This paper reviews the percussion-cup liquid limit, thread-rolling plastic limit (PL) and various fall-cone and other approaches employed for consistency limit determinations on fine-grained soil, highlighting their use and misuse for soil classification purposes and in existing correlations. As the PL does not correspond to a unique value of remoulded undrained shear strength, there is no scientific reason why PL measurements obtained using the thread-rolling and shear-strength-based fall-cone or extrusion methods should coincide. Various correlations are established relating liquid limit values deduced using the percussion-cup and fall-cone approaches. The significance of differences in the strain-rate dependency on the mobilised fall-cone shear strength is reviewed. The paper concludes with recommendations on the standardisation of international codes and the wider use of the fall-cone approach for soft to medium-stiff clays in establishing the strength variability with changing water content and further index parameters.
The true water content of organic soils is overestimated when the standard oven drying temperature of 110 ± 5°C is used due to some oxidation of the solids, and underestimated when the recommended oven drying temperature of 60°C is used due to some residual pore water remaining in the voids. A new method is presented to identify the precise oven drying temperature for which the mass of the residual pore water exactly balances the loss in the mass of solids due to oxidation. The true water content is calculated on the basis of the specimen dry mass recorded for this oven drying temperature. A larger error arose when the water content of the test soil (70% organic content) was determined using the specimen dry mass recorded at 60°C rather than the standard drying temperature of 110 ± 5°C. Longer drying times were also required for the dry mass to equilibrate, making it more inconvenient from a practical standpoint. Some oxidation of the organic solids occurred for oven specimen drying above 80°C. The true value of the water content corresponded to an oven drying temperature of 86°C.
Development of a new hollow cylinder apparatus for stress path measurements over a wide strain range ABSTRACT: The development and operation of a new, automated hollow cylinder apparatus that facilitates accurate stress path measurements from the pseudo elastic domain to failure strain levels are described. Innovative sample loading mechanisms of 19.3 kN axial and 103 N.m torsional capacities facilitate rapid, precise (better than 10 -5 % strain) displacement and rotation of the sample loading piston, with negligible compliance in the mechanisms on reversing the direction of piston motion. Both internal and external instrumentation are used to record the sample deformational response to better than 10 -2 % strain. Significant differences were found between the strain values measured using the internal and external instrumentation, with the external instrumentation underestimating the true stiffness of the sample. A series of drained stress-path tests on Leighton Buzzard sand specimens showed that predefined stress paths can be followed to an accuracy of 0.5 kPa using the new apparatus.
A hollow cylinder apparatus was used to study some engineering properties of hollow cylindrical sand specimens prepared using the wet-pluviation technique. The refined specimen preparation method displayed good repeatability. Wet pluviation produced inherently cross-anisotropic specimens, with the level of initial anisotropy reducing with decreasing initial void ratio. The variation in the initial void ratio of the sand specimens was related to the volume of the specimens. The stress-strain responses under isotropic consolidation were not significantly affected by the small variations in the initial void ratios that occurred for a target initial specimen volume. The levels of membrane penetration recorded for the different specimens was independent of the applied cell confining pressure, and the amount of membrane penetration compared well with other experimental studies.
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