Sub surface Drainage

Sub-surface Drainage

Water normally reaches the sub-surface due to capillary action, seepage from adjacent areas, or percolation of rainwater. When water reaches the sub-surface, it immediately affects the stability of the formation. The situation becomes worse particularly if the soil is bad. A variety of problems arise due to the proximity of the water to the subgrade. The nature of the problems faced and the remedial measures for the same have been discussed in detail in Chapter 9.

The various sub-drainage systems used under different conditions are briefly summarized here.

Provision of inverted filter Some sub-drainage systems consist of a blanket of a non-cohesive graded material, which acts as a capillary break (Fig. 9.3 of Previous few Page).

Paving of catch water drains The entrance of water into the subgrade can be checked by constructing effective catch water drains that are duly paved.

Provision of sand piling Some drainage systems are provided with an adequate number of sand piles of a diameter of about 20 cm. This improves sub-surface drainage (Fig. 9.4 of Previous few Page).

Drainage of water pockets by perforated pipe Perforated pipes with a diameter of about 30 cm are provided at appropriate places to drain off the water pockets (Fig. 9.5 of Previous few Page).

Cement grouting Cement can be used to grout the water pockets so as to ease the situation.