The Impact of Soil Settlement on Foundation Stability


A stable foundation is essential for any building’s support system. Soil plays a critical role in providing strength and support to the foundation. Given this, understanding the fundamentals of foundation soil is evident.

Unfortunately, the soil underneath a building is not always firmly fixed. In fact, soil moves naturally on its own! Ground settling, also called soil settlement, is a natural process influenced by soil composition, moisture, and geological processes. Adding something heavy – like a building – forces air and water from the spaces between soil particles, altering that process.

This article explores how settling soil under and around the foundation impacts stability. We begin by covering definitions and an explanation of why it matters.

Understanding Soil Settlement Basics

Geotechnical engineering defines settlement as the downward movement of soil due to a stressor, which is often a heavy load on the surface. 

Settlement caused by a building can be divided into two categories; primary and secondary settlement. Primary settlement is the immediate compacting that occurs shortly after construction, as the weight of the building and its loads compress the soil. Secondary settlement is a gradual process associated with soil particles’ consolidation and rearrangement under constant effective stress.

Sometimes settlement affects the entire foundation evenly, and sometimes only one section of the substructure sinks. Uniform settlement, or when the whole foundation settles at the same rate, can create structural issues that impact a building’s functionality, safety, and appearance. The potential structural damage from uniform settlement is high but not nearly problematic when the soil settles unevenly.

When different parts of the foundation experience varying degrees of settling, it is called differential foundation settlement. Non-uniform settling exerts more significant pressure on the structure, which causes structural issues that pose a higher risk to the building’s stability and safety.  

Helping the ground maintain its structure and resisting movement is a high priority for building and repairing foundations. One of the essential elements that influence foundation settlement is soil characteristics.

Broken concrete foundation rubble are in the center of the frame with a construction worker's work boot standing on the settling foundation.
Differential settlement exerts more pressure on a foundation.

Types of Soil

Different soil types can have significant impacts on building foundations and soil settlement. The characteristics of the soil directly influence the foundation’s stability and the potential for compaction.

Clay soil has poor drainage and tends to expand when it absorbs water and contract when it dries out. This moisture-driven volume change can cause significant movement of soil, leading to cracks and structural damage in the building. As an expansive soil, building on clay requires careful design and planning.

Sandy soil has good drainage and is less susceptible to swelling or shrinkage. However, its low cohesion from being a fine-grained soil and load-bearing capacity may result in settlement issues if not correctly compacted during construction.

Silt soil has moderate drainage and can be prone to erosion. Its cohesive properties can lead to a higher risk of setting if not adequately prepared for building foundations.

Loam soil is considered the most desirable for building foundations. Its balanced sand, silt, and clay mixture offers good drainage, water retention, and load-bearing capacity, providing stable foundation support.

The suitability of a particular soil type for building foundations depends on several factors, including the building’s weight, the local climate, and the soil depth. Proper site investigation, soil analysis, and appropriate foundation design are essential to address potential settlement issues and ensure the stability and longevity of the building. Builders and engineers must consider the unique properties of each soil type to implement effective foundation construction methods and settlement mitigation.

A soil expert holds a clump of clay soil as she explains what makes it a poor soil for farming and foundations.

What Causes Foundation Soil Settlement?

Soil composition and type of soil aren’t the only things that cause settlement. Various factors, both natural and human-induced, can cause settlement.

Some of the common causes include:

Moisture Content: Changes in soil moisture can lead to settlement. Excess water content can cause soil to expand (swell), while inadequate humidity can cause it to contract (shrink). These volume changes can result in settlement issues. Related is consolidation settlement, where the water is gradually squeezed out from the weight resting above it.

Natural Processes: Geological phenomena like erosion, seismic activity, and sinkholes can alter the support beneath the foundation, leading to settlement problems. The influence of gravity falls into this category, as “soil creep” pulls any loose material down a hill.

A heavy piece of construction equipment dumps a load of soil into the back of a Caterpillar dump truck; a lightly clouded blue sky fills the background.

Human Activities: Human activities such as excavation, mining, or construction can disturb the soil, altering its structure. This is a common side effect of using heavy equipment in construction work before placing a permanent load (e.g., a building) on the site. 

Organic Material Decomposition: In certain soil types, the decomposition of organic material (such as tree roots or vegetation) can lead to voids forming beneath the foundation, resulting in a lack of support.

Changes in Groundwater Levels: Significant changes in groundwater levels can influence soil behavior. A high level of groundwater can soften the ground, increasing settlement potential, and a loss of moisture from drought can cause the ground to contract.

Consolidation of Soil: In areas with soft or compressible soils, consolidation can occur over time due to the weight of the building and its loads, resulting in gradual settlement.

Loading and Applied Loads: Heavy loads placed on the ground, such as large structures or heavy machinery, can compress the ground, leading to settlement.

Why is Differential Settlement So Dangerous? 

Soil settlement, particularly when coupled with differential settlement, can wreak havoc on a building’s foundation, leading to structural degradation that can compromise the stability and safety of the entire structure.

One of the most common consequences is the development of cracks in the foundation. As the foundation soil beneath the building settles unevenly, it exerts varying pressures on different foundation parts, causing the foundation to twist and crack. Cracks may appear horizontally, vertically, or diagonally, and their severity can range from hairline fissures to more significant gaps. Over time, these cracks can widen and propagate, changing from cosmetic signs to weakening the foundation’s ultimate bearing capacity.

Differential settlement can lead to portions of the building’s foundation settling at different rates. This causes the building to become un-level, resulting in uneven floors and sloping surfaces. As the structure adjusts, walls and beams may also become misaligned or tilted, further impacting the structural integrity of the building. In severe cases, a facility may tilt or rotate. Tilting can result in uneven weight distribution, putting additional stress on certain structural elements and possibly leading to further damage to structures.

Differential settlement can affect the building’s load distribution, leading to uneven stresses on the roof structure. Common signs include a sagging or bowed roof, which may lead to water ponding, leaks, and interior finishes and ceiling damage. 

Settlement-induced movement can cause strain on the building’s utilities and services. Plumbing pipes, sewer lines, and electrical conduits may shift or crack, leading to leaks and service disruptions. Sewer line misalignment may also cause drainage issues and sewage backups.

As the foundation settles unevenly, the building’s overall stability becomes compromised. Accumulating damages and vertical displacement can escalate into significant safety risks for occupants and visitors. In extreme cases, if settlement issues go unaddressed, the building’s structural integrity may be severely compromised, leading to partial or total collapse.

Understanding these potential damages and safety risks underscores the importance of timely intervention and preventive measures to address foundation settlement from excessive settlement.

Addressing & Preventing Soil Settlement

There are a range of strategies for addressing and preventing settlement. From site investigation and foundation design to ground improvement methods and regular inspections, these proactive measures play a vital role in safeguarding structures against the impacts of soil as it settles.

What happens when the upper soil layers cannot adequately support the building’s weight? A unique approach called a deep foundation can transfer the load of a building or structure to deeper, more stable layers below the surface.

A person using a shovel digs the soil in preparation for some foundation repair.

Regular inspections and monitoring are crucial for early problem detection. Spotting warning signs early can prevent bigger, more expensive repairs, and trained experts know what to look for. 

Ground improvement methods enhance soil properties and increase its load-bearing capacity. Some common examples of these techniques are compaction methods, soil reinforcement, soil stabilization, grouting techniques, and vertical drains. A thorough soil analysis often precedes these interventions because different methods exist for specific conditions, like soft and expansive soils. 

Soil drainage and moisture management is another area of expertise for addressing problems of settling soil. This specialty uses techniques to control and manage water in the soil to prevent issues like waterlogging, soil erosion, and excessive settlement. Tools and strategies like proper grading, surface drainage systems, subsurface drainage structures, and retaining walls manage water flow to help maintain the stability of foundations and structures.

Learn more >>> Foundation Repairs and Settlement Mitigation Techniques


Soil settlement is a critical aspect that profoundly impacts the stability of building foundations. Understanding the diverse soil conditions and their potential for primary settlement is essential for preemptive planning and effective foundation design. Hiring ground improvement specialists to address settlement issues promptly is vital to safeguarding structures from the damaging consequences of soil settlement, ensuring building longevity and structural integrity for years to come.

Tourists take photos of the Leaning Tower of Pisa, one of the most famous buildings with a tilting foundation from soil settlement problems.

Want to learn more about foundations?

We have lots more informative content! Let’s dive in!