What do holes and voids mean?

‘Voids’ can mean anything from cracks and crevices, up to the huge volume voids caused by a major tunnel collapse.

Holes and voids can be either concealed or open cavities that present naturally as a result of erosion and geological changes, or due to building, mining, and other commercial or industrial ground activity. Ranging from small to large, all holes and voids underneath structures will contain air, and possibly water, which can cause instability. Filling these spaces can prevent wider damage to the ground, on-ground structures, and the surrounding environment.

Some holes and voids may need to be backfilled after operations cease, to prevent them becoming a hazard.

Filling holes and voids under mining and resources

Mainmark has solutions to resolve holes and voids affecting surface mines, underground coal mines, underground hard rock mines, mine shafts, major highways, tunnels, and more.

Utilising a variety of means, Mainmark is able to fill underground voids to stabilise strata in mines and tunnels, including routine and emergent void and cavity-filling of small to very large voids. A range of products may be applied for ground stabilisation and void-filling in all underground mining applications. Innovative resin injection and cementitious grout solutions work to minimise safety risks in these environments, controlling the potential for hazardous ground movement and instability in fractured and unstable rock.

Mainmark also offers a comprehensive range of polymeric, amino-plast and cellular/foam concretes for filling voids and crevices, enabling us to inject the most technically appropriate material to suit the issue. With access to and experience in the widest possible spectrum of materials from a range of industry-leading suppliers, products include polyurethanes, urea silicates, phenolics, amino-plast, cellular/foam concrete, micro- and ultra-fine cement-based grouts. Within each material type, there is a range of formulae differing in setting times, exothermic reaction temperatures, foaming and non-foaming abilities, overall strength and adhesive bond strength.

What causes holes and voids?

Holes are often dug in mining, building, and infrastructure works, while voids may develop over time due to leaks and weather eroding sub-soils underneath a structure. Something as simple as a leaking pipe may wash away surrounding earth, creating voids (or an empty space) around the pipeline. Filling holes and voids ultimately aims to stabilise mines, tunnels, buildings, bridge approaches, bridge abutments, and other operating or decommissioned structures.

Likely causes:

Construction holes and excavation

Earthquake and seismic activity, often resulting in liquefaction



Joints in culverts

Land slippage

Leaking pipes washing away sub-soils

Abandoned tanks and pipelines

Mining and commercial operations

Poorly compacted void fill

Water ingress

How to fix holes and voids

Mainmark has a number of void fill solutions such as polyurethane and cementitious grouting. We assess each situation to determine the best course of action and the best material to use. Smaller voids in underground rock strata are generally filled with a void filling foam or concrete void filler; a material like urea silicate or polyurethane resin that not only fills the void but also ‘glues’ the surrounding rock together.

When greater supportive strength is required, such as for retaining wall backfill or large voids, Mainmark’s Terefil® solution can be applied. A lightweight polymer modified cementitious-based void fill material, Terefil can be used for massive voids that require filling quickly and economically. This large hole filler material can also be used across a variety of void-filling situations, including retaining wall fill, abandoned fuel tanks, pipelines, and manholes, voids behind seawalls, and quick-support, easy-flow backfill for service trenches.

In areas where sandy soils dominate, a multi-stage approach may be required to fill voids safely. Large washouts and holes caused by coastal erosion and flooding can be stabilised using permeation grouting, before void filling commences.

Benefits of Mainmark’s methods to fill holes and voids:

Ensuring safety of abandoned mine sites

Fall recovery in mines of all types, including long-wall coal mines

Long-wall coal mining, pre-excavation planned preventative stabilisation of strata

Consolidation of fractured or unstable rock (‘Rock-gluing’) in walls and roofs

Effectively sealing against water and gas ingress

Down-shaft and cross-shaft plug-sealing

Addressing large and small cavities, tunnels, cracks and crevices

Addressing land slippage

Retaining wall and wing wall backfill

Efficient and economical backfilling of services trenches and manholes

Mainmark hole and void filling methods used for mining and resources: