Measurement of deformation of unsaturated compacted soil triaxial specimen based on digital image measurement method

A new means of strain measurement of unsaturated soil specimen is introduced in suction-controlled triaxial tests based on digital image measurement method. The digital image measurement method can non-contactually and selectively measure the deformation of whole and local specimen and overcomes some critical shortcomings of using conventional strain measurement method for unsaturated soil specimen in suction-controlled triaxial tests. Meanwhile, the deformation process of the unsaturated soil specimen can also be recorded and analyzed after tests finished. The local deformation of middle section of unsaturated soil specimen that is relatively little influenced by end restraint can be handily and accurately measured by adopting the method. The deformation measurement results of unsaturated compacted soil specimens show that the end restraint has material effect on deformation of specimens and deformation characteristics of middle section is evidently different from the whole specimen that is influenced by end restraint in suction-controlled isotropic loading and triaxial compression tests. So the deformation measurement results of middle section can correspondingly really reflect basic deformation characteristics of unsaturated soil.