Calibrations for volume change measurements using osmotic suction control technique

Evaluation of the volume change behavior of expansive soils under controlled suction and boundary conditions is important for the proper design of different geotechnical systems. Osmotic technique was used by several researchers for suction controlled testing of expansive soil specimens. This technique involves circulating polyethylene glycol solution (PEG) over a semi-permeable membrane underlying a test specimen. Different suction controlled testing apparatuses incorporating osmotic techniques were developed included triaxial and oedometric testing conditions to simulate different boundary conditions. This paper describes a series of calibration performed on suction controlled modified oedometer and triaxial equipment used for testing expansive soil. The modified oedometer, developed by the authors, comprises of thin-wall oedometer ring instrumented with strain gauges to measure the lateral stresses evolving during the test. The first part of this paper introduces the errors that arise during osmotic suction testing, concerning the device flexibility and PEG solution losses. The second part of the paper highlights the calibration procedure for estimating lateral stresses in modified oedometer from instrumented strain gauges as well as introduces a correction for the temperature fluctuation. Finally, the effect of triaxial cell flexibility on the volume change measured during osmotic suction controlled testing as well as temperature effect on volume change measurements were evaluated and correction procedures were introduced.