Guidance Notes
GN-05 November 2020
Are Steel Sheet Piles Impermeable?
The answer to this question is a qualified YES!
Steel as a construction material is inherently 100% impermeable to the passage of water. However, steel sheet
piles have interlocks at discrete centres along the wall length, usually at 600 to 800mm centres, which when
left unsealed can allow water to pass through.
There are various methods to reduce or even completely stop water flow through the interlocks, as briefly
described below. Full details can be found in the Arcelor Piling Handbook, 9th Edition, Chapter 2.
Initial & temporary works sealing
For ‘temporary works’ conditions, or for the initial stages of a permanent basement, applying sealant to the
interlock can significantly reduce the flow, such sealants include:
•
Standard bituminous ‘void filler’ type
•
Expanding hydrophilic type.
•
Compression sealant (polymer or modified silane
polymer)
All three types of sealant are usually pre-applied to the sheet
pile interlocks prior to installation. Although some damage or
disturbance to the sealant can be expected during the pile
installation, the resulting voids in the interlocks are reduced
such that the overall wall permeability is also reduced. Any
residual ground water inflow would then be managed with
pumps unless a more permanent solution is required (see
below). Noting that any type of interlock sealant in isolation
cannot assure a 100% impermeable wall structure.
Permanent works
For permanent structures such as basements, reference should
be made to BS 8102 : 2009 ‘Code of practice for protection of
below ground structures against water from the ground’, gives
various Basement ‘Grades’, which are dependent upon the
intended usage of the basement:
Grade 1: Applicable to car parks, plant rooms etc, where ‘some
seepage & damp patches are tolerable’. Depending upon the
prevailing ground water and soil conditions, Grade 1 could be
achieved with no treatment of the pile interlocks, or the use of
interlock sealants as noted above
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Developer Guide - Are Steel Sheet Piles Impermeable?
GN-05 November 2020
Grade 2 to 4: Require a 100% impermeable wall system, where
additional interlock sealing works should be undertaken. This takes the
form of insitu welding of the exposed interlocks following excavation
down to the basement formation levels. Depending upon the type of
sheet pile section, ‘Z’ or ‘U’, either steel plates or round bars are welded
from the slab formation level up to the top of the sheet pile, which is
usually embedded into a reinforced concrete capping beam. At the
basement slab and sheet pile interface joint, a horizontal steel ‘puddle
flange’ water bar can be welded to the full profile of the sheet piles.
Together with hydrophilic strips (if deemed necessary), this forms an
effective barrier to the passage of water through this joint. Other joint
sealing systems are further detailed in the Arcelor Piling Handbook.
The welding of the sheet pile interlocks is not considered to be a structural weld. However, the welding is
carried out to approved welding procedures and using qualified / tested welders, all in accordance with the
requirements of BS EN 10263, with testing regimes for acceptance class C or D to BS EN 5817.
Disclaimer
Although care has been taken to ensure, to the best of our knowledge, that all data and information contained herein are accurate to the extent
that they relate to either matters of fact or accepted practice or matters of opinion at the time of publication, SPG, SCI, the authors and the
reviewers assume no responsibility for any errors in or misinterpretations of such data and/or information or any loss or damage arising from or
related to their use.
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