A Case History of Installation and Load Testing Challenges for Auger-Cast Piles in the Piedmont Geology

This paper presents a case history of auger-cast pile installation and load testing for the expansion of a water reclamation facility near Atlanta, Georgia. Three load test piles were initially installed to bedrock, all of which met the refusal criteria of 0.3 meters (one foot) or less of auger penetration per minute; however, only one of the test piles achieved the test load, which is two times the design capacity of 1,100 kN (125 tons). Furthermore, extreme variability in rock depth was encountered between test piles and reaction piles near one corner of the facility. Additional investigations performed to assess the cause of test pile failure included additional borings and rock cores, pile integrity tests, and probe piles to explore the variability in rock depths and auger penetration rates across the site. These investigations revealed extreme variability in rock depth, steep rock slopes, and variable auger penetration rates in the area adjacent to the three failing load tests. Based on the results of a fourth and final load test located within the area of anomalous rock conditions, the pile design capacity for this area was reduced to 575 kN (65 tons), or 52 percent of the original design capacity. Thus, this case history demonstrates that auger-cast piles installed to rock may not always achieve the design capacity even if the standard auger refusal criteria are met. The importance of load testing and effective monitoring during pile installation is highlighted in this paper.