The undrained shear strength characteristics of silty sand: an experimental study of the effect of fines (original) (raw)
Shear Strength and Stiffness of Silty Sand
Journal of Geotechnical and Geoenvironmental Engineering, 2000
The properties of clean sands pertaining to shear strength and stiffness have been studied extensively. However, natural sands generally contain significant amounts of silt and/or clay. The mechanical response of such soils is different from that of clean sands. This paper addresses the effects of nonplastic fines on the small-strain stiffness and shear strength of sands. A series of laboratory tests was performed on samples of Ottawa sand with fines content in the range of 5-20% by weight. The samples were prepared at different relative densities and were subjected to various levels of mean effective consolidation stress. Most of the triaxial tests were conducted to axial strains in excess of 30%. The stress-strain responses were recorded, and the shear strength and dilatancy parameters were obtained for each fines percentage. Bender element tests performed in triaxial test samples allowed assessment of the effect of fines content on small-strain mechanical stiffness.
INTERNATIONAL JOURNAL OF ADVANCE SCIENTIFIC RESEARCH, 2024
Sandy soil as a foundation material largely depends on the engineering properties of soil governed by its physical properties, behavior, and containing fines (Plastic or Non-plastic). As approximate correlations between SPT N-value, angle of internal friction, relative density, and dry unit weight for cohesion-less materials are already mature. However, the effect of a different range of percentages of fines on sand is not well covered. So, this paper presents a detailed study focused on investigating the effect of non-plastic fines on the engineering properties of sand-silt mixtures. An attempt has been made to establish a relationship between the proportion of sand-silt mixture and shear strength. Mixtures of sand and fines are prepared by mixing clean sand with non-plastic fines (silt). Sand used during the experimentation is classified as poorly graded (SP) as per the Unified Soil Classification System (USCS). Non-plastic fines are obtained locally, having liquid limit (LL) is 21.4%, plasticity index (PI) is less than 4 (PI<4), and contain 97.43% silt particles, 1.77% clay, and sand= 0.8% particles. An experimental study was conducted on the sand and silt under different conditions. The reconstituted well-graded samples containing different silt amounts, i.e. 0%, 10%, 20%, 30%, 40%, and 50% were subjected to the vibration table method to obtain maximum and minimum dry density. For the shear strength parameter, samples were subjected to consolidated drained direct shear tests at three relative densities i.e. 30, 60, and 90%, and three normal stress, i.e. 50, 100, and 200 kPa at the displacement rate of 1mm/min under the dry state. From the maximum void ratio and minimum void ratio curves with percentages of fines content in the sandsilt mixture, the limiting fines content (LFC) range is 21 to 27%. Direct shear test results depict that at constant relative density, up till limiting fines content the angle of internal friction increases, and a further increase in fines it decreases. But different relative density, found different limiting fines content. Hence, it is observed that the percentage of fines alters the engineering behavior of sand.