Effects of non plastic silt on cone resistance
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Liquefaction potential assessment using in-situ tests is a vast area interested by various researchers in the recent years. Ability to obtain a continuous profile has been a key for one of such in-situ tests, CPT (Cone Penetration Test) to gain more attention. Existing liquefaction potential charts are made from laboratory tests and past earthquake case histories which correlate normalized cone resistance (q c1N ) to cyclic resistance ratio (CRR) for a 7.5 magnitude earthquake. Effect of non-plastic fines on q c1N – CRR correlations has been recognized by various researchers. The cause of this influence remains little understood. In this study, a series of miniature CPTs were performed in dry and fully saturated Ottawa F55 sand-silt mixture at 25% fines content (OS-25) in a CPT chamber to explore the effects of presence of non-plastic silts on cone resistance q c1N . An analysis of this data set combined with prior data by Huang, 2014 on the same Ottawa F55 sand and silty sand OS-25 indicate that dry sand, saturated sand, and dry silty sand show similar trend for q c1N at the same equivalent inter-granular relative density, (D rc ) eq . The pore pressures around the cone during penetration in sand are very small. This indicates that q c1N in saturated sand, dry sand, and dry silty sand is a response of ‘drained’ penetration. Results from saturated silty sands at the same rate of penetration, indicate significant pore pressures around the cone and smaller q c1N for the same (D rc ) eq . Further analysis shows that this difference could be captured using a non-dimensional normalized cone penetration rate, T 0 (=vd c /c v , v=cone penetration rate, d c =cone diameter and c v =coefficient of consolidation). Viz, there appears to exist a relationship between qc1N, (D rc ) eq and T o . Additional analysis, incorporating the CRR data available for the same sand and silty sand indicate that a q c1N -CRR-T 0 relationship is possible, and it can lead to an improved liquefaction screening method.