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.

Sea wall embankment

Sea wall void
filled and sealed

Retaining walls

Unique permeable Terefil®
backfills a retaining wall

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 of holes and voids

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.

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