Prediction of Angle of Internal Friction Based on SPT N Values

Abstract

The present study focused to estimate the angle of internal friction (ɸ) of cohesionless soil and cohesive (c-ɸ) soil considering field standard penetration test (SPT) data. Based on the SPT data an empirical correlation has been established between standard penetration number N and internal friction angle to predict the friction angle of soils. All the field standard penetration test data are collected from six different places of East India. Regression analyses were performed using the SPT data collected from 40 different boreholes containing 330 data points. The SPT N values obtained from different sites are observed to vary between 4 and 70. The in-situ bulk density of undisturbed samples recovered through pitcher sampler is in the range of 17.90–18.90 kN/m3. In situ water content and fines content observed plays an important role in case of c-ɸ soil, hence plasticity index (PI) and fines content (p) are also included in model equation in case of c-ɸ soil. The predicted results obtained from developed model equation appears to be in good agreement with existing equations in various literature. By using regression analysis, the empirical equations are developed. The most important thing is to find out the friction angle of c-ɸ soil which is useful for the fields. The estimated equations are verified by validating the correlations with experimental values obtained from field which in turn can be used for geotechnical engineering design problems. Thus, the study provides a simplified and faster analysis of angle of internal friction for different types of soils.