Methods to Reduce Oblique Bending in a Sheet Piling Wall

For over three quarters of a century sheet piling walls are applied in geotechnical practice. For example in quay walls and construction pits in urban surroundings. Sheet piling walls are often composed of so called double U-profiles. These profiles consist of two single U profiles fixed in the common interlock by welding or crimping. A very specific property of the double U-profile is an asymmetric cross-section which can lead to a rotation of the neutral axis. As a result of this, the sheet piling wall tends to deflect both forward (lateral) and sideways (transverse). This phenomenon is called oblique bending. As a result of oblique bending, the strength and lateral stiffness of the sheet piling wall may be decreased considerably up to values of 60 % to 70 % compared to a continuous sheet piling wall. 

Four different methods to reduce oblique bending in a sheet piling wall have been studied:

1) Cantilever sheet piling wall in dry sand.

2) Cantilever sheet piling wall with a fix of the horizontal displacement at the top.

3) Cantilever sheet piling wall with a capping beam on top.

4) Cantilever sheet piling with the sliding interlock welded during the excavation.

The main goal of this study is to determine which method is able to give the highest resistance against oblique bending. Therefore calculations have been made with a 3D-finite element model (DIANA) of a dry excavation of a sand body in front of a cantilever sheet piling wall consisting of double U-profiles. The lower limit of the strength and stiffness is obtained when no transverse bending moment is activated and the in plane deformation is free. The maximum or upper limit strength and stiffness is derived if oblique bending is prevented by fixing the free interlocks (no in plane deformation). Depending on the loading conditions, the stiffness varies from 0.49 to 1 time the maximum stiffness. The strength appeared to vary from 0.59 to 1 time the maximum strength. 3D-finite element calculations have been made for the mentioned four methods to reduce oblique bending. From the 3D calculations it followed that the use of these methods may increase the strength and stiffness up to about 0.8 times the maximum value for strength and stiffness. Welding of the interlock during excavation gave the highest reduction of oblique bending.

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