For determining the ultimate bearing capacity of soil, the recommended size of square bearing plate in a plate load test is 30–75 cm, with a minimum thickness of:
Try it first: pick an option, then read the explanation.
Correct answer: D. None of the above
Asked in SSC JE 2010
Detailed Explanation
The plate must behave as rigid, so that it settles uniformly and the measured settlement is meaningful. That needs a minimum thickness.
Why “None of the above” Is Correct
IS 1888 requires the plate to be of mild steel, 300 mm to 750 mm in size and not less than 25 mm thick. Since 25 mm does not appear in options (a) to (c), the answer is (d) None of the above.
| Item (IS 1888) | Value |
|---|---|
| Plate | Square or circular, 300 mm to 750 mm, mild steel, at least 25 mm thick |
| Pit width | At least 5 × plate width |
| Seating load | About 7 kN/m² (0.07 kg/cm²), released before the test |
| Loading | Steps of about one-fifth of the expected safe load |
| Readings | Settlement of the plate on dial gauges, until it nearly stops for each step |
| Result | Load–settlement curve → ultimate bearing capacity and settlement |
Why the Other Options Are Wrong
- A. 20 mm: 20 mm is thinner than required.
- B. 5 mm: 5 mm would bend under load and is far too thin.
- C. 50 mm: 50 mm is more than the minimum; the minimum is 25 mm.
Key Point
Plate load test plate: at least 25 mm thick.
Key Concepts for Students
- Plates may be bedded on a thin layer of sand or plaster for full contact.
- Dial gauges are fixed to an independent datum bar.
- The test is continued to failure or to about 25 mm settlement.
Practice more: this is question 35 in Shallow and Deep Foundation MCQs – Part 3. Try the whole set and check every answer instantly.