The flow of moisture through a continuum cannot explain the verywet conditions present under pavements in semiarid and arid climates. A possible major cause is the presence of shrinkage cracks. In this manner, the water infiltrates through the cracks where it is slowly absorbed on the crack walls. This water is, then, effectively trapped within the soil mass because the prevailing suction gradients are not large enough or do not act for sufficiently long times to remove significant amounts of moisture. A simplified model to simulate the infiltration of rainfall through the crack fabric and the removal of soil moisture by soil evaporation and plant transpiration alongthe sides of a pavement is described. The moisture movement throughthe crack fabric is sumulated as an open channel flow. The moisturetransfer from the cracks to the soil on the crack walls is assumed to be one-dimensional absorption. The results of simulations for several climatic regions of texas are presented. For all these regions, the model predicts steady closing of the crack fabric under the pavement. The time to closing ranges from less than 1 year for the climatic conditions of houston to more than 8 years for the climatic conditions of el paso. In contrast, the shrinkage cracks under the edgeof the pavement and within the soil adjacent to the pavement close during wet periods and then reopen again during extended dry periods. For the wetter climates, the cracks are generally closed and only open during periods of consistent dry weather. For the drier climates, the cracks remain open at all times. This paper appears in transportation research record no. 1307, Pavement analysis, design, rehabilitation, and environmental factors 1991.
Abstract