NONUNIFORM VOLUME AND WATER-CONTENT CHANGES IN SWELLING CLAY SOIL .2. A FIELD-STUDY ON A VERTISOL

A theoretical model of volume change in swelling clay soil is applied in a held study to determine the swelling-shrinking behaviour of a Vertisol in Guadeloupe (French West Indies). The field experiment estimated the spatial averages of vertical soil movements and soil water content changes by measurements at the intersections of a sampling grid. The geometry of volume change was found to be anisotropic with vertical soil movements slightly larger than horizontal ones. The observed anisotropy seems to arise because the peds slide along oblique slickensides whereas individual peds shrink and expand isotropically. The discrepancy with earlier field results which indicated strictly isotropic volume changes is thought to arise in part from a difference in the nature of the clay soils investigated. An uncertainty analysis of the experiment shows that the main source of error is due to the estimation of the spatial averages of soil elevation.