This article is about causes of foundation settlement, settlement of foundation pdf, foundation settlement types, effects of settlement of foundation, differential settlement of foundation, uniform settlement of foundation and methods to reduce foundation settlement.
Foundation settlement refers to the downward movement or sinking of a building’s foundation. It occurs when the soil beneath the foundation is no longer able to support the weight of the building, causing the foundation to sink or settle.
Foundation settlement can lead to serious structural damage to the building, including cracks in walls, floors, and ceilings, as well as uneven or sloping floors. It is a common problem that can affect both new and old buildings and can be caused by a variety of factors.
What is foundation settlement?
Settlement is a term used to refer to the total vertical displacement that occurs at the foundation level of a structure as a result of soil deformation caused by the weight of the foundation structure. This phenomenon is primarily caused by a reduction in the volume air void ratio in the soil. The magnitude of foundation settlement is influenced by various factors, including the type of soil and foundation structure.
Foundations that are built on bedrock experience minimal settlement. In contrast, foundations built on other types of soil, such as clay, may experience more significant settlement. For instance, the Palace of Fine Arts in Mexico City has settled over 15 feet (4.5m) since its construction in the early 1930s, owing to the clay soil on which it was built.
However, most building foundation settlements are typically limited to measurements in millimeters or fractions of an inch. Settlement of a foundation can cause damage to a structure, particularly if the settlement occurs rapidly. This article aims to discuss various types of foundation settlement, their causes, and their expected effects on the structure.
Types of foundation settlement
There are generally two types of foundation settlement.
- Differential foundation settlement.
- Uniform foundation settlement.
1. Differential Foundation Settlement
Differential settlement is a phenomenon that occurs when different parts of a building settle at varying rates. This can happen due to differences in soil composition, loads, or structural systems within the building. When some parts of a building settle more than others, it can lead to distortion in the building’s frame, sloping floors, cracks in walls and glass, and issues with doors and windows.
Uneven foundation settlement can cause a building to shift out of plumb, resulting in the initiation of cracks in the foundation, structure, or finish. In fact, a majority of foundation failures are caused by severe differential settlement. To prevent this, it is important to ensure that the foundation is constructed with a uniform load-bearing capacity.
In conventional buildings with isolated foundations, it is generally acceptable for there to be up to a 20mm differential settlement between different parts of the structure. However, it is important to keep in mind that a total settlement of up to 50mm is considered tolerable for such buildings. Ultimately, it is crucial to monitor the settlement of a building over time and take appropriate measures if significant differential settlement is observed.
2. Uniform foundation settlement
Uniform settlement is a term used to describe the occurrence of foundation settlement at a nearly equal rate throughout all parts of a building. This type of settlement is most likely to happen when all sections of the building are resting on the same type of soil. Additionally, if the loads on the building and the design of its structural system are consistent throughout, uniform settlement is the expected outcome.
In general, uniform settlement does not have a significant negative impact on the safety of a building. However, it can have an adverse effect on the usability of the structure. For instance, it can cause damage to the sewer, water supply, and mains, resulting in potentially costly repairs. It can also result in doors and windows becoming jammed, making it difficult for occupants to enter and exit the building.
Therefore, while uniform settlement may not be a significant safety concern, it can still cause problems that affect the usability and functionality of a building. As such, it is important for property owners and managers to be aware of the potential issues that can arise from this type of settlement and take appropriate measures to address them.
Foundation Settlement Causes
Direct causes
Foundation settlement is primarily caused by the total weight of a building, which includes both the dead load and the live load. This weight is exerted upon the foundation, which can result in the gradual sinking or shifting of the structure over time. While there may be other contributing factors, such as soil conditions or inadequate construction techniques, the weight of the building is the primary direct cause of settlement. Therefore, it is crucial for builders and engineers to consider the weight and distribution of a building’s load during the design and construction phases to prevent or minimize foundation settlement issues.
Indirect causes
There are several situations where soil and rock can fail or become unstable, causing problems for underground construction and infrastructure. One issue is collapsible soil, which can lead to failed underground infiltration systems. Another problem is the yielding of excavation done near building foundations, which can cause structural damage.
Underground tunnels and mines may also fail due to various factors, including insufficient support or unstable geology. The collapse of cavities in limestone formations can pose a risk to nearby structures, while flooding can lead to undermining of foundations. Earthquakes can also cause settlement in the ground, potentially damaging buildings and other infrastructure. Finally, extraction of ground water and oil can cause subsidence and other problems in the surrounding area.
Components of Total Settlement of Foundations
Immediate settlement
Immediate settlement, also known as short-term settlement, typically occurs in coarse-grained soils with high permeability and in unsaturated fine-grained soils with low permeability. This type of settlement occurs over a short period of time, usually about seven days, and thus it is possible for it to conclude during the construction process.
Immediate settlement is primarily observed in soils that have the ability to quickly dissipate excess pore water pressure. Coarse-grained soils, such as sand or gravel, are known for their high permeability and therefore tend to experience immediate settlement. On the other hand, fine-grained soils with low permeability, such as silts or clays, can also experience immediate settlement when they are unsaturated.
Since immediate settlement occurs over a relatively short time frame, it is crucial to account for it during the design and construction process of a structure. By considering the potential for immediate settlement, engineers can ensure that the foundation and structure are built to withstand any settlement that may occur. With proper planning, immediate settlement can be effectively managed and mitigated, ensuring the longevity and stability of the structure.
Primary settlement
Primary settlement, also known as primary consolidation, is a geological process that can take a significant amount of time to occur, usually ranging from 1 to 5 years or even longer. This process is often observed in saturated inorganic fine grain soil, which is prone to settling under external forces. The primary settlement occurs due to the expulsion of water from the pores of the saturated fine grain soil, leading to a reduction in volume and an increase in density.
The primary settlement process is mainly driven by the physical properties of the soil, particularly its ability to retain water. As the water is expelled from the soil pores, the soil particles become closer together, leading to a reduction in the overall volume of the soil. This reduction in volume can result in significant settling, particularly in areas where the soil is weak and susceptible to deformation.
Overall, the primary settlement is an essential process that occurs naturally in many geological formations, particularly in areas where the soil is saturated with water. Understanding the mechanics behind this process is critical for engineers and geologists, as it can impact the stability of structures built on top of such soil formations.
Secondary settlement
Secondary settlement refers to the process of soil consolidation that takes place under constant effective stress. This type of settlement is commonly observed in organic fine grain soils. Unlike primary settlement, which occurs immediately after the application of a load, secondary settlement continues to occur throughout the lifespan of a foundation structure. This process can be likened to the phenomenon of creep in concrete, whereby the material continues to deform under sustained loading over time. Overall, understanding the process of secondary settlement is crucial for predicting the long-term behavior of foundation structures and ensuring their stability and safety.
Methods to Reduce Foundation Settlement
There are several methods to reduce foundation settlement, depending on the cause and extent of the settlement. Here are some of the most common methods:
- Soil stabilization: This involves treating the soil beneath a foundation to improve its strength and stability. This can be done through techniques such as soil compaction, chemical stabilization, or grouting.
- Foundation underpinning: This involves adding additional support to an existing foundation that has settled. This can be done through techniques such as pile driving, micropiles, or helical piers.
- Drainage improvements: Improving the drainage around a foundation can help prevent settlement by reducing the amount of water that accumulates and softens the soil. This can be done through techniques such as installing French drains or adding gutters and downspouts to direct water away from the foundation.
- Soil removal and replacement: In cases where the soil beneath a foundation is unstable or unsuitable for supporting the structure, it may be necessary to remove the soil and replace it with more stable soil.
- Structural reinforcement: Adding additional structural support to a building or structure can help prevent settlement by distributing the weight more evenly across the foundation. This can be done through techniques such as adding steel or concrete beams or columns.
Effects of Settlement of Foundation
The settlement of a foundation can have several negative effects on a building or structure. Some of the most common effects of settlement include:
- Uneven settlement: Settlement can cause a foundation to sink or settle unevenly, leading to uneven floors, walls, and ceilings, which can cause tripping hazards and make it difficult to close doors and windows.
- Cracking: Settlement can cause cracks to develop in the foundation, walls, and ceilings of a building or structure, which can compromise its structural integrity and lead to water intrusion and other problems.
- Damage to mechanical systems: Settlement can cause damage to mechanical systems such as plumbing, electrical, and HVAC systems, which can lead to leaks, electrical malfunctions, and other issues.
- Door and window problems: Settlement can cause doors and windows to become misaligned, making them difficult to open and close properly.
- Reduced property value: Foundation settlement can reduce the value of a property, as it can indicate potential structural problems and the need for costly repairs.
Causes of Foundation Settlement
There are several common causes of foundation settlement, including:
- Soil movement: The most common cause of foundation settlement is soil movement. This can occur due to natural factors such as soil erosion, soil compaction, or soil consolidation, or due to man-made factors such as excavation or grading.
- Water-related problems: Water can cause soil to become saturated and soft, which can lead to foundation settlement. This can occur due to factors such as poor drainage, plumbing leaks, or inadequate waterproofing.
- Poor construction practices: Foundations that are not properly designed, installed, or compacted can be prone to settlement. This can include factors such as inadequate footings, insufficient reinforcement, or improper grading.
- Geological conditions: The geological conditions of the area can also contribute to foundation settlement. This can include factors such as soil type, slope, or presence of underground water or voids.
- Natural disasters: Natural disasters such as earthquakes, floods, or landslides can cause foundation settlement by disrupting the soil and the foundation.
It is important to identify the cause of foundation settlement in order to address it effectively and prevent further damage to the building or structure. A qualified engineer or foundation specialist can help determine the cause of foundation settlement and recommend appropriate solutions.
FAQs About Foundation Settlement
1. What are the types of foundation settlement?
Foundation settlement is the downward movement of the soil or the foundation on which a building or structure is constructed. The types of foundation settlement are:
- Uniform Settlement: This type of settlement occurs when the entire foundation of a building sinks uniformly. This is usually caused by the compression of the soil or the ground beneath the foundation.
- Differential Settlement: When different parts of the foundation settle at different rates, it is called differential settlement. This can be caused by variations in the soil conditions, the load distribution, or the construction of the foundation itself.
- Tipping Settlement: This type of settlement occurs when one part of the foundation sinks more than the others, resulting in the structure leaning or tilting. This can be caused by uneven soil conditions, uneven load distribution, or inadequate foundation design or construction.
2. What are the causes of foundation settlement?
One of the primary causes of foundation settlement is the movement of soil, which can be due to changes in its moisture content. However, there are several other factors that can contribute to foundation settlement, including:
- Poor soil compaction: If the soil beneath a foundation is not properly compacted before construction, it can settle or shift over time, leading to foundation settlement.
- Expansive soil: Some types of soil, such as clay, can expand and contract depending on moisture content. This can put pressure on the foundation and cause it to settle or crack.
- Soil erosion: Erosion can cause the soil beneath a foundation to shift or wash away, leading to foundation settlement.
- Poor drainage: If water is not properly drained away from the foundation, it can accumulate and soften the soil, leading to settlement.
- Construction on unstable soil: If a foundation is constructed on soil that is inherently unstable, such as fill soil or organic soil, it can settle over time.
- Natural disasters: Earthquakes, floods, and other natural disasters can cause foundation settlement by shifting or destabilizing the soil beneath a foundation.
3. What do you mean by foundation settlement?
Foundation settlement refers to the downward movement of the soil or the foundation on which a building or structure is constructed. It is typically caused by the weight of the building or structure, as well as other factors such as changes in soil moisture content, poor soil compaction, and natural disasters.
Settlement can lead to uneven or cracked floors, walls, and ceilings, and can even compromise the structural integrity of a building or structure if left unaddressed. It is important to identify the cause and extent of foundation settlement and take appropriate remedial action to prevent further damage.
4. What are the components of foundation settlement?
Foundation settlement can be broken down into several components, including:
- Immediate settlement: This refers to the initial deformation or distortion of the soil that occurs when a load is applied to it. Immediate settlement occurs very quickly, often within the first few seconds of loading.
- Primary consolidation settlement: This is the gradual compression of the soil over time due to the expulsion of water from the soil pores. It is a slow process that can continue for years or even decades after construction.
- Secondary compression settlement: This is additional settlement that occurs over time due to the rearrangement of the soil particles and the gradual reorientation of soil structure. It can occur for many years after construction and can be exacerbated by factors such as changes in moisture content or repeated loading and unloading of the soil.