Limiting resistance of a spherical penetrometer in cohesive material

The shear strength of soft sediments may be assessed by field tests, princi pally either vane tests or cone penetrometer tests. The continuous profile of strength obtained from the cone penetrometer is an advantage over the va ne test, although the significant corrections for overburden stress, and po re pressure acting on the back face of the cone, limit its accuracy in soft soils. Alternative shapes for penetrometers have been suggested, for examp le a cylindrical T-bar and a spherical ball, both of which allow full flow of soil around the probe, thereby obviating the need for corrections due to the ambient stress level. Plasticity solutions have been available for som e while relating the (average) shear strength of the soil to the net bearin g pressure for plane strain how around the cylindrical T-bar. This paper do cuments a corresponding solution for a spherical penetrometer, using upper and lower bound approaches supported by finite element analysis. Effects of strength anisotropy are discussed in the light of example results comparin g the measured resistance of cone, T-bar and ball penetrometers.