How To Repair Building Foundation
{ Underpinning Process }
What Is Underpinning ?
The process of providing a new foundation below an existing foundation or strengtheningan existing foundation is called underpinning of foundations.
Purpose of Underpinning :
Underpinning may be done for the various purposes, such as :
Methods Of Underpinning :
The various methods of underpinning are as follows:
1. Pit method
2. Pile method
1. PIT METHOD
In this method, the entire length of the existing wall is divided into suitable sections of 1.20 to 1.50 m. length.
One section is excavated at a time. For each section, a hole is made in the wall, above the plinth level. The needle made from timber or steel section is then inserted through the hole and supported on jacks on both the sides of the wall, as shown in fig.
The pit is excavated and the existing foundation is taken up to the desired level and new foundation is laid. The alternate sections are taken up in first round and then the remaining sections arc strengthened as shown in fig.
If the wall to be underpinned is weak, the raking shores are also provided.
If the space to support needles on outside is not available, the cantilever needles projecting inside may be provided, as shown in fig.
2. PILE METHOD
In this method, the piles are driven at suitable intervals on both side of the existing wall. The needles in the form of pile caps are then provided through the wall; as shown in fig.
Thus, the existing wall is relieved of the loads coming on it. This method is useful for water logged areas and for walls carrying heavy loads. For underpinning very light structures, the piles are driven on both the sides of the structure and the brackets or cantileverneedles are provided to carry the structure.
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