Well Foundations Dr.K.V.Krishna Reddy

Classification based on Construction methodology

Classification based on Shape

BED LEVEL HARD STRATUM

Steps in construction of open foundation

2

3. Steining not more than 1. 5m is cast to ensure the well is 3. Steining not more than 1.5m is cast to ensure the well is floating due to buoyancy and the top surface is always above water level 4. The process is continued till the curb rests on river bed 5. Once river bed is reached, excavation is carried out using cranes positioned on pontoons. Not more than 1 to 2m is excavated at a time. 6. As the well sinks under self weight, further Steining is cast. 7. If required kentledge load is provided to expedite sinking process

Once desired depth is formed 8. 9.

ballast, dry conc Gravel, etc….. It does not penetrate through the soil, but rests on leveled river / canal bed . A concrete cap is provided at the top and riprap is provided at the bottom all round to protect from scour Grounded by

When the velocity of flow is less than 6m/s. BED LEVEL OF CANAL /RIVER Floating or Box Caissons are used where the flow of water is less..i.e.. When the velocity of flow is less than 6m/s. When low volumes of traffic like bullock carts, tractors, men and materials are to be moved across a canal or river tributary.

They are used in case of soft soils, running soils where the caisson just caves in before sinking These are also found useful when hard strata is encountered in the process to reach the desired depth where blasting is required pressure

Misc Equipment

movement of men and excavated material.

top Water level

Reversed when men come back compression and decompression is done slowly to prevent fatal accidents. The Maximum depth of sinking is limited to 35m to 40m as humans cannot bear pressure more than 400kN/sq.m. Men are not allowed to work for more than 2 hours at a stretch. Fresh air is circulated at regular intervals

Greater pressure for prolonged time may result in Caisson sickness / Caisson disease, which is a nerve disorder

Experienced workmen required Accident prone Caisson’s Disease Bearing capacity can be determined Well suited for soft and running soils

Component design parameters

Well cap is designed as a slab considering that the load from the top in the form of a cone with an apex angle of 60 degrees is carried by this and the rest is transfered to the Steining

PROBLEMS IN WELL SINKING Tilts Shifts Obstructions during sinking Wave action during sinking Impact forces due to equipment during sinking

Corrections for tilts