Structural Performance Comparison of U and Z Sheet Piles

You are designing a retaining wall. The engineer gives you a choice between U type and Z type sheet piles¹. Which one performs better? Which one is stronger? Which one costs less?

Z type sheet piles¹ generally have higher structural performance than U type piles² for the same weight. The section modulus per kilogram is higher for Z piles because the steel is placed farther from the neutral axis. U piles are better for curved walls and moderate depths. Z piles are preferred for deep, straight walls where high bending strength is required.

I have supplied both U and Z piles for projects around the world. The riverbank project in Southeast Asia used U piles because the wall was curved. A port project in the Middle East used Z piles because the wall was 18 meters deep and straight. Let me walk you through the structural performance comparison.

What is the difference between Z pile and U pile?

The main difference between Z and U piles is the shape and the position of the interlocks. This affects how the pile resists bending.

U piles have interlocks at the neutral axis and are symmetric. Z piles have interlocks at the outer flanges and are asymmetric. Because the steel in Z piles is spread farther from the neutral axis, they have a higher section modulus per kilogram. This means Z piles are more structurally efficient than U piles for the same weight of steel.

Structural Efficiency Comparison

Let me compare the structural efficiency¹ of U and Z piles.

Section Modulus per Kilogram (Efficiency)

Pile Type	Section	Weight (kg/m)	S (cm³/m)	Efficiency (S/kg)
U Type	U 400 x 125-13	60.0	1,590	26.5
Z Type	AZ 18	75.0	1,800	24.0
U Type	U 400 x 170-15.5	76.1	2,470	32.5
Z Type	AZ 26	109.0	2,600	23.9
U Type	U 600 x 210-18	106.2	5,730	54.0
Z Type	AZ 50	211.0	5,000	23.7

Key Observations

U 600 series has very high efficiency at large sizes
Z piles have consistent efficiency across all sizes
For small to medium sections, Z and U are comparable
For large sections, U 600 series is more efficient

Bending Strength Comparison

Property	U Type	Z Type
Interlock position	Neutral axis	Outer flanges
Moment of inertia	Lower for same weight	Higher for same weight
Bending resistance	Good	Better
Water tightness	Excellent (Larssen)	Good (ball-and-socket)

My Experience
For a 12-meter deep excavation, we compared U 400 x 170 (S=2,470) and AZ 26 (S=2,600). The AZ pile was slightly stronger but 40% heavier. The U pile was more efficient for that application. For deeper walls, Z piles become more efficient.

What is the yield strength of sheet pile¹?

The yield strength of sheet pile¹ depends on the steel grade. Common grades range from 240 MPa to 430 MPa.

The yield strength of sheet pile¹ is 240 MPa (35 ksi) for ASTM A328, 345 MPa (50 ksi) for ASTM A572 Grade 50 and A690, 270 MPa for EN 10248 S270GP, 355 MPa for S355GP, and 430 MPa for S430GP. Higher yield strength allows the pile to resist more bending moment with the same section modulus.

Yield Strength by Standard

Let me provide the yield strength for common sheet pile grades.

ASTM Standards

Standard	Grade	Yield (MPa)	Yield (ksi)
A328	—	240	35
A572	Grade 50	345	50
A690	—	345	50

EN 10248 Standards

Grade	Yield (MPa)	Yield (ksi)
S270GP	270	39
S355GP	355	51
S430GP	430	62

How Yield Strength Affects Design

The allowable stress for design is:
σallowable = Yield strength / Factor of safety

For a safety factor of 1.5:

A328: σallowable = 240 / 1.5 = 160 MPa
A572/A690: σallowable = 345 / 1.5 = 230 MPa
S355GP: σallowable = 355 / 1.5 = 237 MPa
S430GP: σallowable = 430 / 1.5 = 287 MPa

My Experience
For a deep excavation project, we used S430GP piles. The higher yield strength² (430 MPa) allowed us to use a lighter section than S355GP, saving 15% on steel weight.

What is the difference between a PZ and a PZC sheet pile?

PZ and PZC are both Z-type sheet pile series from Nucor Skyline in North America. The main difference is the interlock design.

PZ sheet piles have hook-and-grip interlocks¹. PZC sheet piles have ball-and-socket interlocks². The ball-and-socket interlock on PZC piles provides better driving performance, tighter water tightness, and is more forgiving during installation. PZC piles are also wider (25-28 inches) compared to PZ piles (16 inches).

PZ vs PZC Comparison

Let me compare the PZ and PZC series in detail.

PZ Series (Hook-and-Grip Interlock)

Section	Width (in)	Weight (lb/ft)	S (in³/ft)	Interlock
PZ 22	16.00	22.0	5.6	Hook-and-grip
PZ 27	16.00	27.0	8.1	Hook-and-grip
PZ 35	16.00	35.0	12.1	Hook-and-grip
PZ 40	16.00	40.0	15.0	Hook-and-grip

PZC Series (Ball-and-Socket Interlock)

Section	Width (in)	Weight (lb/ft)	S (in³/ft)	Interlock
PZC 13	27.88	50.4	14.5	Ball-and-socket
PZC 18	25.00	50.4	19.5	Ball-and-socket
PZC 26	27.88	73.9	28.8	Ball-and-socket
PZC 29	27.88	84.0	36.5	Ball-and-socket

Key Differences

Feature	PZ Series	PZC Series
Interlock	Hook-and-grip	Ball-and-socket
Width	16 inches	25-28 inches
Driving performance	Good	Better
Water tightness	Good with sealants	Better
Alignment tolerance	Lower	Higher

My Experience
For a North American port project, we used PZC 18 piles. The ball-and-socket interlock drove smoothly in the dense sand, and the wider width (25 inches) meant fewer piles to install.

Which is better concrete sheet pile or steel sheet pile?

Concrete sheet piles and steel sheet piles are both used for retaining walls, but they have different performance characteristics.

Steel sheet piles are generally better than concrete sheet piles for most applications because they are stronger per unit weight, can be driven faster, are easier to handle, and can be extracted and reused. Concrete sheet piles are heavier, require more time to install, and cannot be reused. However, concrete piles may be more economical in some regions where steel is expensive.

Concrete vs Steel Sheet Pile Comparison

Let me compare the two materials in detail.

Steel Sheet Piles¹

Feature	Performance
Strength-to-weight	Very high
Installation speed²	Fast (vibratory hammer)
Reusability	Yes, multiple times
Water tightness	Good (interlocks)
Corrosion resistance³	Moderate (can be coated)
Cost	Moderate to high
Best for	Most applications, deep excavations, marine

Concrete Sheet Piles⁴

Feature	Performance
Strength-to-weight	Lower
Installation speed²	Slower (requires heavy equipment)
Reusability	No
Water tightness	Fair (tongue-and-groove)
Corrosion resistance³	Good (no corrosion)
Cost	Lower in some regions
Best for	Shallow walls, regions with low steel availability

Comparison Table

Property	Steel Sheet Piles¹	Concrete Sheet Piles⁴
Tensile strength	Excellent	Poor (requires rebar)
Bending strength	Excellent	Good
Weight per meter	40-200 kg/m	200-500 kg/m
Maximum length	30 m+	15-20 m
Installation time	Fast	Slow
Reusable	Yes	No
Corrosion	Requires protection	None

My Experience
For the riverbank project, we used steel sheet piles because the wall was 6 meters high and needed to be installed quickly. Concrete piles would have required a larger crane and taken three times longer to install.

Conclusion

Z type sheet piles¹ have higher structural efficiency than U type for deep walls, but U type is better for curves. Yield strength ranges from 240 MPa (A328) to 430 MPa (S430GP). PZC piles² have ball-and-socket interlocks that outperform PZ hook-and-grip. Steel sheet piles are generally better than concrete for most applications.

Explore this link to understand the structural efficiency of Z type sheet piles and their applications in deep walls. ↩ ↩ ↩ ↩ ↩ ↩ ↩ ↩ ↩ ↩
Discover why PZC piles are superior to traditional PZ hook-and-grip piles for enhanced performance. ↩ ↩ ↩ ↩ ↩ ↩
Discover how corrosion resistance impacts the longevity and maintenance of sheet piles in various environments. ↩ ↩
Learn about scenarios where concrete sheet piles may be more cost-effective, especially in regions with high steel prices. ↩ ↩

Structural Performance Comparison of U and Z Sheet Piles