Example 3: Sheet pile wall

Earth pressure - Design examples - Example 3: Sheet pile wall

Sheet pile walls are typical structures which are exposed to earth pressure, both active andpassive. This example shows excavation in sand with an unsupported sheet pile wall andfocuses on the following two solutions:

1. Original material behind sheet pile wall2. Alternative solution with material replacement behind the sheet pile wall. Leca replaces thesand. Relevant for sheet pile walls used in long-term or permanent structures.

The main intention with this example is to find the maximum moment in the sheet pile wall andnecessary penetration depth below bottom excavation for the two solutions. This will becalculated base on the resulting earth pressure (pr = pP – pA) on the sheet pile wall (see

Figure 15).

Assumptions:- Unsupported, stiff wall- Standard earth pressure - The entire wall will be positioned above the ground water level.- Roughness r = 0.5Table 3 shows the material properties.

Material Unit weightabove G.W.L.

g

[kN/m3]

Frictionangle

j

tanj Earth pressurecoefficient

ActiveKA

PassiveKP

Sand gsand = 18 39 0.81 0.54 0.3 4

Leca8 -20 mm

gLWA = 4 39 0.81 0.54 0.3 4

Table 3 Material parameters

This example uses a safety factor of F = 1.5 for the structure.

The necessary penetration depth below bottom excavation is calculated according to classicalearth pressure theory, and Figure 15 shows the assumed resulting pressure distribution for anunsupported sheet pile wall in sand. The two points m and o indicate the maximum momentand centre of rotation respectively. The active and passive pressure switches side at point o. Above this point the active side is onthe left and the passive side is on the right. It is opposite below this point. This is used to calculate the penetration depth below bottom excavation and the maximummoment.

Figure 15 Assumed resulting pressure distribution (illustration)(click to enlarge)

1: Original material behind a sheet pile wall

Figure 16 shows the profile for solution 1 with the original material behind the sheet pile wall.

Figure 16 Profile for a sheet pile wall with original material (click to enlarge)

Depth [m] Calculation Result [kN/m2]0 3

5 30

5 + Dm 66.6 Dm - 30

5 + Dm + D166.6 (Dm+D1) +

360

Table 4 Calculation of resulting earth pressure at relevant depths

Calculate D0:

ÞD0 = 0.45

Maximum moment (Mmax) at point m results in 0 shear force (Q) at the same point. This givesDm (see Figure 17) which in turn gives Mmax:

Q1 = Q2 Þ Dm = 2.09 Þ Mmax = 285.5 kNm/m

Figure 17 Shear force (illustration)(click to enlarge)

D1 and D2 are calculated from:

Þ D1 = 2,12 m and D2 = 0.36 m

This gives: D = Dm + D1 + D2 = 2.09 + 2,12 + 0.36 = 4.57 m

2: Leca behind sheet pile wall

Figure 18 shows an alternative solution with Leca behind the sheet pile wall. The original sandlayer is also used as a base layer.

Figure 18 Profile of a sheet pile wall with Leca (click to enlarge)

Depth [m] Calculation Result [kN/m2]

0 3

0.8 4.62

5 10.26

5 + Dm 66.6 Dm – 10.26

5 + Dm + D166.6 (Dm+D1)

+136.8

Table 5 Calculation of resulting earth pressure at relevant depths

Calculate D0:

Þ D0 = 0.15

Q1 = Q2 Þ Dm = 1.20 Þ Mmax = 105.91 kNm/m

D1 and D2 are calculated from:

Þ D1 = 1.53 m and D2 = 0.43 m

This gives: D = Dm + D1 + D2 = 1.20 + 1.53 + 0.43 = 3.16 m

The solution using Leca reduces the penetration depth by 1.41 m and the maximum momentby 60 %.

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