In-Plane Air Flow Through Needle-Punched, Nonwoven Geotextiles Under Normal Loading
Knowledge of the in-plane permeability of nonwoven geotextiles to air and other gases has important applications including, for example, the transport and collection of methane gas beneath landfill caps. The results of in-plane flow measurements of air through eight different needle-punched, nonwoven geotextiles are presented. Air flow was measured using a radial flow device under a range of inflow pressures and compressive loads tending to reduce the geotextile´s thickness. Inflow pressures ranged from 6.9 to 20.7 kPa (1 to 3 psi), while compressive loads ranged from 13.8 to 372 kPa (2 to 54 psi). The flow through the radial flow device is described mathematically to account for the compressive load borne by the air pressure between the plates of the device. A dimensional analysis of the important variables results in a description of the flow using five dimensionless terms including a dimensionless permeability. The analysis indicates that all eight needle-punched, nonwoven geotextiles, in spite of their variable thickness, differing materials, and differing post-treatment, are essentially identical in their performance in terms of how air flows through them. The intrinsic permeability of all eight geotextiles can be estimated to within 8% (worst case) by the equation k=[1.7578?4/3g2/3[?p??L]-0.398t-0.659]1.4914 in which k is the in-plane intrinsic permeability, ? is the unit weight of the fluid, ?p is the pressure drop along the flow path, ?L is the length of the flow path (?p/?L is the pressure gradient), t is the thickness of the geotextile, and v is the kinematic viscosity of the fluid.