The Types of Underpinning You Should Know About

Foundation underpinning is a method used to strengthen and stabilize existing foundations that have experienced settlement or have become unstable. This technique involves extending the foundation depth or width to provide additional support and strength.

Underpinning may be necessary when the original foundation is not strong enough to support the weight of the structure, or when the soil beneath the foundation has shifted or settled, causing the foundation to sink or become uneven. Underpinning can also be used to repair foundation cracks or damage caused by soil movement or other factors.

There are several different types of underpinning techniques that can be used to repair or strengthen a foundation. Here are some of the most common types of underpinning:

Mass Concrete Underpinning: This is the most traditional and widely used type of underpinning. It involves excavating beneath the existing foundation and pouring concrete footings underneath. The new footings are wider and deeper than the original ones and provide additional support to the foundation. The excavation is typically done in stages, with each section underpinned and allowed to cure before moving on to the next section. This can be a time-consuming process and can cause significant disruption to the surrounding area. Mass concrete underpinning is most suitable for foundations that have relatively shallow footings and are not too deep.

Beam and Base Underpinning: This method involves excavating individual sections of the foundation and then constructing concrete beams and bases to support the foundation. This can be a faster and more cost-effective solution than mass concrete underpinning, as it requires less excavation and can be completed in smaller sections. Beam and base underpinning is also suitable for foundations that have relatively shallow footings and are not too deep.

Mini-Piled Underpinning: This method involves drilling small, deep holes into the soil beneath the foundation and then inserting steel piles into the holes. The piles are then filled with concrete, providing additional support to the foundation. This method is often used in situations where access is restricted, and heavy machinery cannot be used. Mini piling can also be used in areas where soil conditions are poor or where the existing foundation is particularly deep. This method is also suitable for structures that are sensitive to vibrations caused by excavation.

Screw Pile Underpinning: This method involves driving long, screw-like piles into the ground beneath the foundation using a hydraulic motor. The piles are designed to grip the soil and provide additional support to the foundation. This method is particularly suitable for sites with poor soil conditions, as the piles can be driven to great depths to reach stronger soil layers. Screw pile underpinning is also a fast and efficient method, as there is no excavation required and the piles can be installed quickly.

Resin Injection Underpinning: This method involves injecting a structural resin into the soil beneath the foundation, which then expands and hardens, providing additional support to the foundation. This method is particularly useful for structures that are located in areas with limited access or where excavation is not possible. Resin injection underpinning can also be used to fill voids or stabilize soil, making it a versatile solution.

Plate Anchor Underpinning: This method involves installing steel plates and anchors into the soil beneath the foundation, which are then connected to the foundation using high-strength bolts. The plates and anchors provide additional support to the foundation. This method is particularly useful for structures that are subjected to lateral forces, such as retaining walls or basement walls. Plate anchor underpinning is also a fast and efficient method, as the installation can be completed quickly and there is minimal disruption to the surrounding area.

The choice of type of foundation underpinning will depend on several factors, including:

Soil conditions: The type and condition of soil on which a building is constructed is an important factor in determining the appropriate type of foundation underpinning. Different types of soil have varying levels of strength and stability, which can affect the effectiveness of different underpinning methods. For example, soft and unstable soils such as clay or silt may require more extensive underpinning measures to provide adequate support.

Depth of the foundation: The depth of a building’s foundation can also impact the type of underpinning required. Shallow foundations may require less invasive underpinning techniques, while deeper foundations may require more extensive measures such as deep foundation piles or beam and base underpinning.

Access to the site: The accessibility of the site where the foundation underpinning is to be carried out is also an important consideration. Factors such as the size of the site, the location of the building, and the availability of heavy equipment and machinery can all impact the feasibility of different underpinning methods.

Budget and timeframe: The budget and timeframe available for the foundation underpinning project will also be important factors to consider. Some underpinning methods may be more expensive or time-consuming than others, so it is important to choose an appropriate method that meets the project’s requirements while staying within budget and timeframe constraints.

Structural requirements: The specific needs of the building and the type of structural support required will also be taken into account when choosing the appropriate underpinning method. Factors such as the building’s size, the load it is carrying, and any lateral forces it is subject to (such as wind or water pressure) will all impact the choice of underpinning method.

In conclusion, underpinning is an important process for supporting a structure and ensuring its stability. It can involve a range of techniques, from excavating beneath the structure to installing additional supports. Each application requires careful consideration of the existing structure, soil conditions, and other factors. If a building is showing signs of instability or subsidence, underpinning may be necessary in order to prevent further damage.

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