Any new build project or renovation may need a site investigation, and in the case of subsidence, it could be crucial to avoid expensive depreciation. The experts from Fastrack Site Investigations explain
The three main causes of subsidence are:
Clay Shrinkage: Clay soils can shrink when dry and expand when wet. This is enhanced by vegetation if it is nearby to a property and the roots undermine the building foundations.
Water leaks: Drainage or water main leaks can cause local softening of the ground.
Natural Settling: Over time, the weight of buildings and structures can compress the soil beneath them. This natural settling can contribute to subsidence
Other less common causes can include:
Groundwater Extraction: Over-extraction of groundwater can lower the water table. This often results in the ground collapsing or sinking.
Mining Activities: Historical mining, especially for coal, can leave voids underground. These voids can eventually cause the ground to subside.
A typical site investigation will take between two and four hours to complete. A ground investigation will comprise excavating holes to record foundation details. Trial holes are usually excavated externally to the property, but they can be internal if required. Boreholes are then drilled by hand or machine to examine the geology, collect soils for laboratory testing and to look for the presence of any roots. A drainage camera survey can also be completed to check the condition of the underground drainage network. Level and crack monitoring can determine how and when the building movement is occurring. In most cases the works are small scale, the work areas are reinstated to match existing surroundings on completion of the investigation.
Crack and level monitoring would be set up to determine whether there is a pattern to the building movement. In the case of clay shrinkage and swelling, a year of data will show both downward (clay shrinkage) and upward (clay heave) movement, however one seasonal change may be enough evidence to confirm the cause if backed up with site investigation data. Monitoring for a period following a drain leak repair or water main leak repair will determine whether a property has stabilised. Each subsidence case is treated individually, a monitoring regime is determined based on the likely trigger cause.
Soil testing allows us to determine the properties and bearing capacities of the soil so foundations can be designed correctly. We can determine things such as the water content, compressibility, plasticity, the ability of the soil to hold onto water and the particle make up. The testing allows us to calculate predicted settlements, the probability of heave occurring if vegetation is removed and shrinkage probability if new vegetation is planted. Chemical testing can allow us to determine the class of concrete that will be required for the new foundations.
To investigate the drainage network, a camera is pushed along the drainage runs to visually see if there are any defects. Hydraulic testing can be completed to determine whether the drainage system is watertight. This is done by blocking off the drain run with an inflatable bag or bung and filling it with water, any leakage and the rate that the water is seeping into the ground can then be seen and recorded.
Fastrack can review the planning conditions and carry out the necessary geotechnical and contamination investigations for planning approval. Often investigations are required so engineers can design new foundations or to prove that the site does not contain any hazardous materials that may cause harm to future users of the site.
Fastrack in conjunction with our partner consultants offer contamination surveys as a service. Desktop phase 1 surveys look at the history of sites and the likelihood of contamination being present. This then leads onto a phase 2 intrusive investigation to investigate the presence of contamination. The report will determine if there is anything hazardous in the ground that presents a risk to future workers and users of the site. A remediation method statement is then produced, which if followed, will make the site safe for its end users. Once remediation has taken place a second intrusive investigation is carried out to ensure the remediation has been completed and that the contamination has been removed to a level that is safe for the end user.
Reports can be factual or interpretive and are tailor made for individual clients and can include site location plans, trial pit logs, borehole logs, laboratory testing results with or without interpretation, root identification results, heave assessments, foundation options, bearing capacities and geological mapping data.
We are a second-generation family business, which has grown into a national firm. We work with national loss adjusters, insurers and developers, as well as individual homeowners, structural engineers and architects.
Our founders have held a constant presence in the geotechnical industry since the 1980’s, and still use their depth of knowledge and experience to support the business today.
Now headed by Managing Director, Martin Rush, and Finance Director, Louise Banks, Fastrack strive to maintain the ethos of a family firm, while occupying a substantial presence in the industry.
Our website www.fastrackgroup.co.uk gives a good company overview and details the services offered. If you have a project that we can assist with, then the best thing to do is either send the details to our email address enquiries@fastrackgroup.co.uk or call our office on 01245223033.
