Case Histories of Full-Scale Comparative Load Testing of Base Grouted and Ungrouted Test Shaft Pairs

Base grouting is becoming more widely promoted in the drilled shaft industry as a means to improve shaft response to load. This paper presents several case histories of full-scale static load tests conducted on adjacent shafts with and without base grouting on projects in various parts of the United States. All tests were performed by Loadtest USA using the Osterberg cell (O-cell) test method. The comparisons yielded some intriguing results. In some cases, the results matched theory quite well and showed improvement to stiffness and/or overall capacity. In other circumstances, this was not the case. These case histories illustrate the need for further load testing and research to better understand how drilled shaft capacity is affected by base grouting, particularly, how the capacity is affected by drilling, base cleaning, and base grouting techniques and quality control in various soil materials. Portions of this article appeared previously in the 7th ICCHGE (Sinnreich and Simpson 2013), and are reproduced with permission.