Analysis of load tests on drilled shafts in the Beaumont Formation and the Lissie Formation in the Texas Gulf Coast

Safe and economical design of foundations including deep foundations such as drilled shafts is vital for transportation and infrastructure development sectors. Use of rational prediction methods to determine the total capacity of drilled shafts has undergone appreciable changes in the last three decades. These methods have been verified by full-scale field load tests on instrumented drilled shafts. However, these load tests are prohibitively expensive to perform on a routine basis for design purposes. Empirical and semi-empirical methods based on principles of soil mechanics have been developed for design of drilled shafts. Such methods utilize the observations during soil exploration and the results of laboratory testing. Nevertheless, the prediction of total foundation capacity using the existing methods varies in different geological conditions. Moreover, the existing prediction methods provide conservative shaft capacity in the Texas Gulf Coast resulting in costly foundation construction involving material resources, time, and money.; In the present study, a local database comprising 31 full-scale load tests performed on drilled shafts in the Beaumont Formation and the Lissie Formation in the Texas Gulf Coast has been compiled. Based on the most recent information on load transfer behavior of drilled shafts in cohesive and cohesionless soils, a rational failure criterion was used to determine the total foundation capacity for each test shaft from its load-displacement curve. Average undrained shear strength along the shaft in clay strata and Standard Penetration Test (SPT) blow count (SPT N values) along the shaft in sand strata were used to predict both the side resistance and the base resistance for each test shaft. The widely used Federal Highway Administration (FHWA) method was used to predict the total shaft capacity, side resistance, and base resistance for comparative purposes.; Revised values of alpha-factor and beta-factor are proposed to predict the capacity of drilled shafts based on the results of the load tests for the local geologic conditions. Calculated shaft capacity using these revised values was compared with the capacity obtained using the FHWA method, used frequently for the design of the drilled shafts. These calculated shaft capacities were compared with the interpreted total shaft capacity from the actual field load test results. Statistical analysis of the local database was performed using the least squares linear regression analysis.