Consolidation Time Factor
Settlement magnitude says how far a clay will compress, but the time factor says how long you will wait, and the wait grows with the square of the drainage path.
The equation
t = Tv H² / cv
- Tv is 0.197 for half the settlement and 0.848 for ninety percent
- H is the longest drainage path in meters
- cv is the coefficient of consolidation in square meters per year
Worked example
A clay layer draining both ways with a 2 meter drainage path and cv of 2 square meters per year reaches half its settlement in about 5 months and ninety percent in 1.7 years. Cut the drainage path with vertical drains and the time falls with its square.
When to use it
The reason preloading programs succeed or embarrass. Field cv from dissipation tests routinely beats laboratory values by a factor of ten, so back analyze early monitoring data as soon as it exists.
Related Calculators and Reference
- USCS Soil Classification Tool: classify soils from lab results.
- Slope Stability Risk Calculator: run stability with uncertainty included.
- ISSMGE: the international society for soil mechanics.