In the direct shear test conducted on soils, a proving ring is used to ______.
Try it first: pick an option, then read the explanation.
Asked in SSC JE 06/06/2024 (Evening)
Detailed Explanation
In a direct shear test, a soil specimen in a split box is sheared along the horizontal plane between the two halves. One half is pushed at a constant rate; the other half is held back by a proving ring, a steel ring that deflects in proportion to the force on it. A dial gauge inside the ring measures this deflection.
Why “measure the magnitude of shear load” Is Correct
Multiplying the ring's dial reading by its calibration constant gives the shear force. Dividing by the area of the specimen gives shear stress. So the proving ring measures the magnitude of the shear load.
Why the Other Options Are Wrong
- B. measure horizontal stress: Horizontal stress is not measured separately; the horizontal force is the shear load, measured by the proving ring.
- C. measure vertical strain: Vertical movement (dilation or compression) is measured with a separate vertical dial gauge.
- D. measure horizontal strain: Horizontal displacement (shear strain) is measured with a horizontal dial gauge, not the proving ring.
Key Point
Proving ring → load. Dial gauges → displacements.
Key Concepts for Students
- Normal load is applied by dead weights or a lever on top of the box.
- The test is usually strain-controlled (constant rate of displacement).
- Proving rings are also used in triaxial and unconfined compression machines.
Practice more: this is question 3 in Shear Strength of Soils MCQs – Part 1. Try the whole set and check every answer instantly.