Which one of the following tests is carried out using a relatively large diameter plate to evaluate the load supporting capacity of pavement layers?
- ACalifornia bearing ratio test
- BCalifornia resistance value test
- CTriaxial compression test
- DPlate bearing testCorrect
Solution
Concept
The plate bearing test uses a large rigid plate (usually 75 cm diameter) to find the load-carrying capacity (modulus of subgrade reaction k) of pavement layers.
Formula
k = p / Δ, where p = pressure at 0.125 cm settlement
Step-by-step solution
1. The CBR test uses a small plunger (about 50 mm diameter) in a mould or in the field. 2. The California resistance value (Hveem stabilometer) test is a lab test on a small sample. 3. The triaxial test is a lab test on a cylindrical sample. 4. The plate bearing test uses a large rigid plate (30 to 75 cm diameter) on the layer in the field. 5. So the answer is the plate bearing test.
Explanation
In the plate bearing test, load is applied on a large steel plate placed on the subgrade or base, and the settlement is measured. From this, the modulus of subgrade reaction k is found. It is used mainly in rigid pavement design.
Why the other options are wrong
A: CBR uses a small plunger, not a large plate. B: The R-value test is a lab test on a small sample with a stabilometer. C: The triaxial test is done on a small cylindrical lab sample.
Shortcut
Large plate = plate bearing test = k value.
Common mistake
Choosing CBR because it also measures pavement layer strength, but it uses a small plunger.
Correct answer: D) Plate bearing test