Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 7 RETAINING WALL
Figure 7.24 Various types of Anchoring for sheet pile walls (a) Anchor Plate or Beams; (b) Tie Back;
(c) Vertical Anchor Pile; (d) Anchor Beam with Batter Piles
The above figures also illustrated the proper locations for placement of various types of anchors.
Readers can refer to ‘Principles of Getechnical Engineering’ by M. B. Das for further guidance on the
design of the various types of anchors.
7.6.3.4 Some Considerations on Sheet Pile Wall Design
a) Selection of Analysis Method
Designers must be careful when selecting the design approach to adopt i.e., the Fixed-end or Free
end method. Walls installed in soft cohesive soils, may not generate sufficient pressure to achieve
fixity and in those soils it isrecommended that free earth conditions are assumed. Fixed earth
conditions may be appropriate where the embedment depth of the wall is taken deeper than that
required to satisfy lateral stability, i.e. to provide an effective groundwater cut-off or adequate
vertical load bearing capacity. However, where driving to the required depth may be problematic,
assumption of free earth support conditions will minimise the length of pile to be driven and ensure
that the theoretical bending moment is not reduced by the assumption of fixity. When designing a
wall involving a significant retained height and multiple levels of support, the overall pile length will
often be sufficient to allow the designer to adopt fixed earth conditions for the early excavation
stages and take advantage of reduced bending moment requirements.
b) Construction Sequence
(d) Anchor beam supported by batter (compression or tension) piles
The design of tied-back or braced system should also consider the sheet pile design requirements at
each and every stages of the construction sequence, i.e. excavation, strutting, anchoring and
lowering of ground water table. This construction sequence shall be detailed in the construction
drawings as wrong construction sequence may cause large changes in the bending moment, shear
stress and overall stability of the wall.
c) Permissible Stress of Steel Sheet Pile
In the design of temporary sheet pile wall, the permissible steel stresses for the structural design of
the sheet pile can be increased slightly. For instance, Piling Handbook, Archelor Group suggested
that the permissible steel stresses for temporary works (wall to last not more than 3 months) shown
in Table 7.3 be used in the structural design in the sheet piles and other steel components of the
wall such as walins, struts and tie rod.
March 2009 7-31