Sand Drain is based on principles of rapidly and centrally dewatering day system.

1. Sand Drain is a process of radial consolidation which increases rate of drainage in the embankment by driving casing into the embankment and making vertical boreholes.

2. The holes are backfilled with suitable grade ofsand. Construction Process:

3. Driven casing is withdrawn after sand has been filled.

4. A sand blanket is placed over the top of sand drains to connect all sand drains.

5. They accelerate the drainage; a surcharge load is placed on the sand blanket.

6. The surcharge is in form of dumped soil.

Mechanism of Consolidation:

1. The pose water pressure is increased by applied surcharge load in the embankment.

2. Drainage occurs in vertical and horizontal direction.

3. Horizontal drainage occurs due to sand drains. The sand drains accelerate the process of dissipation of excess pore water created by surcharge.

Spacing of Drains:

1. Drains are laid either in square or triangular patterns.

2. Spacing is kept smaller than thickness of embankment in order to reduce the length of radial drainage path.

Diameter of Sand Drains:

1. It varies from 300-600mm.

2. Too small diameter is not desirable because of difficulties in filling the steel pipe and danger of arching up of sand pipe.

3. Sand pipe is driven to depth where penetration resistance is greater than 15.