What is Well foundation?

• Well foundation is a type of deep foundation which generally provided for construction of bridges.
• The art of well foundation is well known to Indians, since world famous “Taj mahal” stands on well foundation.

Advantages:

1. It can with stand large lateral forces as in case of piers, alignments, tall chimneys etc. in a better way due to rigidity and large cross section.
2. It is possible to examine strata and decide depth of founding the well.
3. No dynamic load is involved during construction of well foundation hence, adjoining structures are not affected.

Components of Well foundation:

Various component of well foundation are described below:

1. Cutting edge
2. Steining
3. Curb
4. Concrete seal or bottom plug
5. Top Plug
6. Well cap

1. Cutting Edge:

• The function of the cutting edge is to facilitate easy penetration or sinking into the soil to the desired depth. 
• As it has to cut through the soil, it should be as sharp as possible, and strong enough to resist the high stresses to which it is subjected during the sinking process.
• Hence it usually consists of an angle iron with or without an additional plate of structural steel.Sinking of well with sharp edge is fast however if strata with boulders is met, then the edge may get damaged.

2. Steining:

• The steining forms the bulk of the well foundation and may be constructed with brick or stone masonry or with plain or reinforced concrete occasionally,
• The steining has uniform thickness throughout its depth. 
• It is considered desirable to provide vertical reinforcements to take care of the tensile stresses which might occur when the well is suspended from top during any stage of sinking.

3. Curb:

• The well curb is a transition member between the sharp cutting edge and the thick steining. 
• It is thus tapering in shape. 
• Reinforced concrete is used to make curb as it carries severe stress during the sinking process.

4. Concrete seal or bottom plug:

• After the well foundation is sunk to the desired depth so as to rest on a firm stratum, a thick layer of concrete is provided at the bottom inside the well, generally under water. 
• This layer is called the concrete seal or bottom plug, which serves as the base for the well foundation.
• This is primarily meant to distribute the loads on to a large area of the foundation, and hence may be omitted when the well is made to rest on hard rock.

5. Top Plug:

• After the well foundation is sunk to the desired depth, the inside of the well is filled with sand either partly or fully, and a top layer of concrete is placed. 
• This is known as ‘top plug’.
• The sand filling serves to distribute the load more uniformly to the base of the well, to reduce the stresses in the stening and to increase the stiffness of the well foundation.
• However, as this adds to the weight and load transmitted to the foundation stratum, the engineer has to consider the desirability or otherwise of providing the sand filling from the port of view of bearing power and settlement.
• The top plug and concrete serve to transmit the loads to the base in a uniform manner.

6. Well cap

• The well cap serves as a bearing pad to the superstructure, which may be a pier or an abutment. 
• It distributes the superstructure load onto the well steining uniformly.