Guidelines on Types of Slab Underpinning

The traditional slab underpinning method is many years old, and the basic protocol has not changed much. In this underpinning method, slabs are used to strengthen the foundation of an existing structure. Those slabs are sequentially placed underneath in a strategic order so as to build a strong foundation.

Concrete slab underpinning is needed for a variety of reasons- if the original foundation isn't strong enough or the structure has changed over the years, or the spoil properly is no longer the same. In such cases, excavation of soil and increasing the depth is necessary.  The cost of slab underpinning when working on the present structure's foundation is certainly more economical in comparison to building a new one.

Slab underpinning house is attained by working on the foundation in depth or breadth so as to create a more supportive soil stratum. The use of slabs can help repair and strengthen an existing foundation. It is a common practice used during the construction of nearby structures and to support neighbouring properties. The first step is to remove the soil from below an existing foundation.

Types of slab underpinning:

There are different methods of slab underpinning such as Mass Pour, Beam and Base, and Mini-Piled.

• The mass pour – This method is the most common and, in this case, a continuous concrete is poured beneath the current foundation. Although a great deal of material is used in this method, it is a simple and effective way of slab underpinning.

• The beam and base- This method is technically advanced, and, in this case, a reinforced concrete beam is laid along the entire foundation. The concrete mass base is transferred along the new beam and used to spread the load evenly across the soil. The feasibility of this method relies on the structural arrangement of the building.

• The mini-piled – When the ground conditions are variable, the mini-piled method is used for slab underpinning. In this case, deep vertical structural elements are drilled into the ground until the piles can rest on stable soil. Although this method is more advanced and expensive, it is useful in most adverse soil conditions and requires special equipment.

A good and strong foundation holds the key to the stability of the entire structure or building. The slab underpinning procedure can be used to make the foundation even sturdier as it can resist any adverse effects of soil movement and prevent the formation of cracks. As the slabs are placed laterally and deep into the soil, they can keep the foundation safe from the seismic activities of the earth and keep the drainage system safe and intact. Use the right slab underpinning design and expertise for the best results. For example, the foundation should be laid at a minimum length of 3 feet, and a minimum width of footing should be 2 feet. There should be ample space for the convenient placement of the slab.

A geotechnical engineer determines the depth of the excavation, and the soil needs to be removed in controlled stages. The engineer will study the soil composition to understand the strata and if it can bear the weight of the building.  He inspects the site carefully before planning slab underpinning and will conduct a soil test.  He will determine the dimensions of underpins and may need permission from the local civic authority for the process of slab underpinning. When the excavated soil is replaced with concrete slabs to form a new foundation beneath the existing one, the whole building gets a new foundation and a new life.  The total material and labour costs may depend on the level of complexity of the project.

To stabilize and further strengthen the building, slab underpinning is essential.