Evaluation of common practice empirical procedures for residual friction angle of soils: Hawaiian amorphous material rich colluvial soil case study

The residual strength of soils has received considerable attention after Skempton suggested that the stability of reactivated landslides may be governed by residual strength. In this respect, numerous studies have been conducted to determine the factors affecting the residual strength of soils. Specifically, research effort was focused on determining correlations between the residual friction angle of soils and soil indexes such as Atterberg limits, and clay fraction. Some of these researchers suggested that strong correlations exist with soil indexes. Other researchers claimed that there is no correlation between the soil index and the residual friction of soils. Thus, there is a need to clarify whether there is a correlation between residual friction angle and soil index properties. In this effort, we describe general properties of landslides in Hawaii with an emphasis on an active landslide; followed by evaluating correlations between the residual strength and soil indexes. The results of this study show that the existing empirical correlations for soil index properties and residual friction angle predict poorly the residual friction angle of colluvial soils that rich in amorphous materials. However, the results also show that a strong correlation between LL and PI and residual friction angle may exist depending on the soil mineral type.