Augered Cast-In-Place Piles Embedded in Cobbles and Boulders in Honolulu

Due to the variable subsurface conditions of the bearing strata consisting of older alluvium with cobbles and boulders at this site in Honolulu, Hawaii, there are concerns as to whether foundation drilling contractors would be able to install augered cast-in-place (ACIP) piles deep enough into the supporting strata to obtain the recommended pile capacity. This project included performing a single static load test and 12 high-strain dynamic load tests to evaluate the ACIP pile capacity embedded in older alluvium containing abundant cobbles and boulders. The ACIP piles were 600 mm in diameter and extended to 13.3–23.9 m in depth. To confirm if the soil/rock bearing stratum will provide adequate end bearing resistance, drilling refusal criteria were incorporated into the foundation installation specifications. By terminating ACIP piles on the hard boulders and basalt formation, end bearing capacities ranging between 490 and 1,380 kilonewtons were realized in the installed ACIP piles tested. The total capacities of the ACIP piles ranged from about 2,620–4,180 kilonewtons. On the average, the end bearing component provided only 20% of the total ACIP pile capacity.