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.

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 fill

Water ingress

How to fix holes and voids

Mainmark has a number of solutions to address void-filling such as polyurethane 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 material like urea silicate or polyurethane resin that not only fills the void but also ‘glues’ the surrounding rock together. Urea silicate is the natural choice for coal mines due to its lower exothermic reaction temperature. Alternatively, when greater supportive strength is required large voids can be filled with urea silicate expanding resin. Lightweight polymer modified cement is another option as the void fill material. Massive voids can be filled quickly and economically using a very low-density synthetic or cementitious-based fill material from our unique Terefil range. This solution can also be used across a variety of void-filling situations, including abandoned fuel tanks, pipelines, and manholes, voids behind seawalls, and quick-support, easy-flow backfill for service trenches.

Holes and Voids Under Mining and Resources

We offer a variety of means 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. Mainmark’s range of polymeric and cementitious injection products are used for ground stabilisation and void-filling in all underground mining applications.  These include innovative resin and cementitious grout injection solutions to minimise safety risks by controlling the potential for hazardous ground movement and instability in fractured and unstable rock.

We also offer 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. And within each type there is a range of formulae differing in setting times, exothermic reaction temperatures, foaming and non-foaming abilities and overall strength and adhesive bond strength. Terefil from Mainmark is our advanced engineered, light-weight, polymer modified cementitious based filler. Terefil creates a uniformly distributed cell structure encapsulated by cementitious materials, creating an engineered, low density void filling solution for solving and assortment of construction and mining challenges. Our applicators have years of experience working underground in coal and hard rock environments and are licensed to operate in NSW underground coal mines. Safety factors are of course paramount in all coal mine work, so approved, non-flammable materials with low exothermic reactions are essential. Urea silicate is the choice for coal mines due to its lower exothermic reaction temperature. In most cases, minimising downtime is the most important aspect. We concentrate on achieving the fastest response time possible, choosing applications and materials with the least impact and allowing the quickest recovery times for our clients.

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:

For more detailed information on our specialist hole and void filling solutions for Mining, visit our Civil & Mining section.