Discussion of “Strength and Consolidation Characteristics for Cement Stabilized Cohesive Soil Considering Consistency Index” by Ahmed F. Zidan, published in Geotechnical and Geological Engineering, https://doi.org/10.1007/s10706-020-01367-6

Excerpt

As stated by the author, the paper under discussion (Zidan 2020) ‘attempts to relate the undrained shear strength of remolded fine-grained soils stabilized by Portland cement to the consistency index’. In this regard, the author used an indirect strength measurement approach—reverse extrusion (RE)—employing Eq. 2, after Whyte (1982), reported in the paper under discussion to estimate the undrained shear strength (c_u) over the plastic range for three different Upper Egypt fine-grained soils, which were reported to have very different plasticity characteristics, as quantified by standard consistency limit tests. The undrained shear strengths of the cement-stabilized soils were also estimated using the same RE approach for different cement contents and curing periods of between 1 and 4 weeks. In employing Eq. 2 for these strength calculations, the author implicitly assumes that, for his extrusion apparatus R value of 40, the ratio of steady-state extrusion pressure to undrained shear strength (P/c_u) has a constant magnitude of 17.5 for the three investigated Upper Egypt fine-grained soils, considering both their remolded and cement-stabilized conditions. However, as described below, the P/c_u magnitude for a given R value is not the same constant value for different fine-grained soils but can vary significantly between them. Additionally, it will be shown that for a given fine-grained soil, higher overall P/c_u values are expected for undisturbed and cured RE specimens compared to remolded RE specimens. …