Empirical equations for calculating the rate of liquid flow through composite liners due to large circular defects in the geomembrane

This technical note presents empirical equations for the evaluation of the rate of advective flow through composite liners, i.e. liners comprising a geomembrane and a low-permeability soil layer. The advective flow considered is due to large circular defects in the geomembrane. The flow rate depends on contact conditions between the geomembrane and the soil layer. Three types of contact conditions (excellent, good, and poor) are considered. The methodology for developing the empirical equations is identical to the one proposed by Touze-Foltz and Giroud for small circular defects. The methodology consists in determining values for the unknowns of the empirical equations such that flow rates calculated using the empirical equations are as close as possible to flow rates rigorously calculated using existing analytical solutions. This was achieved by conducting numerical calculations for more than 38,000 cases defined by a wide range of values of the parameters (contact conditions, soil layer thickness and hydraulic conductivity, and hydraulic head).