Penetration resistance and the bearing capacity of small-diameter steel piles

The objective of this study was to develop an improved relationship between the penetration resistance of small diameter steel pipe piles and their ultimate bearing capacity. Static loading tests were conducted to failure on four 50-mm diameter pipe piles that were driven with a 43 kg jack hammer to four different penetration resistances. The loads and the ultimate bearing capacities interpreted from the jack pressure gauge were 0 to 15 % higher than the capacities interpreted from load cell measurements. The tangent-line method gave loads that were more conservative than those obtained with Davisson method. In the Seattle area, the current permissible load without performing a load test is 18 kN for 50-mm pipe piles continuously driven to a penetration resistance of 25 mm per 1 min with a 43 kg jack hammer. This value was found to be very conservative. Based on our test results, the ultimate observed plunging load was about five to ten times greater than 18 kN. Other interpretation methods also gave significantly higher values.