Back Analysed Interpretation of Yield Pressure from CPT using Bq

Abstract

A sand and gravel quarry has been backfilled with clays and silts washed from the quarried materials. The quarry is now being repurposed for an industrial development. Prefabricated vertical drains and surcharge have been installed to consolidate the soft sediments. Settlement plates and vibrating wire piezometers were installed to track the performance of the surcharge. CPTs have been performed adjacent to the settlement plate / VWP installations in order to confirm thickness of soft soils and to assess their yield pressure in order to facilitate back analyses. A Medusa dilatometer test was also performed as an independent measurement. Correlation between the CPT and DMT showed that Nkt was much smaller than the normal range and the Nkt factor appeared to be consistent with Bq interpretations. Similarly, the coefficients used to interpret yield pressure lay at the high end of the range and could be justified through correlation with Bq.