Whether you’re moving into a new home, developing property, concerned about your building’s safety, or worried about insurance claims, the prospect of ground movement beneath foundations can be daunting. Terms like settlement, subsidence, and heave are often used interchangeably, but they refer to different processes. As structural engineers, we believe it’s vital for property owners to understand these differences and their potential impacts on their buildings.
What is Settlement?
Settlement is a natural process which occurs when the ground beneath a building compressed under the structure’s weight, causing a slight downward movement. Most structures experience some settlement in their early months, although it can also occur years after a building’s construction. Usually, the settlement of a building is uniform, and poses little risk to the property if it is properly accounted for in the building’s design.
However, in some cases, settlement can be differential, meaning one part of the building sinks more than another. Differential settlement can lead to cracks in walls, uneven floors, and doors or windows that stay closed due to the weight of the building above them not being evenly distributed. Factors contributing to differential settlement include variations in soil type, inadequate compaction, or unexpected loads placed on the structure.
What is Subsidence?
Subsidence refers to the downward movement of the ground beneath a building that is unrelated to the building’s own weight. Subsidence most commonly occurs when water is lost from the clay underlying the building, causing it to contract. This removal of water can be a result of warm/dry weather, and may also occur due to tree roots absorbing water from the clays around them. Subsidence can also occur due to mining activity, or due to leaking drains or rivers washing the soil away.
If unattended, subsidence can cause significant structural damage. Typical warning signs include diagonal or stepped cracks in walls, particularly around doors and windows, and gaps forming between walls and adjacent structures. Early diagnosis is essential to limit damage and manage repair costs effectively.
What is Heave?
Unlike subsidence, heave causes the ground around a building to rise. This is often due to clay soils swelling as they absorb moisture. This often happens when clay/clayey soils swell due to increased moisture levels, which can result from prolonged wet weather, the removal of trees that previously absorbed water, or the removal of heavy structures that previously compressed the soil. Without these factors restraining moisture intake, the soil can expand and push upward against the foundations.
Heave can also be caused by the freezing and expansion of groundwater in certain soil types. Signs of heave may include cracks in walls or floors, doors that become difficult to open, and uneven floors indicating upward rather than downward movement.
How Can Structural Engineers Help?
Understanding the difference between settlement, subsidence, and heave is critical for diagnosing structural issues accurately. A professional assessment by a structural engineer can identify the cause of cracks or movement and recommend appropriate solutions, which may include:
- Soil investigations
- Monitoring ground movement over time
- Foundation underpinning
- Drainage improvements
- Root barriers for trees
Ignoring ground movement issues can lead to escalating damage and costly repairs. If you suspect your property may be experiencing settlement, subsidence, or heave, it’s essential to seek expert advice promptly.
At Harban Redwood, our experienced team is here to help homeowners and property professionals diagnose and resolve structural concerns. Get in touch with us today to discuss any issues you’re experiencing, or to arrange a consultation.
