Sheet piles are sections of sheet material with interlocking edges that are driven into the ground to provide earth retention and excavation support. Sheet piles are most commonly made of steel but can also be made of timber or reinforced concrete. They are used in various applications such as retaining walls, land reclamation, underground structures like car parks and basements, and marine locations for riverbank protection, seawalls and cofferdams.
How Sheet Piling Works
Sheet piling is simple. Steel sheets are wedged into the earth at set intervals, driven into the soil with vibratory or impact hammers or sometimes installed with hydraulic presses. The placed sheets interlock with each other and can be designed for specific retention jobs. If more strength is needed, anchors are easy to add. Sheet piling is used to protect or build:
- Car parks
- Seawalls and bulkheads
- Basements
- Pump houses
- Foundations
- Cofferdams
- Below ground facilities
Safety of Sheet Piling
Properly designed and driven sheet piling can eliminate almost all risks of landslides, erosion, collapse or water breaches. Construction sites are full of people and expensive equipment, so there is no excuse to take risks. A good retention plan can reduce construction costs and safety risks and provide excellent protection to construction sites and permanent retention walls.
Driving Sheet Piling
Using the right impact drivers is key to not compromising the strength of the sheets. Each material has recommended driving methods to avoid costly mistakes and it’s important to drive steel sheets according to manufacturer’s recommendations. Driving steel sheets into solid ground is not a low intensity process and must be monitored.
Types of Retention Walls for Sheet Piling
Different sites require different walls. Common retention walls are:
- Cantilever: These walls rely on the strength of the sheets.
- Braced and Anchored: For high pressure situations, adding lateral bracing and anchors to increase retaining strength.
- Soldier Piles: H-section pipes or piles are inserted into drilled holes.
- Secant or Tangent Piles: Drilled out sections are filled with soil to stiffen the walls.
- Structural Slurry Walls: Trenches are dug and filled with concrete instead of steel.
Types of Sheet Piles
Sheet piles are made from materials like timber, reinforced concrete and steel. Here’s a breakdown:
- Timber Sheet Piles: For short spans in temporary structures to resist light lateral loads, connected by tongue and groove joints.
- Reinforced Concrete Sheet Piles: Formed from precast concrete members connected by tongue and groove joints, used in permanent river embankments and canals.
- Steel Sheet Piles: The most common type, good resistance to high driving stresses and excellent water-tightness. There are four types:
- Normal Sections: Including Larssen and Frodingham, for good strength and low weight. The interlocking system allows easy positioning and driving and in some cases a sealant can be brushed into the joints for a watertight seal.
- Straight Web Sections: Interlocked and driven to form cellular cofferdams.
- Box Sections: Formed by welding sheet pile sections for heavy loads and high bending moments.
- Composite Sections: Used in waterfront protection for large bending moments and heavy axial loads.
Benefits of Sheet Piling
- Recyclable and reusable: Eco-friendly and cost effective.
- Various lengths, sizes and steel options: Flexible for different projects.
- Temporary and permanent structures: Versatile for various applications.
- Silent and vibration free installation methods: Minimal disturbance.
- Fast installation: Faster than contiguous or secant walls.
- Water tight: Close fitting joints form a tight seal.
- Lightweight: Easy to handle and lift.
- Adjustable length and design: Customizable for your needs.
- Durable: Minimal maintenance above and below water.
Installation
Before installation piles should be inspected for straightness, cracks and integrity. Driving should be monitored and obstacles addressed promptly. Techniques to counter deviation are driving in panels and using trestles and walings for support. Vibratory hammers are often used but impact hammers or hydraulic pressing may be required depending on soil conditions.
Hot Rolled vs Cold Formed Sheet Piles
Hot rolled sheet piles are made at high temperatures and are stronger and more resilient interlocks. These are used in demanding infrastructure projects where high bending strength and section modulus is critical. Cold formed sheet piles are made at room temperature and are for less demanding applications. Both have their place in construction projects and offer flexibility for immediate needs.
Applications and Shapes
Sheet piling is used in various construction projects across the industry. In marine structures like quay walls sheet piles resist tensile forces and bending moments. Wide flange beams and other structural shapes like z piles and h piles are used in these applications to strengthen and stabilize the retaining walls. Flat sheet piles and continuous wall systems are ideal for deep excavations and earth retaining structures. The selection of materials and shapes from structural steel to specialty sections ensures each project meets its needs.
Sheet piling is the answer to many retaining wall applications, durable, flexible and cost effective. Whether temporary or permanent structures, investing in quality sheet piling systems will protect your worksite and your construction project. Design and installation is key to getting the most out of sheet piling, it’s a must in modern engineering.
