What is Steel Pile?

What is Steel Pile?

Steel piles mainly consist of a steel pipe body and connecting devices at both ends. Open or closed end plates can be installed at the pile ends as needed, and pile segments are connected by welding the end plates or using an outer sleeve.

Steel piles are manufactured using high-quality carbon structural steel or low-alloy high-strength steel, featuring high bearing capacity, adjustable pile length, small soil discharge volume, and fast construction speed. They are widely used in building pile foundations, bridge foundations, port terminals, offshore wind power, and other fields.

Core Features:
High Bearing Capacity: High steel strength, effectively penetrating hard soil layers
Flexible Pile Length: Can be lengthened or cut on-site
High Construction Efficiency: Small soil discharge volume, minimal impact on the surrounding environment
Reliable Connection: Welded end plates or outer sleeve connection, safe and secure

Complete Specifications: Diameter φ219mm ~ φ1422mm, Wall Thickness 6mm ~ 25mm

Steel pipe piles can be designed with either open or closed ends depending on geological conditions:
Open piles: During driving, soil enters the pile tube, forming a soil plug. Suitable for geological conditions with obstacles such as gravel, boulders, and rock strata.
Closed piles: The pile end is sealed, utilizing the full end bearing capacity. Suitable for soft soil and unobstructed geological conditions.

Steel pipe piles bear loads through two mechanisms:
End-bearing piles: Directly transfer the load to stable rock or dense soil layers.
Friction piles: Bear the load through the friction between the pile surface and the surrounding soil.

Manufacturing Process:
Steel pipes are divided into two types according to the processing technology:
Spiral Submerged Arc Welded Pipe (SSAW Pipe): Good pressure bearing performance, wide diameter range.
Straight seam submerged arc welded pipe (LSAW Pipe): The weld seam is straight, with high dimensional accuracy, suitable for high-pressure and high-precision requirements.

Production process: 

Strip steel/plate → Uncoiling/leveling → Milling → Forming → Submerged arc welding → Non-destructive testing → Cutting to length → End processing → Anti-corrosion treatment → Factory inspection

Characteristics of steel piles:
(1) Lightweight and rigid, easy to load, unload, transport, and stack, and not easily damaged.
(2) High bearing capacity. Due to the high strength of steel, it can effectively penetrate hard soil layers, the pile body is not easily damaged, and the bearing capacity of a single pile can be significantly improved.

(3) Pile length is easy to adjust. The pile length can be adjusted by lengthening or cutting as needed.
(4) Small amount of soil excavation, minimal impact on adjacent buildings. The lower end of the pile is open, and during driving, the soil is squeezed into the pile pipe, reducing the amount of soil excavation and minimizing disturbance to the surrounding foundation. This avoids soil uplift and reduces vertical displacement of adjacent piles and horizontal displacement of the pile top.

(5) The connector is simple to connect, easy to operate, has high strength, and is safe and reliable using electric welding.
(6) Reliable project quality and fast construction speed. However, steel piles consume a large amount of steel, resulting in high construction costs; the piling equipment is relatively complex, generating significant vibration and noise; and the pile material has poor protective properties and is susceptible to corrosion. Therefore, a thorough technical and economic analysis and comparison should be conducted when selecting a pile.

Why are Steel Pipe Piles Crucial for Heavy Construction?

Heavy construction (such as high-rise buildings, large bridges, port terminals, offshore wind power, stadiums, etc.) has much higher foundation requirements than ordinary buildings: large loads, strict settlement control, and complex geological conditions. Steel pipe piles, due to their unique performance advantages, are the ideal choice for these projects.

1. High Bearing Capacity, Able to Penetrate Hard Soil Layers
Steel pipe piles are manufactured using high-strength steel (such as Q355B, yield strength ≥355MPa), possessing extremely high compressive, bending, and tensile strength. During piling, steel pipe piles can effectively penetrate hard soil layers, sand layers, and even weakly weathered rock layers, transferring the enormous load of the superstructure to deep, stable bearing strata. For super high-rise buildings (such as skyscrapers over 500 meters), the bearing capacity of a single steel pipe pile can reach thousands of tons, which is difficult for concrete piles to achieve.

2. Flexible and Adjustable Pile Length, Adaptable to Complex Geological Conditions
Heavy buildings are often constructed in areas with complex geological conditions and significant variations in the depth of the bearing stratum. Steel pipe piles can be lengthened or truncated on-site according to actual geological conditions, flexibly adapting to changes in pile location. In contrast, precast concrete piles have a fixed length and are difficult to cope with variations in the bearing stratum.

3. Minimal Soil Displacement and Environmental Impact

During the driving process of steel pipe piles (especially open-face piles), the soil is compressed into the pile tube rather than being displaced outwards, thus significantly reducing soil displacement. This characteristic is particularly important in heavy engineering construction in densely populated urban areas or near existing buildings:

● Reduces disturbance to the surrounding foundation
● Prevents soil uplift and ground heave
● Reduces negative impacts on nearby buildings, subways, and pipelines
● Reduces horizontal displacement at the pile top

4. Fast Construction Speed and Shortened Construction Period

The construction efficiency of steel pipe piles is far higher than that of bored piles. Piling equipment can directly drive steel pipe piles into the soil, eliminating the need for complex procedures such as drilling, hole cleaning, reinforcement cage installation, and concrete pouring. For heavy construction projects with tight schedules, steel pipe piles can significantly shorten the foundation construction period and accelerate the overall project progress.

5. High Bending Stiffness and Capacity for Horizontal Loads

Heavy buildings must withstand not only enormous vertical loads but also horizontal loads such as wind loads and seismic loads. Steel pipe piles possess high cross-sectional stiffness and bending resistance, effectively resisting horizontal forces and ensuring structural stability under extreme conditions. This characteristic is particularly crucial for projects with extremely high horizontal bearing capacity, such as offshore wind power foundations and viaduct piers.

6. Reliable Quality and Convenient Testing

Steel pipe piles are prefabricated in factories, ensuring controlled quality. Each steel pipe undergoes rigorous chemical composition analysis, mechanical property testing, and non-destructive testing. During construction, pile driving records (such as hammer blow count and penetration depth) can be monitored in real time, facilitating the assessment of pile bearing capacity and final pile conditions. In contrast, quality control of cast-in-place concrete piles is more challenging, and testing is more complex.

Steel Pile Construction:
Steel pipes are generally made of Q235B or Q355B material, with a yield strength of not less than 235MPa and tensile strength meeting the relevant standards. Based on the processing technology, steel pipes are divided into two types: spiral submerged arc welded pipe (SSAW) and straight seam submerged arc welded pipe (LSAW). Spiral seam steel pipes are more widely used in engineering due to their better pressure-bearing performance and wider diameter range.

For ease of transportation and due to limitations in pile frame height, steel piles typically consist of an upper pile, a lower pile, and several middle piles, with each section generally 13m or 15m in length.

The lower end of the steel pile can be either open or closed. The common diameter range for steel piles is φ219.1mm ~ φ1422mm, and the wall thickness ranges from 6mm to 25mm (determined based on diameter and bearing capacity requirements). Commonly used steel pile specifications include φ406.4mm, φ609.6mm, and φ914.4mm, with wall thicknesses of 10mm, 11mm, 12.7mm, and 13mm. The specific selection should be determined comprehensively based on engineering geology, load, foundation surface, superstructure load, and construction conditions.

Generally, the wall thickness of the upper, middle, and lower sections of the steel pipe is the same. Sometimes, to enable the pile top to withstand greater hammer stress and prevent radial instability, the wall thickness of the upper section of the steel pipe can be appropriately increased, or a 200~300mm wide, 6~12mm thick flat steel reinforcing hoop can be welded to the outer ring of the pile pipe.

To reduce the frictional resistance during the sinking of the steel pipe and prevent the pile end from being damaged due to deformation when entering the hard soil layer, a reinforcing hoop (pile end reinforcing ring) is also installed at the lower end of the steel pipe. For steel pipes with diameters of φ406.4mm to φ914.4mm, the height of the reinforcing hoop is 200 to 300mm and the thickness is 6 to 12mm.

FAQ:

Q1: What are the advantages of steel piles compared to concrete piles?
A: Steel piles have higher bearing capacity, more flexible pile length adjustment, less soil removal and less impact on the surrounding area, and faster construction speed. However, they use more steel, have higher costs, and are more susceptible to corrosion; therefore, selection should be based on a comprehensive consideration of project conditions.

Q2: How to choose the appropriate steel pile specifications?
A: Factors such as engineering geological conditions, superstructure load, foundation elevation, and construction equipment capabilities need to be considered. It is recommended to consult professional technicians for selection calculations.

Q3: How to perform anti-corrosion treatment on steel piles? 

A: The choice depends on the service environment: For freshwater/terrestrial environments, coating protection (epoxy, polyurethane) can be used; for seawater/marine environments, a combination of coating and cathodic protection is required.

Q4: What are the connection methods for steel piles?
A: There are mainly two methods: end plate welding connection and outer sleeve connection. Both methods are characterized by reliable connection and convenient construction.

Read more: ASTM A252 Steel Pipe Piles