Underpinning foundation: What it is,How it is done, when it is done?

Buildings and structures can become affected by failures of different sorts that are caused by several factors such as age, change in soil conditions, environmental effects, and change in use and purpose. One way or another that can require strengthening of foundations.

Do you have questions about the types and methods used in the underpinning industry? Have you planned to rehab or remodel your house and wonder if your home ever needs a foundation check? Do you want to know if your house may have a need for underpinning and when and how to do that?

We will look into the fundamental aspects of underpinning foundations in the following sections, providing you with valuable insights and guidance.

What is underpinning a foundation?

Underpinning is the process that is used to improve and strengthen existing foundations to increase the load-bearing capacity of a foundation. It is necessary when the building’s original foundation is no longer able to support it.

The loss of load-carrying capacity typically is the result of a change in the soil’s structure, whether brought on by the soil’s composition or an outside force such as groundwater table rise, erosion of soil, or seismic activity. Underpinning could be necessary also to accommodate extra loads due to additions to the building.

The work encompasses tasks such as creating a new foundation or relocating the existing one to a more stable and deeper level. To strengthen the foundation, various approaches are employed, such as increasing the depth into a stable soil layer, enlarging the foundation area to distribute loads more effectively, or stabilizing the soil to enhance its load-carrying capacity. The underpinning process is indispensable for a diverse range of structures, including buildings, bridges, masts, and others.

Underpinning is common in restoration projects where the faulty foundation is repaired. It is also a common practice in real estate property development where renovation and rehabbing of buildings is done to increase the value of the property and sell with high-profit margins.

In the real state sector development of rehab projects such as conversion(buildings use is changed), pop-top” renovations where more stories are added to a property), and condo conversion (property is converted to multiple units of condos, the weight of the buildings can exceed the foundation’s capacity. Those works usually require underpinning to account for the increase in building weight and to ensure the building’s safety.

Additionally, in adding basements to existing buildings underpinning might be necessary to create a supporting structure beneath the existing foundation, enabling ground lowering within the building to form the new basement.

How underpinning is executed

Ingeniously capitalizing on the wall’s ability to span a short length without support, the underpinning work involves selectively undermining specific localized sections called pins to erect a fresh foundation below them. In a methodical manner, new sections of foundations, basements, and walls are systematically constructed until the entire length of the existing wall is adequately supported.

Executing underpinning involves excavating the ground beneath the existing foundation, potentially leaving the foundation and excavated soil faces unsupported for a brief period. Depending on the foundation’s condition and the soil’s characteristics, temporary support may be necessary for one or both elements.

The excavation is typically limited to a relatively short length of the foundation, usually up to 1 meter. This approach relies on the stability of walls when excavated over such short distances, resulting in the foundation experiencing a temporary loss of support in comparison to its overall length.

A comprehensive assessment of the foundation and supported wall’s ability to “span” or “arch” across the excavation is essential, as well as evaluating the soil’s capacity to sustain the increased load at the excavation’s edges. Such assessments demand the expertise of a qualified professional, preferably a civil engineer or structural engineer.

Once the excavation has been safely managed in its temporary state, concrete is meticulously poured into the hole up to the underside of the original foundation. This process is methodically repeated in a prescribed sequence around the building until it is entirely re-supported on deeper, more robust foundations at an increased depth.

The careful orchestration of underpinning ensures the stability and durability of the entire structure, exemplifying the ingenious fusion of technical expertise and innovation in the realm of civil engineering.

Structure categories based on its age:

The procedures and remediation of the underpinning of foundations differ with the age of the structure. The reason is the structural systems of the buildings have dramatically changed over time for instance a lot of ancient buildings lack foundations. This remediation of underpinning also changes accordingly.

Ancient Structures: Age greater than 150 years

Recent Structures: Age between 50 – 150 years

Modern Structure: Age less than 50 years

The purpose of is underpinning

An experienced professional needs to be consulted since this is a crucial step in providing an underpinning solution. Nowadays underpinning is considered when all other options are considered and considered only as a last resort solution. That is because the work is risky that can cause permanent damage. So it should not be attempted as a DIY solution or without consulting experienced professionals.

The main reason for underpinning is to strengthen the foundation to prevent settlement or subsidence due to the movement of the foundation. The other application of underpinning is to increase the capacity of the foundations due to additions to buildings that are commonly done in the real state sector.

Building Conversion works

Buildings are frequently put to different uses for a variety of reasons, with remodeling and profit-maximizing sales being one of the most frequent. For instance, in condo conversion, the building is divided into multiple units of living rooms, kitchens, and bathrooms.

The Change in usage of buildings may require the strengthening of the foundation. The conversion of a residential property into a commercial space, or a residential room into a factory, can result in increased load because of additional users, pieces of equipment, and machines involved.

Underpinning may be necessary to accommodate the increased foot traffic and installation or operation of heavy machinery or equipment. Therefore, the foundation must be underpinned accounting for all additional loads.

Foundation remedial or protection

The first step in the underpinning process is to identify the reason for the movement of the foundation. The remediation measures are taken after carefully investigating the causes of the movement to arrive at an effective solution

The reasons for the movement of foundations could be:

-Age of building

-Mistake in design

-Problem in construction or workmanship

-Inadequate compaction or lack of leveling

-problematic soil that causes consolidation or subsidence

-Soil dehydration, which causes soil shrinkage and settlement

-Soil expansion brought on by excessive moisture or frost action, which causes the foundation and its components to be uplifted

-change in groundwater level

-Excavation of the foundation of a nearby building

-Damage due to seismic activity or floods, erosion

Remodeling of buildings by adding stories or basements

Remodeling of buildings may result in additional loads on the foundation. It is common to add stories in pop-top renovations or to add new basements to a building. In such projects “underpinning” is needed to improve and strengthen an existing foundation and allow for more load-bearing capabilities.

Particularly If you see cracks in a foundation or other parts of the building and plans for a taller building or a new basement, there’s a good chance that the property needs to undergo underpinning

According to ASUCplus guidelines for basement underpinning, the application of Underpinning by adding basements can be done for single-level basements or multiple-level basements. There are also different ways of underpinning basement foundations such as Mass concrete, reinforced concrete, and piling.

The addition of basements according ASUCplus, in retrofitting buildings is made in 3 ways

Cellar extensions

This type of retrofit construction is the simplest. The existing cellar or vault’s head height is typically increased by underpinning the existing walls in order to extend the existing foundations downward.

Single-level basements

Single-level basement construction entails adding a new basement level below the lowest internal floor or a garden.

Multiple-level basements

Multi-level basement construction entails adding more than one new level of basement below the building’s lowest floor or the garden.

Finally, if you are building a new structure but have discovered that it will be more cost-effective to reuse the existing foundation, underpinning may be required. The foundation will be strengthened through underpinning to ensure future use.

It is often employed when the building’s use or load-bearing requirements have changed or the existing foundation is deemed insufficient or unstable due to a variety of reasons, including soil subsidence, structural damage, or both.

When Is Underpinning NOT Recommended?

Underpinning may not be a solution to the presence of the signs of cracks or sloping of the building components. That is why the advice of an expert is a fail-safe way to an effective and secured underpinning solution.

Signs that may not necessarily mean underpinning is a solution.

1. What Causes Footing Movement?

Foundation movement that might reverse is caused by uneven changes in soil moisture content in clayey soils (also known as slab heave). These types of soil are called reactive clays and the resulting movement is reversible and may not need underpinning. Underpinning is not recommended for solving slab heave due to reactive clay movement.

2. Cracks: Check for cracks on your house’s walls, floors, or outside walls. Are they getting bigger or longer? If they stay the same for a long time, the ground might have settled, and you might not need underpinning.

3. Uneven Floors: If you notice that the floors in your house are not level and are leaning to one side, it could be a sign of foundation issues. But remember, not all uneven floors mean you need underpinning.

4. Doors and Windows Troubles: Are your doors or windows hard to open or close? Do you see gaps around them that are getting wider? It might be related to foundation problems, but underpinning isn’t always the answer.

Will Underpinning Always Fix the Problem?

The answer to this question depends on what kind of soil your house is sitting on and the type of underpinning you use. Not all types of underpinning can fix all foundation problems. Before deciding on underpinning, it’s essential to know if it will provide a permanent solution. So do not hesitate to consult an underpinning expert.

A proven least disruptive, reliable, and reversible solution for your foundation woes: screw pile or helical pile

One type of underpinning that has proven to be very reliable and versatile is called “screw pile underpinning.” It’s a method that can work well in various situations and provide a lasting fix if underpinning is needed. It does not pose a risk of damage and is reversible which means if it does not work, you can remove it and try another solution. But it works almost for most foundation problems and conditions.

Remember, it’s always best to consult a professional if you’re not sure about foundation issues. They can help you understand if your house needs underpinning or if there’s another solution.

Signs that indicate settlement of foundation

Determining whether your house is in need of underpinning requires careful observation and assessment of the structure. While it is always recommended to consult a professional, the following signs can indicate the need for underpinning.

Visible Foundation Cracks: Pay attention to size, number, and direction; horizontal or stair-step cracks are concerning.
Uneven or Sloping Floors: Significant or worsening slope suggests foundation settlement.
Doors and Windows Misalignment: Difficulty opening/closing, gaps, or misalignment point to foundation movement.

Sagging or Bouncing Floors: Spongy, sagging, or bouncing floors signal compromised foundation support.
Gaps and Spaces: Check for gaps between floor walls, especially near corners; these could indicate settlement.
Cracked or Leaning Chimney: Visible signs of foundation issues, are addressed promptly to prevent further damage or safety hazards.

Plumbing and Drainage Problems: Recurring leaks, water pooling, and slow drainage can relate to foundation problems.
Cracked Walls can indicate the presence of foundation movement especially if the cracks are horizontal, step, or diagonal.
Dry, Cracked Soil can cause foundation settlement

What to do in case you observe those signs

If you notice any of the above signs or have concerns consult a professional
Request a foundation repair professional for assessment.

Ask for a thorough inspection to determine the need for underpinning.
Make use of that some underpinning companies offer free foundation inspections.

Methods of underpinning

Generally, there are three main types of underpinning foundation methods:

Mass concrete underpinning is the older method, which involves excavating beneath the foundations, section by section, and filling with concrete. This is the cheapest but fairly disruptive method, but there are cases where it still offers the best option.

Underpinning using needle beams and bases, piers or piles, and mini piles. In such type of underpinning beams are used to distribute and carry the loads to deeper and strong soil layers. Mini piling is relatively a newer technique, in which piles are driven or bored through the weaker soil to a level of bedrock or stronger soil, allowing them to support the weight of the building.

The third type is Underpinning with modern methods such as push piles and helical piles. These types of piles are installed at systematic and selected positions and brackets are used to fix them on existing foundations to be underpinned. This underpinning technique has the advantages of being relatively quick and non-disruptive. Those types of methods pose the least risk of damage and are reversible because of the least disruption to the existing foundation and the surroundings.

The method chosen for underpinning depends on the type of structure, structural requirements, the ground condition, the severity of the foundation problem, and the depth of the foundation. The choice of piling technique used will be governed by the site layout, site restrictions, access, geology and hydrology, environmental and occupants as well as operational needs.

In order to utilize the best method suitable for a specific case of underpinning a wide range of plant and equipment, from mini piling rigs, specifically designed to gain access into inaccessible sites, to larger piling rigs for use in general open sites are used. That enables the construction of suitable foundation solutions for a variety of ground conditions.

A key aspect to consider is how much disturbance to the building the underpinning method will cause. As you will see below, some methods will cause extreme disruption to the ground floor and external areas of the building.

It is essential to stress that only qualified structural engineers, following careful research and calculations, should perform any underpinning work. A building’s structural integrity could be severely compromised or perhaps completely destroyed by improper implementation.

Therefore, when selecting and implementing underpinning methodologies, careful thought and professional competence are vital.

Underpinning in shallow foundations

(pit method)Mass concrete or reinforced concrete

This method has been in existence for centuries and is a common well proved and the traditional method of underpinning. The technique involves adding a new foundation that extends below the existing foundation to a stable soil stratum.

The soil is excavated in a controlled manner in sections called pins of 1-1.2m to form box-shaped voids. The excavated pit is filled with concrete in a specified order to make the new foundation under the existing one.

After the concrete cures, the excavation work continues to the next pin. In order to transfer the load from the old foundation to the new one, a new pin is provided by means of placing a dry sand-cement pack. This method does not require heavy machinery and is a low-cost method suitable for shallow foundations.

Beam and Base Underpinning

This method is a refinement of the mass concrete method and involves the construction of a concrete or steel beam above or below the existing foundation. The purpose of the beam is to redirect the weight of the structure onto several mass concrete or steel bases placed at strategic positions. The positions and the type and size of which depend on the ground conditions and the type of building and the size of the affected surrounding area.

Underpinning by cantilever needle beam method

The cantilever pit method of underpinning, an extension of the pit method, is suitable for cases where foundation extension is required on a single side and the building features a robust interior column. This method offers advantages such as faster implementation than traditional approaches, requiring access from just one side, and exhibiting a high load-bearing capacity. However, there are drawbacks, including the uneconomical excavation when dealing with deep existing foundations and limitations in access that restrict the use of needle beams.

Pynford underpinning

Pynford Underpinning: Strengthening Foundations with Precision

In the world of construction and structural engineering, ensuring the stability and safety of a building’s foundation is paramount. When faced with the challenge of a foundation resting on soil with low bearing capacity, the Pynford underpinning technique emerges as a reliable solution. This method not only addresses the issue at hand but also ensures a continuous and robust support system, thanks to its unique approach.

At its core, Pynford’s underpinning involves a meticulous process that allows a structural needle to seamlessly traverse the walls, providing enduring reinforcement.

Let’s delve into the intricacies of the Pynford Stool Underpinning Technique to understand its distinctiveness.

1. Creating Stool Sitting Areas: The process commences with the creation of designated areas on the wall to accommodate steel or precast concrete stools. These stools act as the foundational pillars for the underpinning process.

2. Stool Insertion and Securement: Steel or precast concrete stools are inserted into the designated areas, and effectively secured to the underside of the brickwork. This step establishes a secure base for subsequent stages.

3. Selective Brickwork Removal: A calculated and controlled removal of brickwork is executed between the pinned stools. This strategic removal ensures that the wall is propped on the firmly anchored stools, offering immediate support.

4. Reinforcement Placement: To fortify the underpinning structure, additional reinforcement is meticulously fabricated and positioned around the pinned stools. This reinforces the stability and resilience of the newly established foundation.

5. Beam Casting and Formwork: A critical phase involves erecting formwork and casting beams. These beams are carefully constructed to provide supplementary load-bearing capacity to the foundation.

6. Curing and Integration: Once the formwork is removed, the cast beams undergo a curing process, allowing them to attain optimal strength. Subsequently, the beams are securely fastened to the underside of the wall, completing the underpinning procedure.

Ideal Solution for Unstable Foundations

Pynford underpinning stands out as an ideal solution when the existing foundation’s soil exhibits poor bearing capacity. This method’s effectiveness lies in its ability to seamlessly traverse the walls, providing continuous reinforcement. The multi-stage process, from stool insertion to beam integration, showcases a meticulous and calculated approach that guarantees the structural integrity of the building.

Jacking underpinning

Jacking in underpinning is a specialized technique used to strengthen and stabilize shallow foundations of buildings or structures. When the existing foundation is deemed inadequate due to factors like soil settling, ground movement, or changes in load-bearing requirements, jacking in underpinning comes into play. This process involves strategically inserting hydraulic jacks beneath the foundation and incrementally lifting the structure to relieve pressure and create space.

As the structure is raised, new concrete or steel piers are inserted to provide additional support at deeper, more stable soil layers. This innovative method ensures enhanced structural integrity, preventing further subsidence and ensuring the longevity and safety of the building.

Underpinning in deep foundations

Pile and beam underpinning method

In this method, a pair of mini piles are installed at either side or at the opposing sides of the existing wall to be supported. A subterranean pocket of brickwork is removed and a reinforcement cage is passed through the hole to be joined to the piles and concreted.

Pile and cantilever beam Method of Underpinning:

This method is the type of pile and beam underpinning but the construction is undertaken from the exterior. This method enables avoidance of the removal of internal floors and fixtures. This reduces the cost and makes the work more convenient. This method can be performed in conjunction with screw piling.

Piled raft underpinning:

This system of underpinning is used when the whole property has been affected by subsidence. All floors need to be removed and mini-piles need to be constructed before pockets of brickwork can be taken out for the reinforcement to be placed under an engineer’s instruction. After inspection, the modifications are concreted to complete the underpinning.

Jack Pile Method of Underpinning:

In this type of underpinning steel sections are hydraulically jacked into the soil up to a stable soil is reached. The method is less costly than traditional methods when the depth of good bearing capacity soil is large. The pile depth could be adjusted to suit the existing underlying soil conditions, thus it is adaptable. The method is nonintrusive, vibration-free, silent, and versatile. It offers immediate load transfer thus minimizing the cost of construction.

The piles can be installed in a controlled and accurate manner using this method, ensuring that they achieve the necessary depth and load-bearing capacity. By immediately supporting the structure above, the jacking operation stops additional settlement and maintains structural stability during the underpinning procedure. There are patented jack pile underpinning systems today such as ram jack system.

Push piers underpinning

Push peris are pipe sections typically 30 inches long and comprised of hot-dipped-galvanized steel, with a maximum load capacity of 68 thousand pounds.

These are hydraulically driven into a load-bearing stratum and attached to the footing of the structure with a remedial bracket. Push piers offer a long-lasting solution to address foundation issues and prevent further structural damage.

Helical Piers underpinning

Helical piers consist of sections of square or round tubes typically 30 inches long that have a screw-like bottom part that is driven into the load-bearing layer of soil. They are galvanized for corrosion protection. Helical piers are driven into the earth by screwing with motor drives that apply prescribed torque until the desired depth is reached. The piers are attached to the footing of the structure with a remedial bracket. Helical piers offer a permanent underpinning solution and lifting or leveling of the settled foundations. Helical piers are the most preferred type of underpinning that can easily be applied to any underpinning works.

Slab pier underpinning

This is used to stabilize a slab foundation affected by settlement. Slab piers constitute interlocking steel tube sections that are driven deep in the soil to a stable stratum. The tubes are installed by cutting holes in the slab and they are fixed to the sides of the slab by adjustable brackets. The tubes are galvanized steel and therefore corrosion-free. Moreover, they offer the opportunity to lift the slab to its prior state.

Helical Tiebacks underpinning

Helical tiebacks are square galvanized steel tubes with helices or screws at their end. They are used to support, strengthen, anchor, and straighten retaining walls or bowed basements. The tubes are screwed by simple motor screws that apply torque to drive the pieces into stable soil.

Columns underpinning

In the process of column underpinning, the connection between the existing column and the new foundation is a critical aspect. This connection is typically established using specialized steel collars or brackets that securely link the column to the newly constructed support. These collars are designed to evenly distribute the load from the column to the new foundation, ensuring stability and load-bearing efficiency.

Key takeaways

The traditional underpinning of the mass concrete method is the cheapest, simplest, and most common way of underpinning.

Traditional piles require large space and access, are more disruptive because of more excavations and grouting works, and are more costly.

Minipiles are comparably less disruptive, applicable to a variety of soils, have high load capacity, are applicable in tight access conditions, have minimal excavation, and provide cost-reduction

Push piers and helical piers are types of mini piles that offer the least disruption of all other methods, are applicable in tight access conditions, are clean install because of no grouting, and no excavation, and provide cost reduction and immediate load testing

Minipiles also serve as friction piles while push and helical piers serve only as end-bearing piles.

Minipiles in underpinning

The minipile underpinning method is suitable when transferring foundation loads to strata over 5m away, adaptable for variable soil, when there is restricted access, and environmental pollution concerns. It involves driving 150-300mm diameter piles, augured or steel-cased. Mini piling is a variation of traditional piles with a narrow diameter. This makes them light and inexpensive, but still able to support a considerable load to 250 tons.

Drilled grouted hollow steel section micro piles: The underpinning micropile

This type is regularly used for underpinning unstable/distressed buildings and on overhead transmission line projects to enhance or found the tower structures. They are installed using rotary percussive drilling techniques. The bore’s stability is maintained by the grout flush, which is pumped through the center of the steel bar as the pile is progressed. The steel hollow bar is advanced into the ground using sacrificial drill bits selected to suit the ground conditions.

This technique is suitable for use in all ground conditions and is not susceptible to issues relating to groundwater. It is particularly effective in granular soils where the geotechnical capacity regularly exceeds those calculated and achieved by more conventional methods.

Alternatively, especially if there’s limited headroom, sectional auger mini piles can be used. This involves boring down and adding multiple flight sections as you go. Depending on the soil’s stability, the sections can either be removed or left in place while pouring the concrete in. Other mini pile types are rotary bored mini piles and driven mini piles

One of the standout features of mini piles is their adaptability across a wide range of soil types. Whether the project involves firm ground or softer strata, mini piles have proven their ability to perform reliably. They find particular utility in underpinning or strengthening existing structures, both internally and externally, allowing for innovative solutions even in challenging retrofit scenarios. Moreover, they excel in slope stabilization, constructing retaining walls, and resisting hydrostatic uplift pressures. This flexibility makes minipiles a valuable tool in the arsenal of modern foundation engineers.

The advantages of minipiles extend beyond their versatile application. One of the standout benefits is their ability to work in restricted conditions, including low-headroom spaces. This characteristic is particularly valuable when working within existing premises or cramped construction sites. Furthermore, their virtually vibration-free operation minimizes disturbances to neighboring structures and ongoing operations, contributing to a more harmonious construction environment.

Minipiles exhibit impressive penetration capabilities, enabling them to bore through masonry or concrete foundations with ease. This is especially crucial when extending the pile toe and increasing capacity, demonstrating their ability to work seamlessly in conjunction with other construction elements.

minipile drill rigs in various sizes can be used ensuring adaptability to different site conditions. These rigs are not only versatile but also environmentally conscious. Some rigs are equipped with remote power packs to minimize noise and fumes, particularly advantageous when working in enclosed spaces.

Underpinning using soil stabilization

Alternatives to Underpinning

Underpinning involves as its name implies strengthening or reinforcing the foundation directly. So if we face a failing foundation because of settlement or other reasons, do we have other alternatives? Yes, perhaps the solution is another than underpinning because nowadays the work is considered a last resort as it is associated with the risk of damage to the building as well as adjoining property.

One alternative is the stabilization of the soil which aims to strengthen the soil by changing the chemical, physical, or environmental characteristics of the soil. Check our post on ground improvement methods and stabilization of soil by injection of foam resin.

The soil is strengthened by methods such as grouting of cement or lime materials or by novel materials called geopolymers which are urethane-based chemicals that expand – such as Polyurethane.

Those methods offer less cost, and time and are less risky, however, the downside is that they are not permanent solutions to your problem. Mudjacking and resin injection also are not effective for expansive clays as the nature of the clay is not altered by their application.

Mudjacking

Mudjacking, also known as slab jacking or pressure grouting, is a foundation repair technique aimed at restoring and stabilizing sunken or uneven concrete slabs, such as sidewalks, driveways, and basement floors. This method involves injecting a specialized slurry mixture, often composed of cement, soil, water, and additives, beneath the settled concrete.

As the slurry fills voids and compacted areas, it exerts pressure, raising the slab back to its original level. Mudjacking is an efficient and cost-effective way to address minor foundation settling issues, providing renewed support and evenness to concrete surfaces without the need for extensive excavation or replacement.

Grout injection

Underpinning by grouting is a foundation stabilization technique that involves injecting a specialized cementitious grout material via a sleeve port pipe which is inserted into a pre-dug hole beneath an existing foundation. The grout is henceforth pumped out and allowed to permeate the soil, essentially calcifying the affected area so that the soil is stronger, thicker, and less permeable.

This method is employed to address issues such as settlement, soil voids, or weak soil layers that can compromise the structural integrity of a building. The grout, once injected, fills voids, consolidates loose soil, and creates a stable foundation base. As the grout hardens, it enhances the load-bearing capacity of the soil and provides increased support to the foundation.

Underpinning by grouting is a cost-effective and minimally disruptive solution that helps prevent further settlement and ensures the long-term stability of the structure above.

This method of foundation repair is where grout is injected directly into the soil, changing the chemical makeup of the adjacent native soils so that they develop low viscosity.

Expanding Foam Resin:

Underpinning with Expanding Foam Resin is an innovative and non-intrusive technique used to strengthen and stabilize the foundation of a structure. This method involves injecting a specialized expanding foam resin into voids or weak soil layers beneath the foundation. As the resin expands, it fills voids, compacts loose soil, and creates a solid support system and even can lift the slab to its previous level. The foam’s expansive nature ensures even distribution of pressure, effectively increasing the foundation’s load-bearing capacity and minimizing the risk of settlement or structural damage. This approach is particularly suitable for situations where traditional underpinning methods might be challenging or disruptive, offering a quick, cost-effective, and environmentally friendly solution to foundation stabilization and reinforcement.

The foam resin is also claimed that achieves the lifting of sunken slabs and is widely applied in slabs, roads, airports, and railway tracks. However, for some expansive clays where foundation settlement is because of dehydration of expansive clay, it is not an effective method. That is because the injection and densifying of the soil at the time of application does not prevent any further settlement if expansive clays continue to dehydrate and shrink. In the case of weak base soils or an issue with granular soils or permafrost, this method may be a good solution.

Pros and cons of underpinning

Advantages of Underpinning

It’s important to note that while underpinning offers numerous advantages, it should be performed by qualified professionals following proper engineering and construction practices to ensure its effectiveness and safety.

Underpinning is a construction technique used to strengthen, stabilize, or support the foundation of a building or structure. It offers several advantages, including

Foundation Strengthening: Underpinning can significantly improve the structural integrity of a building’s foundation, especially if it has been compromised due to soil movement, settling, or other factors.

Stability and Safety: By addressing foundation issues, underpinning enhances the overall stability and safety of the structure, reducing the risk of collapse or structural damage.

Property Value: Underpinning can increase the value of a property by ensuring that it meets modern safety standards and is less prone to foundation-related problems.

Structural Renovation: Underpinning enables structural renovation or expansion of existing buildings, making it possible to add additional floors or make changes to the layout without compromising the integrity of the foundation.

Sinking or Settling Prevention: Underpinning can help prevent further sinking or settling of a building’s foundation, halting the progression of foundation-related issues.

Cost-Effective Alternative: Underpinning can be a cost-effective solution compared to demolishing and rebuilding a structure with foundation issues.

Preservation of Historic Buildings: Underpinning allows for the preservation of historic or heritage buildings that may have foundation problems, allowing them to be restored and maintained for future generations.

Versatility: Underpinning techniques can be tailored to suit various types of soil, foundation types, and structural requirements, making it a versatile solution for different situations.

Minimized Disruption: Modern underpinning methods often involve less invasive techniques, resulting in minimized disruption to the occupants or the surrounding environment during the construction process.

Long-Term Solution: Properly executed underpinning provides a long-lasting solution, reducing the need for ongoing maintenance and repairs related to foundation issues.

Prevention of Further Damage: Underpinning can stop the progression of foundation problems, preventing them from causing additional damage to the building over time.

Increased Load-Bearing Capacity: Underpinning can increase the load-bearing capacity of a foundation, allowing it to support heavier loads and resist external forces.

Insurance and Legal Compliance: Underpinning can help a property owner meet insurance and legal requirements, ensuring that the building meets safety standards and codes.

Peace of Mind: Knowing that the foundation of a building has been properly underpinned provides peace of mind to property owners, occupants, and stakeholders.

Disadvantages of Underpinning?

When it comes to addressing foundation issues, underpinning undoubtedly offers a reliable solution. However, like any construction process, it’s essential to weigh the pros and cons before diving in. While the advantages of underpinning are well-documented, there are certain disadvantages that homeowners should be aware of to make informed decisions.

Cost Considerations:

Undoubtedly, one of the most significant factors that homeowners need to reckon with is the cost associated with underpinning. The price tag can vary widely, influenced by factors such as the scale of the project, the chosen underpinning technique, and the severity of the foundation problems. As homeowners evaluate the potential solution, it’s crucial to allocate a realistic budget, taking into account the long-term benefits that underpinning can provide.

Disruption to Daily Life:

Underpinning involves a level of excavation and construction activity around the foundation of your home. This process, while essential, can introduce disruptions to your everyday routine. From the noise of construction work to the inevitable dust that accompanies such projects, these inconveniences may impact your daily life. Additionally, restricted access to certain areas of your property during construction can further compound these disruptions.

Time-Consuming Endeavor:

While the promise of a solid foundation is alluring, it’s essential to acknowledge that underpinning is not a quick fix. This process demands meticulous planning, engineering assessments, securing necessary permits, and the careful execution of construction work. Homeowners embarking on underpinning projects should set realistic expectations regarding the timeframe involved, understanding that quality work takes time to ensure a stable foundation for years to come.

Potential Landscaping Impact:

The sight of mature trees, lush shrubs, and vibrant vegetation gracing your outdoor spaces is a joy for any homeowner. However, underpinning may require sacrificing some of this greenery. Excavation work around the foundation could necessitate the removal of certain plants, potentially impacting your landscaping efforts. Balancing the structural needs of your home with the aesthetic appeal of your outdoor spaces becomes a critical consideration.

FAQ

What is the difference between underpinning and foundation?

Underpinning involves strengthening or stabilizing an existing foundation, typically due to settling or structural issues. The foundation refers to the base upon which a building or structure is constructed, providing support and distributing its weight to the ground.

How underpinning a foundation is done?

Underpinning a foundation involves reinforcing or strengthening an existing foundation by either extending its depth, increasing its load-bearing capacity, or both. This is often done by excavating beneath the existing foundation in sections, placing new structural elements like concrete, steel beams, or piles, and then allowing them to cure and provide additional support. The chosen method depends on factors like the type of soil, building structure, and the specific issues the foundation is facing, such as settlement or instability.

What is the difference between mini pile underpinning and traditional pile underpinning?

Minipiles underpinning

Uses smaller, more manageable machinery, which causes less disruption to the surrounding area.
Can be used in more restricted spaces, such as in urban areas.
Can be installed more quickly than traditional pile underpinning.
Is more cost-effective than traditional pile underpinning in some cases.

Traditional pile underpinning

Uses larger, more disruptive machinery, which can cause more damage to the surrounding area.
Requires more space to install the piles.
Takes longer to install than mini piles underpinning.
Is more expensive than mini piles underpinning in some cases.

What is the difference between mini piles and traditional piles?

In general, mini piles underpinning is a good option for underpinning buildings in urban areas or where there is limited space. Traditional pile underpinning is a good option for underpinning buildings in rural areas or where there is more space available.

What are a bored pile and a driven pile?

Bored pile underpinning involves drilling a hole into the ground and then filling it with concrete or grout. This method is more time-consuming and expensive than driven pile underpinning, but it is also more versatile and can be used in a wider range of soil conditions. Bored pile underpinning is also less disruptive to surrounding structures, making it a good choice for urban areas.

How to differentiate between driven and bored piles?

Driven pile underpinning involves driving a steel or concrete pile into the ground. This method is faster and less expensive than bored piles underpinning, but it is also more limited in terms of the soil conditions that it can be used in. Driven pile underpinning can also be more disruptive to the surrounding structure

Friction pile underpinning relies on the friction between the pile and the surrounding soil to transfer the load. This type of underpinning is typically used in soft soils where there is no strong, load-bearing layer at shallow depths. The piles are driven or drilled into the ground, and the surface of the pile is roughened to increase the frictional resistance.

End-bearing pile underpinning relies on the end of the pile bearing on a strong, load-bearing layer of soil or rock. This type of underpinning is typically used in hard soils or where there is a strong, load-bearing layer at shallow depths. The piles are driven or drilled into the ground until they reach the load-bearing layer, and the end of the pile is then enlarged to increase the bearing area.