Technical aspects

Specific technical aspects such as durability, imperviousness of steel sheet pile walls, seismic design, etc. may need to be dealt with. Below are the most common issues and their solutions.
Sustainability is handled more in depth in dedicated section of the website.

Durability

Steel sheet piles are widely used in permanent earth retaining and structural foundation works. In the majority of circumstances, they can be used in an unprotected condition. The degree of corrosion and whether protection is required depends upon the working environment - which can vary even within the same installation.

In general, marine environments are the most corrosive and unpredictable. In the few metres of vertical zoning which most structures encompass, parts of the sheet piles are in contact with soil, and exposed to seawater immersion, inter-tidal, splash and marine atmospheric environments.

For most environments, characteristic corrosion rates have been measured (soil, atmospheric, fresh water, marine environment…). The ideal case is to consider corrosion rates measured in adjacent structures, but most often, these data are either not available or not reliable. Typical corrosion rates can be taken from the European standard EN 1993 – Part 5. Note that in specific situations, corrosion due to local conditions may lead to higher corrosion rates, requiring detailed site examinations and data analysis.

In many circumstances steel corrosion rates are low and the use of protective methods is not necessary. However, there are circumstances where corrosion can be more significant, so that measures capable of increasing the service life of a structure should be considered. Protection measures and design considerations include one or a combination of following methods:

coatings (typically only in zones with high corrosion probability),
use of a stronger / thicker section, or a higher steel grade, to create a "statical reserve",
design to avoid the maximum bending moments in zones with high corrosion rates,
extension of the concrete capping beam below the low-water level,
use of AMLoCor® steel grade (most efficient in the permanent immersion zone and low water zone),
use of Mariner steel grade ASTM A690 (splash zone)
cathodic protection by impressed current or by sacrificial anodes (protects the surface constantly in contact with water).

The adverse effects of abrasion and erosion should be taken into account in the design or in the selection of protective methods, e.g. the use of a special coating.

Finally, pitting corrosion, a local phenomenon usually limited to a small portion of the surface of the structure, should be monitored. Measures to prevent retained soil form being washed out through the small holes are easy to implement. Note that generally speaking, pitting corrosion does not affect the overall stability of the retaining wall.

In most cases, the design with a sacrificial thickness of steel is the most cost-effective.

In harsh maritime environments, for the portion below water, cathodic protection can be designed right from the beginning and installed later if monitoring of the structure shows that the corrosion rates after several years are higher than foreseen in the design assumptions.

You can use our free software "Durability" to design a standard sheet pile wall with the reduced section properties (see link below for the dedicated page).

Notes:

Measuring the loss of steel thickness on existing structures
The measuring method as well as the precision of the measuring devices can have a significant influence on the results and their conclusions. ArcelorMittal worked out a quite simple measuring procedure that should allow an adequate analysis of the results of the measurements performed after a few years on the structure. Due to the fact that during the first years the loss of thickness is relatively low, an extrapolation after only a few years of service life could lead to an excessive over-estimation or under-estimation of the corrosion rates if the initial thickness is not known. Therefore, we strongly recommend to perform the first measuring campaign right after the installation of the sheet pile wall (or a couple of months later), and all the successive measures shall be made at the same location. Additionally, the thin layer of corroded steel protects the steel from the corrosion process, so that removing this layer for measuring may have a significant influence on the future corrosion rates.
Corrosion inside the interlocks can be neglected
This statement is based on several structures where the sheet piles were pulled out after the service life and the thickness of the flanges and webs were measured. No corrosion was apparent inside the interlocks.

Watertightness of sheet piles

The ability of retaining walls to prevent or restrict the flow of water in the ground is of utmost importance in many civil engineering applications, e.g. in basements, underground car parks, underground reservoirs, temporary cofferdams and containment barriers.

Steel sheet piles are per se impervious, the exception being the interlocks. A sealing system provides a cost-effective solution to control water seepage through the wall, for instance to minimise the risk of settlement of adjacent property, or keeping excavations dry.

The watertightness of ArcelorMittal’s Larssen interlocks invariably improves with time, but a sealant provides a means by which the flow of water can be controlled faster and more reliably.

The flow of water through sealed interlocks can be calculated with a realistic design method which is backed-up by several in-situ full scale tests.

Each construction project is unique because ground conditions, watertightness requirements, installation methods, and so on, vary from site to site. Therefore, the choice of a sealing system must be made carefully considering all the specific constraints and requirements.

The integrity of a sealant will depend upon its suitability regarding the installation and the driving method, as well as the soil and water conditions.

ArcelorMittal provides several sealing systems which are suitable for almost any project situation

Beltan®Plus, a bituminous product, for water pressures up to 1 bar (10 m),
Arcoseal™, an environmentally-friendly mix of wax and mineral-oil, for water pressures up to 1 bar (10 m),
Roxan®Plus, a water-swelling product, for water pressures up to 2 bars (20 m),
Akila®, a silane modified polymer, for water pressures up to 3 bars (30 m).

Although welding of the interlocks is the most expensive solution, it yields a 100% watertight wall, which may be considered the ideal solution for underground car parks for instance.

Note that sealing systems can also prevent soil from clogging the interlocks, which in specific soils can ease the driving
Double piles to be delivered and/or installed with a sealing system must be crimped before application of the sealing products.
Beltan®, Roxan® and Akila® are registered trademarks of ArcelorMittal, Arcoseal™ is a trademark of ArcelorMittal.

AMLoCor® - steel grade for maritime structures

AMLoCor is ArcelorMittal's "low corrosion" steel grade which revolutionizes the design of port structures.

The key advantage of AMLoCor is a significant reduction of the corrosion rates in the "Low Water Zone" (LWZ) and in the "Permanent Immersion Zone" (PIZ), which is normally the location of the maximum bending moments, and consequently the location of the highest steel stresses.

AMLoCor is the solution to address the major concern of designers and port authorities: durability of marine structures such as quay walls, breakwaters and jetties.

Eurocode 3 ‑ Part 5 (EC 3‑5) contains reference tables with typical corrosion rates valid for standard carbon steel in northern European countries. In-situ tests that lasted more than 15 years proved that the loss of steel thickness of AMLoCor is reduced by a factor 3 (PIZ) to 5 (LWZ) compared to standard structural steel in the critical zones.

AMLoCor leads to considerable savings in steel weight compared to the unprotected carbon steel piling solution, as soon as the predicted loss of steel thickness in the immersion zone is significant (higher than in EC 3‑5). Cathodic protection or coatings can be used to increase the service life of the sheet pile structure, but AMLoCor will in many cases yield the most cost-effective solution in the long-term when including maintenance and repair costs.

Note that AMLoCor is compatible with cathodic protection and coatings.

Steel grades of AMLoCor are covered by the German National Technical Approval Z‑30.10‑55 of the DIBt (Deutsches Institut für Bautechnik) issued in 2017, and a patent is pending.

The mechanical properties of AMLoCor are fully equivalent to standard piling grades, so that structural resistance can be determined according to all relevant design codes used for steel sheet piling structures, for instance EC 3‑5 in European countries.

Some AZ sections are already available in AMLoCor, ranging from AMLoCor Blue 320 to Blue 390 (yield strength of 320 MPa up to 390 MPa). Please check our website for regular updates on available sections.

An extensive driving test was performed in 2010 in Denmark. The same sheet pile profiles in S 355 GP and AMLoCor Blue 355 were driven into very hard soils containing some boulders. The sheets were monitored during driving, then pulled out and inspected. The test proved that the behaviour of AMLoCor sheet piles is equivalent to regular carbon steel sheet piles.

Please check our brochure "AMLoCor®" for more detailed information.

Fire Protection

Fire safety is an important design criteria for steel sheet piles that will be used as permanent structural elements in underground car parks, basements and infrastructure (tunnels, underpasses...). ArcelorMittal carried out extensive research on this subject and can assist with the required fire design verifications.

A comprehensive description of the design is available in the brochure “Underground car parks. Fire resistance” (see below). Furthermore, it includes an easy-to-use verification procedure allowing a simplified assessment of the fire safety of the steel sheet pile structure at the pre-design stage.

ArcelorMittal's R&D department developed years ago a software for internal use that can account for the influence of the (saturated) soil behind the sheet pile wall in case of fire.

Feel free to contact us for more detailed information or for a complimentary preliminary design with our exclusive software.

Seismic design

Although sheet piles have proven their performance under earthquake loading in many countries around the globe, a reluctance to use sheet piles in seismic areas remains among some designers. This concern may come from their experience of conventional design methods which do not favour flexible walls in seismic conditions. These design methods usually comprise of pseudo-static calculations using the Mononobe-Okabe theory (1931).

Numerical studies and physical experiments (centrifuge testing) have shown that these conventional methods of design are overestimating the loads on retaining walls, and especially in the case of flexible walls.

Today, powerful design tools using Finite Element Modeling (FEM) allow dynamic calculations that can accurately predict the behaviour of the retaining walls undergoing different seismic loadings. A research project led by ArcelorMittal R&D and a study carried out by world-leading maritime consultant engineering company SENER have shown substantial optimization potential when using these advanced design methods.

Feel free to contact us for more detailed information or for assistance with dynamic design of sheet piles using FEM.