Evaluation of cyclic resistance of providence silts using mini-cone penetration and standard penetration tests.

SPR-229-2292
Most areas of coastal Rhode Island are underlain by thick layers of non-plastic silt and it is important to
know if the existing standard-of-practice liquefaction potential evaluations (e.g. Robertson and Wride (1998) or
Seed et al. (1985)) are accurate. The objective of this research was to critically evaluate the applicability of CPT
and SPT based approaches to Providence silts. This was accomplished through a laboratory testing program
involving the URI mini-cone calibration chamber and cyclic triaxial tests to develop a new relationship between
cyclic resistance ratio and tip resistance for Providence silt. The new relationship was compared to the standard-ofpractice
liquefaction potential evaluation methods from the literature. There was good agreement between the
approaches which shows that the existing field-based CPT methods are applicable to Rhode Island silts. This is
consistent with previous RIDOT funded research on the liquefaction potential evaluation of silts in Rhode Island
(Bradshaw et al. 2007; 2007a; Baxter et al. 2008).
An attempt was also made to evaluate SPT-based approaches in silt using the mini-cone and laboratory
cyclic data. A qc/N60 correlation was evaluated from two loose silt sites in Rhode Island where SPT and CPTs
were performed adjacent to each other. The agreement between blow counts and tip resistance was very poor, most
likely due to the small number of tests and small range of in situ densities. Because of the poor agreement, it was
not possible to directly evaluate the SPT-based liquefaction evaluation approaches in the study.