The void ratio for which the change of volume remains constant (zero) during shearing is called the:
Try it first: pick an option, then read the explanation.
Asked in SSC JE 16/11/2022
Detailed Explanation
When sands are sheared, dense sands expand (dilate) because grains must ride up over each other, while loose sands contract as grains fall into voids. Somewhere in between is a void ratio at which shearing causes no volume change.
Why “Critical void ratio” Is Correct
That void ratio is the critical void ratio. A saturated sand looser than this tends to contract on shearing; under undrained conditions this raises pore pressure and can lead to liquefaction. A sand denser than this dilates and develops negative pore pressure.
Why the Other Options Are Wrong
- A. Point of harmony: ‘Point of harmony’ is not a soil mechanics term.
- C. Point of contra-flexure: Point of contra-flexure is a structural term: where bending moment changes sign.
- D. Bulking: Bulking is the increase in volume of moist sand due to surface-tension films, not a shearing effect.
Key Point
e > e_crit: contracts (risk of liquefaction). e < e_crit: dilates. e = e_crit: no volume change.
Key Concepts for Students
- The critical void ratio depends on the confining pressure.
- Casagrande introduced the idea from drained tests on sands.
- Critical state soil mechanics generalises this idea to all soils.
Practice more: this is question 17 in Shear Strength of Soils MCQs – Part 2. Try the whole set and check every answer instantly.