This paper presents dissipation tests performed at the Sarapuí Ⅱ very soft clay test site in the metropolitan area of Rio de Janeiro, Brazil, with the BAT probe, a special type of piezometer. The tests performed indicated that the BAT probe is a useful tool for determining the coefficient of horizontal consolidation in situ. The obtained values of c_h in the very soft clay decreased from 10^-5 m²/s at 1 m depth to 10^-6 m²/s at 3 m depth, remaining constant to 6 m depth, consistently in the upper range of piezocone values. The quality of the dissipation curves, based on comparison with theoretical dissipation curves, was rated, in general, as fair, which agrees with evidence that the match quality between experimental and theoretical curves decreases as the distance from the cone mid-face increases. Dissipation tests and permeability tests conducted with the BAT probe were used to directly assess the coefficient of volume change in situ. Differences between in-situ and oedometer test results have been attributed to anisotropy, stress state differences, and influence of probe insertion on the coefficient of permeability values. The obtained data seemed to indicate that consolidation during dissipation takes place in recompression mode, as suggested by other studies.