Geotechnical Engineering

DHARM

SETTLEMENT ANALYSIS 411

11.9 ILLUSTRATIVE EXAMPLES

Example 11.1: A reinforced concrete foundation, of dimensions 18 m × 36 m, exerts a uniform

pressure of 180 kN/m^2 on a soil mass, with E-value 45 MN/m^2. Determine the value of immedi-

ate settlement under the foundation.

The immediate settlement, Si, is given by:

Si =

qB

E

I

s

s

.( 1 −ν^2 ).

Es = 45 MN/m^2 , q = 180 kN/m^2 , B = 18 m

Assume ν = 0.5

Is for L/B = 36/18 = 2 is 1.00

∴ Si =

180 18 1 0 5

45 1000

100

×−^2

×

×

(.)

.m

= 0.054 m = 54 mm.
Example 11.2: The plan of a proposed spoil heap is shown in Fig. 11.13(a). The heap will stand
on a thick, soft alluvial clay with the E-value 18 MN/m^2. The eventual uniform bearing pres-
sure on the soil will be about 270 kN/m^2. Estimate the immediate settlement under the point
X at the surface of the soil.
The area is imagined to be divided into rectangles such that X forms one of the corners
for each. This is as shown in Fig. 11.13(b).

The structure is flexible and the soil deposit is thick.

Therefore, Si = q. B

()

.

1 −ν^2

E

I

s

t

It being Terzaghi influence value, dependent on L/B.

By the principle of superposition,

Si = q.

()

..

1 2

121233

−

++

ν

E

IB I B I B

s

ejtt t

For Rectangle (1):

L/B = 150/50 = 3, It 1 = 0.88

For Rectangle (2):

L/B = 50/50 = 1, It 2 = 0.56

For Rectangle (3):

L/B = 50/25 = 2, It 3 = 0.76

Es = 18 MN/m^2 , q = 270 kN/m^2

Assume ν = 0.5

∴ Si =

270 1 0 5

18 1000

×−^2

×

(.)

(0.88 × 50 + 0.56 × 50 + 0.76 × 25)

=

270 0 75

18 1000

×

×

.

× 91 m ≈ 1.024 m.