Due to their availability and ease of use, sheet pile retaining walls are widely used in the construction sector.
Sheet piles are used as permanent structures to protect adjacent structures. They prevent earth movement near a foundation, especially if the soil is very soft. In addition, sheet pile retaining walls are used as support during excavation work, etc.
The procedure described in the “Static Analysis” section explains the method for calculating the required length of a sheet piling wall to accommodate the excavated mass.
Structural analysis
A general method is available for the analysis and design of sheet pile retaining walls. The required length of the sheet piles is taken into account during design.
Design process in the book Basic Construction Principles by Braja M. Das is used for structural analysis and design.
Figure 01 shows the arrangement of the sheet pile penetrated into the ground and its deformation pattern.
Figure 01: Application of ground pressure on sheet piles penetrated into the ground
The variation of earth pressure on the sheet pile wall is shown in Figure 2.
The net pressure parameters required to determine the required depth of the sheet piling wall and the bending moment variation required to determine the section modulus of the sheet piling wall are given in Figure 2.
The equation derived from the variation of the soil pressure diagram in Figure 2 is used to determine the required sheet piling depth to accommodate the excavation.
Figure 02: Variation of bending moment in the sheet piling wall
WORKING EXAMPLE
ASSUMPTIONS AND PARAMETERS
The analysis and design considered the following assumptions and design data.
Height to water table from finished ground level 1.5 m
- Concrete density 25 kN/m 3
- Soil density 18 kN/m 3 ·
- Density of saturated soil 20 kN/m 3
- Density of submerged soil 10 kN/m 3
- Water density 10 kN/m 3
- Angle of friction with the ground 30 0
CALCULATION OF INVESTMENT LENGTH
The structure analysis was carried out according to the procedure discussed previously.
In this section, the calculation of lateral earth pressure is carried out by calculating the relevant parameters and evaluating the length of the sheet piling wall.
Taking into account the nature of the soil layer, the average friction angle is assumed in this calculation.
CALCULATION OF THE SIDE PRESSURE COEFFICIENT OF THE EARTH
Angle of friction with the ground = 30 0
Ka = (1-Sin φ ) / 1+sin φ )
= (1-Sin 30) / 1+Sin 30)
= 0.333
Kp = (1+Sin φ ) / 1-sin φ )
= (1+Sen 30) / 1-Sen 30)
= 3,000
Penetration depth = L 4 + L 3
= 3.368 + 0.524
= 3.892m
Total length of sheet piling wall = L 1 + L 2 + L 3 + L 4
= 1.5 + 1.5 + 3.368 + 0.524
= 6.892m
The minimum required length of the sheet piling wall is 6,892 m. Sheet pile walls with a length of 9 m can be used for construction. If sheet piles with a length of 9 m are used for construction, the safety factor is 1.3.
The Retaining Wall Design article provides a method for calculating the stability of normal concrete walls that is simpler than the one we discussed in this article.
