Subsidence Caused by Weak and Unstable Ground

The ground beneath us is constantly shifting.

Subsidence is the propensity for upward, lateral, or downward ground movement, which can result in structures moving, sinking in one area or across the entire foundation footprint. During construction, ground instability can cause soil slippage which often requires stabilisation prior to conducting additional excavation for building foundations or swimming pools or building retaining walls. Once a building is already in place, ground instability can cause movement of the building or structure, resulting in internal or external wall cracks, inability to open and close windows and doors, sunken floors, and more.

Equally, weak ground cannot adequately support the weight of structures, thereby causing subsidence. Uneven floors, fractured floor tiles and wall cracks are all strong indicators of weak ground beneath the structure.

If a building or structure has subsided due to ground instability or weak ground, it is important to fix it right away, or risk further damage and potential hazards.

Download Our Guide to Subsidence

What causes weak ground and subsidence?

Subsidence can happen naturally as part of the earth’s constantly shifting crust. It can be exacerbated by issues such as soil compaction, loss of ground moisture, excessive excavation, or erosion. Ground instability causes subsidence and, often, the damage can seem to be reversed as the ground shifts back and forth over time.

	Soil Types: Clay soil can shrink, crack and shift during hot weather, and then expand during wetter weather. After a drought, sandy or fine gravel soil is much drier, and moves more easily which can impact building footings.		Excess Water: Leaking drains and water mains or burst water pipes can wash away or soften soil, causing it to compact under the foundation weight.
	Tree Roots: Neighbouring trees and shrubs absorb water using their roots causing movement in the soil as it soaks up moisture in the ground and grows.		Extreme & Seasonal Weather: Natural disasters such as flooding, drought and earthquakes affect soil moisture levels in particular clay where it compresses and expands resulting in excessive foundation movement. Erosion is another natural cause.
	Footing Systems: Flawed foundation design or inadequate compaction of soil during construction results in movement of the structure as it settles. Older properties may have shallower footings and foundations hence greater movement.		Renovation or Construction: Vibration caused by nearby construction or machinery activity such as drilling or piling, or heavy road traffic causing soil particles to shift and weaken the ground. Liquid, gas or mineral resources being removed from the ground affecting stability, can cause voids and sink holes.

How to fix subsidence?

Mainmark specialises in soil stabilisation and ground compaction, foundation repairing, and strengthening weak ground to improve support for buildings, roads, bridges and other on-ground structures. We treat the ground beneath them to raise, re-level, and re-support these structures.

There are a number of options available to stabilise the ground, such as soil and embankment stabilisation, and void or hole-filling.

For example, Mainmark’s Terefil is the most advanced structural lightweight polymer modified cementitious-based filler. It flows into spaces to fill voids, making it a fast and effective way to stabilise the ground. Compared to typical foams, the patented foam used in Terefil has increased stability, a greater lift thickness, and can be pumped greater distances. It’s a cost-effective and environmentally-inert option that suits a range of applications such as mass fill for large voids, tanks, and abandoned mines.

Permeation grouting can create ground cohesion before excavation. It’s the longest-established and most widely-used technique, which involves filling cracks, joints, and other small defects in non-cohesive soils, sand, or other porous media. It can stabilise the ground at depths of up to 60 metres.

Alternatively, Mainmark can inject our proprietary Teretek engineered resin solution into the foundation ground under a building’s footings. The resins expand together chemically, creating pressure. That pressure lifts the building back to its correct level. Then, if there are weak layers in the ground, continuing injection at deeper levels can resolve this by compacting the ground, densifying and strengthening it to increase its bearing capacity. In some soil conditions, Mainmark can increase the bearing capacity of weak strata by as much as 500 per cent.

In cases of weak ground, Teretek engineered resin also assures sub-grade stability under existing on-ground structures including buildings, concrete floors, driveways, roads, paved airport runways, bridge approach slabs, bridge abutments and more.

Mainmark’s methods are quick, precise, don’t leave a mess, and don’t generally require occupants to vacate a building while work is being done.

Various product warranties and Building Code requirements apply (please contact us to see which apply to your region or country).

Mainmark ground stabilisation and strengthening methods used on homes:

• Teretek
• Permeation Grouting
• Jet Grouting

For expert advice on identifying the causes of movement in a building, download a copy of ‘Foundation Maintenance and Footing Performance: A Homeowner’s Guide’ from CSIRO.