In testing a pile by load test, pile platform is loaded with one and half times the design load and a maximum settlement is noted. The load is gradually removed and the consequent rebound is measured. For a safe pile, the net settlement (i.e. total settlement minus rebound) per tonne of test load should not exceed A. 10 mm B. 15 mm C. 20 mm D. 25 mm

The correct answer is A. 10 mm.

The net settlement (i.e. total settlement minus rebound) per tonne of test load should not exceed 10 mm for a safe pile. This is because a pile that settles more than 10 mm per tonne of test load is likely to be unstable and could fail under load.

Option B is incorrect because 15 mm is too much settlement for a safe pile. Option C is incorrect because 20 mm is too much settlement for a safe pile. Option D is incorrect because 25 mm is too much settlement for a safe pile.