Environmental modeling of vegetative protection from wind erosion and rainfall infiltration, drainage, and load-carrying capacity of pavements

Abstract

Two independent research analyses were conducted. Part I investigates the aerodynamic protection of soil by various arrangements of plants from wind erosion. Theory of free turbulent flows, airflow momentum, and vegetative characteristics are incorporated into the construction of an environmental model of vegetative protection from wind erosion. Superposition principles are applied to describe wind force-reducing effects from areas with regular, alternate, clumped, and random distributions of plants. Heterogeneous longitudinal and transverse spacings are also evaluated to compare the effect of wind shear near the ground. The results of this study show that: (1) an alternate distribution; (2) evenly spaced trees along a row; and (3) evenly spaced tree rows approaching the windward side provide the best protection from wind-force impacts. The patchy pattern is less effective than the sparse ones; the effectiveness of soil protection under a random arrangement of trees is estimated to lie somewhere between alternate and regular patterns. Regression analyses of basal area index, foliage profile index, and tree height index were evaluated. The overall regression model which incorporates these three indices were also established. Part II presents a systematic analysis simulating the rainfall infiltration into the base course and subsequently the rate of drainage from the base course into the subgrade and into lateral drainage. This method incorporates the distribution of rainfall amount, probabilities of wet and dry days, infiltration of water into the pavement through cracks and joints, and the drainage of a base course. The effects of saturation on the resilient moduli of the base course and the subgrade are calculated. A new model employing a parabolic phreatic surface and allowing drainage through a permeable subgrade, has been developed for computing the drainage of the pavement base and subgrade. An example result indicates that the pavement performance is better in a high rainfall area where a permeable subgrade is furnished, when compared to the pavement performance in a low rainfall area where an impermeable subgrade is utilized.