碎(块)石路堤孔隙空气对流运动的Darcy定律适用性

Applicability of the Darcy's Law to Convection of Pore Air in Crushed/Blocked Rock Embankments

针对青藏高原多年冻土区路基工程中采用的碎石路堤地温调控技术,分析了碎石层孔隙空气对流运动符合Darcy定律的适用范围及其可能偏离Darcy定律的非线性效应,并给出了考虑非线性效应的Darcy定律修正方程.同时,讨论了适合于路堤碎石层的空气渗透系数及其表征空气流动非线性效应的Ergun常数的估算公式.

For adjusting the ground-temperature of crushed rock embankment in permafrost regions of the Tibetan Plateau, the validity and nonlinear drag effects of Darcy＇s law applied to the pore air convection in crushed/blocked rock embankments were analyzed. The pore air convection in crushed/ blocked rock embankments can be grouped into two： natural convection and forced convection. For the nature one, the appropriate extensions of Darcy＇s law, taking the nonlinear drag effect into account, are obtained. In general, the transient effect of the pore air convection in the crushed/ blocked rock media can be ignored, thus the problem becomes a quasi-steady two-dimensional flow through porous media. For convenient application to engineering, the appropriate formulae for evaluating the air-permeability in the crushed/blocked rock media of embankment and the Ergun constant representing nonlinear drag effects of the pore air motion are discussed. Finally, the appropriate values of the intrinsic air-permeability and Ergun constant in the crushed rock media of embankment for four grain sizes （2.2-5.0, 6.0-8.0, 8.0-15.0 and 15.0-25.0 cm） are evaluated using the formulae proposed in the present study.