Volume changes in undrained triaxial tests on sands

The error in dimension measurement and the volume changes during saturation, consolidation, and undrained loading were investigated in the conventional triaxial tests on a Unimin sand. A Hall effect radial displacement transducer (HRDT) was developed. With the help of the HRDT and the linear varying displacement transducer (LVDT), the volume change during saturation and the membrane penetration during consolidation can be easily determined by directly measuring radial and axial dimensional changes of a triaxial sample. The test results show that for a Unimin sand sample with nominal dimensions of 50 x 100 mm, the volume change due to saturation increased with a decrease in the initial density of the sample, varying from 2.79 cm(3) at Dr = 1.9% to 0.87 cm(3) at Dr = 54.7%. The volume change during undrained loading resulted mainly from the variation of membrane penetration due to the buildup of pore-water pressure, increasing with the effective stress at consolidation. The steady-state Lines with volume correction at the onset of collapse and at phase transformation were much lower than that without volume correction.