How extreme weather can affect your home’s foundations

Teretek_resin_being_injected_zoomed

Extreme weather events, natural disasters and extended dry spells have a significant impact on the ground and subsequently, on building foundations.

Summer 2018/19 was the third-warmest ever recorded in Australia, and the hot weather pattern has continued, with January one of the hottest on record across both Australia and New Zealand.  While many of us have sweltered through record high temperatures, others have experienced ongoing drought conditions and a series of natural disasters, including floods, fires, monsoonal rain and cyclones, which have had a sudden and devastating impact on many homes and the wider community. After months of very little rain, numerous suburbs in South East Queensland have experienced dry ground conditions, and a reported increase in cracks and crumbling walls in homes.

How weather conditions affect the ground

The most common soil types in our region have different characteristics and responses to weather conditions and can seriously impact a building’s structural foundations. Houses built on loosely packed soils, sand and reactive clays can be particularly affected by seasonal or extreme rain, floods and drought.

  • Reactive clay expands and contracts during wetting and drying, resulting in cracking during prolonged dry periods and swelling under moisture.
  • Sand and silt is prone to settlement due to water flow which can wash away finer grains in the soil leaving larger grains to settle.
  • Fill often consists of soil as well as other materials such as aggregate, rock or crushed construction waste. When a significant volume of water works its way through fill and washes away finer particles, it can lead to settlement. This may initially present as a depression on the ground’s surface, and can be exacerbated by poor compaction and the general composition of the surrounding soil.

When the ground changes and can no longer support the building’s foundations, they  gradually move downwards, causing the home to sink in one area or across the entire footprint. This is known as ground subsidence.

The ground’s moisture level is a key consideration.  For instance, clay soils in temperate areas tend to be moist, making it susceptible to shrinkage during prolonged dry weather, leading to ground subsidence.  During a flood, fast flowing water can wash soil away creating erosion and sinkholes.  Both scenarios can cause serious foundation damage to homes, buildings and surrounding roads

The escalating impact of extreme weather is worldwide. After a record-breaking summer in the UK last year, heatwave conditions affected many building foundations as sustained warm weather caused water from subsoils to dry out, resulting in shrinkage. This has resulted in a subsidence surge with insurers receiving an unusually high number of related claims.

How to address subsidence

Thankfully, there are methods available to quickly, efficiently and cost-effectively treat foundations impacted by subsidence, using advanced solutions that offer an alternative to the traditional invasive and time-consuming method of concrete underpinning.

Mainmark’s proprietary resin injection solution, Teretek®, requires no excavation, creates minimal mess, and homeowners can often continue living in the property while the work is carried out.

Remember, when the signs of subsidence appear, seek expert advice from structural and geotechnical engineers or ground engineers to ensure you have all the information and facts needed to determine the right solution.

For more information and advice about ground issues and remediation solutions, contact Mainmark on 1800 623 312 in Australia, 0800 873 835 in NZ or visit mainmark.com.


By James O’Grady

James O’Grady is the Sales and Business Development Manager at Mainmark. He is a civil engineer with 25 years’ experience in structural engineering, construction materials and ground treatment.

What to do if your home is subsiding

What to do if your home is subsiding

Foundations are a structurally significant part of any building.

While solid, stable foundations help ensure your home has the support it needs for years to come, buildings can and will move. A fundamental reason for this movement is often due to changes in the ground under your home’s footings.

Many homes experience foundation movement due to changing ground conditions; this is known as subsidence. Regardless of where they live, homeowners share a common goal – to protect their biggest asset. That’s why it is important to identify the signs of subsidence early and act without delay.

The signs to look for

When the ground can no longer support the building, the foundations gradually move downwards, causing the home to sink in one area or across the entire foundation footprint. Every home is different and the signs may not be immediately obvious, so it’s important to know what to look for.

Pay attention to sinking or sloping floors, cracks in walls, paths and driveways as these may be the first signs of structural issues caused by subsidence. Windows and doors becoming jammed or misaligned, skirting boards separating from the wall or the formation of puddles around the perimeter of your home may also indicate foundation ground issues.

When to worry about cracks in walls

While smaller hairline cracks in walls are fairly common and not usually cause for concern, large cracks may appear because the property’s foundation has shrunk or lost its strength, causing all or a part of a building to sink.

Problematic wall cracks typically start at windows, doorways or corners of buildings, and are often zig-zag/stepped cracks in brickwork which usually follow the mortar lines. They are usually wider than 5mm (or half a centimetre) or big enough for you to insert your little finger in them.

Be aware of conditions beneath your foundations

Understanding what’s happening in the ground beneath your home, including the type of soil your house is built on, may be the key to identifying the cause of subsidence and possible solutions.

This is especially important for homeowners in areas where soil is known to be unstable. Houses built on loosely packed soils, old landfill sites, sand and reactive clays can be particularly affected by seasonal or extreme weather conditions, drought and floods. Historical mining activity can also impact properties in certain areas, like this home in New South Wales.

Structural problems often result from varying moisture levels in reactive clay soil which can shrink, or crack and shift during hot weather, and then expand during wetter seasons. Other problems can arise due to tree roots removing moisture from the soil or penetrating pipes to create underground leaks. Poor drainage beneath a concrete slab was the issue identified as the likely cause of the subsidence of a sunroom patio in a brick veneer home. The homeowner worried that the entire building would need to be replaced. Fortunately, after addressing the underlying drainage issues, the home was re-levelled within a few hours, at a fraction of the cost of replacement or other solutions.

Seismic activity such as earthquakes can cause soil to temporarily lose stability, known as liquefaction, which may then lead to subsidence. After a major earthquake in New Zealand, the owner of a large family home near Wellington noticed cracks appearing around door frames and along the ceiling joint as well as plaster detaching. Using a precise application method, the ground under the slab was treated via tiny injection points, to strengthen the ground. The cracks have since closed and the doors and windows have come back into alignment.

Subsidence can also occur when nearby excavation, tunnelling or drilling activity causes vibration and ground movement, impacting foundation stability. Whether it’s a neighbour adding an inground pool, new developments in the area or major infrastructure projects underway, it’s important to understand the cause of subsidence to treat the problem effectively. Remediation solutions can usually be applied with minimal impact, to protect the integrity of even the most fragile structures, like a heritage church in central Sydney where the foundations were impacted by deep excavation during a nearby infrastructure development project.

Simple and affordable remediation solutions

Today, there are innovative solutions available to help address structural issues which are non-invasive, fast and cost effective when compared to traditional underpinning methods. Homes can usually be re-levelled within just a few hours without the need for occupants to vacate the property or move furniture.

Ask an expert

If signs of subsidence have appeared, consult structural and geotechnical engineers or ground engineering experts. Mainmark has treated more than 30,000 sites throughout Australasia, from single-storey homes to large commercial buildings. The Teretek® engineered resin injection solution uses a “key-hole” approach, has been extensively tested for local conditions and comes with a 50-year product warranty, providing long-term peace of mind.

For more information and advice about ground issues and remediation solutions, contact Mainmark on 1800 623 312 in Australia, 0800 873 835 in NZ or visit mainmark.com.


By James O’Grady

James O’Grady is the Sales and Business Development Manager at Mainmark. He is a civil engineer with 25 years’ experience in structural engineering, construction materials and ground treatment.

Protecting critical infrastructure from the ground up

Road damaged by earthquake

How ground improvement can deliver long-term resilience to earthquake prone infrastructure

How can you make an earthquake-prone structure more resilient? This was the question posed recently by operators of a waste water treatment plant in Wellington, New Zealand, as they sought proactive measures to protect the asset following the introduction of The Building (Earthquake-prone Buildings) Amendment Act 2016 (EPBA) on 1 July 2017.

Wellington lies along an active seismic fault with the area recording approximately 31,300 earthquakes since 2017 alone[1]. While the 2010 and 2011 Canterbury earthquakes were not New Zealand’s largest seismic events, they caused the most damage and significant loss of life, leading to a renewed focus on earthquake engineering and the strengthening of structures.

Waste water treatment plants are categorised as Importance Level 3 of 4 (IL3), meaning that they must remain operational post a seismic event. Wellington’s water infrastructure facilities cater to around 146,000 residents and a large number of industries. The plants must be built to the highest engineered standards to ensure they are able to withstand seismic conditions and prevent wastewater from escaping into the ocean.

The decision by the asset operators to undertake seismic strengthening through ground remediation is a smart move. While there has been growing awareness about the interaction between building structures and foundation ground during an earthquake, there is only brief consideration for Soil-Foundation-Structure Interaction (SFSI) in current New Zealand guidelines. This is despite much of the structural damage that was experienced in the aftermath of the Canterbury sequence being due to poor performance of the ground rather than the strength of the buildings.

Following the Canterbury earthquakes, Mainmark’s ground improvement research trials in the Christchurch Red Zone showed that new resin injection techniques can demonstrably improve the density and stiffness of earthquake affected ground and increase the resistance of soils to liquefaction. This has led Mainmark to release Terefirm™ Resin Injection, a proven, non-invasive, ground improvement and liquefaction mitigation technique that can be easily applied beneath existing structures.

Validated by geotechnical testing, the Terefirm™ Resin Injection method is now included in New Zealand’s Ministry of Business, Innovation and Employment (MBIE) Module 5: Ground Improvement of Soils Prone to Liquefaction. This follows the internationally peer reviewed research conducted in partnership with the Earthquake Commission (EQC) and the MBIE, with the full research report now available on the New Zealand Geotechnical Society online library.

Terefirm Resin Injection is applied with surgical precision in a non-invasive process to densify the soil and increase liquefaction resistance. Geotechnical field testing is undertaken prior and post application to validate the ground improvement performance outcome.  Mainmark tailors the testing in line with the project requirements and the engineer’s specification.

During injection of the treatment zone, the low viscosity resin both permeates the soil to a limited extent, and also penetrates under pressure along planes of weaknesses within the soil profile. The material reacts soon after injection, rapidly expanding to many times its original volume. The expansion of the injected material results in compaction of the adjacent soils, due to new material being introduced into a relatively constant soil volume and thereby better protects structures from damage as a result of liquefaction in future earthquakes.

While the waste water treatment plant is the first asset of its kind to undergo proactive ground remediation using Terefirm Resin Injection, this solution would be highly beneficial for many other critical infrastructure sites located in New Zealand’s high risk seismic regions.

[1] https://www.theguardian.com/cities/2017/dec/11/earthquake-proof-city-christchurch-japan-colombia-ecuador


Theo Hnat

Theo is a R&D and Technical Manager at Mainmark. Based in New Zealand, Theo’s responsibilities include research in new technologies in ground improvement and liquefaction mitigation, structural risk assessment of existing structures, design, and analysis.

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Loaders in modern storehouse

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Christchurch House deep injection-Teretek

With unique climates and landscapes, homes in Australia and New Zealand face diverse ground conditions that can cause subsidence, affect building foundations and result in  structural issues.

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Mainmark presents STRAAM at International Conference on Bridge Maintenance, Safety and Management in Melbourne

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