Similar to the Hazen formula for estimating permeability from the gradation curve of soil, can we identify the angle of shearing resistance of silty sand and sandy silt type of soil?
It will be difficult to assess the shear strength parameters merely based on the grain size distribution. One needs to account the drainage conditions that prevails, relative density as well as the plasticity of the soil.
Though based on density and soil type, you may be able to have a guess on friction angle. Please refer books: 'Craig's Soil mechanics' or locally well known 'Soil mechanics' by Dr. Gopal ranjan.