Blackfriars Shaft, London - Advances in Deep Jet Grouting-PPT Presentation

PPT Presentation

Pdf Summary

The Blackfriars Shaft project in London used deep jet grouting to stabilize granular soils and reduce groundwater ingress around a shaft beside a listed river wall and two gas mains.<br /><br />Designers recognized that borehole deviation and variations in soil conditions could leave untreated gaps between grout columns. To assess this risk, Keller used Monte Carlo analysis to estimate the number and size of gaps, the proportion of untreated soil, and the optimum column dimensions. Trial works then verified achievable column sizes, borehole deviation, and the effects of variable soils, while helping optimize the grouting parameters.<br /><br />The design incorporated verified column diameters, optimized borehole spacing, acceptable gap sizes for different soil types, and contingency infill columns. During construction, boreholes were surveyed, their positions reviewed, and grouting parameters adjusted as needed. As-built records were used to locate gaps and guide infill work.<br /><br />The perimeter was successfully grouted to a depth of 52 metres. The SuperJet system produced large columns in challenging ground conditions, and survey data validated the predicted gaps and enabled them to be filled with additional columns. The shaft was subsequently excavated successfully.<br /><br />The project showed that understanding achievable performance and quantifying likely shortfalls enables a more integrated design, targeted contingencies, and cost-effective solutions.

Keywords

Blackfriars Shaft

deep jet grouting

London

granular soils

groundwater ingress

Monte Carlo analysis

borehole deviation

grout columns

SuperJet system

construction excavation