Shear Wave Velocity Testing Using a Seismic Cone Penetrometer in Bentonite Backfilled Boreholes in Hawaii

Seismic cone penetration test (SCPT) is an effective method to determine the shear wave velocity of in-situ subsurface materials. In Hawaii, highly variable subsurface conditions with boulder content and Intermediate Geo-Materials (IGM) are prevalent; therefore, this method can become very problematic and time consuming to perform. When these hard zones are encountered in the subsurface, the seismic cone penetrometer cannot advance into the material for testing until drilling methods are used to advance into and past the hard zones. In order to efficiently perform SCPT in these problematic conditions, especially IGM, a different method of shear wave velocity profiling using the seismic cone penetrometer in bentonite backfilled boreholes is presented. A side-by-side comparison study was conducted in natural ground and through a bentonite backfilled borehole to determine the effect of the bentonite on the shear wave velocity test results. Results of the side-by-side comparison are presented and discussed. Based on the results, the alternative method of SCPT in bentonite backfilled boreholes is an acceptable method in these difficult subsurface conditions.