The term sheet piling refers to any retaining wall type that is a) installed into the ground by driving or pushing, rather than pouring or injection, and b) is of relatively thin cross-section and low weight so that the weight of the wall does not assist in the wall’s stability.
The modern sheet piling industry is a little more than 100 years old with perhaps the most important changes in type and selection of products occurring since the early 1970’s. Sheet piling have been used in a wide variety of applications, especially marine bulkheads and retaining walls where space is limited. In addition to these, a special type of retaining wall is the cellular cofferdam, which are used extensively for both temporary and permanent structures.
Sheet piling are made in a number of materials. The material chosen depends upon a number of factors including both strength and environmental requirements. The designer must consider the possibility of material deterioration and its effect on the structural integrity of the system. Most permanent structures are constructed of steel or concrete. Concrete is capable of providing a long service life under normal circumstances but has relatively high initial costs when compared to steel sheet piling. They are more difficult to install than steel piling. Long-term field observations indicate that steel sheet piling provides a long service life when properly designed. Permanent installations should allow for subsequent installation of cathodic protection before excessive corrosion occurs.
1. STEEL SHEET PILING
Metal sheet piling was a natural advancement in the evolution of this product as we entered the “Iron Age” in the mid-1800’s. Cast iron was used to make some crude sections, but these were not successful due to lack of ductility. Toward the end of the century, Bessemer steel was developed and mills began hot-rolling I-beams, channels and angles,
among other structural shapes. Freistadt-type piling appeared about 1890, fabricated from a rolled channel section as shown in Figure1. Z-bars riveted to the web provided a groove into which the flange of a channel could slide, thus forming a crude but innovative interlock. A “Universal” type sheet piling introduced in Great Britain about 1895 utilized hot-rolled I-beams and special clips to join the flanges of the I-beams together. The efficiency of this wall was low because the I-beams were aligned in the weak structural direction.
Figure 1: Freistadt Sheet Piling
2. VINYL SHEET PILING
Vinyl sheet piling is a relatively new type of sheeting which can be applied in a wide variety of ways for seawalls and other applications of sheet piling. It is generally manufactured by continuous extrusion. The raw material, plastic resin compound, is melted and pushed through a die. This die shapes the plastic into the computer aided design cross section. The sheet is then cooled and cut to length. The sheets can be extruded to the length required for different retaining wall applications.
Vinyl sheeting comes in a number of configurations. The most common configuration is a Z-sheet type of configuration similar to those shown in Figure 2. Others are similar to aluminium sheeting shown in Figure 3. The individual sheets have interlocking male and female edges. The interlocking edges are extruded as part of the sheet to insure consistent strength throughout the retaining wall. As is the case with other sheeting, vinyl sheeting requires transition pieces such as corners and intersections. These are designed to interface properly with the other sheeting the manufacturer makes.
Figure 2: Typical Hot-Rolled Steel Sheet Piling
Figure 3: Typical Aluminium Sheet Pile Sections
Vinyl sheeting is made of a modified polyvinyl chloride (PVC), which makes it suitable for most marine environments and not subject to leaching, corrosion or similar deterioration mechanisms. The technology that has brought us vinyl siding for homes, plastic automotive parts such as bumpers and dashboards, and durable home appliances, is now being utilized to produce a sheet piling for marine retaining walls, sea walls or bulkheads. The vinyl also includes a UV stabilizer to reduce deterioration due to sunlight.
Because vinyl sheet piling generally has a low modulus of elasticity and strength relative to metal sheet piling, deflection frequently becomes the governing factor in the design of the wall, and should be determined in the design process.
3. PULTRUDED FIBERGLASS SHEET PILING
Pultruded sheet piling is a section of piling that is manufactured by the continuous processing of raw materials by pulling resin-rich reinforcements through a heated steel die to form profiles of constant cross section of continuous length. The first reinforcement utilized in the profile arelong continuous glass fibres referred to as “roving”. Glass roving runs the length of the pultruded profile and gives the shape its “longitudinal strength”. To add multidirectional reinforcement, continuous glass “matting” is added. The roving and matting is now pulled through a resin bath where the glass fibres are saturated with a liquid thermosetting resin. This process is typically referred to as the “wet-out” process.
The coated fibres are now assembled to the proper shape by a forming guide and finally drawn through a heated (curing) die. Once exiting the die, the pultruded shape is cooled and the resulting high strength, reinforced composite sheet piling is cut to length.
Pultruded sheet piling is suitable for a wide variety of applications for light bulkheads. As is the case with vinyl sheeting, deflection is frequently the controlling factor in design, although the strength of the material is several times higher than vinyl.
This article comes from Pile Buck edit released