HR: 1340h
AN: H53F-1486    [Abstracts]
TI: Direct laboratory quantification of dynamic coefficient of a field soil for drainage and wetting cycles
AU: * Sakaki, T
EM: tsakaki@mines.edu
AF: Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States
AU: O'Carroll, D M
EM: docarroll@eng.uwo.ca
AF: The University of Western Ontario, 1151 Richmond St., London, Ont N6A 5B9, Canada
AU: Illangasekare, T H
EM: tissa@mines.edu
AF: Colorado School of Mines, 1500 Illinois St., Golden, CO 80401, United States
AB: The constitutive relationships between capillary pressure and wetting fluid saturation (retention curve) are needed in the modeling of unsaturated and multi-phase flow in porous media. These relationships are usually measured under equilibrium conditions of the two phases (wetting and non-wetting). The question is whether such curves adequately describe the relationships between capillary pressure and saturation in drainage or imbibition events with time scales on the order of hours. Hassanizadeh et al. [2002] suggest that differences in capillary pressures measured under equilibrium and non-equilibrium conditions is due to a phenomenon that is referred to as dynamic effects in capillary pressure. Typically, the difference between dynamic and static capillary pressures is defined as a product of a dynamic coefficient (tau) and rate of change in wetting phase saturation (- dSw/dt). In this study, we quantify tau in a direct, systematic, and consistent manner through careful laboratory experiments. Using a fine field sand filled in a 10 cm-tall cell, we performed drainage and wetting experiments under identical packing conditions, but differing imposed boundary conditions (i.e., static and dynamic with various drainage/wetting rates). The dynamic coefficient was estimated for primary drainage, main wetting, and main drainage cycles. In the primary drainage cycles tau values increased with decreasing wetting phase saturation. In the case of the main wetting cycle, performed under the same dynamic conditions, tau values were somewhat smaller and increased slightly with increasing wetting phase saturation. These findings imply that tau may be hysteretic. Finally, tau values for the main drainage cycle were similar to those of the primary drainage cycle (tau increases with decreasing wetting phase saturation). Overall, the estimated tau values varied over a range of 2e5 to 1e7 kg/m/s. This is consistent with the range of tau that Hassanizadeh et al., [2002] estimated based on published studies that exhibited dynamic effect in capillary pressure. A numerical simulator, modified to incorporate dynamic effects in capillary pressure, was used to model the outflow experiments and yielded good agreement between observed and modeled outflow.
DE: 1829 Groundwater hydrology
DE: 1866 Soil moisture
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting