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A DIRECT IN SITU APPROACH FOR EVALUATING LIQUEFACTION CHARACTERISTICS OF SOIL DEPOSITS

GRADUATE RESEARCH ASSISTANT: Wen-Jong Chang (graduated 2002)
COLLABORATOR: K. Stokoe

FUNDED BY: NSF CAREER Award

DESCRIPTION
This research project involves the development of an in situ testing procedure that directly evaluates the liquefaction characteristics of near-surface soils. The testing procedure entails dynamically loading the soil deposit using a large hydraulic shaker, called a vibroseis, and measuring the response of the soil with embedded instrumentation. The embedded instrumentation includes geophones and pore pressure transducers. The data from the instrumentation are used to evaluate the relationship between excess pore pressure ratio, shear strain amplitude, and number of cycles of loading.

Figure 1 shows the vibroseis, the reconstituted test specimen, and instrumentation layout used in this research.  The vibroseis was used to vertically vibrate the ground surface at 20 Hz and induce shear strains and excess pore pressure in the reconstituted test specimen.  Figure 2 shows a typical pore pressure ratio-time history obtained during dynamic loading.  Note the capture of both the hydrodynamic and permanent excess pore pressure by the transducers.  Figure 3 shows a family of pore pressure generation curves (ru vs. shear strain) for the reconstituted test specimen.  These curves can be used to predict the excess pore pressure as function of induced shear strain and number of loading cycles.

Figure 1a - Click on image to enlarge	Figure 1b - Click on image to enlarge
Figure 2 - Click on image to enlarge	Figure 3 - Click on image to enlarge

PUBLICATIONS

Rathje, E.M., Chang, W.-J., and Stokoe II, K.H. 2005. “Development of an In Situ Dynamic Liquefaction Test,” ASTM Geotechnical Testing Journal, 28(1), pp. 50-60.

Chang, W.-J., Rathje, E.M., Stokoe II, K.H., and Cox, B.R. 2004. “Evaluation of Effectiveness of Prefabricated Drains in Liquefiable Sand,” Soil Dynamics and Earthquake Engineering, 24(9-10), pp. 623-731.

Rathje, E.M., Chang, W.-J., Stokoe, K., and Cox, B. 2004. “Evaluation of Ground Strain from In Situ Dynamic Testing,” Paper No. 3099, 13th World Conference on Earthquake Engineering, Vancouver, Canada, August.

Stokoe, K.H., Rathje, E.M., Chang, W.J., and Cox, B.R. 2004. “Using a Large Hydraulic Shaker to Induce Liquefaction in the Field,” International Conference on Cyclic Behaviour of Soils and Liquefaction Phenomena, Bochum, Germany, April.

Rathje, E.M., Chang, W.-J., Cox, B.R., and Stokoe II, K.H. 2004. “Effect of Prefabricated Vertical Drains on Pore Pressure Generation in Liquefiable Sand,” 11th International Conference on Soil Dynamics & Earthquake Engineering and 3rd International Conference on Earthquake Geotechnical Engineering, Berkeley, CA, January, Vol. 2, pp. 529-536.

Rathje, E.M., Chang, W.-J., and Stokoe, K.H. 2002. “Direct Evaluation of the Liquefaction Characteristics of Soil In Situ”, 8th US-Japan Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures against Liquefaction, Tokyo, Japan, December.

Wen-Jong Chang (August 2002). "Development of an In Situ Dynamic Liquefaction Test," PhD Disseration, Univ. of Texas at Austin