Sheet pile design - sheet pile

Sheet pile design must account for earth, water, and adjacent structures. Sheet pile design can be straightforward in simple cases, and quite complex in some other conditions. Many unknowns and factors that influence the behavior of the sheet pile wall. Typically, there are two systems in sheet pile wall that must be designed: A) the sheet pile wall that retains the earth and water ( etc.), and b) the Support System (i.e. the internal or external bracing such as rakers, struts, or tiebacks) that supports the sheet pile wall.

The image above shows a sheet pile design with two levels of struts for a cofferdam inside a water body. The AZ48 sheet pile walls are designed to resist bending moments, while the sheet pile design capacity is shown with the red lines next to the bending moment diagrams. Within the image we can also see the structural demand to capacity ratios for the struts and the walls. These ratios should be kept below 1 for a safe design. In this case, the safety factors must be applied either in the applied earth and water loads or within the structural steel yield strength. The overall safety factors should be about 1.5.

Sheet pile design can be performed with both traditional and non-linear analysis methods . While it is realized that traditional methods of analysis have obvious limitations in predicting real behavior accurately, they are important for framing the problem and providing a back-check for more rigorous finite element methods.

Performing detailed calculations for both systems can be a very time consuming process, especially when parameters have to be changed. In addition, many current software programs do not offer an integrated platform of structural and geotechnical analyses required to design shoring excavations. As a result, the designer is forced to use numerous software programs to analyze the excavation and the structural system seperately. With the exception of finite element analyses, there are very few theoretical solutions for calculating lateral soil pressures from complex surface profiles. Furthermore, the designer has to save under different filenames different stages for the same excavation. As a result, the whole process can become unescessarily complicated and time consuming. DeepXcav addresses most of these issues and provides an integrated structural and geotechnical platform for designing deep excavations.

When the sheet pile wall will not experience any axial loads the structural capacity of the pile can be determined from the section modulus and the yield strength of the steel. In the case of allowable stresses for temporary structures the allowable moment is typically taken as:

Mallow = 0.65 * Sxx * Fy

Where Sxx = Section modulus (in3 or cm3), and Fy= yield stress of steel (ksi, MPa)

In case of an LRFD design the ultimate moment can be calculated from:

Mult = 0.9 * Sxx * Fy
This article comes from DEEPEXCAVATION edit released