Question 4 a A pile needs to be driven to the bedrock as part of the foundation for a water intake structure (Figure Q4). Geotechnical studies in the area indicate that the chance of the depth to bedrock exceeding 10 m is 0.25 and this depth does not exceed 20m. Two types of piles are available; one costing R150000 applicable for depths to bedrock of up to 10m and a longer type for depths of up to 20m which costs R 250000 . If the shorter pile is used and it turns out inadequate (i.e. depth to bedrock exceeds 10m ), it will need to be taken out at a cost of R 60000 and replaced with the longer pile.