Common Underpinning Methods To Remedy Subsidence

22/11/2018

Owning a house is a big commitment that homeowners are ready to make. Once families settle in and make it their home, some get too attached to let it go. On the other hand, even if the house is put up for sale, it is the responsibility of the homeowner to keep it safe for the next owners.

A house is only as strong as its foundations. Proper maintenance is critical for the property to stand the test of time. As soon as homeowners notice diagonal cracks on walls or floors, then that usually indicates a problem with the foundation.

It is of utmost importance to get that repaired as soon as possible. Foundation damage can be caused by many different factors. Underpinning is the best method to fix subsidence which causes damage to structural foundations.

What is subsidence

Land subsidence is the sinking or gradual settling of the ground or soil. In this case, it is the shifting of soil underneath a property or structure.

Common causes for subsidence

Subsidence occurs naturally but is sometimes caused by human activity as well. These are some of the significant causes of subsidence in residential and rural areas.

Flooding

Any areas that have been affected by severe flooding have also been known to experience subsidence. Stagnant water in and around a structure will cause water damage and jeopardize its integrity.

Faulty structural design

In some instances, the foundations of the home or structure have been poorly designed. The foundations were not built to support the correct weight of the composition above.

Tree roots

Planting trees too close to the walls of the house or structure pose the risk of the roots damaging the foundations. If the full grown trees that are too close to the home are removed the roots that rot away underground could also cause subsidence.

Failed drains

Some older properties do not have a well thought out drainage system. The pipes inside the house are routed to drain into the ground around the house or worse under the house and not into a sewer or septic system.

The water would then wash the soil away from the foundations and cause even more water damage to the concrete as well.

Underground Mines

In some areas where underground mining was practised which the unused tunnels would collapse. Naturally, if there are homes built above the tunnels, then the soil would shift accordingly.

Definition of underpinning

The process of underpinning is used to strengthen the damaged foundations of a home, building or structure. The strengthening process usually involves digging to the existing foundation and extending its depth. Another technique in underpinning is to distribute the weight of the structure across a wider area.

Different methods of underpinning

There are several effective underpinning methods used today. The process to be used should correspond to the current damage affecting the entire foundation.

Piled underpinning

The method of piled underpinning is generally used when the surface soil is superficial and cannot bear the necessary load of the structure. The piles are structural membranes that are typically made of reinforced concrete and steel.

The pile foundation is then set on the firm soil or rock which is usually located several a few feet below the surface soil. Then the pile cap supports the column which then carries the load of the above structure. Suitable for areas with restricted access and is faster to accomplish that traditional underpinning.

Jet Grouting

Since a lot of drilling and heavy equipment is used in this method, the property needs to be accessible for the heavy-duty machines to work their magic. Jet grouting is accomplished by first drilling down to the required depth where the more solid soil or rock is situated.

Then using a high-velocity rotating jet which will start emitting cement grout from the bottom. The machine will then slowly pull up the rotating jet forming a column of cement grout going to the surface.

The column is usually made up of water, cement and in-situ soil. This method does not require load transfer structures since the cement grout can be created up to the existing foundations of the structure.

Mass concrete underpinning

One of the more traditional methods of underpinning. It is only suitable for shallow foundations that are strong enough to span over the block-shaped concrete underpinning pits. All one needs to do is first create large reinforced concrete blocks.

Those will become the new support system for the structure above. Then dig deep enough past the existing foundations and make room for the mass concrete blocks to be positioned under the existing foundations.

Geo-polymer

The most modern and non-disruptive form of underpinning. Unlike traditional underpinning where extensive drilling or excavation is required, using geo-polymer is less invasive.

There is no need to drill or dig past the current foundations and install various support structures, you just need to drill and reach the depth of the required depth of treatment. There are two distinct methods of using geopolymer.

The first one is called the extraction method. It only needs one hole and a single injection tube. A measured quantity of the geo-polymer is then injected into the hole, and at the same time, the tube is extracted.

The second option is the multi-tube method where one hole is drilled to the required depth, and multiple injection tubes of various lengths are inserted in the hole. Measured quantities are then injected into each tube.

Once injected the geo-polymer will expand both vertically and horizontally to fill any voids and reinforce the surrounding treatment area.

Conclusion

Have the property surveyed and evaluated by a structural engineer so they can analyse the property and asses if there is any damage to the foundation. As soon as an engineer confirms that the foundations need to be repaired keep these options in mind and ask them which method would work best.

It will be an investment towards the well being of the property. The process of underpinning is the most effective way to ensure the safety and structural integrity of a house or structure.

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