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.

Bulk infill grouting is typically used to infill large voids beneath the ground such as those left by abandoned mine workings. The technique is normally carried out from temporary cased boreholes drilled within a predetermined square grid pattern across the treatment area. 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. 

Common Uses

 

  • Treatment of abandoned mine workings including single or multi-seam coal, sandstone, ironstone, lead, chalk and fireclay workings
  • Treatment of abandoned mine shafts, crown holes and other mining features
  • Infill of open or collapsed voids
  • Infill of underlying unconsolidated deposits or fractured rock strata as a result of subsidence
  • Treatment of abandoned underground transport systems or drainage
  • Facilitating the installation of shallow footings and piles

Construction Process

 

Bulk infill grouting is normally carried out from temporary cased boreholes drilled within a predetermined square grid pattern across the treatment area. These initial boreholes are known as the “primary” positions.

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, in between the primary positions, might be required to increase effectiveness.

Where multiple seams are encountered or expected, grouting commences from the upper seam progressing down to the lowest seam. The grout infill process is repeated across the treatment area until the required consolidation is achieved. Other materials may be used as required, such as sand or pea gravel to fill major voids or bentonite to form containment barriers.

bulk-infill-grouting-illustration
Close ×