What does ground instability or weak ground mean?

The ground beneath us is constantly shifting. Ground instability is the propensity for upward, lateral, or downward movement, which can be caused by natural factors like earthquakes.

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.

What causes ground instability or weak ground?

Ground instability 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. However, without soil stabilisation, damage to buildings, such as wall cracks, are prone to reappear. In infrastructure or at large industrial sites, embankment slippage can be an issue, leading to further erosion and damage. Ground instability should be mitigated where possible. Furthermore, a number of different things can cause weak ground, whether it’s a natural or man-made occurrence. For example, the ground may already be made up of loosely-packed materials such as soil or sand. Or human activities such as drilling and excavating can loosen previously-dense ground. Weak ground can happen over a large area or in smaller areas. Ground that is not uniformly weak will still lead to subsidence issues. Different types of ground are susceptible to different conditions. For example, clay is prone to contracting in drought conditions, gravel can be affected by nearby construction or heavy traffic, and dirt can be softened by excess water. Regardless of the cause, weak ground is reason to be concerned. Subsidence is the most common issue, which needs to be fixed to protect the building and its inhabitants.

Likely causes:

Water flooding the ground

Drought drying out soil

Washaways from broken pipes (such as water, sewer, stormwater drainage)

Poorly compacted fill

Liquid, gas or mineral resources being removed from the ground

Erosion

Earthquake and seismic activity

Tree roots, which can suck moisture from the ground

Vibrations caused by heavy road traffic or by machinery

Absence of an organised footing system – in very old buildings or in buildings with additions or alterations

Nearby excavation

Heavy loading

Deterioration of retaining walls

How to fix unstable and weak ground?

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 in your region or country).

Key benefits of Mainmark’s building levelling methods include:

Floors and buildings are brought back to level

Non-invasive techniques keep further damage to the building, and the landscaping around it, to an absolute minimum

We don’t tear up floors and excavate ground, so historical integrity remains unaffected

Internal and external wall cracks generally close up, leaving only cosmetic treatment (plastering, painting, and re-pointing brickwork)

Jammed doors and windows can usually operate properly again

Methods are effective on various foundations, such as, bluestone, brick and sandstone.

Mainmark building levelling methods used for Heritage Buildings: