Drilled Shaft Load Tests in Weakly Cemented Sandstone-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines drilled-shaft load tests in weakly cemented sandstone at three Midwestern bridge sites: Minneapolis, Oak Park Heights, and Lansing. The tests, conducted between 2007 and 2024, evaluated rock sockets with lengths of approximately 31 to 47 feet.<br /><br />Results showed substantial axial resistance. Average maximum mobilized unit side resistance ranged from 16.6 to 31.3 ksf, while individual segments reached 30.3 to 54.2 ksf. Resistance was mobilized at relatively small displacements. Side and base resistance developed together at compatible displacements, consistent with earlier research. The shafts carried loads beyond the capacity of the bidirectional jacks.<br /><br />The measured resistance generally exceeded estimates from traditional empirical design methods, which can underestimate both side and base resistance in weakly cemented sandstone. However, performance depends strongly on construction quality. Groundwater control—especially under artesian conditions—support-fluid management, excavation cleanout, concrete mix and placement, and quality verification are critical.<br /><br />Because representative bedrock samples can be difficult to obtain and construction practices significantly affect performance, load testing can help establish project-specific design capacity and reduce required socket lengths. A non-production test shaft can also serve as a demonstration shaft to verify construction methods.<br /><br />The presentation concludes that similar projects may benefit from load testing, provided proper construction practices and quality controls are maintained.

Keywords

drilled-shaft load tests

weakly cemented sandstone

bridge sites

rock sockets

axial resistance

side resistance

base resistance

load testing

construction quality

bidirectional jacks