Method for determining stress-strain state of deformable constraint triaxial apparatus soil sample

The invention provides a method for determining the stress-strain state of a deformable constraint triaxial apparatus soil sample, and belongs to the field of geotechnical engineering in civil engineering discipline. A sample is constrained by adopting a deformable thin-wall cylinder, and a triaxial compression test is carried out under a deformable constraint condition. Marking grids are printed on the outer wall of the thin-wall cylinder, the radial (annular) deformation and the axial deformation of the thin wall in the compression process are tested through a digital image measurement technology, and the strain state of the soil sample can be determined by combining the axial deformation, collected by the axial displacement sensor, of the soil sample. Based on the assumption of plane stress, according to Hooke's law, the circumferential stress of the thin wall can be determined according to the elastic modulus and Poisson's ratio of the thin-wall material and the circumferential strain and axial strain of