Bulk infill grouting is typically used to infill large voids beneath the ground such as those left by abandoned mine workings. The stability provided from the grout further reduces the risk of void migration that could cause settlement or collapse at the ground surface to facilitate follow on construction activity.
Bulk infill grouting is normally carried out from primary temporary cased boreholes drilled within a predetermined square grid pattern across the treatment area.
An injection pipe is inserted into the cased boreholes and a weak cement pulverised fuel ash (PFA) stiff grout is pumped under pressure commencing at the maximum treatment point, compressive strength in the order of 1.0 N/mm2.
As the grout is pumped in, it gradually forms a bulb which overlaps with grout bulbs from adjacent holes to fill the worked seam. The degree of infill depends on the level of workings requiring treatment, secondary and tertiary treatment boreholes might be required to increase effectiveness.
Where multiple seams are encountered grouting commences from the lowest seam working to the surface. The grout infill process is repeated across the treatment area until the required consolidation is achieved. Mixes may include sand and bentonite as required and pea gravel is introduced to fill major voids and/or to form containment barriers.