For standard compaction test done on soil, the mass of hammer and drop of the hammer are:
Try it first: pick an option, then read the explanation.
Asked in SSC JE 25/09/2019 (Morning)
Detailed Explanation
In India, the standard (light) compaction test is specified in IS 2720 (Part 7) and the heavy (modified) test in IS 2720 (Part 8). The rammer mass and drop height are the most frequently asked numbers.
Energy per unit volume for light compaction: \[ E = \frac{2.6 \times 9.81 \times 0.310 \times 3 \times 25}{1000\times10^{-6}} \approx 593\ \text{kJ/m}^3 \]
Why “2.60 kg and 310 mm” Is Correct
The standard (light) test uses a 2.6 kg rammer falling freely through 310 mm, so option D is correct.
| Item (IS 2720 Part 7 / Part 8) | Light (standard) compaction | Heavy (modified) compaction |
|---|---|---|
| Mould volume | 1000 cm³ | 1000 cm³ |
| Rammer mass | 2.6 kg | 4.9 kg |
| Free drop | 310 mm | 450 mm |
| Number of layers | 3 | 5 |
| Blows per layer | 25 | 25 |
| Energy per unit volume | ≈ 593 kJ/m³ | ≈ 2700 kJ/m³ |
The original Standard Proctor test (ASTM/AASHTO) uses a 944 cm³ mould, 2.495 kg (5.5 lb) hammer and 305 mm (12 in) drop.
Why the Other Options Are Wrong
- A. 4.80 kg and 310 mm: 4.80 kg with 310 mm mixes the heavy rammer mass (≈4.9 kg) with the light drop height.
- B. 2.60 kg and 450 mm: 2.60 kg with 450 mm mixes the light rammer with the heavy test’s drop height.
- C. 5.40 kg and 450 mm: 5.40 kg and 450 mm does not match either IS test.
Key Point
Light: 2.6 kg, 310 mm, 3 layers. Heavy: 4.9 kg, 450 mm, 5 layers. Both: 25 blows per layer, 1000 cm³ mould.
Key Concepts for Students
- Heavy compaction delivers about 4.5 times the energy of light compaction.
- Heavy compaction is used for airfields and heavily loaded pavements.
- The original Proctor (ASTM) values are 2.5 kg (5.5 lb) and 305 mm (12 in).
Practice more: this is question 4 of Compaction of Soil MCQs – Part 2. Try the whole set and check every answer instantly.