The expansion of soil due to shear at a constant value of pressure is called:
Try it first: pick an option, then read the explanation.
Correct answer: C. Dilatancy
Asked in SSC JE 2015
Detailed Explanation
In a dense granular soil the grains are tightly interlocked. To shear, grains must ride up and over their neighbours, which pushes them apart.
Why “Dilatancy” Is Correct
This increase in volume during shear, at constant confining pressure, is called dilatancy (dilation). It adds to the strength of dense sands; under undrained conditions it causes negative pore pressure.
Why the Other Options Are Wrong
- A. Apparent cohesion: Apparent cohesion is temporary strength from capillary suction in moist soil.
- B. True cohesion: True cohesion is bonding between clay particles.
- D. Consistency: Consistency describes the firmness of a clay at a given water content (soft, stiff, etc.).
Key Point
Dense → dilates; loose → contracts; at critical void ratio → no change.
Key Concepts for Students
- Reynolds first described dilatancy (1885).
- The peak strength of dense sand includes a dilation component.
- Footprints on wet beach sand turn dry briefly because of dilation.
Practice more: this is question 38 in Shear Strength of Soils MCQs – Part 3. Try the whole set and check every answer instantly.