A Double Cell Triaxial System for continuous measurement of volume changes of an unsaturated or saturated soil specimen in triaxial testing

This paper presents an improved Double Cell Triaxial System (DCTS) for continuous measurement of the volume change of an unsaturated or saturated soil specimen in triaxial testing. The DCTS developed by the author overcomes the two critical shortcomings of the conventional triaxial system and has advantages over the existing modified triaxial cells for measuring the volume changes of unsaturated/saturated soils during water flushing, consolidation, and compression. The calibration of the DCTS has been done using both a dummy solid copper specimen and a fully saturated marine clay specimen. The water volume changes of the inner cell and the outer cell are measured and compared on the copper specimen under compression of the inner/outer cell pressure up to 400 kPa. It is found that the volume changes of the outer cell are significant, while the volume changes of the inner cell are negligible. On the saturated marine clay, volume changes of the clay specimen under isotropic consolidation and drained axial compression are measured using two methods: the conventional method (Method A) by measuring the volume of water coming out from inside the specimen and the method (Method B) by using the DCTS to measure the internal cell water volume changes. The volume changes using the two methods are compared. It is found that the differences of the volume changes using the two methods are within 5.6%. The calibration results using both the solid copper specimen and the saturated marine clay specimen show that the DCTS is accurate and reliable for continuously measuring the volume changes of unsaturated or saturated soil specimens during consolidation and compression.