Compaction Grouting Beneath Brownstone Buildings Founded on Soft Ground

This paper presents the design and installation of compaction grout columns beneath four brownstone buildings through fill and organics and founded on silty sands. Grouting was carried out in three bottom up stages in two rows of inclined holes. A column diameter of 3 ft was generally achieved in the organics. Diameters in the fill were more variable ranging from 1.2 to 3.6 ft. The buildings were monitored during grout injection. During grouting of the first five holes, detectable displacements up to 0.1 ins were observed in the facade walls and up to 2 ins in a floor slab in the basement. No significant upward displacements were observed during sequential grouting in holes at twice the spacing. However, grouting adjacent holes immediately after completing a previous hole resulted in significant displacements. A 14-h waiting period between grouting operations was necessary to allow dissipation of generated pore pressures and relaxation of the soils to take place. An observational approach was adopted where injection volumes were progressively reduced when either 0.1 ins of accumulated displacement or 0.024 ins per stage has been reached.