027-060-ngm_2016_-_extended_interpretation_basis_for_the_vane_shear_test_gylland.pdf

027-060-ngm_2016_-_extended_interpretation_basis_for_the_vane_shear_test_gylland.pdf

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NGM 2016 Reykjavik Proceedings of the 17 th Nordic Geotechnical Meeting Challenges in Nordic Geotechnic 25 th 28 th of May IGS 233 NGM 2016 - Proceedings Extended interpretation basis for the vane shear test A. S. Gylland Multiconsult, Norway, [email protected] V. Thakur & A. Emdal The Norwegian University of Science and Technology (NTNU), Norway ABSTRACT The vane shear test has been widely used as an in-situ test device in Norway from the sixties to the eighties. However, the last decades, its popularity has decreased, partly because of the increasing popularity of the CPTU-test, but also because of uncertainties related to interpretation of the vane shear test. With the aim of an improved and extended interpretation basis for the vane shear test, a database consisting of parallel vane shear tests and laboratory tests performed on high quality block samples has been compiled. The work focus on correlations between the vane shear test and active undrained shear strength and stiffness as well as factors that could improve the vane test as a “quick -clay- detector”, e.g. sensitivity and remoulding energy. The latter factors are important in areas where mapping of sensitive clays is necessary and an efficient tool is needed. The work show that it is possible to establish a strong relation between the active undrained shear strength and the undrained shear strength as interpreted from the vane shear test as a function of the plasticity index. If is further seen that there is a potential for deducing OCR from the vane test. There is not a one-to-one relation between sensitivity as measured from the vane test and by the falling cone test in the laboratory. The vane appears to measure too high values for the remoulded undrained shear strength. On the other hand, work on deducing disintegration energy from the shear vane tests show promising results. In total, the shear vane holds several advantages and further research on the device is recommended to strengthen its position in the geotechnical tool case. Keywords: In-situ testing, clays, undrained shear strength, interpretation 1 THE VANE SHEAR DEVICE The vane shear test (VST) is mostly used in clays and clayey silts for determination of undrained intact and remoulded shear strength. The vane shear device consists of two rectangular plates forming a perpendicular cross (Figure 1). The cross is penetrated into the ground to a given depth before rotation is applied. Torque and rotation is measured. Despite its simplicity, the VST suffers from several uncertainties related to installation- effects, equipment and interpretation. In order to shed new light on the VST, a database of test results is here presented where the potential of deducing active undrained shear strength, soil stiffness, remoulded shear strength, disintegration energy and OCR from the test is investigated.
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