shear strength and failure of structured soils

Structured soils with high porosity are highly prone to lose their structure. the objective of this study was to evaluate the effect of the degradation of the structure of soils on their shear strength. the specimens of structured soil were papered in the laboratory mixing fine grained soil, expanded granular polystyrene foam and cement. shear strength of specimens was determined by direct shear test under wide range of normal stress ranging from 7 kpa to 760 kpa. the results of the laboratory tests indicated that the cohesion and internal friction angle of structured soils extremely change with increasing the normal stress level. the failure of structured soils could be in brittle or ductile mode. logarithmic relationships between normal stress and cohesion and friction angle of structured soil were observed. a nonlinear failure criterion was proposed for failure envelope of structured soil based on the mohr-coulomb and griffith failure criterion and a destruction function to employ both brittle and ductile failure modes. the proposed failure criterion verified using laboratory tests conducted in this study.