DHARMCAISSONS AND WELL FOUNDATIONS 81119.15 Enumerate the various methods for the analysis of lateral stability of a well acted on by horizon-
tal forces.
19.16 How is the I.R.C. Method for the analysis of the Lateral Stability of a Well Foundation superior?
19.17 Discuss the construction aspects of Well Foundations. What are ‘Tilts and Shifts’? What are the
remedial measures to control these?
19.18 Design a Cylindrical Open Caisson to be sunk through 30 m of sand to support a load of 50 MN.
The allowable bearing pressure is 1700 kN/m^2. Test the feasibility of sinking the caisson, taking
the skin friction as 27 kN/m^2. What is the thickness of the concrete seal required?
19.19 A Cylindrical Open Caisson, 18 m deep, has the external and internal diameters of 7.5 m and 6
m respectively. Taking the water level to be 1 m below the top, determine the thickness of the
concrete seal required. Assume σc = 2360 kN/m^2 and γc = 24 kN/m^3. Allowable perimeter shear
stress = 660 kN/m^2.
19.20 A Box Caisson is 20m × 10m × 12 m high. The weight of the Caisson is 12 MN and its centre of
gravity is 5.4 m above the base. Check if the caisson is stable. If it is not, suggest how it can be
made stable. The unit weight of water is 10.1 kN/m^2.
The total load is 55 MN, acting at an eccentricity of 0.20 m. If the base is at a depth of 10.5 m
below water level after installation, determine the net soil pressures.
19.21 A Cylindrical Well is of 6 m external diameter and 3.6 m internal diameter, and is to be sunk to
a depth of 15 m below the scour level. It is subjected to a horizontal load of 600 kN at a height of
9 m above the scour level. Determine the allowable resisting force due to earth pressure, using
Terzaghi’s approach assuming that (a) the well rotates about a point above base, and (b) the well
rotates about the base. γ′ = 9.9 kN/m^3 ; φ = 30°, and factor of safety against passive resistance
= 2.5.
19.22 A Cylindrical Well has an external diameter of 8 m and is sunk into sand to a depth of 21 m
below the scour level. The well is acted upon by a moment of 40,000 kN.m about the scour level
due to a horizontal force of 2,000 kN. Check whether the well is safe assuming (a) it rotates
about a point above the base, and (b) it rotates about the base. γ′ = 10 kN/m^3 , φ = 30°. Use
Terzaghi’s Approach, with a factor of safety of 2 against passive resistance.