For dewatering in cohesive soils, which technique is typically ineffective?

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Question

This question was previously asked in

RRB JE CBT 2 (Civil Engineering) ReExam Official Paper (Held On: 04 Jun, 2025)

Answer 1

Explanation:

Sump pumping involves collecting groundwater in shallow pits (sumps) and then pumping it out.
It works well in coarse-grained, permeable soils like sand and gravel, where water flows freely toward the sump.
However, in cohesive soils such as clay and silty clay, water moves very slowly due to low permeability.
As a result, sump pumping is ineffective in drawing out sufficient water to lower the water table in cohesive soils.

Additional Information Deep Wells

Suitable for moderate to highly permeable soils.
Can be partially effective in fine-grained soils if properly spaced and used with filters, but not ideal for clays.
Not the best choice for purely cohesive soils due to slow water movement.

Electro-osmosis

Highly effective in cohesive (clayey) soils.
Works by applying a direct electric current, which causes water to move from the soil toward electrodes.
This method is specifically used where conventional methods fail, such as in very fine clays.

Well-point System

Involves a series of shallow wells connected to a header pipe and vacuum pump.
Very efficient in sandy or silty soils, but inefficient in cohesive soils due to low permeability and difficulty in drawing water through fine pores.