Abstract: The existing plane-strain apparatuses can not avoid the friction between the soil specimen and the constraint panel, which influences greatly the accuracy of soil deformation measurement. This paper presents a brief review of the plane-strain apparatuses. The plane-strain apparatuses are classified into four types according to their loading models. The advantages and disadvantages are discussed for each type of the plane-strain apparatus. A newly developed plane-strain apparatus with modified loading chamber uses the special designed front and rear panels with 3 mm water film to reduce the friction. Friction between soil sample and panel can be eliminated during the test, since the rubber film touches the water-sealing silicone membrane instead of touching the panel. A digital image measurement system is integrated into the apparatus to measure the deformation distribution on soil specimen surface with high accuracy and capability of identifying shear band and its characteristics. The improved and conventional chambers are employed to measure the deformation of Fujian standard sand, respectively. The peak values of the stress-strain curves obtained by the new plane-strain apparatus can be reduced by 60%. Both triaxial and plain-strain tests on the soil specimen with same dry density under different confining pressures measure the soil’s shear strength. It is shown that the shear parameters obtained by using the new type of loading chamber are closed to that of the triaxial test. However, the results by using the old one are obviously unreasonable.

Key words: plane-strain apparatus, new type of loading chamber, friction between soil specimen and constraint panel, digital image measurement