Solved Problem on Foundation Engineering

Linked Answer Questions
Statement for Linked Answer Questions Q1 and Q2:
A multistory building with a basement is to be constructed. The top 4 m consists of loose silt, below which dense sand layer is present up to a great depth. Ground water table is at the surface. The foundation consists of the basement slab of 6 m width which will rest on the top of dense sand as shown in the figure. For dense sand, saturated unit weight = 20kN/m3, and bearing capacity factors Nq = 40 and Nγ = 45. For loose silt, saturated unit weight = 18kN/m3, Nq = 15 and   Nγ = 20.Effective cohesion c’ is zero for both soils.Unit weight of water is 10 kN/m3. Neglect shape factor and depth factor.
Average elastic modulus E and Poisson’s ratio μ of dense sand is 60 x 103kN/m2 and 0.3 respectively.

 

 

Q1. Using factor of safety = 3, the net safe bearing capacity (in kN/m2) of the foundation is:

 

(A) 610 (B) 320 (C) 983 (D) 693

 

 

Q2. The foundation slab is subjected to vertical downward stresses equal to net safe bearing capacity derived in the above question. Using influence factor If = 2.0, and neglecting embedment depth and rigidity corrections, the immediate settlement of the dense sand layer will be:

 

(A) 58 mm (B) 111 mm (C) 126 mm (D) 179 mm