Assistant professor, Montana State University, Bozeman, MT
Highly angular dense soils are known to possess secant friction angles well in excess of commonly encountered sands. These soils also exhibit a significant variation of the friction angle over a common range of mean normal stress confinement. These characteristics raise questions regarding the ability of conventional solutions to predict bearing capacity and how linear strength parameters are to be determined for a nonlinear material. To examine these issues, centrifuge experiments were performed on shallow foundations at three embedment depths. Linear strength parameters required for three conventional solutions were obtained from the nonlinear envelope first by a simple averaging technique. To indirectly account for the material nonlinearity, tangent and secant linear strength parameters were estimated once an appropriate level of mean normal stress was determined. A relationship between mean normal stress and the resulting footing bearing capacity was developed using classical plasticity theory. The latter approach offered significantly better predictions than the averaging method, yet the results indicate the inability of conventional theories to model experimentally observed behavior.
Paper ID: GTJ11020J