A graphical method for membrane penetration in triaxial tests on granular soils

In granular soils, membrane penetration is significant which will affect the measurement of the specimen volume change since it is measured from the specimen water that came out of the specimen when the specimen is compressed. The volume of the expelled water represents both the specimen shrinkage and the membrane penetration. Correction has to be made to eliminate the effect of membrane penetration. A graphical method to determine the membrane penetration is described and the results are compared with the actual membrane penetration determined from the consolidation of dummy specimens. There are four test materials involved which are sands of uniform grain size of 0.3, 0.6, 1.18 and 2.0 mm. Four test series dealt with consolidated drained triaxial tests on saturated specimens. The effective stresses applied are 50, 100, 200, 300 and 400 kPa. The fifth test series was the tests on dummy specimens made from thin layer of test materials enclosing a solid concrete cylindrical core. The specimen water expelled from the consolidation of the dummy specimens is purely due to membrane penetration. In this study, it is observed that membrane penetration increases with effective confining pressure and as well as the grain sizes. The result shows that half of the cases complied with the proposed method. It indicates the potential to be a good and simple alternative for the determination of membrane penetration. However further investigation is required