A system to measure volume change of unsaturated soils in undrained cyclic triaxial tests

It is common to employ a traditional double cell system, of which an open-ended inner cell is installed in an ordinary triaxial apparatus, tomeasure the volume change of unsaturated specimens. In such a system, the total apparent volumetric strain of the specimen (ev) is deduced fromthewater level change in the inner cell,monitored by a differential pressure transducer (DPT) considering,meanwhile, the top cap intrusion into the inner cell recorded by a vertical displacement transducer (VDT). Severe apparent volumetric strain, caused by the compliance of the double cell system(ev,SC), was observed during the undrained cyclic loading tests in a previous study. Test results on a steel-spring dummy specimen revealed that ev,SC was induced not only by such as themeniscus effect, but unexpectedly also by the asynchronous responses between the DPTand the VDT (i.e., the response of the DPTwas delayed compared with that of the VDT). By doing some treatment ev,SC could be reduced to some extent, whereas themagnitude of ev,SCwas still too high to be acceptablewhen the tested specimen approached the liquefied state. To radically solve these technical difficulties, amodified double cell system, named the linkage double cell system, was developed in this study. In thismodified system, a linkage rod moving simultaneously with the loading shaft was introduced, through which the DPTcould directlymeasure ev without considering the top cap or loading shaft intrusion. Test results for the steel-spring dummy specimen aswell as for saturated and unsaturated soil specimens demonstrated that the linkage double cell systemhasmajor advantages inmeasuring accurately the volume change of the specimen during undrained cyclic triaxial loading tests compared with the traditional double cell system.Copy; by ASTM Intl (all rights reserved); Wed Jul 27 07:25:09 EDT 2016.