EVALUATION OF FIELD BASED LIQUEFACTION APPROACHES FOR CALCAREOUS SANDS USING SHEAR WAVE VELOCITY

The objective of this research is to assess the applicability of current field-based liquefaction approaches for calcareous sands. This is of importance because a.) there are many coastal communities in areas of high seismicity founded on calcareous sands (e.g. Haiti, Puerto Rico, Hawaii, Dubai, etc.), and b.) existing field-based approaches were developed almost entirely for case studies in silica sands. Recent earthquakes in Guam (1993), Hawaii (2006) and Haiti (2010) caused significant damage to coastal infrastructure, in part, because of liquefaction of calcareous sand deposits. Despite this field evidence, a review of existing research involving laboratory studies shows contradictory results as to how the cyclic behavior of these unique soils compares to silica sands. This research was accomplished by performing a combined in situ and laboratory-testing program. The in situ testing program was conducted at a site in western Puerto Rico, which is an ideal site for this research because of the extent of calcareous deposits throughout the island, the relatively high seismicity of the region and the high population density. The in situ testing program consisted of conventional drilling and sampling techniques, Standard Penetration Tests with hammer energy measurements, Cone Penetration Testing with shear wave velocity measurements and Dilatometer testing with shear wave velocity measurements. The laboratory testing program consisted of cyclic triaxial and cyclic simple shear tests with shear wave velocity measurements. This work builds upon existing research that shows that values of shear wave velocity measured iii appropriately in the laboratory and in situ can provide a link between laboratory testing and field measurements for characterizing the in situ behavior of soils that are difficult to sample, such as loose, uncemented, calcareous sands. The laboratory tests results suggests that the cyclic resistance - shear wave velocity relationship (CRR-Vs1) for the Monterey and Cabo Rojo sand appears to be soil-specific and independent of sample preparation techniques. Also, this relationship appears to be less sensitive to changes in shear wave velocity than those reported in previous studies. Overall, the Cabo Rojo sand exhibited higher resistance to liquefaction than the Monterey sand. The comparison of tests results for this study with existing field-based correlations suggests that the Monterey and Cabo Rojo sand lies outside the liquefaction resistance curves used in practice, which means that existing shear wave velocity field-based approaches would significantly overestimate the liquefaction resistance of both the Monterey and Cabo Rojo sand. There was reasonable agreement between the soil specific CRR-Vs1 and the CPT field-based approaches, however the soils at the site were so loose that definitive conclusions regarding the field-based approaches cannot be made at this time