Underpinning: Know meaning, uses in construction and various methods

What is underpinning and why is it Important?

Having a secure home is a top priority for every homeowner. However, there is the possibility of danger to the home if the foundation isn’t solid. The safety of the family depends on a strong and stable structure; thus, fixing a foundation that has been broken or is otherwise compromised is essential.

If you have seen a number of cracks appearing in your home, it is possible that you have foundation issues. In this instance, underpinning is the most effective method for reinforcing your structure’s base. In this article, you will understand the meaning of underpinning, its advantages, and its approaches.

What is underpinning? 

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What does underpinning mean in construction?

Underpinning refers to the practice of fortifying the base of already-existing houses, buildings, or other structures. Underpinning is a useful method that may be used either during or after the building process in order to strengthen the foundation. In most cases, an existing structure’s foundation and the ground’s condition will need to be improved in order for it to be able to support a greater weight.

What is underpinning in construction? The process of underpinning in construction is one that must be carried out with a great deal of caution and under the close supervision of an experienced professional. The structure’s vulnerability to failure is increased if the strategy, techniques, and underpinning methods used are incorrect.

See also: All you need to know about Pile Cap

Reasons for underpinning

The requirement for underpinning arises from a variety of factors, some of which are detailed in the following paragraphs.

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The original base was weak or unsteady

There must be reinforcements added to the base when the underlying foundation cannot support the weight of the building. It is also possible to strengthen the soil under the base when there are uneven settlements caused by the poor construction of the foundations.

There is a shift in how the structure is being used

There is the potential to alter the functions that can be performed in each of the structures. When these adjustments result in an increase in the loads that are being imposed, underpinning is performed as a foundation improvement.

Modification of the subsoil under the building

When there are soils that are deformable, soils that are decaying, and so on, the characteristics of these soils change throughout time. As a direct outcome of this, the foundations could shift. Under these circumstances, work to ameliorate the soil conditions is carried out.

Poor ground conditions

The assessment of soil design factors like load carrying capacity, frictional forces, etc., might be off if the improper features of soil are taken into account or if the soils are not properly classified. It is possible that this will cause the structure to settle unevenly even while it’s still being built.

The digging of an adjacent structure

The excavation has a considerable effect on the structure that is already there. The effect could be avoided or reduced if the shoring were done correctly. Nevertheless, the way of underpinning that is deemed to be the most suitable should be used.

Boost the foundation’s load capacity

It is necessary to apply appropriate underpinning techniques when the loads transmitted to the foundation must be increased. There are a variety of underlying techniques that may be used according to the circumstances, such as when an additional floor must be added to an existing building rather than a whole new one being built.

known about: considerations

Considerations prior to underpinning

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Because of the complexity of this procedure, it must be carried out by an underlying specialist who is highly knowledgeable. Therefore, it is recommended to work with a professional contractor that focuses on underpinning as their area of expertise. Also, take into account the following factors:

Cost

This method is fairly pricey. When it comes to repairing a foundation that is either too weak or has been damaged, most homeowners always consider underpinning as the very last feasible alternative. Because of the inherent dangers of this technique, the cost may be rather high. In light of this, you should compile a rough estimate of the whole cost of the job before beginning the underpinning of your foundation.

Insurance

Insurance companies will always want you to provide specific details on any home improvement work you intend to do on a property that they insure before they would provide coverage. As soon as you begin a home improvement project such as underpinning, the insurance company will switch your plan to one that covers a property through a remodelling project.

If you begin such a venture without notifying your insurer, they may consider your policy null and worthless. You run the danger of being unprotected in the case of an incident if you decide to remain in an unsuitable location. Because of this, it is important to let your insurance company know about the job before beginning work.

Construction Permit

In the event that the underpinning contractor you have chosen does not have the required building permits, you might be in for some serious legal and financial trouble. If you start underpinning your house without a permit, you might end up lowering the value of your property. It will also make filing an insurance claim very difficult. So, before commencing the job, make sure your contractor has a valid construction permit.

Methods of underpinning

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There are a few different approaches that may be used when underpinning foundations. However, the following four approaches are the most common ones:

Mass pouring underpinning method

This underpinning method is used where a lot of digging is not required. A concrete foundation is poured to increase the strength of the base. This is a very easy underpinning method and doesn’t require heavy machinery. Also, it is a very cost effective method.

Beam and base underpinning method

In this method, a traditional mass concrete base is used and is supported by beams so that the foundation is strong. In this kind of underpinning, the foundation’s weight will be taken care by the beam that will be either constructed above or below the concrete base.

Pit underpinning method

The pit technique of underpinning is often performed by methodically digging the area in phases. In order to do this, the old wall was cut into sections with widths ranging from 1.20 to 1.50 metres. At the predetermined locations, holes are cut out of the existing wall. After that, needles that have bearing panels attached to them are placed through all of these perforations and stabilised by jacks. After this, excavation will begin, first to a depth equal to the level of the existing foundation, and later to the desired depth.

Pile underpinning method

In some circumstances, such as those involving swampy areas, severe loads on already-existing structures, and loads that need to be shifted to a deeper depth, the pit approach may not be feasible or cost-effective. 

Using a pile technique might be used in these instances. The piles are positioned on each side of the current wall in this way. The pile caps act as needles and are inserted into the wall. As a result, the pressure is taken off the current wall. 

This approach is very helpful in clayey soils, as well as locations that are prone to waterlogging, and walls that are required to handle large loads. Pile driving occurs concurrently with the construction of light buildings, followed by the installation of clamps or cantilever needles.

Pier underpinning method

When dealing with dry terrain, this strategy is often the one that is used. This is a straightforward approach to the process of underpinning. The placement of piers beneath the foundations of buildings is done via the approach trenches as part of this process. After the holes have been filled with concrete, the compacting process may begin so that the weights can be transferred to a new pier.

Chemical underpinning method

Chemicals are used in this technique for the purpose of consolidating the foundation dirt. Under the foundation, perforated pipes serve as a motor that moves in an angled direction. The slopes are designed in such a way that the whole region is under the current footing corners beneath the section that was reinforced.

Injecting a sodium silicate in a mix of water via the pipes is the next step once the pipes have been placed. The procedure involves two injections. Calcium chloride is pumped via the pipes while they are being removed. These two compounds react chemically, leading to soil consolidation as a byproduct. If you have granular soil, this technique will work for you.

Underpinning: How much does it cost?

Underpinning costs depend on factors like how serious the issue is, what is the type of foundation that exists, what is the type of underpinning method that is chosen etc.  It is advisable to enquire with a contractor who will come with the best quote upon inspection.

FAQs

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