Primary piles will first be installed alternately, these piles will be of un-reinforced concrete of M15 mix with a minimum slump of 175mm. These piles do not have to be installed to the same length as the secondary or intermediate or reinforced piles which follow. Secondary piles will then be installed between the primary piles, 24 hours after the construction of primary piles. Pile overlap will be 0.5% of pile length or 75mm or 12% of pile diameter, whichever is more. Thus by the 2nd criteria, pile centre to centre spacing will be D-75mm. The secondary piles will be reinforced piles of M25 concrete strength with a minimum slump 150mm. These piles will be installed with rotary hydraulic piling rigs, equipped with a heavy coring pipe whose cutting edge toothed and enables to cut into the concrete of initial primary piles.