Closure to “Drained Residual Shear Strength of Some Claystones from Front Range, Colorado” by Mandar M. Dewoolkar and Robert J. Huzjak

Abstract

The authors have compared select published correlations relating the drained residual friction angle to the liquid limit LL , plasticity index PI , clay fraction CF , and effective normal stress and with the test data of claystones from Front Range, Colorado. Empirical correlation of shear strength with index properties of soil is very useful when soil samples and funds are not available for soil testing. Various correlations have been proposed so far for the r and index parameters, either the particle size or the Atterberg limits. The first correlation attempt was by Skempton 1964 relating r to CF, followed by a number of others, the best known probably being Lupini et al. 1981 , Mesri and CepedaDiaz 1986 , Collotta et al. 1989 , Stark and Eid 1994 , Wesley 2003 and Tiwari and Marui 2005 . The authors have produced correlation charts in Fig. 8, for an estimate of drained residual strength of similar material relating the r to effective normal stress range of 30 kPa to 960 kPa. It is clear that no general correlations are apparent since the spread is so wide. However, the authors have quoted that some trends are evident which is not justifiable. It is discusser’s opinion that the description of an important soil property such as the residual shear strength should be applicable to the complete stress range from zero to elevated pressures. To demonstrate that this is possible, the discusser has processed the data of shearing strength on all materials shown in Table 2 using the general expression proposed by Maksimovic 1988, 1989a,b,1993, 1995,1996 . The nonlinear failure envelope in terms of effective stress assuming zero cohesion, is described as: