Tel: 1-206-279-3300

2-Day Deep Excavation and Soil nail wall design Workshop

16 PDH @ Plano, TX

Sep 30, Oct 1st, 2019

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Renaissance Hotel, Legacy West

Renaissance Hotel Plano Legacy West

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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.

\Sheet pile design, sheet pile wall design

Sheet pile design with our DeepXcav software

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

a) Earth - Water pressures in sheet pile design

Before all, a designer has to appropriately select the type of lateral earth pressures that are expected to act on the sheet pile. For most sheet pile walls active or at-rest earth pressures are appropriate. Passive soil resistance should be used with caution. The possibility of including water pressures has to be considered if sufficient drainage is not provided. In the USA, depending on the design approach, some design codes (LRFD) apply safety factors that multiply each pressure by a safety factor. In Europe, a strength design approach is applied where soil strength is divided by safety factors and loads are multiplied according to their nature (temporary and permanent). Each method has its benefits and its shortcomings.

b) External Stability checks in retaining wall design

External stability checks refer to calculations that represent the overall stability of the shoring system. Two calculations are typically performed:

b1) Passive resistance of shoring systems: This calculation considers the available earth resistance in the horizontal direction below the excavation.

Factor of safety sliding = Resisting horizontal forces / driving horizontal forces

For temporary conditions a safety factor of atleast 1.2 is required.

b2) Moment - rotational stability: This type of calculation considers the stability of the shoring for rotational failure of the wall.

Factor of safety overturning = Resisting moments / driving moments

Under normal conditions a safety factor of atleast 1.5 is required.

c) Bearing Stability in sheet pile wall design: In all cases a retaining wall has to be founded in some kind of base material (be that rock or soil). When a retaining wall is based on soil the bearing stability tends to be more critical. The first task in this check is to properly compute bearing stresses on the toe and heel of the wall. The reason why bearining stresses have to be computed on both sides is because the overturning causes increased stresses in the toe and reduced stresses on the heel base. The bearing stresses have to be examined againgst the permissible bearing stresses and a minimum safety factor of 3.0 is typically specified. Using such a high safety factor typically ensures that wall settlements are kept within acceptable levels. Otherwise detailed settlement alculations are required if settlement control is critical.

d) Global stability in for sheet pile design Another item of concern is the overall global stability of the excavation. In some cases, while the other checks yield acceptable factors the sheet pile wall might be succeptible to an overall rotational type failure that extends well below the retaining wall itself. Such a failure mode is most commonly accounted in hillsides where weaker soil zones exist or when a soft geomaterial is found below the wall base.

e) Structural checks in a sheet pile wall: Once a stability checks are satisfactory then one can design the actual individual shoring components. For concrete retaining walls this involves the proper sizing of longitudinal and shear reinforcement if required.

Sheet pile design with DeepXcav software

10 Reasons to choose deepxcav

1. One program solves both geotechnical and structural issues!

2. Interactive game like environment!

3. US, AASHTO, EC7, BS, ITA, DIN + more standards!

4. Extensive verification and documentation library!

5. Extensive range of wall types!

6. Archived databases of structural sections!

7. Non-linear and limit-equilibrium analysis methods!

8. Developed by engineers for engineers!

9. Open-box philosophy: most calculations open for review!

10. Permanent annual support for expert engineers!

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DeepXcav gives us a competitive advantage!

We have been waiting for a program like this for 25 years!

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