Regional spotlight series: assessing the geological landscape in Queensland, Australia

Mainmark services Queensland with a dedicated team based in Brisbane, the Gold Coast and Sunshine Coast, and in Northern Queensland, with expertise in the residential, commercial, civil infrastructure and mining sectors.

While each region has its own unique challenges, Mainmark leverages its collective local expertise and skillsets to provide a range of specialised bespoke ground engineering solutions for customers, tailored to their specific needs.

Surf, sand and the impact of high-rise development

Queensland is affectionately known as the ‘sunshine state’ with the Gold Coast and Sunshine Coast offering a quintessential coastal lifestyle that appeals to home buyers and property developers alike.

The Gold Coast is renowned for its large-scale high-rise developments that are prevalent along the main beachside strip with old houses, originally constructed in the 60s and 70s, being knocked down to make way for multi-storey apartment buildings – some as high as 30 storeys or more. These sites often require deep excavation for basements and underground carparks, however, excavation within these tightly confined spaces can weaken surrounding soils and cause subsidence issues for neighbouring houses and apartment buildings, especially those built to the boundary.

Sites with unstable sandy and non-cohesive soils can be addressed either during or after construction using solutions such as Mainmark’s Permeation Grouting, a widely used low pressure grouting technique that can be used to support excavation, shore up adjacent structures where unstable ground may be a safety hazard, or provide additional ground bearing capacity to accommodate the increased load of a new structure.

While engineers may consider conventional piling and jacking techniques to re-level subsided buildings, these processes require the use of large heavy machinery. Site access is becoming increasingly problematic due to the Gold Coast’s urban density which has made piling an expensive and time consuming option. However, Mainmark’s advanced range of proprietary grout and chemical injection solutions, such as JOG Computer-Controlled Grouting and Teretek® resin injection, can be smart solutions for high rise residential and commercial buildings as cost effective, non-intrusive alternatives to traditional piling.

Building on reclaimed land and low lying flood plains

Poorly compacted land is also a growing concern for homes and businesses built on reclaimed land in the low lying marshy flood plains of South East Queensland where it is not uncommon for a 20m layer of soft, highly compressible soil to extend down from the surface. This issue can also create problems for commercial sites such as transport yards where the movement of heavy vehicles and shipping containers can put pressure on the ground beneath driveways and hardstands, causing subsidence. This was the case at South East Queensland Hauliers (SEQH), a wharf logistics business that was built on reclaimed mangroves. The company’s concrete hardstand area was ‘dishing’ in the middle due to water ingress from the high water table. The company engaged Mainmark to help improve the ground beneath the hardstand and re-level the concrete slab using JOG Computer-Controlled Grouting.

As population migration to the sunshine state grows, so too has the number of wetlands and agricultural farms, such as cane farms located near the Gold Coast, that have been developed into residential housing estates. While building on reclaimed land can bring enormous economic benefit to local regions, the construction process often requires ground improvement modifications prior to building to ensure the ground is suitable for construction. Failure to undertake appropriate ground improvement measures prior to construction can result in serious issues, leaving homes at risk of differential settlement. Mainmark has helped remediate numerous homes built on reclaimed land, including a single storey brick residence in Warner, Queensland where the property’s concrete floor had dropped up to 120mm. Mainmark was able to successfully re-level the floor using Teretek®.

The effects of wild weather in tropical North Queensland

As Queensland is a predominantly tropical state, the region is prone to extreme weather conditions which can cause havoc on building foundations. The issue is largely due to the prevalence of clay soils which swell during wet weather and shrink during extended dry conditions such as drought.

In some Queensland areas, the state’s tropical wet weather can cause soils to swell and shrink by up to 70mm throughout the year with Mainmark receiving many enquiries from homeowners worried about cracks that have appeared in the walls of their home as a result of such movement. The constant ground shift can cause serious cracking and structural damage with cracks becoming bigger and more pronounced the longer the dry spell continues.

Extreme weather not only affects homes but also infrastructure, particularly in North Queensland where Mainmark has seen an increase in demand for remediation work on culverts and bridges that have been damaged due to torrential rainfall. Underground culverts are vital for North Queensland’s road network as they allow the flow of flood water and runoff, however, sometimes the infrastructure struggles to cope during heavy rain events as water gradually compromises the culvert lining and causes voids to form around the culvert as surrounding soil is washed away. This was the case on a North Queensland windfarm, when two culverts located beneath an access road and an embankment were seriously damaged during a tropical cyclone. Mainmark was able to successfully restore the culverts’ structural integrity by injecting the area surrounding the culverts with Teretek® engineered resin.

Mainmark’s team addresses the geotechnical challenges of Queensland’s diverse geography, extreme weather and high density development by thoroughly assessing the underlying ground conditions to understand what is achievable. With nearly 30 years experience and intimate knowledge across the Queensland region, our highly skilled engineers and technicians assist homeowners, engineers and civil contractors to address a range of ground problems with innovative, state-of-the-art ground engineering solutions and methodologies that are non-invasive, efficient, cost-effective and environmentally inert.