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Boston mix

I would like to clarify and amplify the information given concerning the soil mixing and jet grouting treatment for the Boston Central Artery ('Stirring Stuff', Ground Engineering July 1999).

The soil stabilisation work, at a value of $73M (£46M) and some 50% of the main contract award, is understood to be the largest work of its kind ever undertaken in the USA. It comprised approximately 35,000m3 of shallow soil mixing of the upper soft organic sediments, 33,000m3 of jet grouting and 460,000m3 of deep soil mixing in clay to the glacial till below. It was carried out from land and over water using technology developed in Japan and Europe and re-specified for the blue clay of Boston.

The jet grouting columns were formed by a double-fluid system using conventional hydraulic rigs and Rodinjet tools to depths in excess of 40m. Incidental soldier pile walling, micro-piling and chemical grouting were also performed. The work was severely impacted in several areas by timber pile and granite block foundations for old bridges and marine walls. Conventional wet grab sampling and coring together with observation shafts and deep trial pits confirmed the acceptability of the insitu soil stabilisation.

Due to the unusually high proportion of geotechnical work, a specialist joint venture of Nicholson-Kajima-Seiko combined with Cashman/PKA for the project, under the management of Nicholson Construction Company, the US subsidiary of Italian foundation contractor Rodio. Complex construction sequences and difficult site logistics are a feature of the work that was awarded in August 1996 and will continue into 2000.

John Cockcroft

President, Nicholson Construction Company

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