A 40 x 40 cm reinforced concrete pile 20 m long is driven through loose sand and then into dense gravel to a final set of 3 mm/blow, using a 30 kN single-acting hammer with a stroke of 1.5 m. Determine the ultimate driving resistance of the pile if it is fitted with a helmet, plastic dolly and 50 mm packing on the top of the pile. The weight of the helmet and dolly is 4 kN. The other details are: weight of pile = 74 kN; weight of hammer = 30 kN; pile hammer efficiency \eta_{h}=0.80 and coefficient of restitution C_{r}=0.40.
Use the Hiley formula. The sum of the elastic compression \bar{C} is
\bar{C}=c_{1}+c_{2}+c_{3}=19.6 mm.