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Drilling and Bulk Infill Grouting

Bulk infill grouting is a ground stabilisation technique involving the drilling of boreholes into abandoned old mine workings and underground voids and then stabilising using bulk grout infill.

What is drilling and bulk infill grouting used for?

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.

What are the advantages of Drilling and Bulk Infill Grouting?

  • More cost effective than traditional methods such as removal and replacement
  • Reduces the risk of void migration that could cause settlement or collapse at the ground surface
  • Capability to drill through dense layers to treat low strength strata at depth
  • Treatment can be carried out within existing basement or locations with restricted access
  • Capability to drill through dense layers to treat low strength strata at depth

Common Uses

  • Infill of abandoned mineworking’s including single or multi-seam
  • Treatment of coal, sandstone, ironstone, lead, chalk and fireclay workings
  • Old mine shafts
  • Open or collapsed voids
  • Infill underlying unconsolidated deposits or fractured rock strata as a result of subsidence
  • To facilitate the installation of shallow footings and piles

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.

Van Elle Bulk infill grouting illustration
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