Cost-Benefit Analyses for Load Resistance Factor Design (LRFD) of Drilled Shafts in Arkansas

To achieve more cost efficient transportation infrastructure within the state of Arkansas, a series of cost-benefit analyses were performed. The analyses, specifically developed for load resistance factor design (LRFD) designed drilled shaft foundations, were designed to compare the fiscal impacts of the drilling and sampling, in-field and laboratory testing, full-scale load testing, and concrete mixing techniques utilized by the University of Arkansas (UofA), the Arkansas Highway and Transportation Department (AHTD), and the Missouri Department of Transportation (MODOT). The methodologies were compared at three test site locations within the state of Arkansas: Siloam Springs, AR, Turrell, AR, and Monticello, AR. These sites were selected to represent the predominant geological deposits within the state. Three drilled shaft foundations (two four-foot diameter drilled shafts and one six-foot diameter drilled shaft) were each constructed at the Siloam Springs Arkansas Test Site (SSATS) and the Turrell Arkansas Test Site (TATS). A drilled shaft database was developed containing soil properties, and predicted and measured results of the full-scale load tests performed upon each drilled shaft. Cost-benefit analyses for each methodology were compared by means of predicted and measured static axial capacity. Values of predicted axial capacity were generated for each methodology using the Bridge Software Institute FB-Deep, Ensoft SHAFTv2012, and Microsoft Excel® spreadsheet programs. Based on the results of the full-scale load testing, the FB-Deep program utilizing the data from the UofA sampling and testing method was selected as the best methodology for predicting the axial capacity values for drilled shaft foundations in the state of Arkansas. Results of the cost-benefit analyses indicated a potential savings of $262,800 (32 percent) for drilled shaft foundations in rock. A potential savings of $323,800 for performing full-scale drilled shaft load tests in rock were attained. Unit cost per ton of resistance values of $24.11 and $82.70, and $75.47 and $141.57 were determined for the UofA and AHTD sampling and testing methods at the SSATS and TATS, respectively. Drilled shaft foundations tested in liquefiable soil were concluded to cost $137,500 (8.7%) more than driven pile foundations, but provided the benefit of additional lateral resistance