Types Of Underpinning For Basement Foundation Repair
Underpinning is the process undertaken for increasing the strength of a prevailing foundation system in an subsisting building.
Underpinning is done in the following conditions:
Possibility of sinking into the ground or cracking of the building, as a result the foundation system is not capable of tolerating the weight of the building.
The building is either being expanded or changed to a new type of activity, that leads to greater loading beyond it's bearing strength.
A large new building containing deep foundations or basements is built up adjacent to a subsisting building, that can impact the existing building significantly.
TYPES OF UNDERPINNING
Underpinning is provided to make the foundation system stronger by expanding the subsisting foundations or joining new foundations as well as enhancing the properties of the soil underneath the foundations devoid of touching the building in any way.
UNDERPINNING METHOD 1: PIT METHOD
It is performed in the following way:
Initially, a temporary foundation system is built up around the prevailing one.
Then a pit is dug around and underneath the subsisting foundations, to lessen load-bearing process.
After that, a new foundation is constructed underneath the prevailing one by filling the pit with concrete.
As soon as the concrete is set, the temporary foundations are removed so that the load is stabilized onto the improved foundation system.
The whole process is completed in small sections at once, not for the complete building. Each section ranges from 8' to 12' long (2 - 4m approx) based on the size of the building. The new sections are intercalated among the old to make the entire system secured.
UNDERPINNING METHOD 2: NEEDLE BEAM METHOD
It is performed in the following ways :
Initially two micropiles are built up at a certain distance from the building with a micropiling rig.
After that a big hole is cut to capture the needle beam.
The RCC needle beam is built up over the piles and inside the foundation wall.
As soon as the beam is set, fill in the earth over the beam. The new foundation system is now capable of bearing the extra load.
With this method, the inside of the building remains unaffected.
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UNDERPINNING METHOD 3: MICROPILING METHOD
It is performed in the following ways :
The micropile should be built up just underneath the subsisting foundation at an angle.
Excavate earth till the top of the micropile.
After that take out all earth by hand between the pile and the subsisting foundation, developing a cone shaped void that stands on the micropile.
Fill in this void with concrete. As soon as it is set, the subsisting foundation can move forces to the micropile, as a result the strength is increased significantly.
Reiterate this process periodically.
