MASS STABILISATION MANUAL

DESIGNING
Rate of settlement
When the effective stress in the soil is less than the preconsolidation pressure, settlement develops
rapidly.
When the effective stress in the soil exceeds the preconsolidation pressure, the rate of consolidation
settlement in the stabilised soil stratum is calculated in the same way as for vertically
drained soil. Experience shows that the changes in the macrostructure of the stabilised soil may
affect the permeability, but whether the permeability increases or decreases depends on the
type of binder and stabilised soil.
As stated earlier, it is essential to make a prediction of the magnitude and rate of settlement
during the preloading time. The rate of settlement as above holds only for the stabilised volume.
Calculation of the rate of settlement below the stabilised volume is performed in the normal way,
bearing in mind that the permeability of mass stabilised soil is often higher than the permeability
of untreated soil and it can work as drain leading water into the top of the stratum.
The design and time of placement of the fi rst preloading stage are of outmost importance due to
the fact that 70 to 90 % of the total settlements occur during fi rst 30 days.
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Mass stabilisation 2005