Subtopic: Measurement of infiltration, soil moisture and irrigation water infiltration
Question Statement:
A natural colloidal clay, having the characteristics of absorbing water and swelling 8 to 15 times its dry size, used as an efficient and effective sealing material for farm ponds, is
Options:
(A) EPDM
(B) Butyl
(C) Bentonite
(D) Soil cement
Official Answer Key:
C
Step-by-Step Solution & Explanation
Bentonite is a natural colloidal clay dominated by montmorillonite. On wetting, water enters between the clay platelets and the material swells many times its dry volume (commonly quoted as 8–15 times). The swollen gel fills the voids of the pond bed, collapsing the permeability and forming a self-healing seal — the standard low-cost sealing treatment for farm ponds.
Why not the others:
- EPDM and Butyl — synthetic flexible membrane liners (rubber sheets), not natural clays and not swelling materials.
- Soil cement — a compacted mix of soil with Portland cement; a rigid stabilised lining, not a colloidal swelling clay.
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