Retaining Structures - Elements of Soil Mechanics - page 240

Now we see that treating the passive thrust as a permanent, unfavourable action affects Design
Approach 1 (Combination 1) and Design Approach 2. In the UK where Design Approach 1 is adopted,
the earth resistance partial factor γ Re = 1.0 and thus it is appropriate to treat passive pressure as a per-
manent, unfavourable action since the thrust derives from the same source as the active pressure and the
level of uncertainty in its value is the same (i.e. application of single source principle).

Example 8.3: Cantilever sheet pile wall

Calculate the minimum depth of embedment, d, to provide stability to a cantilever sheet pile wall,
retaining an excavated depth of 5 m using:

(a) Eurocode 7 GEO limit state, Design Approach 1;
(b) Gross pressure method.

′ = °

The soil properties are φ peak 30 , c ′ = 0, γ = 20 kN/m 3 .

Solution:

The problem is illustrated in Fig. 8.13a .
(a) Eurocode 7, GEO Limit State, Design Approach 1
Allowance is made for a future unplanned excavation Δ a equal to 10% of the clear height
( = 0.5 m). The pressure distribution is shown in Fig. 8.13b .
1. Combination 1 (partial factor sets A1 + M1 + R1)
From Table 5.1: γ G; unfav = 1.35; γ φ ′ = 1 0 . .

tan ′ tan 30

1 0

φ °

=

= °

φ ′ = tan

− 1

tan

− 1

30

d

γ φ .

′

5m

0.5m

P a1

P p1

d 0

d

O

P p2

P a2

B

(b) Pressure distribution

(a) Wall geometry

P a1

P p1

R

(c) Simplified pressure distributino

Fig. 8.13 Example 8.3.