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EFFECTS OF ELECTROOSMOSIS ON SOIL TEMPERATURE AND HYDRAULIC HEAD: I. FIELD OBSERVATIONS
Citation:
Chen, J. L., S R. AlAbed*, J A. Ryan*, M H. Roulier*, AND M Kemper*. EFFECTS OF ELECTROOSMOSIS ON SOIL TEMPERATURE AND HYDRAULIC HEAD: I. FIELD OBSERVATIONS. JOURNAL OF ENVIRONMENTAL ENGINEERING 128(7):588-595, (2002).
Description:
A field test to quantify the changes of soil temperature and hydraulic head during electroosmosis was conducted. The anode (3.1 m x 3.4 m) was created by laying pieces of titanium mesh coated with mixed metal oxides on top of a 3 cm thick sand layer at a depth of 0.4 m. The cathode (2.5 m in radius) was a hydraulic fracture filled with granular graphite at a depth of 2.2 m. A constant voltage of 47 volts was applied for 4 weeks resulting a near constant current of 42 amperes between the electrodes. The electrical potentials and soil temperatures were monitored at 7.5 cm depth intervals at distances of 0.6, 1.2, 2.1, and 3.0 m from the cathode well. Arrays of piezometers were installed at various depths and radial distances from the cathode well to monitor the hydraulic head distribution. The initial soil temperature decreased by 2-3C per m of depth with minor radial gradient. After the power was turned on, the temperature of soil in the civinity of the graphite well increased. The increase of temperature propagated outward as a contour in the radial direction from the graphite well causing the vertical temperature gradient to disappear. The propagating speed of the temperature decreased with energy input. On a unit k@-h basis, the speed decreased from 1.7x10(-3) m/kW-h at 4780 kW-h to 1.4x10(-3) m/kW-h at 1,320 kW-h of energy input. In addition, the temperature contours close to both the edges of the mesh and graphite electrodes increased and propagated outward vertically. In the regions where these three propagating fronts met, the soil temperature profiles were distorted and formed "S" shaped contours. The hydraulic head close the anode decreased as much as 10 cm, whereas it increased between 2 and 6 cm close to the cathode. The results show that electroosmosis caused a hydraulic gradient that was opposite to the electroosmotic flow.