The angle of friction of soil has been correlated empirically with SPT blow counts by various investigators. Peck et al. (1953) suggested the curve in Figure 1.5, which is well represented with ?’ = 0.3N60 + 26° to a N value of 40. The impact of effective overburden stress on the angle has been incorporated into the estimation (e.g., the Japan railway). JSCE (1986) suggests
This expression offers essentially similar values to those obtained from the Pecks expression to a N of 50 (Peck et al. 1953) at a v < 100 kPa, and otherwise results in an angle ~7 degrees smaller. The former prediction is close to the extended curve of the Chinese code (SD 128-86) of 0.3N + 19°
