Underpinning is basically a process of strengthening a structure. This may become necessary for a variety of reasons. It could be due to a weakening of a foundation or the original function of the structure is being changed. It may also be necessary to complete a new underpinning if the characteristics or the conditions of the soil beneath the foundation of the building have changed. In this regard therefore, underpinning can be performed using various methods. These include wall anchors, piering, mudjacking and mass concrete.
Piering is one of the most common types of foundation underpinning. This is especially so due to its durability and efficiency. There are two main types of piering; round shaft piers and square shaft piers. Each of these piers has its role based on the situation of the foundation stabilization.
The round shaft piers are designed for compression purposes. This is because they have a higher moment of inertia or resistance to bending. Furthermore, it has a higher installation torque rating as well as a higher lateral resistance due to the large surface area that is exposed to the soil. On the other hand, the square shaft piers work perfectly in tension applications like soil nails, wall anchors or tie backs. However, in a case where it is installed under a building the square shaft is bent and warped under the pressure. This is as a result of the socket and pin coupling which tends to increase variances from straightness and can thus increase the buckling potential.
Helical Screw Piles
The other type of underpinning is wall anchors. A square shaft in this case is used for the helical wall anchors that are installed in tension applications. These anchors are meant to give lateral stability for foundation walls. The helical wall anchors can still be installed even in limited access areas without using heavy machinery.
The third type of foundation underpinning is mudjacking. This is one of the methods used to stabilize the foundation of a shallow concrete surface such as a driveway or sidewalk. In this case, holes are drilled under the foundation or into the slab before pumping concrete under the foundation. The idea in this case is that the concrete will eliminate settlement problems. However, there is a need to be careful when using this type of underpinning. The stabilization solution should be extended all the way to the bedrock in order to ensure that the building does not settle and shift again. In order to offer a long term solution however, it is advisable to combine mudjacking and piering.
Concrete Piles and Piers
The historical method of underpinning however has been the mass concrete method. This involves digging up box-shaped voids under the existing foundations of the structure and filling them with concrete in a certain order in order to create the “foundation below foundation” effect.
Basically, it is important to ensure that you understand how to underpin properly no matter the method used. Always make sure that you extend foundations in depth and breadth. This ensures that it redistributes the weight over a bigger surface area. Whatever the case, ensure that you choose the right foundation contractor who will use the right type of underpinning depending on the state of your foundation.