When a building becomes weakened to the point of being structurally unsafe, instead of having to demolish and rebuild large parts or even the entire structure, underpinning can be used to strengthen the foundations of the existing building or structure.
Underpinning works by extending the depth of the foundations or expanding the foundations to increase the weight bearing load over a larger surface area. Underpinning can be a major project to undertake so it is important that you know the different methods available and how they can benefit different situations.
Underpinning can be required for a number of reasons; maybe a change in soil conditions have altered the foundations; maybe the original foundation is old and worn and no longer strong enough to support the structures; maybe additional floors or extensions have been added to the structure which means the foundations are now under increased pressure, pressure that they are unable to withstand. Luckily, there is an underpinning method for every eventuality:
Mass Concrete Underpinning
One of the most common methods of underpinning sees the soil underneath and immediately surrounding the structure replaced with concrete which is poured in box shaped compartments, pre-dug by the underpinning team in a predetermined sequence that will be able to bear the weight of the structure. This method is commonly used for relatively shallow foundations.
If a structure is situated above layers of firm and superficial soil then piling underpinning is used. Piling underpinning is also considered if there is limited access to the construction site, any environmental concerns or minimal structural movements during the underpinning process. Steel cased piles are driven at strategic points before being filled with the concrete.
Suitable across a wide range of soil types, jet grouting involves creating geometric patterns of grouted soil using a high-velocity jet. The jets are used to create columns of grouted soil which can withstand greater loads than the previous soil. Because the grouting is applied using high-pressure jets the current soil is disturbed, which means the process can never be used if the foundations are very sensitive.
For more information on underpinning and piling in Chester, contact the team at Rhinopiling today.