Geotechnical Engineering

DHARM

SETTLEMENT ANALYSIS 415

12 m

48 m

6m

24 m

12 m Centre of

clay layer

(a) Plan (b) Pictorial view

Fig. 11.16 Details of foundation (Ex. 11.6)

The vertical stress increment at the centre of the clay layer may be obtained by dividing

the loaded area into four rectangles as shown.

m = B/z = 6/12 = 0.5

n = L/z = 24/12 = 2.0

Influence factor from Fadum’s chart = 0.135

σz = 4 × 1800 × 0.135 = 97.2 kN/m^2

Immediate settlement:

Since the thickness of the layer is less than 4B, Steinbrenner’s coefficient Is from Fig. 11.3

may be used in

Si = q. B

() 1 −ν^2.

E

I

s

s and applying the principle of superposition for the four rectangles as in

the case of stress.

L/B = 24/6 = 4, H/B = 24/6 = 4 (H here is the thickness of the clay layer).

Since all four rectangles are identical,

total value of Is = 4 × 0.48 = 1.92

∴ Si = 180 × 6 ×

075

33000

.

× 1.92 × 0.8 (assuming ν = 0.5 and rigidity factor as 0.8)

= 0.0377 m = 37.7 mm

Consolidation settlement:

Initial effective overburden pressure at centre of clay layer

= 18 × 12 – 9.81 × 8 = 137.52 kN/m^2

Consolidation settlement, Sc = H.

∆e

()1+e 0

= 24 ×

002

169

.

. m = 0.284 m = 284 mm
Total settlement S = Si + Sc = 37.7 + 284.0 mm = 321.7 mm.