Types of Foundation and Subsidence Risk
How do foundation types and subsidence go together? Different types of foundations show different signs of subsidence. Often, the foundation type will be more prone to different types of subsidence or settlement and require a different approach to treatment.
The majority of houses and light domestic buildings are built using shallow foundations. By definition, a shallow foundation is when the depth is equal to or less than the width of the foundation. Shallow foundations are typically used where the load of the structure are relatively low in comparison to the bearing capacity of the surface soils. Essentially, when the soils can hold more weight than the structure you're placing on the soil. Deep foundations, in contrast, are used to accommodate pads on weaker ground or where significantly higher loads are required.
A strip foundation is a type of shallow foundation used to provide a strip of support to a linear structure such as a wall. Strip foundations are used in many subsoils. They are particularly suited to light structural loads such as those in residential properties. In most cases, a mass concrete strip foundation is used. When strip foundations fail, it's often because subsidence has caused the strip to sink in one corner or down the length of the wall. This can be a consequence of either shrinkage of clay soil or excess water such as leaking drains.
At Geobear, the most frequent use of our geopolymer solutions is treating houses affected by subsidence. We identify the affected area through soil investigations and design a solution that sees bulbs of geopolymer material injected at intervals beneath the strip foundation. The material expands and forms a solid base beneath the existing strip preventing any further movement (subsidence). The solution is commonly used ahead of underpinning, which is an older traditional method.
Pad foundations are rectangular or circular pads used to support localized loads such as columns. Pad failure is less common than strip foundation subsidence. When failure does happen, there are a couple of possible reasons. Sometimes, settlement occurs when the load from the building is greater than the pad and subsoil can withstand. The compaction of the soil can cause failure of the pad. Subsidence can also occur due to erosion from excess water.
Geobear's geopolymer solution can strengthen the ground beneath a pad to prevent further movement. We inject material at several depths beneath the pad, depending on the extent of the weak soil. When the solution hardens, it creates a firm base beneath the pad foundation. The selected material provides additional bearing capacity to the soils, allowing greater loads to be placed upon the existing pad foundation. This is the perfect solution where a new story or roof is being built.
Raft foundations are formed by reinforced concrete slabs that cover most or all of the footprint of a building. They spread the load imposed by a number of columns or walls over the area of foundation. Foundations like this are commonly used for light domestic buildings on poorer soils. Because raft foundations are more prone to settlement overtime, they are designed to tolerate downward movement. Excess downward movement can be caused by poor compaction of the fill material beneath or water ingress through cracks causing voiding.
When this happens, Geobear will design a solution in which geopolymer material is injected just beneath the slab in a grid pattern across the affected area. The material will expand to fill voids and compact the existing fill. In some cases, we can use our material to lift the slab back to previous levels. If the foundation is required to hold a greater load, we can also use our material in localized areas to improve the ground strength. This approach enables new support columns to be fixed to the raft.
Worried about Subsidence?
Our team provides complimentary consultations to help you understand your subsidence issues and address settlement or subsidence on your property. To learn more, fill out the contact form below or visit our resource center.