Secant pile walls are constructed by forming interconnecting reinforced concrete piles. A guide wall is constructed to set out the position of the secant piles which is followed by the installation of the ‘Female’ piles whilst ensuring enough space is left in between for the ‘Male’ piles to be constructed. This type of retaining wall is reinforced with either steel rebar or steel beams and are installed by an augering technique. Secant walls are recommended when water tightness is a requirement
The advantages of installing Secant pile walls are:
- Potential increased wall strength compared to sheet pile methods
- Low noise levels
- Can be installed in difficult ground conditions and in low headroom
Manchester Metro-link
The new Metro-link in Manchester was to be constructed through to the Sports City Stadium, the home of Manchester City F.C. The Metro-link was to run next to, and several metres below an existing canal, requiring a hard / hard secant wall, to retain the canal. Martello Piling were employed to construct the secant wall and a contiguous bored pile wall, where the Metro-link was to pass underneath the link bridge servicing the stadium. Martello Piling employed 2 of their MP4000 series machines, working in 4.0m of headroom, constructing 900mm diameter secant piles and 750mm diameter contiguous piles to depths of 10.0m. The pile reinforcement was installed in short sections of 2.5m and coupled together, and all the piles were constructed by tremie technique, at an output of approximately 1 pile per day. The MP4000 series rigs were ideally suited to this contract, being the only rigs able to construct piles of 750mm and 900mm in these conditions.
