I have to calculate the optimal thickness of well steining for a well foundaton having external diameter 11.6 m and depth 30 m.
IRC 78-2014 gives the formula h =kd√l .Using this formula, thickness will be about 1.9 m. It has been proposed to use Jack down method of well sinking.
Clause 708.2.3.5 of IRC:78-2014 allows to adjust the steining thickness according to design and construction requirement if specialised method of sinking such as jack down method are adopted.
Some case studies to mention here are:
Signature bridge, wazirabad in north delhi having 0.8m steining thickness for a well diameter 8m and depth 35-39 m (jack-down method used here)
Pretensioned sutlej bridge in Punjab having steining thickness 1.05m tapered to 0.75m for well having diameter 6m and depth 32m. (jack down method not used here)
According to the book "Soil Mechanics and Foundation" by B.C. Punmia page 789, steining thickness is given by
t =D/2{1-√1-4r/ρD} ; t is thickness, D is Dia of well, r is unit skin friction, ρ is unit weight of concrete for steining.
As per this equation for a constant skin friction, steining thickness should decrease with increase in diameter of well.
According to the book "Structural detailing in Concrete" by M. Y. H. Bangash, thickness of steining is given by
t=k(0.01H+0.1D) ; t is thickness, k is sub soil constant, D = external dia of wall , H is depth of well.
Using any of the formula, the thickness of steining wont come close to the thickness provided in the case studies i mentioned above.
By using Jack-down method of well sinking, thickness will be reduced, but how to calculate the optimum thickness of well steining in case of jack-down method?
I notice that the steining thickness equation provided in IRC 78-2014 gives the thickness which increases cost of the project.
Your esteemed comments and experiences are highly welcomed and appreciated on this topic.
Finite element model -- try AXISHELL from UCB or similar.
Do a plastic rather than an elastic analysis.
Good question.. Please share me the best answer might you trust...
Regards…
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