Drilled Shaft Construction and Some NDT Surprises at the Portal North Bridge-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes construction and quality assurance of drilled-shaft foundations for the new Portal North Bridge over the Hackensack River in New Jersey. The focus was on 36 main-pier and catenary shafts, built through soft deposits and glacial till into Passaic Formation bedrock. Construction used permanent casing, polymer support fluid, rotary drilling of rock sockets, bottom cleaning, and tremie concrete placement. A full-scale test shaft passed a bidirectional load test, exceeding design resistance.<br /><br />Extensive construction QA/QC included sidewall video, verticality and diameter measurements, and bottom-cleanliness inspections. These checks indicated sound construction. However, post-construction testing produced unexpected results. Crosshole sonic logging (CSL) showed poor signals in the upper, fully cased portions of shafts. Retesting weeks later improved results, but not enough to satisfy specifications. The presenters attributed the persistent signals to delayed concrete hydration and debonding of CSL tubes in the cold, tidal river environment. Tomography based on debonded tubes was considered unreliable.<br /><br />Thermal integrity profiling (TIP) also raised concerns. Temperature and calculated-radius anomalies occurred near the river and where shaft geometry changed, but interpretation did not adequately account for casing and geometric conditions. TIP results were therefore not used to accept the shafts.<br /><br />Cores from 16 of 36 shafts generally showed good concrete, with many strengths meeting or exceeding the 5,000-psi design value. Some low results were attributed to possible mishandling or poor specimen preparation. The investigation led to extensive coring and, in some cases, unnecessary chipping in difficult-access locations.<br /><br />The authors conclude that the installation method and construction QA/QC were robust, but NDT methods can be misleading under unusual environmental and geometric conditions. They recommend selecting tests suited to the application and establishing project-specific acceptance provisions where known limitations exist. The testing and resolution process added substantial cost and time.

Keywords

drilled-shaft foundations

Portal North Bridge

quality assurance

construction QA/QC

crosshole sonic logging

thermal integrity profiling

tremie concrete

permanent casing

bidirectional load test

Passaic Formation bedrock