IN-SITU LIQUEFACTION RESISTANCE OF CLEAN SANDS OVER A WIDE DENSITY RANGE

The Paper describes a method of obtaining undisturbed samples of satur ated clean sand by freezing it in situ using a single freezer pipe. Te sts have shown that the method can yield high-quality samples that ret ain the density and the undrained cyclic strength of the sand in situ. Undrained cyclic triaxial tests were run on in situ frozen samples an d on samples obtained with conventional tube samplers. The liquefactio n resistance of the frozen samples of clean sands correlates well with a normalized N value of the standard penetration test over a wide ran ge of N values. The in situ liquefaction resistance of the clean sands estimated from the results of the undrained cyclic tests on the froze n samples is consistent with a criterion based on field performance da ta during earthquakes. For dense sands, the samples obtained with the tube samplers are looser and much weaker than those obtained by the in situ freezing method. The reverse is true for very loose sands. The c orrelation between relative density and normalized N value is fairly g ood for the in situ frozen samples, but very poor for the tube samples .