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Field experiments in a fractured clay till: 1. Hydraulic conductivity and fracture aperture
Author(s) -
McKay Larry D.,
Cherry John A.,
Gillham Robert W.
Publication year - 1993
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/92wr02592
Subject(s) - piezometer , hydraulic conductivity , geology , geotechnical engineering , fracture (geology) , groundwater flow , infiltration (hvac) , groundwater , hydraulic head , soil science , mineralogy , aquifer , materials science , soil water , composite material
Field values of horizontal hydraulic conductivity measured in the upper 1.5–5.5 m of a weathered and fractured clay‐rich till were strongly influenced by smearing around piezometer intakes, which occurs during augering, and by the physical scale of the measuring device. Values measured in conventional augered piezometers were typically 1–2 orders of magnitude lower than those measured in piezometers designed to reduce smearing. Measurements of hydraulic conductivity in small‐scale seepage collectors or piezometers, which typically intersect fewer than 10 fractures, vary over a much greater range, 10 −10 to 10 −6 m/s, than large‐scale values based on infiltration into 5.5‐m‐deep trenches which intersect thousands of fractures (range 10 −7 to 3×10 −7 m/s). Values of hydraulic fracture aperture, 1–43 μm, and fracture porosity, 3×10 −5 to 2×10 −3 , were calculated using the cubic law with fracture orientation/distribution measurements and the small‐scale hydraulic conductivity measurements. This paper provides the first reliable determination of the magnitude and spatial distribution of hydraulically derived fracture parameters in a clay deposit. The absence of such data has, until now, severely limited the application of quantitative groundwater flow and contaminant transport models in this type of deposit.