DHARMBEARING CAPACITY 605(b) Give the approximate formula you will use for the design of:
(i) square footing; (ii) circular footing; and
(iii) rectangular footing. (S.V.U.—B.E., (R.R.)—Dec., 1968)
14.11 A strip footing, 1 m wide, rests on the surface of a dry cohesionless soil having φ = 25° and
γ = 18 kN/m^3. What is the ultimate bearing capacity? What is the value, if there is complete
flooding? Assume Nγ = 10.
14.12 Compute the safe bearing capacity of a 1.2 m wide strip footing resting on a homogeneous clay
deposit at a depth of 1.2 m below ground level. The soil parameters are c = 40 kN/m^2 , φ = 0°, and
average unit weight of soil = 20 kN/m^3. Factor of safety = 3.
(S.V.U.—B.Tech., (Part-time)—Sept., 1983)
14.13 Compute the safe bearing capacity of a continuous footing 1.5 m wide, at a depth of 1.5 m, in a
soil with γ = 18 kN/m^3 , c = 18 kN/m^2 , and φ = 25°. Terzaghi’s factors of φ = 25° are Nc = 25, Nq =
12.5, and Nγ = 10. What is the safe load per metre run if the factor of safety is 3?
14.14 What is the safe bearing capacity of a square footing resting on the surface of a saturated clay of
unconfined compression strength of 90 kN/m^2? Factor of safety is 3.
14.15 What is the ultimate bearing capacity of a square footing, 1 m × 1 m, resting on a saturated clay
of unconfined compression strength of 180 kN/m^3 and a bulk density of 18 kN/m^3 , at a depth of
1.5 m? (S.V.U.—Four year B.Tech.,—Oct., 1982)
14.16 Compute the allowable bearing capacity of a square footing of 2 m size resting on dense sand of
unit weight 20 kN/m^3. The depth of foundation is 1 m and the site is subject to flooding. The
bearing capacity factors are: Nc = 55, Nq = 38, and Nγ = 45.
(S.V.U.—B.E., (Part-time)—Dec., 1981)
14.17 What is the safe bearing capacity of a circular footing of 1.5 m diameter resting on the surface of
a saturated clay of unconfined compression strength of 120 kN/m^2 , if the factor of safety is 3?
14.18 A three-storey building is to be constructed on a sand beach. Ground water rises to a maximum
of 3 m below ground level. The beach sand has the following properties: γd = 17.5 kN/m^3 , φ = 32°
(Nc = 40, Nq = 25, Nγ = 30).
The maximum column load will be 700 kN. Determine the sizes of footing for depths of 1 m and
2 m using a factor of safety of 3. Settlement are not to be considered. Evaluate the two alterna-
tives from practical consideration (difficulties of construction and cost).
(S.V.U.—B.Tech., (Part-time)—Sept., 1982)
14.19 A circular footing rests on a pure clay with qu = 270 kN/m^2 , at a depth of 1.8 m. Determine the
diameter of the footing if it has to transmit a load of 720 kN. Assume the bulk unit weight of soil
as 18 kN/m^3 and the factor of safety as 3.
14.20 Determine the size of a square footing at the ground level to transmit a load of 900 kN in sand
weighing 18 kN/m^3 and having an angle of shearing resistance of 36° (Nγ = 46, Nq = 43). Factor of
safety is 3. What will be the modification in the result, if the footing may be placed at a depth of
1 m below ground surface? Assume, in this case, the water table may rise to the ground surface.
γ′ = 9 kN/m^3.
14.21 Determine the net ultimate bearing capacity of a rectangular footing, 1.2 m × 3.0 m, placed at
1.8 m below the ground in a saturated clay with a unit weight of 90 kN/m^2. Use Skempton’s
approach.
14.22 A machine with base 6 m × 3 m weighs 9,000 kN. It is to be placed on a clay with cohesion of 120
kN/m^2 , at a depth of 1 m, γ = 20 kN/m^3. Assuming a factor of safety of 3, design a rectangular
footing foundation to support this machine.