HR: 14:20h
AN: NS43A-02    [Abstracts]
TI: Geophysical Characterization Of A Cover With Capillary Barrier Effect
AU: * Chouteau, M
EM: chouteau@geo.polymtl.ca
AF: Ecole Polytechnique, Depart. CG&M; C.P. 6079, succ. C-V, , Montreal, Qc H3C 3A7, Canada
AU: Anterrieu, O
EM: olivier.anterrieu@polymtl.ca
AF: Ecole Polytechnique, Depart. CG&M; C.P. 6079, succ. C-V, , Montreal, Qc H3C 3A7, Canada
AU: Aubertin, M
EM: michel.aubertin@polymtl.ca
AF: Ecole Polytechnique, Depart. CG&M; C.P. 6079, succ. C-V, , Montreal, Qc H3C 3A7, Canada
AU: Bussieres, B
EM: Bruno.Bussiere@uqat.uquebec.ca
AF: Ecole Polytechnique, Depart. CG&M; C.P. 6079, succ. C-V, , Montreal, Qc H3C 3A7, Canada
AB: Covers with capillary barrier effects (CCBE) can be used to limit gas flux into or out of mine waste disposal sites. The hydraulic behaviour of such type of cover is influenced by slope inclination, which can induce a local desaturation that is detrimental to its efficiency. The covers we have studied consist of three layers, from bottom to top: a 0.5 m layer of sand used as support and a capillary break layer; a fine-grain moisture-retaining layer with a thickness of 0.8 m; and a 0.3 m sand and gravel layer on top for drainage and used as a protective layer against erosion and evaporation . The fine-grain layer must remain permanently saturated in order to be an effective barrier. TDR probes are installed to monitor saturation level; however the number of probes installed is always too small over the very large area of mine wastes protected by CCBE to lead to a good spatial estimation of water content. Also, suction can vary, especially on slopes, which can lead to desaturation by drainage of the moisture- retaining layer and the loss of imperviousness to oxygen. We have investigated ways to estimate water saturation changes of the cover using geophysics. Modelling show that changes in water content within the cover will affect the GPR and resistivity responses. We have carried out a survey over the flanks and the top of a large mining waste site located in North-western Quebec (Canada). We use GPR with 200 MHz, 450 MHz and 900 MHz antennas as well as a Lund resistivity imaging system from ABEM with 0.30 m dipoles to image stratigraphy and water content from surface to 1.7 m depth. Thicknesses of each of the three layers within the cover can be mapped with detail. Correlations with TDR data show that the techniques can be used to estimate saturation conditions within the fine-grained barrier with good lateral resolution. The survey has also allowed mapping a suction break installed within one of the slope profile.
DE: 0925 Magnetic and electrical methods (5109)
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly