Liquefaction is a costly phenomenon where soil shear modulus degrades as the generation of excess pore pressures begins. One of the methods to mitigate liquefaction, is the use of prefabricated vertical drains. Prefabricated vertical drains provide a drainage path to effectively mitigate the generation of pore pressures and aid in shear modulus recovery. The aims of this study were to define shear modulus degradation vs. shear strain as a function of excess pore pressure ratio; define the effects of prefabricated vertical drains on the behavior of pore pressure generation vs. shear strain; and to define volumetric strain as a function of shear strain and excess pore pressure ratios. A large-scale laminar shear box test was conducted and measured on clean sands with prefabricated vertical drains spaced at 3-feet and 4-feet. The resulting test data was analyzed and compared to data without vertical drains. The results show the effect of increasing excess pore pressure ratios on shear modulus and curves where developed to encompass these effects in design with computer programing like SHAKE or DEEPSOIL. The data also suggests that prefabricated vertical drains effectively mitigate excess pore pressure build-up, thus increased the shear strain resistance before pore pressures were generated. Regarding volumetric strain, the results suggests that the primary factor governing the measured settlement is the excess pore pressure ratio. This indicates that if the drains can reduce the excess pore pressure ratio, then the resulting settlement can successfully be reduced during a shaking event. The curves for shear modulus vs. cyclic shear strain as function of pore pressure ratio were developed using data with high strain and small strain which leaves a gap of data in the cyclic shear strain range of 0.0001 to 0.01. Further large-scale testing with appropriate sensitivity is needed to observe the effect excess pore pressure generation on intermediate levels of cyclic shear strain.



College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering



Date Submitted


Document Type





Landon S. Kinney, Kyle M. Rollins, shear modulus, pore pressure ratio, prefabricated vertical drains, volumetric strain, cyclic shear strain



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Engineering Commons