Measurement of Fully Softened Shear Strength: Fid-Bau Portal

Measurement of Fully Softened Shear Strength

Castellanos, Bernardo / Brandon, Thomas L. / Stephens, Isaac / Walshire, Lucas

The fully softened shear strength, equivalent to the normally consolidated peak shear strength, can be the controlling shear strength in cut slopes in stiff-fissured clays, slopes in mudstones, and compacted embankments made of highly plastic clays subjected to weathering, that have not experienced previous slides. There has been a renewed interest in the proper techniques to measure the fully softened shear strength. A laboratory testing program was undertaken to examine the difference in the measured shear strength of ten different remolded normally consolidated natural clays using the direct shear apparatus and ring shear apparatus. The results showed that the fully softened shear strength measured with the ring shear device is always lower than the fully softened shear strength measured with the direct shear device. Based on these results, it was concluded that the ring shear device provides a very conservative measurement of the fully softened shear strength. An investigation to evaluate the influence of the sample preparation technique on the fully softened shear strength measured was also conducted. Tests were carried out on a subset of three of the soils using the direct shear apparatus. Some samples were mixed in a blender (blenderized), while others were only processed through a No. 40 (425 μm) sieve. The results showed that, in some cases, blenderizing the soil can lower the fully softened shear strength measured.