In situ measurement of the vertical linear shrinkage curve of soils

Abstract

In situ studies on soil shrinkage has been limited so far to highly swelling soils due to the limited precision of the in situ measurements. We present a new experimental set-up for the in situ measurement of the vertical linear shrinkage curve (LSC) of soils that uses electronic linear displacement transducers to measure soil layer thickness variations. We used block kriging, instead of arithmetic averaging as done by former authors, to estimate locally the water content of the soil layers at the same spot where the thickness measurements are done. We tested this in situ LSC measurement method in the borderline case of two weakly swelling soils from Senegal. The precision of the soil layer thickness measurements are better than or equal to ±10 μm. With block kriging, the gravimetric water content of the soil could be estimated with a precision less than ±0.02 kg kg −1, in average, from only 3 samples. The global in situ shrinkage of the two weakly swelling soils ranged from 0.02%–0.36% in relative values, which is two orders of magnitude less than that measured on highly swelling soils. Owing to the precision of the measurements, LSCs of both soils could be drawn. They had a shape similar to that of highly swelling soils, with a structural shrinkage phase followed by an uncompleted basic shrinkage phase. Residual shrinkage was never observed, except for the sandy top layer of the ferrallitic soil.