EFFECT OF DEGREE OF SATURATION ON THE LIQUEFACTION STRENGTH OF IN-SITU SANDY SOILS

This paper presents the results of a series of field and laboratory tests designed to indicate the extent to which degree of saturation (S-r) affects liquefaction strength of in-situ sandy soils and also discuss the possibility of estimating S-r for in-situ soils based on longitudinal velocity (V-p). Many researchers have reported that liquefaction strength of sand is significantly affected by the degree of saturation, based mainly on laboratory tests on reconstituted samples. There are only limited data on the effect of S-r on in-situ soils. In order to investigate the effect of the degree of saturation on the liquefaction strength of in-situ sandy soils, a series of cyclic undrained triaxial compression tests were performed on high quality undisturbed samples recovered by the in-situ freezing sampling method before and after sand compaction using the sand compaction pile method (SCP). The longitudinal wave velocity of in-situ sandy soils was dramatically reduced to about 300 to 700 m/s after soil improvement. The degree of saturation of in-situ sandy soils after sand compaction was reduced to 87%similar to 95%. The liquefaction strength of partially saturated sandy soils after sand compaction increased significantly compared to samples that were fully re-saturated in the laboratory. The V-p of reconstituted samples was measured in the laboratory and was related to the pore pressure coefficient B-value. The V-p of undisturbed samples was also measured. Test results suggest that it is possible to estimate the Sr of in-situ soils from V-p.