The Mechanism of Liquefaction in Layered Soils
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In no event will this web foundations: page or webmaster be held liable, nor does this web page or its webmaster provide insurance against liability, for The Wave Equation Page for any damages including lost profits, lost savings or any other incidental or consequential damages arising from Piling the use or inability to use the information contained within. Online books on all aspects of This site is not an official site of Prentice-Hall, soil mechanics, foundations and Pile Buck, the University of Tennessee at marine construction Chattanooga, or Vulcan Foundation Equipment. All references to sources of software, equipment, parts, service Free general engineering and or repairs do not constitute an geotechnical software endorsement. And much more... Visit our companion site http://www.vulcanhammer.org August 1992 An Investigation Conducted by NCEL Gregg L. Fiegel and Bruce L. Kutter Contract Report University of California, Davis THE MECHANISM OF LIQUEFACTION IN LAYERED SOILS Abstract Results from six centrifuge model tests are presented. Four of the model tests involve layered soil deposits subject to base shaking; two model tests involve uniform soil deposits of sand subject to base shaking. The layered soil models consisted of a saturated liquefiable fine sand overlain by a layer of relatively impermeable silica flour (silt). Pore water pressures, accelerations, and settlements were measured during all six tests. Results from the model tests involving layered soils suggest that during liquefaction, a water interlayer or very loose zone of soil develops between the sand and the silt due to the difference in permeabilities. Soil volcanos or boils were seen on the surface for all four of these layered model tests. The locations of these boils, in each test, were found concentrated in the weakest zones ~f the over-lying silt layer; cracking of the weak silt zones provided a release or a vent for the excess pore water pressure generated as a result of particle rearrangement in the liquefiable fine sand. NAVAL CIVIL ENGINEERING LABORATORY PORT HUENEME CALIFORNIA 93043-5003 Approved for public release; distribution is unlimited. METRIC CONVliRSION 1:ACTORS Approximate Conversions to Metric Measures Appoximate Conversions from Metric Measures Symbol When You Know Multiply by - To- Find Symbol- -Symbol When You Know Multiply by Symbol- LENGTH LENGTH in inches '2.5 centimeters cm millimeters 0.04 inches ft feet 30 centimeters cm centimeters 0.4 inches yd yards 0.9 meters m meters 3.3 feet mi miles 1.6 kilometers km meters 1.1 yards kilometers 0.6 -AREA miles AREA in2 square inches 6.5 square centimeters cm2 - ft2 square feet 0.09 square meters m2 Square centimeters 0.16 square inches yd2 square yards 0.8 square meters m2 square meters 1.2 square yards mi2 square miles 2.6 square kilometers km2 square kilometers 0.4 square miles acres 0.4 hectares ha hectares (10,000 m2) 2.5 acres MASS (weiahtl MASS (weight) ounces 28 grams grams 0.035 ounces pounds 0.45 kilograms kilograms 2.2 pounds short tons 0.9 tonnes tonnes (1,000 kg) 1.1 short tons (2.000 Ibl VOLUME VOLUME m~liiliters 0.03 fluid ounces tsp teaspoons 5 milliliters ml liters 2.1 plnts Tbsp tablespoons 15 milliliters ml liters 1.06 quarts fl oz fluid ounces 30 milliliters ml liters 0.26 gallons C cups 0.24 liters I cubic meters 35 cubic feet Pt pints 0.47 liters I cubic meters 1.3 cubic yards quarts 0.95 liters I qt TEMPERATURE (exact) gallons 3.8 liters I 3 cubic feet 0.03 cubic meters m3 Celsius 915 (then Fahrenheit yd3 cubic yards 0.76 cubic meters m3 temperature add 32) temperature TEMPERATURE (exact1 OF Fahrenheit 5/9 (after Celsius OC temperature subtracting temperature 32) - '1 ~n = 2.54 (exacrlvl. For other exact converslons and more detailed tables, see NBS Msc. Publ. 286. Unttr of Weaghts and Measures. Price $2.25. SD Catalog No. C13.10 286. Fam Appoved REPORT DOCUMENTATION PAGE I OMB No. 0704-018 Public reporting burden for this collection of information is estimated to average 1 hour pec response. including the time for reviewing inSbudh8, searching existing data sww, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send canments regarding this bwden estimate or any other aspect of thin collection information, including suggestlons for reducing this burden, to Washington Headquarters Servkes, Directcwste for Infamation and Reports, 1215 Jettenon Davis Hlghway, Suke 1204,Arlington, VA 22202.4302, and to the Onice of Management and Budget, Papenvork Reduction Project (07044188),Waahington, DC 20503. 1. AGENCY USE ONLY (Leave blank] 2 REPORT DATE 3. REPORTTYPEANDDATESCOVERED August 1992 Interim; October 1990 thru September 1991 4. TITLE AND SUBTITLE 5. FUNDING NUMBERS THE MECHANISM OF LIQUEFACTION IN LAYERED SOILS C - N47408-89-C-1058 6 AUTHORIS) Gregg L. Fiegel, Graduate Research Assistant Bruce L. Kutter, Associate Professor 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESSEIS) a PERFORMING ORQANIUTION REPORT NUMBER University of California, Davis Davis, CA 95616 CRzW 0. SPONSORINGlMONlTORING AGENCY NAMEIS) AND ADDRESSE(S) 10. SPONSOWNCiNONITORING AGENCY REPORT NUMBER Office of the Chief of Naval Research1 Naval Civil Engineering 800 North Quincy Street Laboratory Arlington, VA 22217-5000 Code L51 Port Hueneme, CA 93043 11. SUPPLEMENTARY NOTES I& DISTRIBUTION/AVAILABlUTY STATEMENT 12b. DISTRIBUTION CODE Approved for public release; distribution is unlimited. 13. ABSTRACT (Maximum 200 wwds] Results from six centrifuge model tests are presented. Four of the model tests involve layered soil deposits subject to base shaking; two model tests involve uniform soil deposits of sand subject to base shaking. The layered soil models consisted of a saturated liquefiable fine sand overlain by a layer of relatively impermeable silica flour (silt). Pore water pressures, accelerations, and settlemel~tswere measured during all six tests. Results from the model tests involving layered soils suggest that during liquefaction, a water interlayer or very loose zone of soil develops between the sand and the silt due to the difference in permeabilities. Soil volcanos or boils were seen on the surface for all four of these layered model tests. The locations of these boils, in each test, were found concentrated in the weakest zones of the overlying silt layer; cracking of the weak silt zones provided a release or a vent for the excess pore water pressure generated as a result of particle rearrangement in the liquefiable fine sand. 14. SUBJECT TERMS 15. NUMBER OF PAGES Dynamic testing, geotechnical centrifuge models, liquefaction, pore pressure, sand boils, 34 failure mechanisms I6 PRICE CODE 17. SECURITY CLASSlFlCATlON 18. SECURITY ClASSlFlCAllON 10. SECURITY ClASSlflCATION 1Q UMITATION OF ABSTRACT OF REPORT OF THIS PAGE OF ABSTRACT Unclassified Unclassified Unclassified UL NSN 754041-2806500 Standard Fam 298 (Rev. 2-89) PresMby ANSI Std. 23418 298-102 THE MECHANISM OF LIQUEFACTION IN LAYERED SOILS Gregg L. Fiegel ' and Bruce L. Kutter - Graduate Research Assistant and Associate Professor, respectively; University of California, Davis ABSTRACT: Results from six centrifuge model tests are presented. Four of the model tests involve layered soil deposits subject to base shaking; two model tests involve uniform soil deposits of sand subject to base shaking. The layered soil models consisted of a saturated liquefiable fine sand overlain by a layer of relatively impermeable silica flour (silt). Pore water pressures, accelerations, and settlements were measured during all six tests. Results from the model tests involving layered soils suggest that during liquefaction a water interlayer or very loose zone of soil develops between the sand and the silt due to the difference in permeabilities. Soil volcanos or boils were observed on the surface for all four of these layered model tests. The locations of these boils, in each test, were found to be concentrated in the weakest zones of the overlying silt layer; cracking of the weak silt zones provided a release or a vent for the excess pore water pressure generated as a result of particle rearrangement in the liquefiable fine sand. INTRODUCTION Recent earthquakes in Northern California and the Philippines have helped to emphasize the importance of geotechnical earthquake engineering. Ground failures and, in particular, liquefaction were responsible for the loss of many lives and millions of dollars worth of damage in both of the above mentioned earthquakes (EERI 1990; Wieczorek et. al. 1991). Studying the phenomenon of liquefaction is, however, difficult due to the fact that earthquakes occur relatively infrequently and are difficult to predict with any accuracy. As an alternative, dynamic centrifuge modeling can be used to study the effects of earthquakes on soil. The centrifuge permits small scale models to be tested in a controlled environment. Realistic scaled earthquake time histories can be applied to centrifuge models, and small scale instrumentation can be used to study the dynamic response. In particular, the centrifuge can be used to study failure mechanisms. The ability to study failure mechanisms makes the centrifuge a valuable tool for the geotechnical engineer; a fundamental understanding of the underlying mechanism of any geotechnical engineering problem is essential before more thorough investigations can proceed and analytical models can be developed.