Soil types: the key to structural problems for homeowners

soil types cracked walls

Media Release On Behalf Of Mainmark

30 May 2018

Cracking walls and uneven floors are usually symptoms of a deeper problem. Many structural issues are the result of unstable ground or subsidence, so understanding what’s happening in the ground will help identify the cause of any structural effects that are happening to the building itself. Different soil types in particular give rise to different problems and require different solutions.

James O’Grady, Sales and Business Development Manager at ground engineering specialist Mainmark said, “Having an expert on hand who knows how soils behave can help make sure that when you solve one issue you don’t cause another. Getting it wrong can have disastrous results.”

“One home I recently visited was substantially damaged after a trench was dug beneath the floor to fix a leaking pipe. It was then back filled with sand,” he explained.

The property was built on reactive clay soil. The sand-filled trench created a channel that funnelled ground water under the home, saturating the clay and ‘heaving’ the entire building.

“The fix caused far more extensive damage than the original problem, all because the soil type hadn’t been considered.”

“Understanding soils is key to finding an effective, sustainable solution to structural issues, so it’s important to get advice from both structural and geotechnical experts before deciding on the right remediation plan for your situation,” said O’Grady.

The soil types commonly encountered in ground remediation work include reactive clay, sand and silt, fill, and organic soils. Each have different characteristics and require different solutions to address building subsidence issues.

Reactive Clays

Structural problems often result from varying moisture levels in reactive clay soil. It swells when wet and shrinks when dry causing subsidence in drier, or heave in wetter, areas. Over- saturated clay also loses its bearing capacity causing building footings to settle in the weakened soil and can sink even further if it dries out. It often gets oversaturated by moisture from broken sewers and storm water pipes, burst mains or sometimes even poor overland drainage.

Mainmark’s Teretek® resin injection solution is generally used to re-level buildings and remediate issues in foundation ground. It is ideal for smaller, discrete areas typically affected by reactive clay soils and works well to strengthen building foundations. It expands in the ground on application, both compacting and strengthening the soil. Teretek is applied at very precise and specific injection points, and is a less invasive process than traditional underpinning remedies, as it doesn’t require extensive excavation and subsequent backfilling.

Sand and Silt

Structures on sand and silt soils often experience settlement caused by ground water, a natural underground watercourse or a leaking sewer or storm water pipe. The finer grains are washed away leaving larger grains to settle, and the building’s footings and foundations become unsupported, compromising the structure above.

Permeation Grouting can remediate these problems by binding or ‘cementing’ the soil particles together. This stops the water flow, halting the migration of fine material, and strengthening the soil to support the structure above.

Alternatively, in very soft ground, Teretek resin injection can be an effective solution. Resin injection as an engineered solution is also suitable for mitigating liquefaction in sand and silt soils and has been successfully used to remediate earthquake damaged homes and commercial buildings in Christchurch, where it is recognised in the MBIE Module 5 in NZ for earthquake strengthening.

Fill

Fill is earthen material placed and compacted in a hole or depression. It can consist of soil, and can also include aggregate, rock or crushed construction waste. Structures built on fill are susceptible to the same issues as those on sand and silt, as fill is also prone to settlement, especially when water flows wash away finer material. Settlement is worse if the fill is poorly compacted.

Teretek resin injection is an effective remediation solution for fill soils. It works by binding the fill to provide extra strength and alleviate the problem of poor compaction. It is non-invasive, quick and cost-effective, as it can be applied in situ under existing structures, without the need for major excavation work, or manual compaction.

Organic

Organic soils, especially peat, are weak and highly compressible. This makes them prone to settlement as the weight of any structure causes compaction. Primary settlement decreases over time, but can total 100s of millimetres, resulting in significant structural issues.

When building on organic soils, it’s important to balance the total overburden by using soil substitution. Terefil®, a very strong yet lightweight cementitious fill, can be used to replace the top soil layer and provide a new-build platform. It can withstand significant pressure, maintaining its integrity under heavy loads, and is lighter than soil.

For more information and advice about how to address these types of ground problems, contact Mainmark on 0800 873 835 or visit www.mainmark.com.

Kim Viney at Write Away Communication + Events
Email: [email protected]

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