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Vinyl sheet piles, made of durable and resistant material, are gaining popularity due to their versatility. Its applications include small retaining walls, temporary excavation work, slope stabilization, duct cladding, and even anti-chipping protections around bridge foundations.

One of the key advantages of vinyl sheet piles is their ease of transportation and the possibility of using recycled materials. This solution eliminates the need for heavy construction equipment, resulting in minimized logistical costs. Additionally, vinyl sheet piling is not subject to corrosion, unlike traditional steel structures, translating into their long-term durability in aggressive environments.

Vinyl sheet piling also exhibits exceptional resistance to weather conditions, seawater, and extreme temperatures. Their aesthetic appearance makes them suitable for various conditions without requiring maintenance or anti-corrosion protection.

Key aspects of design

Basic geotechnical analysis is based on standards applied to traditional retaining walls, albeit with consideration of the specific properties of the material. It's worth noting that designing vinyl sheet piles requires certain modifications compared to their steel counterparts. Due to the lower strength of PVC, allowable internal forces are reduced. Additionally, considering the material's specificity, the possibility of its parameters changing over time, influenced by environmental factors and loading conditions, must be accounted for.

In the design of vinyl sheet piles, an essential aspect becomes not only stress analysis but primarily allowable displacements. Under conditions of prolonged loading, the displacements of vinyl sheet piling become a key criterion for determining their dimensioning.

In the design of durable retaining structures with vinyl sheet piling, according to PN-EN 1997 standards, a key challenge is to consider the effects of aging of plastic materials. These effects can result from the action of ultraviolet radiation, ozone, temperature, stress, and chemical degradation effects. Adopting an appropriate approach to these factors is necessary to ensure the durability and strength of vinyl sheet piling in soil-water environments.

It's necessary to consider the effects of sustained long-term loading, known as creep. Designers must also carefully analyze the influence of sheet pile temperature, atmospheric conditions, and electrochemical properties of the surrounding soil.

If the sheet pile profile is protected from atmospheric factors for a month, the factor A₃ = 1,0 can be assumed throughout the entire service life.

Traditional methods of analysis, such as the limit equilibrium method or limit state analysis, may not be optimal for vinyl sheet piling. Their flexibility means that the value and distribution of soil pressure, internal forces, and bending moments strongly depend on the stiffness of the structure, the stiffness and strength of the subsoil, and the state of stress in the subsoil.

Furthermore, adopting classical calculation methods can lead to overestimation of displacements of vinyl sheet piling, especially considering their greater susceptibility compared to steel sheet piling. The final choice of the analysis method lies with the designer, however, it is recommended to use more versatile software packages or advanced computational methods.

It's also important to note the determination of the friction angle δ at the interface between the wall and the soil. Assuming that plastic sheet piling is "low-rough," the value of the friction angle δ can be determined using an appropriate formula, taking into account the constant k:

According to the DIN 16456-2 standard, it can be assumed that the factor k=0,5.

Neglecting initial frictional resistance and adhesion after driving vinyl sheet piling into cohesive soil is a recommended practice, assuming that conditions without drainage occur immediately after driving. The final increase in these values may occur after some time, which should be considered in the analysis. (As for steel sheet piling being driven). Proof in the ultimate limit state should be carried out according to the theory of elasticity.

Ultimate limit state

In the design and verification of the load capacity of a sheet pile wall with vinyl sheet piling, the principles specified in DIN 16456-2 are applied. This process involves a comprehensive analysis of geotechnical failure mechanisms acting on the retaining structure, taking into account both material strength and structural safety.

The calculated load capacity of vinyl sheet piling, denoted as R_B,d, is determined based on the long-term characteristic strength, R_B,k, using the equation:

The coefficient  YM is a partial safety factor for the material safety of the sheet piling.

The ultimate limit state condition for section capacity is fulfilled when:

, where E_d is the design value of the action, with the relevant strength for dimensioning being the strength at the highest expected temperature.

Vinyl sheet piling undergoes verification for bending and shearing. For the section capacity limit condition under a bending moment M_Ed, the calculated bending moment must be less than or equal to the calculated section capacity of the sheet piling under bending, M_C,Rd:

, where W is the strength indicator of the sheet piling and R_b,k  is characteristic value of the long-term tensile strength of the sheet pile.

The verification of vinyl sheet piling for shear involves a limit condition for the section under the action of shear force V_Ed, which must be less than or equal to the calculated shear load (V_Rd). There is no need to reduce the bending load capacity M_C,Rd if the calculated shear force V_Ed is limited to half of the shear capacity V_Rd.

Although vinyl sheet piling is not primarily designed to carry vertical loads, they may be subjected to such loads in certain situations. In such cases, it is necessary to conduct analyses of vertical load capacity and stability in accordance with PN-EN 1997-1 standards, as well as to check the load capacity and stability of the cross-section under combined bending and compression.

When considering the vertical load capacity of vinyl sheet piling, designers should adhere to European standards.

The resistance values of the side wall and the base of vinyl sheet piling can be adopted according to the guidelines of the EAB (German Geotechnical Society, 2014), similar to those for steel sheet piling. This consistent principle allows for the utilization of experiences regarding steel sheet piling, while simultaneously adjusting them to the specifics of vinyl sheet piling.

Serviceability limit state

In the realm of stress and deformation analysis, the characteristics of sheet piling made from plastics exhibit significant differences compared to steel or concrete structures. Particularly noticeable are the greater deformations, which play a crucial role in designing such retaining walls. It's worth noting that under small loads, creep deformation is not a concern, as the deformations are minor and progress very slowly. However, under increased loads and higher temperatures, creep deformation can significantly accelerate, which must be taken into account during the design and evaluation of the usability of these structures. When calculating deformations, the nonlinear behavior of stress and strain, as well as the influence of temperature, must be considered.

Criteria regarding the serviceability limit state encompass several significant aspects. Firstly, the limiting deformations necessary to ensure the usability of the retaining wall itself must be considered. Secondly, restrictions on horizontal displacements and vertical settlements are crucial for ensuring the usability of structures directly adjacent to the retaining wall.

All analyses of the serviceability limit state should be conducted following applicable standards and guidelines, such as the PN-EN 1997-1 standard, which contains instructions regarding the determination of limit values and calculation procedures.

Although there are no universal guidelines regarding allowable displacements, values around 1.5% of the wall height are typically accepted. However, the final values will depend on the specific project requirements and environmental considerations.

Summary

It is worth noting that traditional methods of analyzing sheet piling, developed for steel sheet piles, mainly focus on stresses as the criterion for dimensioning. In the case of vinyl sheet piling, characterized by greater deformability, dimensioning becomes more conditioned by the displacements of the structure than stresses. This condition, especially regarding deflection, is crucial.

Safety and usability of the designed structure are paramount, especially if they rely on the effective operation of the drainage system. As a rule, it is recommended to install drainage behind the sheet pile profiles. The consequences of drainage failure, in terms of safety and the costs of potential repairs, should be carefully considered. This emphasizes the need for a holistic approach to design, taking into account both structural and functional aspects, to ensure the durability and effectiveness of vinyl sheet pile walls.

The application of the DIN 16456-2 standard provides a comprehensive methodology for verifying the load-bearing capacity of sheet pile walls with vinyl sheet piling, allowing for precise adaptation to specific project conditions and requirements. Through stress and deformation analysis, as well as appropriate determination of limit values and displacement constraints, safe and efficient utilization of these materials in construction practice can be ensured.

Please, note that a detailed analysis dedicated to the design process involving vinyl sheet piles may be found on the Designer 3.0 platform.

Bibliography

1. Amorim F.C., Souza J.F.B., Mattos H.S., Reis J.M.L., Temperature effect on the tensile properties of unplasticized polyvinyl chloride, DOI: 10.1002/pls2.10067, 14.12.2021
2. Army Corps of Engineers, A study of the Long-Term Applications of Vinyl Sheet Piles, Cold Regions Research and Engineering Laboratory,72 Lyme Road,Hanover,NH,03755, 08.2003
3. Army Corps of Engineers, Design of sheet pile walls. Engineer Manual 1110-2-2504. (2014). Washington: Department of the Department of the U.S.
4. DIN 16456-1 Plastic sheet piling - Extruded sheet piling of plasticizerfree polyvinylchloride (PVC-U) - Part 1: Product. (2017)
5. DIN 16456-2:2017-10 Plastic sheet piling - Extruded sheet piling of plasticizerfree polyvinylchloride (PVC-U) - Part 2: Dimensions. (2017)
6. DIN 16456-3 Plastic sheet piling - Extruded sheet pilings of plasticizerfree polyvinylchloride (PVC-U) - Part 3: Construction of sheet-pile buildings based on plastic sheet pilings. (2017)
7. EN 1997-1 Eurocode 7 - Geotechnical design - Part 1: General rules. (no date)
8. EN 1997-2: Eurocode 7 - Geotechnical design - Part 2: Ground investigation and testing. (no date)
9. Pietrucha, Guide SuperLock EN
10. Wang Z., et al., Vertical and Lateral Bearing Capacity of FRP Composite Sheet Piles in Soft Soil, Hindawi, Advances in Civil Engineering, Volume 2020, Article ID 8957893