Laboratory Evaluation of Undrained Shear Strength of a Soft Fine Grained Soils

Abstract

The determination of undrained shear strength of soils is commonly achieved using triaxial testing in which specimen is carefully prepared before testing to maintain its original field condition. However, for soft soils preparing and handling specimens without causing any disturbance is a difficult job and may not always be successful. Other laboratory testing techniques can be adopted provided they can produce reliable results for such cases and can overcome the problem of pretest preparation process and hence avoiding any alteration of sample field condition. Extensive laboratory investigation on a soft marine soil recovered from sea bed offshore of Benghazi city, the testing program involves investigation of the basic geotechnical properties, focusing specifically on the determination of the undrained shear strength of such soils as determined by both the conventional unconsolidated undrained triaxial testing (UU) and the simple laboratory vane shear testing device (Miniature shear vane MV). The resulting shear strength obtained by UU-triaxial test, and resulting shear strength measured by Miniature shear vane MV were examined, compared and discussed on the light of other research works. Furthermore, the problems faced during testing soft samples in triaxial apparatus was also presented. The resulting undrained shear strength obtained by UU-triaxial test was found generally lower than that produced by Miniature shear vane MV which is attributed to sample disturbance before testing in triaxial. The study also demonstrates that despite of high scatter, the undrained shear strength obtained by MV can be reasonably comparable with the results of other investigations on soft soils.