Volume Change Test

Purpose of Tests

Measuring the volume change of a soil specimen during a test has become a standard routine in laboratory testing.

Accurate volume change measurement does not depend solely on the resolution of the measurement devices used but also on other factors such as the measurement method, cell pressure, temperature fluctuations, system creep, and system compliance. A typical triaxial test involves confining a cylindrical soil or rock specimen in a pressurised cell to simulate a stress condition and then shearing to failure, in order to determine the shear strength properties of the sample. Most triaxial tests are performed on high quality undisturbed specimens. Conventional procedures for the determination of volume changes in triaxial tests are based on the amount of pore fluid changes into or out of the fully saturated cylindrical specimen.

As a triaxial soil specimen shears, the total volume may increase or decrease depending on the soil density, current state of stress, and the stress history. The measurement of these changes in volume is of great importance in the characterization of the soil's mechanical properties. This paper presents an innovative or alternative technique that has been used for measuring the volumetric deformation that cylindrical specimens experience during the shearing stages of a triaxial test. This method incorporates digital imaging techniques and computer-aided analysis to assess the changes in volume throughout a test. A detailed description of the hardware and other equipment is provided along with the data analysis methodology used to simplify the operation.

Comparisons are made between the observed results and those obtained from conventional measurement techniques. This paper examines volume change measurement inferred from the volume of the confining water in a triaxial cell. In particular, the effects of stiffness of the pressure cell and temperature fluctuations on the accuracy of the volume change measurements are investigated. A method to correct for temperature effects on the volume of water in a triaxial pressure cell for providing a more reliable measurement of the volume change of a soil specimen is suggested. The suggested method can also be applied in triaxial apparatuses using double cells.