Ground Stability Assessment

Ground Stability Surveys

What is ground stability?

Ground stability refers to the ability of the ground to remain structurally sound and not undergo movement, such as subsidence, landslides or settlement, that could impact buildings, infrastructure, and natural landscapes.

The stability of the ground depends on various geological, hydrological, and man-made causes. Issues such as soil composition, groundwater levels, past coal mining activities, past brine pumping, quarry excavations, slope geometry and subsidence create potential hazards which may all contribute to ground stability concerns.

What is a Ground Stability Report?

A ground stability report is an evaluation of the potential risks associated with land stability issues. This assessment examines geological conditions, previous land use such as coal mining and environmental factors to determine whether an area is prone to unstable land and ground movement.

The findings of the assessment inform construction and development plans to ensure health and safety safeguards are adhered to and compliance with relevant regulations such as building regulations and permitted development rights.

A ground stability report is carried out by a geo-environmental consultant and typically involves a comprehensive desk study using geological information and maps.

Natural hazards and problems resulting from man made causes will be taken into account and a site investigation may be followed by geotechnical investigations such as borehole drilling and soil testing to assess the make up of the ground. The necessary data is complied into a ground stability report that can be presented to a local authority.

In cases where significant risks or potential hazards are identified, stability surveys may recommend mitigation measures such as soil reinforcement, drainage improvements or foundation modifications.

Why is a Ground Stability Report needed?

These assessments are crucial when considering a development project for several reasons:

1. Safety and structural integrity. Assessing ground stability issues helps prevent damage to buildings, roads, and infrastructure due to subsidence, soil slope failure, landslides, or other ground movements.
2. Regulatory compliance. Many planning authorities require ground stability surveys as part of the development approval process to ensure construction projects adhere to safety regulations.
3. Risk management. Identifying potential ground stability issues in advance helps mitigate financial and legal risks associated with property damage or liability claims.
4. Environmental protection. Ground stability surveys contribute to sustainable land use by identifying areas at risk of erosion, flooding, slope stability, subsidence from coal mining activity or natural hazards and suggesting appropriate mitigation measures.

When is a Ground Stability Report needed?

The following scenarios typically require professional reports:

• Applications for planning permission: A local planning authority may require a ground stability report before granting permission for a development site, particularly in areas where particular consideration must be given to known ground instability risks.
• Infrastructure projects: Large-scale infrastructure projects, such as roads, bridges, and tunnels, require land stability assessments to ensure long-term structural integrity.
• Property purchases: Homebuyers and investors often commission assessments when purchasing properties in areas with potential subsidence or past coal mining activity.
• Post-mining and brownfield sites: Areas with a history of coal mining activity, mine entries or contaminated land require thorough assessments to determine potential subsidence risks before redevelopment.
• Natural subsidence areas: Specific areas prone to natural hazards from subsidence, such as karst landscapes, clay-rich soils, running sand or coastal erosion zones, require land stability assessments for any significant construction.

Types of Ground Stability Report

There are several types of ground stability surveys to suit the specific risks and requirements of a project:

• Preliminary desk study:  Utilises geological data, historical records, and environmental databases (such as British Geological Survey and Coal Authority data) to identify potential risks of ground instability including natural hazards.
• Site investigation reports: Involves a site visit and inspection, borehole drilling, soil sampling, and laboratory analysis to assess ground conditions in detail.
• Geotechnical surveys: Provides in-depth engineering analysis, including soil mechanics, groundwater monitoring and stability modelling.
• Coal mining subsidence assessments: Focuses on assessing risks in former metal and coal mining areas, using data from the Coal Authority and the Mining Redemption Authority.
• Landslide risk assessments: Examines slope instability and terrain stability in unstable locations prone to landslides. The slope instability analysis uses geotechnical and hydrological data.

Are Ground Stability Surveys mandatory?

The requirement for a land stability assessment depends on location, land history, the type of development that is planned for the land and the local authority in question.

In the UK, a planning authority will often require stability assessments for developments in high-risk areas, such as former mining sites or regions prone to natural subsidence.

While not universally mandatory, assessments are strongly recommended for due diligence and to fully understand potential hazards when it comes to ground instability risks, particularly when acquiring land or property.

A Ground Stability Report and the Planning System

The UK planning system recognises land stability as a key factor in sustainable development. The National Planning Policy Framework emphasises the importance of considering ground stability risks in planning decisions. Local planning authorities must ensure that proposed developments do not increase risks related to land instability and that a site operator puts appropriate mitigation measures in place.

Natural Hazards

Several natural geological factors contribute to unstable locations and subsidence hazards in the UK, including:

• Clay shrinkage and swelling. Soils with high clay content expand and contract with moisture changes, leading to ground movement.
• Karst landscapes. Dissolving bedrock in areas of soluble rock such as limestone and chalk may develop natural cavities or sinkholes.
• Peat shrinkage. Peatland areas can experience ground subsidence as organic material decomposes and compacts.
• Landslides and coastal erosion. Steep terrain and unstable coastal regions are susceptible to slope stability issues and landslides, especially after heavy rainfall or human disturbances.

Who is responsible for land stability issues?

Responsibility for land stability varies depending on the specific circumstances:

• Property owners and developers play an important role and have the primary responsibility to assess and mitigate ground stability risks before construction or land use changes.
• Local Planning Authorities ensure that applications for planning consent account for ground stability issues and impose necessary conditions on development.
• The British Geological Survey provides geological data and mapping resources to help identify ground stability risks.
• The Coal Authority offers guidance and detailed subsidence risk assessments for areas affected by past coal mining.
• The Mining Redemption Authority addresses stability issues related to historical mining operations and provides remediation measures.
• Environmental regulators may intervene in cases where collapsible ground poses significant environmental or health and safety risks.

Assess Potential risks from Unstable Locations

Ground stability surveys are an essential part of land development, infrastructure planning, and property risk management. While not always legally required, they play a crucial role in ensuring safety, regulatory compliance, and long-term land use sustainability.

Data from the British Geological Survey, Coal Authority, and Mining Redemption Authority provides valuable insights into ground stability issues, helping stakeholders make informed decisions about land use and development.

As land instability remains a significant concern in the planning system, proper assessment and mitigation strategies are vital to minimising risks and safeguarding future developments.

If you are concerned about a land instability issue or need to present a ground stability report with a planning application, Arbtech has an ongoing relationship with a knowledgeable geo-environmental consultancy. They cover the UK and are adept at carrying out these assessments. For further information, complete the contact form at the top of this page.