One of the main factor of rate of consolidation and the time of the consolidation is the single or the double drainage. When there is a double drainage, i.e. drainage from both of the opposite faces, the drainage path becomes half of the total thickness of the clay layer. In such cases the time of settlement decreases significantly. The following example illustrates the same.
Example: (a) A 20 mm clay layer with double drainage reaches the 90% of total consolidation in 30 minutes. Find out the coefficient of consolidation.
If the same clay has a thickness of 10mm, find out the time it would take to reach 90% consolidation with (b) single drainage (c) Double drainage. Draw the settlement curve/consolidation curve in each case.
Solution: For solution please zoom into the picture below.