The modified pressure plate apparatus is used to study the volume change behaviour of unsaturated soils (Ng et al. 2002). Prior to its development, measurements of the volume change had limited accuracy.
The basic principle of the measuring system is to record the changes in the differential pressure caused by volume change in the specimen. This differential pressure is due to changes in the water level inside an open-ended bottle shaped inner cell. The pressure is measured using a high-resolution differential pressure transducer (DPT). This apparatus is suitable for measuring the SWCC, isotropic compression and other unsaturated tests where volume change measurements are required.