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 Ver tisol in Guadeloupe (French West Indies). The field experiment estimat ed the spatial averages of vertical soil movements and soil water cont ent changes by measurements at the intersections of a sampling grid. T he geometry of volume change was found to be anisotropic with vertical soil movements slightly larger than horizontal ones. The observed ani sotropy seems to arise because the peds slide along oblique slickensid es whereas individual peds shrink and expand isotropically. The discre pancy with earlier field results which indicated strictly isotropic vo lume changes is thought to arise in part from a difference in the natu re of the clay soils investigated. An uncertainty analysis of the expe riment shows that the main source of error is due to the estimation of the spatial averages of soil elevation.