Construction Methods And Associated Risks For Rigid And Flexible Retaining Walls

This paper describes two types of retaining wall systems, one is a stiff secant piled wall (usually resulting in small wall deflections) the second one is a less rigid and more flexible sheet piling wall (usually having larger allowable wall deformations). Furthermore the water retention capability of both wall types will be discussed as well as the requirement to laterally support the walls with props or anchors.

It is important to design the retaining wall system according to the medium which needs to be retained (usually soil or water); the surrounding ground conditions, the allowable movements of the retained soil behind the wall after excavation and the intended purpose of the retaining structure. Allowable movement is of particular importance to minimize the settlements of adjacent buildings and structures.

The different construction methodologies of the retaining wall types will be described and the main advantages and disadvantages of each system will be highlighted. Furthermore the major construction risks will be discussed.

The paper will also include a case study of a recently completed retaining wall project in NSW. Piling Contractors successfully installed a sheet piling wall for the construction of a cofferdam in the middle of a watercourse. Additionally a hard/hard secant pile retaining wall was installed inside the cofferdam with sockets into high strength rock using 1180 mm and 1300 mm piles. The requirements for both, water tightness and tight vertical wall tolerances of 1:200 were successfully achieved and the paper points out the major construction activities and monitoring techniques of this challenging project.