ABSTRACT
The geological heterogeneity of the Siwalik subdivisions, characterized by abrupt fine–coarse transitions, poses significant challenges to geotechnical design in Nepal. Generalized investigations misrepresent internal friction angle (φ), contributing to structural design failures, project delays, and cost overruns. The influence of particle size distribution on internal friction angle (φ) is commonly underrepresented in routine design practices. Linking particle size distribution with internal friction angle (φ) provides a practical and readily quick initial screening measure at the pre-feasibility stages of projects, particularly in geologically sensitive regions such as Siwalik. This study confirms a positive correlation between coarse fraction and internal friction angle φ based on the study of 220 soil samples collected from the Lower, Middle and Upper sub-divisions of Siwalik of Nepal. This study offers a quick reference table for early desktop studies, giving preliminary friction angle ranges for Siwalik subdivisions while highlighting risks of misinterpretation of internal friction angle (φ).
