Foundations and land subsidence

These soil processes can lead to tilting, settlement and damage to homes, buildings, roads and underground utilities. For homeowners, this type of damage directly affects living comfort, safety and property value. For municipalities, provinces and the national government, it results in increasing maintenance and repair costs.

As climate change leads to more frequent and intense periods of drought and extreme rainfall, the urgency of identifying and addressing foundation risks at an early stage continues to grow.

Nature and extent of foundation problems

Foundation problems arise from a combination of processes in the soil, the water system and the structure itself. Changes caused by drought, ground raising activities or fluctuating groundwater levels can trigger ground movements that affect foundations. The vulnerability of a foundation depends largely on its type: deep concrete piles are generally stable, whereas shallow foundations and short or timber piles are much more susceptible to movement. Ultimately, it is the interaction between the ground and the foundation that determines whether damage occurs and what the consequences are for buildings, infrastructure and public spaces.

Key soil processes that can lead to land subsidence and foundation damage include:

• Consolidation and creep: Land subsidence in saturated soils below the groundwater table caused by compression of the subsoil under load. This load may result from the structure itself, an added fill layer, or a lowering of the groundwater table (consolidation). Additional settlement may occur through the gradual rearrangement of the soil particle structure over time (creep).
• Peat oxidation: Peat decomposes when it is located above the groundwater table and is exposed to oxygen. This process is accelerated by warmer and drier conditions.
• Shrink–swell behaviour of clay: Clay shrinks during periods of drought and swells when conditions become wetter. These cycles can cause seasonal settlement and heave of several centimetres beneath parts of a foundation and generate significant stresses. The degree of susceptibility depends strongly on the properties and thickness of the clay layer, as well as on factors that determine how drying and rewetting affect the ground beneath a building.

Foundation risks and costs

In the Netherlands, there is no comprehensive overview of which buildings have vulnerable foundations or how the condition of foundations is evolving over time. To improve this understanding, Deltares has developed a foundation risk model that integrates knowledge on land subsidence, groundwater levels and climate-related impacts. The model indicates that approximately 425,000 buildings face an elevated foundation risk and, without intervention, are expected to reach the end of their technical service life within the next fifteen years. Around a quarter of these buildings are founded on timber piles, while the remainder are primarily supported by shallow foundations. Due to climate change, the number of buildings at risk is expected to increase further in the coming decades.

The total cost of foundation-related problems cannot yet be determined precisely, as uncertainties remain in both risk assessments and damage estimates. Without preventive measures, the number of buildings affected by foundation damage is expected to increase significantly. Total damages could rise to as much as €54 billion.

Commissioned by the Council for the Environment and Infrastructure (Rli), Deltares mapped the current state of technical knowledge on foundation problems, investigated their underlying causes, and examined the interaction between subsurface conditions and foundations. This knowledge forms an important basis for the Rli advisory report 'Goed gefundeerd' (in Dutch only) and provides insight into foundation risks, methods for assessing foundation condition, and possible mitigation and preventive measures.

Deltares is closely involved in the Dutch National Foundation Strategy (Nationale Aanpak Funderingen). Commissioned by the Netherlands Enterprise Agency (RVO), Deltares and TNO translated key knowledge needs into a Knowledge Agenda for an Effective Approach to Foundation Problems and we developed a framework for risk modelling. We also work closely with the Knowledge Centre for Land Subsidence and Foundations (KBF) to share expertise and develop practical tools for professionals.

Improved foundation data, a clearer distinction between foundation types, and an approach based on building typologies are needed to enable targeted prioritisation and the development of effective measures.

Knowledge of soil processes and climate impacts is also essential for accurately assessing foundation risks. Deltares therefore continuously works to improve data, models and understanding, enabling governments, professionals and residents to take informed action to reduce these risks.

Shrink–swell behaviour: an increasingly important damage mechanism

Shrink–swell behaviour of clay is a well-known and significant cause of damage in many parts of the world, including the United Kingdom, France, the United States and Australia. Until recently, shrink–swell processes were thought to be of little relevance to foundation damage in the Netherlands. This perception changed following the exceptionally dry summer of 2018, which led to numerous reports of damage to buildings founded on clay soils. Figure # illustrates the extent to which clay layers beneath foundations can contribute to shrink–swell movements.

Deltares is developing a risk assessment framework to identify the areas most vulnerable to shrink–swell effects and to determine which precautionary measures can be taken to prevent damage.

The research includes geotechnical laboratory testing of clay samples from across the Netherlands, field monitoring, and modelling of shrink–swell behaviour in and beneath foundations. It also draws on scientific knowledge and practical experience from countries where shrink–swell behaviour has long been recognised as a major issue.

Read the story - How we uncoverthe mysteries of expansive soils

At the Deltares Geotechnical Laboratory, we investigate the shrink–swell behaviour of clay samples from different parts of the Netherlands. We also carry out field measurements and monitoring at various locations across the country, including Rekken, Groningen and Arnhem. Our research examines the composition and structure of the subsurface, loading conditions, fluctuations in groundwater levels, soil moisture content and the influence of vegetation. We use this knowledge to develop and refine models that enable us to predict risks and assess the effectiveness of mitigation measures, among other applications.

Foundation damage mechanisms

Whether foundation damage actually occurs depends on several factors, including the foundation design, the loads acting on the structure, and the extent of environmental changes.

The main damage mechanisms are:

• Deterioration of timber piles: Timber pile foundations can be affected by fungi or bacteria when the piles become temporarily exposed to air as a result of lowered groundwater levels or drought. This can lead to degradation of the timber and a reduction in load-bearing capacity.
• Negative skin friction (downdrag): As the ground settles, the surrounding soil can ‘stick’ to foundation piles and exert additional downward forces. This effect is particularly significant when surface loading increases, for example due to the placement of additional fill material.
• Differential settlement: Soil processes such as drought, land subsidence and changes in groundwater levels can cause one part of a foundation to settle or heave differently from another. If the foundation is unable to accommodate these uneven movements, cracking and structural deformation may occur.
• Loss of bearing capacity in shallow foundations: Changes in groundwater conditions can weaken the soil beneath shallow foundations, reducing its bearing capacity and potentially leading to settlement.
• Damage caused by construction activities: Both direct ground deformations and indirect effects, such as changes in groundwater levels resulting from construction works, can cause damage to nearby foundations.

Infrastructure and public space

Infrastructure such as bridges, viaducts, quay walls, railways, cables, pipelines and sewer systems is also vulnerable to ground movements. Increasing loads, heavier traffic and more extreme variations in rainfall and evaporation can cause uneven settlement of foundations. This leads to higher maintenance costs, operational limitations and, in some cases, safety risks.

In areas with soft soils, public spaces such as squares, parks and streets also subside more rapidly. This affects the quality of the living environment and requires more frequent refurbishment and maintenance. For residents, this may mean that gardens, pavements and other outdoor areas need to be relevelled on a regular basis.
These developments underline the importance of an area-based approach and a thorough understanding of soil and foundation behaviour, enabling us to work together towards climate-resilient infrastructure and a safe living environment.

Future outlook for foundations

The latest KNMI climate scenarios indicate that drier summers and wetter winters will lead to greater fluctuations in groundwater levels. This increases the likelihood of land subsidence, ground heave and the exposure of timber piles to dry conditions. As a result, existing risk areas are expected to come under increasing pressure, while new vulnerable areas may emerge. Higher soil temperatures may also accelerate the decomposition of organic matter, causing additional settlement. In addition to these climate-related factors, developments in groundwater abstraction for drinking water and industrial use, as well as changes and interventions in major river systems, can influence groundwater levels and, consequently, the occurrence of foundation damage.

Measures such as rewetting, in line with the Dutch policy principle of water and soil guiding spatial planning, can help slow land subsidence. However, excessively high groundwater levels may introduce other risks, including a loss of bearing capacity in the soil. Modern foundations are generally better able to cope with these variations, but infrastructure, cables and pipelines remain vulnerable, particularly in areas with soft ground conditions. Because active groundwater management in urban areas has only a limited effect, further research and knowledge development—particularly regarding the shrink–swell behaviour of clay—remain essential. This will help identify where the greatest challenges are likely to occur and which measures are most effective in reducing future risks.