6 BASIC ELEMENTS OF A WELL FOUNDATION

Well foundations have their origins in India and have been used for hundreds of years to provide deep foundations to important buildings and bridges. The foundations of wells were freely used for bridges over major rivers during the Mughal period. Mughal monuments including the Taj Mahal are built on the foundations of wells. A good foundation provides a solid and spacious structure. This foundation has a maximum sectional modulus for a given cross-sectional area. Wells can resist large horizontal forces and vertical loads, even when the unsupported length is large in a bad river bed. The foundation of a well is monolithic and relatively rigid in its structural behavior.

A good foundation is a type of foundation that is usually built in parts to a surface and sinks to its final position, where it forms a permanent foundation. Figure 1 Shows a typical section of the foundation of a circular well.


Figure-1 Section of Well Foundation
Figure-1 Section of Well Foundation

1. well-cap

It is an RCC slab placed on top of the well stabilizing so that loads and moments can be transmitted from the pier to the well or the well below. The size of the well cap is the same as that of the well, with 150 mm of potential overhand all the way around to accommodate longer piers. It is designed as a two-sided slab with partial stability on the supports. The top of the well cap is usually placed at a low water level in the case of seasonally flowing rivers or in the case of perennial rivers. good cap thickness usually occurs between 1500mm 2000 mm. So far,

2. staining

It is the main body of the well that transfers the load to the base of the well. Staining is usually of reinforced concrete. The minimum grade of concrete used in staining is M20 310kg/m with cement content. not less than3, To facilitate sinking well a 75 mm to 100 mm. off-set of Well at its junction with the curb is provided in Steining.

The thickness of the staining of the well is 500 mm. should not be less than nor less than the one below.

T = Kd*(L1/2,

Where,

Tea = minimum thickness of concrete staining, M,

D = outer diameter of circular well or small plan dimension of dumbbell bell-shaped well or twin D well, M,

Took = depth of the well M Below LWL or above the well cap whichever is higher,

K = a constant (taken as) depending on the nature of the subsoil and the Steining material 0.30 For circular well And 0.039 for twin – de well 10% above the respective value for concrete staining in sandy layer and in case of clayey soil).


3. Well Ankush

It is wedge-shaped RCC ring beam located at the bottom of the well provided for sinking convenience. Well curbs are state-of-the-art for the well and made of reinforced concrete using grade controlled concrete M25, The cutting edge usually consists of mild steel of an angle equal to 150 mm. In case of anticipated blasting, the exterior of the well should be protected with a 6 mm thick steel plate and a 10 mm thick plate on the inner face up to the top of the curb and a 6 mm plate further up to a height of 3. m above the top of the curb.

4. bottom plug

After the well is submerged to the required depth, the base of the well is filled with concrete. This is called the bottom plug. It acts like an inverted dome supported by stenting on all sides and transmits the load to the subsoil and acts as a raft against soil pressure from below. The minimum grade of concrete used in the bottom plug is M15. The thickness of the bottom plug shall not be less than half of the dredge-hole diameter nor less than the value calculated using the following formula.

plug down equation

Where,

woo = total bearing pressure at the base of the well,

FC = the flexural strength of the concrete at the bottom plug, and,

? = Poisson’s ratio to concrete, 0.18 to 0.20,

5. top plug

The top plug is a non-reinforced concrete plug, usually provided with a thickness of about 600 mm below the well cap to transmit the load from the pier to the steering. The minimum grade of concrete used in Top Plug is M15.

The space inside the well between the top of the top plug and the top of the bottom plug is usually filled with clean sand, to increase the stability of the well against overturning. While this practice is good in the case of wells located on sand or rock, the desirability of sand filling for wells resting at soil level is questionable, as it increases the load on the foundation and may lead to over-settlement. In the latter case, sanding is done only for the part up to the top of the well, and the rest is left blank.

6. intermediate plug

As discussed above, for wells resting at soil level, it is preferable not to completely fill the space inside the well with sand. In such cases, sand filling is not carried out or sand is not filled to the score level. A solid plug covering the fill is usually provided, known as an intermediate plug. Usually, the thickness of the intermediate plug is taken as 500 mm.


Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.