Constant-Volume Triaxial Tests to Study the Effects of Membrane Penetration

In conventional undrained triaxial tests a rubber membrane is used to confine soil samples. This rubber membrane penetrates the peripheral voids of the sand sample and causes volume changes under varying effective confining pressures during shear. These volume changes invalidate the no-volume-change condition of an undrained test and lead to considerable and even unsafe errors in pore pressure measurements and thus in measurements of static undrained strength and liquefaction resistance. In order to make a qualitative study of the influence of membrane penetration on pore pressure development in static and cyclic tests, constant-volume triaxial tests were performed on saturated sand samples. Resulting pore pressure response and stress path behavior are discussed.