ILC ARTICLE

Mainmark reaches new level of subsidence repairs


Mainmark has revealed how its innovative JOG technology was employed to stabilise two buildings in London that suffered from very different subsidence issues.

The first building showed cracks as an indicator of ground heave damage, caused by tree roots and the expansion of unsettled soil. Traditional underpinning with a piled raft successfully stabilised the building with its active movement so that repair works could occur, but during the nine-month project it was revealed that an adjacent building was also impacted by subsidence.

Subsequent surveys identified severe distortion, which presented as a 140mm lift to one side, with 84 of the 240 points surveyed found to be outside the tolerance levels and National House Building Council standards. This informed the minimum and maximum lift specification, relevant gradient and tolerances.

Again the chartered engineer PAH Building and Construction relied on Mainframe, whose JOG Computer Controlled Grouting uses an advanced grout monitoring system with progress reports, allowing for fine-tuning to achieve a high degree of accuracy with minimal stress on separate sections of the building.

This meant the sections that were worked on were supported and precisely lifted using small, sequenced injections of high-mobility cementitious grout that is very fluid but fast curing.

In total, 70 cementitious grout injections were used beneath the block and beam foundations and upon completion only nine of the survey points were outside the NHBS standard tolerance level.

Tom Griffiths, PAH Building and Construction, said, “Mainmark certainly proved the success of its technology and what they are able to do. The benefits of their process – including time, overall cost, and impact on residents – far outweighs any other type of solution on the market.”

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