Understanding Bulk Infill Grouting
Boreholes are first cased to rock head and drilled to the target depth in a predetermined grid pattern, covering all areas of the proposed development.
Grouting is carried out via an injection pipe inserted into the cased boreholes. Cementitious grout (typically containing pulverised fuel ash (PFA) and sometimes additives such as sand or bentonite, with a compressive strength of around 1.0 N/mm² depending on the mix) is pumped from the base of the borehole.
As pumping continues, the grout forms a bulb that overlaps with adjacent bulbs to fill the worked seam or void. The extent of grout infill is determined by the level and size of the voids or seams requiring treatment.
Secondary and tertiary boreholes may be required between primary positions to improve effectiveness. Validation or test holes can be drilled and pressure-grouted on completion to confirm treatment success.
Where multiple seams are present, grouting starts at the upper seam and progresses downward. The process is repeated across the treatment area until the required consolidation is achieved.
Alternative materials, including sand, pea gravel, or bentonite, may be used where necessary to fill major voids or form containment barriers.
