Dissipation testing

If the drainage and/or consolidation characteristics of the soil are to be evaluated, dissipation tests may be carried out at pre-selected depths in the deposit. In a dissipation test, the pore pressure decay is obtained by recording the values of pore pressure with time. In fine, low permeability soils, the pore pressure record is used to evaluate the coefficient of consolidation.

Pore pressure and cone resistance shall be measured with time. It is particularly important to take frequent readings at the beginning of the dissipation test. The dissipation shall be performed with the rods unclamped.

The duration of the dissipation test should normally correspond to at least t50, the time needed for 50 % pore pressure dissipation (ut ≤ u0 + 0,5 × Δui), since t50 is the time used in most interpretation methods. If u0 is not known, a cautious estimate of the value should be made.