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Mechanisms Affecting Liquefaction Screening of Non-Plastic Silty Soils Using Cone Penetration Resistance

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Mechanisms Affecting Liquefaction Screening of Non-Plastic Silty Soils Using Cone Penetration Resistance Mechanisms affecting liquefaction screening of Non-Plastic silty soils using Cone Penetration Resistance USGS Award Number: 07HQGR0113 Final Report October 2014 S. Thevanayagam Principal Investigator & V. Veluchamy and Q. Huang Research Assistants University at Buffalo State University of New York Department of Civil, Struct. & Env. Eng. 212 Ketter Hall, Buffalo, NY 14260 Tel: 716-645-4376; [email protected] Program Element: III Key Words: Liquefaction, sand, silty sand, Cone Penetration Resistance "Research supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award number (07HQGR0113). The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government." i Abstract Effect of non-plastic fines on the cone resistance and cyclic resistance of sands and silty sands remains an unresolved problem. This study focuses on: (a) cone penetrometer experiment study on penetration resistance of sands and silty sands at 15 and 25% silt content, (b) numerical study on the effect of permeability and compressibility (representing the effect of silt content), diameter of cone (dc) and penetration rate (v) on cone resistance in sands and silty sands, (c) comparative analysis of the results from (a) and (b) of the effect of silt content on cone resistance through a non-dimensional parameter To (=vdc/cv, where v is the penetration rate, dc is the cone diameter and cv is the coefficient of consolidation) for all soils at the same equivalent inter-granular relative void ratio [(ec)eq] or relative density [(Drc)eq], and (d) relationship between cyclic resistance and cone penetration resistance and the non-dimensional parameter To, and its utility for liquefaction screening. In both experimental and numerical studies for saturated sands and silty sands, the normalized cone resistance (qc1N) decreased with an increase in silt content, at the same [(Drc)eq], from 0 to 25%. However this influence of silt content on penetration resistance was absent for dry sands and silty sands at the same [(Drc)eq]. The difference of cone resistance in saturated sands and silty sands, is thought to be due to partial drainage occurring in saturated silty sands whereas the penetration process is thought to be nearly drained in saturated sands. In the case of dry soils, this pore pressure influence is absent and hence the same penetration resistance is observed in sands and silty sands. ii This indicates the important influence of pore pressures and its dissipation rates, depending on the silt content, on cone resistance. Both experimental data and numerical results indicate that for the same (Drc)eq, qc1N decreases as To increases, which implies a decrease in cv (or increase in silt content), because of the penetration process transition from drained to partially drained or even undrained condition. In addition, the numerical analysis shows that v and dc also influence qc1N in silty sands. qc1N decreases as v increase or dc increases (To increases) in the partially drained condition. Since fines content is not the only factor affecting cone resistance, a To dependent relationship between cyclic resistance ratio (CRR) and qc1N for sands and silty sands is proposed for liquefaction screening. Further research is needed to evaluate and validate such a procedure using further cone penetration tests in a large chamber setup, refined numerical simulations, and cyclic tests on the same soils as those used in chamber tests, field data from liquefaction and non- liquefaction sites, and physical model liquefaction tests and cone penetration tests using laminar box shaking facilities. The data and initial analyses presented herein are part of continuing research by the investigators. This report presents a snap shot of the present state of this research. A number of publications have already been made. More concise and definitive conclusions and findings from this research will be disseminated in future publications in the literature. iii Table of contents Abstract ................................................................................................................ iiii Table of contents ......................................................................................................... ivv List of Figures ............................................................................................................... ix List of Tables .............................................................................................................. xxii Notations……… ....................................................................................................... xxiv Chapter 1. Introduction .................................................................................................. 1 1.1. Background and statement of problem .................................................................. 1 1.2. Scope of research ................................................................................................... 2 1.3. Organization of dissertation ................................................................................... 3 Chapter 2. Literature review .......................................................................................... 6 2.1. Introduction ............................................................................................................ 6 2.2. Liquefaction screening using CPT for sands and silty sands ................................. 7 2.3. Effect of fines on mechanical behavior in silty sands .......................................... 13 2.3.1. Framework of inter-granular contact density indices of silty sands .................. 14 2.3.2. Example on the inter-granular contact density index......................................... 18 2.4. Effect of fines on permeability and coefficient of consolidation in silty sands ... 19 2.5. Normalized penetration rate-To ............................................................................ 22 2.6. Effect of Drainage conditions on cone resistance and liquefaction screening in sands and silty sands .................................................................................................... 23 2.6.1. Laboratory study ................................................................................................ 23 2.6.2. Finite element method........................................................................................ 28 2.7. Summary .............................................................................................................. 32 Chapter 3. Design of CPT testing chamber ................................................................. 34 3.1. Introduction .......................................................................................................... 34 3.2. Design concepts of testing chamber .................................................................... 34 3.2.1. Boundary conditions .......................................................................................... 35 3.2.2. Chamber size effect ............................................................................................ 38 3.2.3. Design consideration of testing chamber system ............................................... 39 3.3. Design of testing chamber system ....................................................................... 40 3.3.1. Reaction frame and pushing system .................................................................. 41 3.3.2. CPT chamber (Cell) ........................................................................................... 42 3.3.3. Miniature cone ................................................................................................... 45 3.3.4. Instrumentation and data acquisition system (DAQ/DAS) ................................ 47 3.3.5. Chamber compliance ......................................................................................... 51 3.4. Summary .............................................................................................................. 53 Chapter 4. CPT chamber tests and analysis: Sands and silty sands ............................. 54 4.1. Introduction .......................................................................................................... 54 iv 4.2. Test procedures .................................................................................................... 55 4.2.1. Sample preparation and saturation ..................................................................... 55 4.2.2. Sample consolidation ......................................................................................... 56 4.2.3. Cone penetration ................................................................................................ 56 4.2.4. Disassemble of sample ....................................................................................... 57 4.3. Analysis of chamber test results .......................................................................... 57 4.3.1. Dry sand-silt mix................................................................................................ 60 4.3.2. Saturated sand-silt mixture ................................................................................ 67 4.3.3. Summary of experimental results ...................................................................... 77 4.4. Summary .............................................................................................................
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