Geotechnical Engineering

DHARM

772 GEOTECHNICAL ENGINEERING

determine the minimum thickness of the seal required. Check for perimeter shear also.
Assume σc = 2400 kN/m^2 and γc = 24 kN/m^3 , for concrete. Allowable perimeter shear stress
= 650 kN/m^2.

Solution:

Referring to Fig. 19.8,

H = 20 – 2 = 18 m

From Eq. 19.6,

q = (γwH – γct)

t being the thickness of concrete seal.

∴ q = (10 × 18 – 24t)

From Eq. 19.4,

t = 059.D

q

i

σc

Squaring, t^2 = (0.59)^2 (6)^2 ×

()180 24

2400

− t

1.8 m

33 m

Concrete

seal

2.4 m

6.0 m

Fig. 19.7 Open Caisson (Ex. 19.1)

or t^2 + 0.125t – 0.940 = 0

or t = 0.91 m

t may be taken as 1 m.