8/2/2019 Assignment 5 CE533 December 2011

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CE533 Advanced Foundation Engineering

 Assignment 5   Date of Submission: Tuesday 7th

April 2012

 Full Marks: 80 Caution: Always convert the units to the SI system for any numerical

Remark: Assume any values required with justification

1.  A mat foundation of size 15m x 10m rests on a general c-φ soil having c = 95 kN/m2, φ =

28° and unit weight of 18.5 kN/m3. The base of the footing is located at a depth 3m

below the ground surface and is subjected to a centric vertical load. Determine the gross

allowable bearing capacity of the foundation system. Find all the factors from

expressions and not from tables. Use Caquot and Kerisel’d expression to find N γ. (5) 

Considering a factor of safety of 2.5, what would be and net allowable bearing capacity

of the concerned foundation? (2) 

2.  A mat foundation of size 12m x 18m is located at a depth of 1 m in a fully saturated clay

stratum having an undrained cohesion 125 kN/m2 and a unit weight 19.5 kN/m3. What is

the net ultimate and net allowable bearing capacity of the foundation? (2+2) 

Consider a factor of safety of 2.5. Under such condition, what is the maximum

superstructure load that the foundation can carry? (2)

In order to reduce the net pressure increase on the foundation soil to a minimum, what

should be the depth of embedment of the foundation? (2) 

3.  A mat foundation of size 7m x 12m is constructed on homogeneous dense sand having an

embedment depth of 2.5m. The average standard penetration value is obtained as 18.

Under the applied loading, the maximum settlement of the mat foundation is observed to

be 18mm. Determine the net allowable bearing capacity of the foundation. (2) 

Following Meyerhof’s recommendation, determine the ratio of the calculated and

observed maximum settlement for this foundation. (2) 

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4.  Following conventional rigid analysis, pictorially represent the stress distribution at the

marked points for the mat foundation detailed in Figure 1. Consider the size of all the

columns to be 200mm x 200mm. (15) 

5.  Considering the strip AGH'J' of Figure 1, perform a ‘Factored Load Analysis’ to find out

the BMD of the strip (5+3) 

In the light of the above, investigate the applicability and limitation of the adopted

technique. Support the investigation with logical and mathematical evidence. (5)

Suggest an improved methodology to overcome the observed limitation, supported by

mathematical computations. Based on the suggestion, draw the BMD and SFD of the

strip AGH'J'. (8)

With the aid of the flexural response of the strip AGH'J' as obtained from the suggested

technique, determine the thickness required for the mat foundation from moment, one-

way and two-way shear considerations. (2+2+6)

6.  If the mat foundation describe in Figure 1 is located in a sandy stratum of depth 15m and

having  E s = 30 MPa and ν s = 0.3, what modulus of subgrade reaction should be

considered for a flexible footing design. The depth of embedment of foundation is 5 m.

Consider the settlement to be determined at the centre of the mat. (5) Considering the total thickness of concrete mat to be 1000 mm, determine the net

deflection, shear force and moment at the point P(2m,2m) due to the columns 3 and 4.

The modulus of elasticity and Poisson’s ratio of concrete is E  f = 25GPa and  µ  f = 0.15.(10) 

 x

 x' 

 y' y

12 m

8 m

1 2 3

4 5 6 

7 8 9

 A B C 

 D E 

F 

G H I  H' 

 I' 

 J' 

2 mP 2,2

Figure 1

Q1=500 kN 

Q2=280 kN 

Q3=900 kN 

Q4=1450 kN 

Q5=930 kN 

Q6=220 kN 

Q7=1560 kN 

Q8=2200 kN 

Q9=340 kN