Measuring "Fast" shear strengths along slickensided surfaces in the Bromhead ring shear

Fast and slow ring shear tests were performed in the Bromhead ring shear device to examine the effect of the displacement rate on the shear strength measured along slickensided discontinuities in Rancho Solano Fat Clay. For each test, initial drained shearing was performed at a displacement rate of 0.018 mm/min, fast shearing was performed at a rate of 44.5 mm/min, and drained shearing was recommenced at a displacement rate of 0.018 mm/min. Significant variations in measured post-peak shear strengths were observed, and problems with the pore pressure response in the soil surrounding the slickensided plane are discussed. As a result of these problems, it was concluded that fast Bromhead ring shear tests may not be suitable for evaluating the effects of fast shearing on the strengths of slickensided surfaces.