Underpinning is a method used to increase the foundation depth. This may be done in case a developer wants to add more storeys to a building. Also the foundation could be damaged by tree roots and thus this method used for correction. The adjacent construction may have foundations lower than the existing thus requiring to be lowered. If basements are constructed very near an existing building, the foundation may need to be changed. The reason is for stability of the existing house. Cracks may appear in a building up to the base thus needing a foundation remedy.
The underpinning in foundations may be undertaken and but supervised by an engineer. This works should follow instructions keenly for safety. Before any commencement, of work the area of operation should be hoarded. The works take from excavation to finishes approximately a month to complete.
The area to work on is measured and mapped out. The work should commence from the corners working inwards. This is done on load bearing walls only.
Foundations without any load bearing walls are exempted. The defects on these walls can be corrected using most simple methods.
The underpinning in foundations starts with excavations. This should be done under a strip footing. A length of one meter, a width of half a meter and depth of half a meter pit is dug. This is done in stages of two meters. This is distance between the pits. After the excavations, mass concrete is added to the cavity. Mixes are one part cement, three parts sand and six parts aggregates. Concrete is made to a good consistence and is poured into the cavity. Use form work on the edges. Use a rod bar ensuring that the cavity under the existing foundation is filled up.
After the underpinning concrete is placed in the cavity, its allowed to set for two days. The operation is repeated for the next bay. This continues until the required foundation is complete. Ensure that the concrete is cured thoroughly before loading it. The next thing is to break off the projecting foundation. Cut the concrete flush with the mass concrete surface. after this is completed for all the bays, soil is then back filled and compacted thoroughly. Watering with a hose is done for consolidation of the soil. This is done upon completion of the work.