Experimental study on stress-strain characteristics of coarse-grained soil under different intermediate principal stresses

In order to study how the intermediate principal stress (short for IPS) influences the stress-strain characteristic of coarse-grained soil, using the large-scale true triaxial apparatus developed by Changjiang River Scientific Research Institute (CRSRI), a series of true triaxial compression tests and plane strain tests are carried out. The test results show that: (1) When the IPS ratio (also called b value) is a constant, the slope of stress-strain curves and the peak strength increase with the increasing consolidation pressure; (2) Under the relative low confining pressure conditions, with the increasing axial strain, the volumetric strain exhitits shear contracting firstly and then dilating, but when the confining pressure rises to a higher level, the volumetric strain shows shear contracting in the whole deformation process; (3) When the consolidation pressure is the same, with the increase of b value, the stress softening effect after the peak stress becomes more obvious. Under a relative lower consolidation pressure, the volumetric strain exhibits the characteristics of shear contracting firstly and then dilating. For the relation curves between the minimum and the maximum principal strains, the absolute value of slope also increases. The above results can be treated as the research foundation in establishing the constitutive model for coarse-grained soil under complex stress paths.