Pore pressure, effective stress and drainage - The Mechanics of Soils and Foundations - page 81

Figure 6.13 Stress in the ground - Example 6.2.

u = γ

w h w

= 10 ×− 3 =− 30 kPa

σ z = σ

− u = 60 + 30 = 90 kPa

z

(b) Water surface 3 m above ground level:

σ z = γ z + γ w z w = (20 × 3) + (10 × 3) = 90 kPa

u = γ w h w = 10 × 6 = 60 kPa

σ z = σ − u = 90 − 60 = 30 kPa

z

Example 6.3: Calculation of stress in the ground below a foundation The concrete
bridge pier in Fig. 6.14 is 4 m tall, it has an area of 10 m 2 and carries a load of
1 MN. (The unit weight of concrete is 20 kN/m 3 .) The pier is founded on the

bed of a tidal river where there is at least5mofsand with a unit weight of 20 kN/m 3 .
The river bed is at low tide level and at high tide there is 3 m depth of water.

γ =

c

Figure 6.14 Stress in the ground - Example 6.3.