cover materials are commonplace, and significant in some cases, monitoring of covers should be conducted to ensure they are functioning as intended. This presentation compares as-built to in-service hydraulic properties of cover soils, provides methods to estimate changes in the hydraulic properties over time, provides recommendations regarding cover construction methods that will minimise the propensity for change in hydraulic properties, and makes recommendations for monitoring. The material in this paper is taken from a much larger report – Engineered Covers for Waste Containment: Changes in Engineering Properties and Implications for Long-Term Performance Assessment (Benson et al., 2011).