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Wednesday, 27 November 2019 00:00cat

New pile monitoring system by Keller divisions

Written by  TheStructuralEngineer.info
One of the base grouted columns is tested using the new extensometers alongside traditional strand anchors One of the base grouted columns is tested using the new extensometers alongside traditional strand anchors

Two Keller divisions, GEO-Instruments and the Geotechnique, have been working together to develop a new, bespoke pile monitoring system on a prestigious project in the heart of the City of London.

They are on-site at 8 Bishopsgate carrying out monitoring and jet grouting works on behalf of main contractor Keltbray. The 8 Bishopsgate project is located next to the iconic Cheesegrater. Construction began in early 2019 and is planned for completion in 2022.

Keltbray is installing piles of diameters varying from 1.5 to 2.1 meters to a depth of 64 meters. The geology of the site consists of London clay and Thanet sand. These conditions require the piles to be base-grouted to increase stability and improve the bearing capacity. Keller has been employed to undertake the base grouting works, based on their extensive experience of similar projects. The process requires grout to be injected at depth, using high-pressure grout pumps. Subsequent uplift of the piles is monitored to judge the effectiveness and consistency of the base-grouting.

Usually, this uplift monitoring is done using an anchor strand inserted to the full 64-meter depth. The strand is then removed and re-inserted at the next pile position, requiring the use of a crane. However, the Geotechnique and GEO-Instruments teams came up with a new monitoring system installed alongside the anchor strand method. The system, which is still in its trial stages, uses multiple VW (vibrating wire) extensometers to precisely measure displacement. Data from the sensors is collected on-site at a logger then processed in custom software developed by GEO-Instruments for this application.

"Our aim is to judge how it compares to the traditional method as a more efficient, safer alternative," said Mihhail Lonkin, GEO-Instruments' monitoring manager.

When complete the tower will be 50 stories, 221 meters tall and provide 56,0000 square feet of offices, retail, and public space.

Source: Keller UK

 

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