Steel Sheet Pile Buying Guide: U-Type, Z-Type, and Straight Web Sections for Excavation and Marine Projects
When you are quoting a retaining wall, a cofferdam, or a deep excavation job, the steel sheet pile you specify will make or break the project budget. Pick the wrong profile and you either over-design by 30 percent or, worse, drive a section that buckles under the first heavy tide. As a China-based exporter supplying piling steel to port contractors and civil fabricators worldwide, we have seen every mistake buyers make at the RFQ stage. This guide walks you through the three profile families, the EN 10248 and ASTM grade ladder, section modulus selection, coatings, and a checklist you can copy straight into your next enquiry.
What a Steel Sheet Pile Is and Where It Is Used
A steel sheet pile is a hot-rolled (or cold-formed) interlocking profile driven into the ground to form a continuous vertical wall. Each section is connected to its neighbour through an interlock, so once driven, the wall acts as a single structural element resisting lateral earth pressure, hydrostatic pressure, and surcharge loads.
You will find steel sheet piles used in five broad scenarios:
- Cofferdams for bridge piers, intake structures, and dry working areas below water table.
- Retaining walls for cuttings, embankments, and basement excavations in urban sites where space is tight.
- Marine and port structures — quay walls, dolphins, bulkheads, and breakwaters.
- Riverbank and canal protection, including flood walls and levee cutoffs.
- Temporary excavation support that is extracted after the permanent structure is cast.
Compared with reinforced concrete diaphragm walls, driven sheet piles are fast to install, fully recoverable for temporary works, and tolerant of difficult ground. The trade-off is that the section has to carry bending moment efficiently — which is where profile geometry and steel grade come in.
The Three Steel Sheet Pile Profile Types
All sheet piles interlock, but the way they carry load differs by profile family. There are three main types you will encounter when sourcing from China and Europe.
U-Type (Larsen) Profiles
U-type piles — often called Larssen piles after the original Swedish designer — are the most widely specified profile globally. Two Z-shaped legs are joined by a common intermediate web, and the interlocks sit on the neutral axis. Common designations include PU 12, PU 16, PU 22, PU 32 and the wider GU 16-400, GU 22-400, GU 28-400. U-piles are symmetric, easy to pitch and drive, and accept standard corner and junction piles without bespoke fabrication.
Z-Type Profiles
Z-type piles position the interlock at the extreme fibres of the wall — on the flange line rather than the neutral axis. This means the full section modulus contributes to bending resistance, giving Z-piles a higher strength-to-weight ratio than U-piles of comparable mass. Typical designations include AZ 13, AZ 18, AZ 26, AZ 36, AZ 48, and AZ 52. They are the preferred choice for tall walls, deep cofferdams, and high bending moments. The trade-off is that Z-piles must be driven in pairs or pairs-and-singles patterns to maintain wall continuity, and rotation in the interlock is lower, so drivability in hard ground is more demanding.
Straight Web Profiles
Straight web piles (designations such as AS 500-9.5, AS 500-12.0, AS 500-12.5) have a flat web with interlocks on both edges. They are designed to carry axial tension, not bending — the classic application being cellular cofferdams (circular or diaphragm cells) where the wall works in hoop tension. If your design uses a circular cell cofferdam, you are almost certainly specifying a straight web section.
| Profile Family | Common Designations | Interlock Position | Best Suited For | Drivability |
|---|---|---|---|---|
| U-Type (Larssen) | PU 12, PU 16, PU 22, GU 16-400, GU 22-400 | Neutral axis | General retaining walls, basements, quays | Easy, good in mixed soils |
| Z-Type | AZ 13, AZ 18, AZ 26, AZ 36, AZ 48 | Extreme fibre (flange) | Deep walls, high moment, marine bulkheads | Moderate, pairs preferred |
| Straight Web | AS 500-9.5, AS 500-12.0 | Both edges, on web line | Cellular cofferdams, tension structures | Easy, low rotation |
Steel Sheet Pile Grades: EN 10248 and ASTM A328/A572
Grade selection sets the minimum yield strength of the pile, and therefore the bending capacity of the wall. For hot-rolled piles to EN 10248, the European standard, the grades run from S240GP up to S430GP. The “GP” suffix denotes a hot-rolled sheet pile product, and the number is the minimum yield strength in MPa at 16 mm thickness.
| Grade (EN 10248) | Min Yield (MPa) | Min Tensile (MPa) | Min Elongation (%) | Typical Use |
|---|---|---|---|---|
| S240GP | 240 | 340 | 26 | Light temporary walls, low moment |
| S270GP | 270 | 410 | 24 | Standard temporary and permanent walls |
| S320GP | 320 | 440 | 23 | Permanent retaining walls, port quays |
| S355GP | 355 | 480 | 21 | Most common marine and basement grade |
| S390GP | 390 | 490 | 19 | High moment, deep cofferdams |
| S430GP | 430 | 510 | 18 | Heaviest Z-piles, deep water walls |
For North American projects, the equivalent specifications are ASTM A328 (minimum yield 270 MPa / 39 ksi, the workhorse grade) and ASTM A572 Grade 50 (minimum yield 345 MPa / 50 ksi), with ASTM A690 specified where the pile sits in the marine splash zone and corrosion resistance is critical. When you cross-reference a European grade to ASTM, S355GP broadly corresponds to A572 Gr 50, and S270GP to A328.
Spec tip: EN 10248-1 requires the manufacturer to issue an EN 10204 3.1 MTC with each heat. If your project requires third-party witnessing (Lloyd’s, DNV, ABS), ask for a 3.2 certificate at quotation stage — it adds days, not weeks, if flagged early.
Section Modulus and Moment of Inertia: Sizing for Wall Height
The two numbers that govern wall design are section modulus (W, in cm³/m of wall) and moment of inertia (I, in cm⁴/m). Section modulus sets the bending capacity — multiply it by the design yield strength and you get the plastic or elastic moment of resistance. Moment of inertia governs deflection, which matters for serviceability and for walls where crane or surcharge loads are close to the wall head.
As a rough rule of thumb for cantilever sheet pile walls in medium-dense granular soil, the section modulus required scales with the cube of the retained height. A 4 m cantilever typically wants W ≥ 800 cm³/m, a 6 m cantilever W ≥ 1,500 cm³/m, and an 8 m cantilever W ≥ 2,500 cm³/m. These are starting points only — final design must account for soil parameters, water level differential, surcharge, and whether the wall is cantilever or propped.
| Profile | W (cm³/m) | I (cm⁴/m) | Mass (kg/m²) | Indicative Cantilever Height |
|---|---|---|---|---|
| PU 12 / GU 12 | 1,200 | 18,000 | ~75 | 4–5 m |
| PU 22 / GU 22-400 | 2,200 | 38,600 | ~96 | 6–7 m |
| AZ 26 | 2,600 | 49,200 | ~144 | 7–8 m |
| AZ 36 | 3,600 | 73,500 | ~170 | 8–9 m (propped) |
| AZ 48 | 4,800 | 106,000 | ~210 | 10 m+ (propped/anchored) |
If your designer calls up a profile near the top of the table for a deep basement, ask whether a single-anchor or single-prop solution with a smaller section would be cheaper overall — propping often beats bigger steel.
Length, Thickness, and Interlock Tolerance
Steel sheet piles are supplied in custom lengths, typically from 6 m up to 31 m for hot-rolled U and Z profiles, with section thicknesses from 6.0 mm to 12.5 mm in the web and up to 22 mm at the interlock on heavier Z-piles. Three tolerances drive drivability and water-tightness:
- Interlock clearance: typically 0.5–1.5 mm. Tight clearance improves sealing but increases the risk of declutching on hard driving.
- Straightness: EN 10248 limits deviation to roughly 0.6–1.2% of length depending on profile.
- End squareness: critical for welding splice joints; out-of-square ends force bevel rework on site.
For walls requiring a watertight joint — dry cofferdams, contaminated land cutoffs — you can specify sealants (bituminous or hydrophilic rope) pre-applied into the interlock, or weld the interlocks after driving. Both add cost but eliminate seepage.
Hot-Rolled vs Cold-Formed Sheet Pile
Cold-formed piles (such as the CP, CPN, and CPT ranges from Chinese and European mills) are rolled from hot-rolled coil into U or Z shapes. They are cheaper, lighter, and available in shorter lengths — but their interlocks are formed rather than forged, so strength and watertightness are lower.
| Attribute | Hot-Rolled (EN 10248) | Cold-Formed (EN 10249) |
|---|---|---|
| Max length | up to 31 m | up to ~16 m |
| Interlock strength | High (forged) | Moderate (formed) |
| Section modulus range | 800–5,000+ cm³/m | 200–1,800 cm³/m |
| Cost | Higher | 15–25% lower |
| Best for | Permanent, marine, high moment | Temporary, light, low moment |
If the wall is permanent, marine, or carries significant moment, specify hot-rolled. For a temporary 4 m trench shoring job with light soil, cold-formed will save you money without compromising safety.
Coating and Corrosion Protection for Marine and Brackish Water
Corrosion of a steel sheet pile is rarely uniform. The aggressive zones are the splash and tidal zones, where oxygen and chloride cycles accelerate metal loss. EN 1993-5 gives indicative corrosion loss values from 0.03 mm/year in fresh water (low attack) up to 0.15 mm/year in the splash zone of temperate seawater. Over a 50-year design life, that is 7.5 mm — a real reduction in section modulus.
Three protection strategies cover most projects:
- Bare steel with a corrosion allowance: add 2–4 mm to the design thickness. Cheapest, used for temporary works and freshwater structures.
- Coated piles: epoxy or coal-tar epoxy systems (200–600 μm DFT), often with a sacrificial primer. Common for port and quay walls in the splash zone.
- Weathering steel (ASTM A690 / equivalent): forms a stable patina that resists further corrosion in the splash zone, but only where chloride concentration is moderate and the wall cycles wet/dry.
For permanent marine walls, a common specification is coating in the splash and tidal zone only, with a corrosion allowance below dredge line. This focuses protection spend where it actually buys you life.
Driving and Installation Considerations
Buying the right section is only half the battle — drivability matters as much as strength. Three points should shape your purchase:
- Section modulus vs drivability: a heavier Z-pile (AZ 48) carries more moment but drives harder in dense granular or cemented soils. Pitching in pairs helps, but vibro-driving may be required.
- Corner and junction piles: every wall changes direction. Standard 90° corner piles and T-junction piles are available off-the-shelf for U-type profiles; for Z-piles, fabricated corners are often needed. Order them with the main batch — they take longer to source than straight piles.
- Sealing: for cofferdams, specify whether interlock sealant or post-driving weld sealing is needed. This affects which interlock orientation you order.
Common Applications at a Glance
- Port construction — quay walls in AZ 26 to AZ 48, S355GP or S390GP, often coated in the tidal zone.
- Riverbank protection — GU 16 or GU 22 walls, frequently cantilever, S270GP or S355GP.
- Basement excavation — propped PU 22 or PU 32 walls acting as both temporary support and permanent basement wall.
- Flood walls — straight web or U-type cut-off walls, often driven to a low-permeability stratum.
- Cellular cofferdams — AS 500 straight web sections, S355GP, designed in hoop tension.
Steel Sheet Pile RFQ Checklist
Use this list when you send out enquiries — it removes 80% of the back-and-forth we see every week:
- Profile and designation (e.g. AZ 26, PU 22, AS 500-12.0).
- Steel grade (EN 10248: S240GP to S430GP, or ASTM A328/A572/A690).
- Length(s) per piece and total quantity per length.
- Interlock type and orientation (Frodingham, Larssen, ball-and-socket; single or paired).
- Corner and junction piles — quantity, angle (90°, 45°, T-junction).
- Coating — bare, epoxy system with DFT, weathering grade.
- Standard — EN 10248-1, ASTM A328/A572, or other (JIS A5528).
- Inspection document — EN 10204 3.1 or 3.2, third-party body if needed.
- Packaging — bundled in pairs, interlocked, with lifting holes if requested.
- Incoterms and destination port — FOB, CFR, CIF; this affects how bundles are stacked in containers or breakbulk.
How Yihang Metal Supplies Your Steel Sheet Pile Project
Yihang Metal supplies hot-rolled steel sheet pile in U-type, Z-type, and straight web profiles to EN 10248 (S240GP through S430GP) and to ASTM A328 / A572 / A690. We ship custom lengths from 6 m to 31 m, paired and bundled for container or breakbulk loading, with standard corner and junction piles cut and drilled to your drawing. Every batch ships with an EN 10204 3.1 MTC, and we can arrange 3.2 certification through Lloyd’s, DNV, SGS, or BV for marine projects.
If you have a retaining wall, cofferdam, quay, or basement project on your desk, send us the pile list, the design grade, and the destination port. We will come back with a quotation, mill options, and a delivery schedule that lets your piling crew keep driving. Request a quote today and let Yihang Metal be your sheet pile supplier of choice.