Underpinning is the process involved in the repair and strengthening of the building. In this article, the discussion will be made on the different underpinning methods and procedures involved in strengthening the foundation. In a few cases, the failure has occurred in terms of the foundation or footing of the complete structure. In a few emergency cases, a remedial approach is suggested to regain the stability of the structure. Underpinning is responsible to boost the strength of the foundation of the property. To build the strength installation of permanent or temporary support is required to provide additional depth and enhance the bearing capacity. Howsoever, re-stumping house opts to quite similar to underpinning houses but in few aspects re-stumping work only for new material.

The condition that requires underpinning:

There are suitable reasons that make use of the underpinning method for stabilizing the substrate. The reasons are discussed below:

Degradation of timber piles due to water table fluctuation would require settling.
Rising and lowering of water table would help decrease the bearing capacity of the soil that is used to construct the structure.
In case, the structure that is built on the soil with bearing capacity may not suit the structure and would cause settlement.

Needs of underpinning foundation:

The decision of underpinning is completely dependent upon observation. It is needed when the existing structure displays a few changes due to distress. To make out the necessary changes, it is required to establish the vertical level and offset level reading on a timely basis. The timeframe completely depends upon the condition of the settlement. In the case of a new project, professional before excavating need to look forth toward examine and determination of soil capacity to emphasize the resisting the ability of the structure. Based on the report further decision is made for the underpinning or re-stumping house.

Pit method:

This is the traditional method used for underpinning as it is practiced for a longer time. The method particularly emphasizes the old foundation that opts to reach the stable stratum. The soil is excavated with the use of stages and pins in a controlled manner. When strata can be reached according to then the excavation is filled with concrete which helps in curing until the initiation of the next excavation.

Cantilever needle beam method:

This underpinning foundation method is the extension of the Pit method and is used when the extension is executed only on one side and the plan is going to make use of the stronger interior column. This is the method faster than the traditional method and only one side and has the potential to bear a higher load. Howsoever, digging would be completely uneconomical if the foundation is ground to be deeper. The use of a needle beam is restricted due to constraints in the access.

Pier and beam underpinning method:

This method is concerned with base and beam which concept was introduced after the 2nd world war. This method came into demand due to the failure of the mass concrete method that could work for the huge depth foundation. Besides this, this method is feasible for other ground conditions. In this method concrete beam is used to transfer the load of the concrete base. It is discovered for depth shallower more than 6m.

Mini piled underpinning:

This method is utilized in the place where the load of the foundation gets transferred to strata and the distance may range greater than 5m. This method is highly adapted to the soil that is restrictive to access; execute variable nature and can even lead to environmental pollution issues. The piles are generally made of augured or driven steel and the diameter can vary from 150mm to 300mm.

Pile method:

Piles are commonly used to support the weak foundation and get driven on the adjacent side of the wall. A needle-like shape connected to the piles is inserted into the wall to support the foundation. This needle acts like a pile caps and this technique is useful to settle down the soil caused due to water clogging or because of clay nature.

Pre-test methods:

This is the method employed for pad or stripe foundation and can be utilized for the building of 5 to 10 stories. In this technique, the subsoil is made compact and compressed till the next level of excavation that is sure to provide a predefined load to the subsoil layer. And, this is the technique that needs to be accomplished before underpinning gets started. This method cannot be applied for raft foundation and reduction of noise is accepted in this particular region.