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EFFECTS OF ELECTROOSMOSIS ON SOIL TEMPERATURE AND HYDRAULIC HEAD: I. FIELD OBSERVATION
Citation:
Chen**, J. L., J A. Ryan*, S R. AlAbed*, M H. Roulier*, AND M C. Kemper*. EFFECTS OF ELECTROOSMOSIS ON SOIL TEMPERATURE AND HYDRAULIC HEAD: I. FIELD OBSERVATION. Presented at American Geophysical Union 1999 Meeting, San Francisco, CA, 12/13-17/99.
Description:
A field test to quantify the changes of soil temperature and hydraulic head during electroosmosis has been conducted. The anode (3.1 m x 3.4m) was created by laying pieces of titanium mesh coated with mixed metal oxides on tope of a 3 cm thick sand layer at a depth of 0.4 m. The cathode (2.5m 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. An array 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 to 3 oC per unit m of depth with minor radial gradient. After the power was turned on, the temperature of soil in the vicinity 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 kW-hr basis, the speed decreased from 1.7x10-3 m/kW-hr at 470 kW-hr to 1.4x10-3 m/kW-hr at 1,320 kW-hr of energy input. In addition, the temperature contours close to both the edges of the mesh electrode and graphite fracture increased and propagated outward vertically. In the region where these three propagating fronts met, the soil temperature profiles were distorted and formed "S" shaped contours. The hydraulic head close to 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 the electroosmosis flow.