TOWER FOUNDATION

SUBMITTED BY-DISHANT KUMARB.TECH(CIVIL ENGG.)ROLL NO.- 111000054

What is foundation ?

“The lowest load-bearing part of a building, typically below ground level”.

Why do we make a foundation ?

“To support a structure and transmits loads directly to the underlying soil or rock”.

Material use in tower foundation !

Concrete -• All the properties of concrete regarding its strength under compressing , tension, shear, punching and bending etc. as well as well as workmanship will conform to IS :456 FO 1978.• cement concrete used for the foundations shall be M-150, 1 : 2 : 4 : 4 mix ratio.•  water used for mixing concrete shall be fresh clean and free from oil, acid and alkali, organic material .•  concrete shall be mixed in a mechanical mixer. Hand mixing shall not be permissible.•  stub angle shall be free of rust and cleaned thoroughly and painted with cement paste, made of 1 part of cement and3/4 part of  water .

TESTING OF SOIL !

• sub-soil water table• bearing capacity of soil• possibility of submergence• other soil properties

foundations should be casted and installed only after proper checking and approval.

Steps followed in designing of tower foundation !

How to find sub soil water table ?

• by using test borings, provided by soil engineer (geotechnical).• Number of borings and location of borings depends on site conditions.• Location of borings samples are indicated on engineer plan.• Borings indicate:  soil classification

EXCAVATION !

• all excavation for footings shall be made to the lines and grades of the foundation.• excavation walls shall be vertical.• Any sand, mud, silt or other undesirable materials which may have accumulated in the excavation pit shall be removed before placing concrete. 

Setting up of stubs !

• stub shall be set correctly in accordance with approved method at he exact location and alignments.• Setting of stub at each location shall be approved by the Assistant Engineer/Executive Engineer.

BACK-FILLING AND REMOVAL OF STUB TEMPLATE

• Back filling shall normally be done with the excavated soil, unless it consists of large boulders which shall be broken to a maximum size of 80 mm.•  back fill materials should be clean and free from organic or other foreign materials.• earth shall be deposited in  maximum 200 mm layers.• backfilling is started from the foundation end of the pits, towards the outer ends.• backfilling and grading shall be carried to an elevation of about 75 mm above the finished ground level to drain out water. • backfilling, 150 mm high earthen embankment (bandh) will be made along the sides of excavation pits and sufficient water will be poured in the backfilled earth for at least 24 hours.

CURING !

•  concrete after it is 24/72 hours (as the case may be) old shall be cured by keeping the concrete wet continuously for a period of 10 days after laying.• pit may be backfilled with selected earth sprinkled with necessary amount of water .• uncovered concrete chimney above the backfilled earth shall be kept wept wet by providing empty cement bags dipped in water fully wrapped around the concrete chimney for curing and ensuring that the bags are kept wet by frequent pouring of water on them.

PROTECTION OF TOWER FOUNDATION !

Special measures for protection of foundations shall be taken in respect of locations close to nallah, river beds, etc. Protection of foundations is also to be provided in the case of foundations located on the sloping ground of sand dunes or hills.

a) Benching b) Protection against cutting of soil by flow of water c) Revetment

Various method used for protecting foundation

PROTECTION AGAINST CUTTING OF SOIL BY FLOW OF WATER -

• By providing suitable crate of galvanized wire netting and meshing packed with boulders.

BENCHING -

• Soil at the higher level is cut and spread in the lower level so that the soil near the foundation becomes level.

RIVETMENT -

This method is generally used if the soil is gently sloping and there is no significant difference in the levels of the soil around the foundation.

This method is generally used where the tower foundation is located at a distance from the edge of river / nalla, etc.

This method is generally used where the ground surface is irregular or where there is significant difference in the levels of soil around the tower foundation.

• revetment protection is provided in the form of stone masonry walls around those sides of the foundation