May 15, 2020

AFT Participates in Possible World Record Drilled Shaft

Recently AFT took part in a big accomplishment on our Honolulu Light Rail Project on Oahu, Hawaii.

A possible record drilled shaft was installed by our client Legacy Drilling. The mammoth drilled shaft was 10-feet in diameter, drilled to an astonishing depth of 357.3 feet.

It was installed using an oscillator to place full-length temporary casing, excavation by hammer grab, and water as the drilling fluid. AFT’s Yue Xin, based in Hawaii, performed video inspection of the very deep excavation bottom using our AFT-SID (Shaft Inspection Device). Because the behemoth foundation relied on end bearing, the EOR required a robust base cleaning and video inspection to verify no more than ½” of bottom sediment. Due to the great depth, unconventional bottom cleaning methods were employed using a dredge pump normally used for channel deepening. Obtaining successful SID video feed from this kind of depth underwater required the AFT team to design a special umbilical cable. Our SID equipment engineering efforts rewarded the operation by efficiently confirming an acceptable cleanout method that met the stringent sediment criteria.

This is the deepest SID inspection AFT has ever done in company history.

Our involvement did not stop there. To verify the very challenging 900-yard concrete placement, post-construction CSL (Crosshole Sonic Logging) was done. With 10 access tubes going the enormous 357-foot depth, the same challenges with data feed had to be overcome. Unusually high signal gains were used to overcome long cable voltage drops. To everyone’s excitement, CSL results indicated an anomaly free drilled shaft.

From beginning to end, this was indeed an outstanding accomplishment by the construction and engineering team. It is something to be proud of for everyone involved.

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