Steel sheet piles are one of the most common construction materials typically used for retaining walls. Depending on the needs of the project, these retaining structures may be permanent or temporary.
Projects such as ports and bridges may require permanent installation of steel sheet piles to prevent the backfill from collapsing during the design life of the structure.
On the other hand, building construction projects involving basements and/or deep footings will require temporary foundation support while concrete basement walls are being constructed.This article will focus on the grades of sheet piles, the types of sheet piles and the uses of sheet piles.
In the United States, sheet piling is specified by reference to ASTM standards. The basic grade is ASTM A572 Gr 50 and many manufacturers produce ASTM A572 Gr 60 as a new standard.
U Type Sheet Pile
Other grades of steel for piling have been developed for possible uses considering corrosion. astm a690 and a588 are 50 ksi (345 MPa) yield strength steels with formulations that have been shown to have longer service life. astm a690 has been shown to reduce corrosion rates in the splash zone by a factor of 2 to 3. a588 is also known as a weathering steel and is resistant to corrosion in the atmospheric zone.
Steel sheet piles are manufactured in three basic configurations: "Z", "U" and "straight" (flat). Historically, this shape has been the hot rolled product produced by structural mills. Like other shapes such as beams or channels, the steel is heated in a furnace and then passed through a series of rolls to form the final shape and interlock so that the sheet piles can be threaded together. Some manufacturers use a cold forming process in which coils of steel are rolled at room temperature to form the final sheet pile shape. Cold formed sheet piles have a hook and clip interlocking device.
U type sheet pile is a U-shaped profile interlocked on both sides to form a continuous wall with its centerline in the middle of a double U section wall. u type sheet piles can be stacked more consistently than any other shape and therefore can be used for both permanent and temporary projects.
Z type sheet piles are produced in zigzag form and are usually driven in crimped or welded doubles. Z type sheet piles are more widely used than U type piles in port construction and deep foundations because Z type sheets can have greater modulus and can be used as intermediate piles in tubular and HZ combination walls.
Z Type Sheet Piles
Flat sheet piles are used for circular cell applications where the cells form a gravity structure. The sheet piles are interlocked together to form individual cells, or a series of cells, and are then filled with soil. Whereas z-type sheet piles require resistance in bending, the strength of the flat sheets come from their interlocks. Flat sheet interlocks are larger than those on z-type sheet piles and are designed to resist significant tensile forces. Flat sheet piles have limited bending capacity.
Steel sheet piles are elongated structural elements with different lengths and cross sections which are connected at each end of the panel using interlocking devices to form a continuous wall. Sheet piles are usually installed as part of retaining structures for slope protection and excavation protection.
Marine structures such as wharves and quay walls use sheet pile walls to retain backfill and are used to raise the finished ground level in docking areas. Sheet piles also help mitigate rapid groundwater seepage on such projects.
For most projects, sheet piles are typically used for scaffolding or temporary excavation protection applications. These include basement and tunnel construction.
Sheet piles are installed with multiple components, such as beams and struts, to form a support cut/excavation.
Sheet piles with crossbeams and struts installedSheet piles with crossbeams and struts installed.
Sheet pile walls can also be installed as part of a permanent retaining structure (e.g. diaphragm wall) to prevent collapse of the structure above the soil held by the sheet pile wall.
Another example of a permanent application of steel sheet pile walls is a flood wall construction project. This situation typically requires cantilevered sheet pile walls for retained soil heights up to 6.00 m and anchored sheet pile walls for higher retained heights.