Book Description
This report presents a new method for analysis of the drainage of a saturated base. Starting from basic principles of water retention and flow in porous media, this analysis leads to some new methods for the estimation of minimum degrees of saturation, drainable porosities and drainage times. This study found that current practices in the FHWA subdrainage design manual tend to overestimate the amount of drainage from fine-grained bases and greatly underestimate the amount of drainage from coarse-grained bases. Also of importance is the ability to estimate the lowest degree of saturation that can be achieved through gravity drainage. The new methods for the analysis of pavement subdrainage are implemented in two computer programs: (1) SUBDRAIN - simulates the drainage of water from a pavement base that is initially saturated and provides estimates of the minimum degree of saturation in the field and key drainage times; and (2) SUBDRAIN-C - simulates the flow of water into and out of the base over a period of years - the inputs include a long-term record of 15-minute rainfall data and the output shows how often the base is likely to be saturated or nearly saturated.
