LETTER: Insight into engineering
You may consider this newsworthy. Yes it's a bit technical, but why not? I've written to the Herald before, bemoaning the fact that engineers don't get enough coverage compared with other professions!
The photo, taken on March 5, shows a length of steel piling being driven into the riverbank opposite Beach Green childrens’ playground.
It will form part of the new flood defences being provided by the Environment Agency. Points to note...
The pile is being driven in by a ‘Giken’ machine (made in Japan). Unlike the more usual, and much cheaper approach using a hydraulic hammer, this machine is very quiet, and can work in limited spaces. It uses hydraulic pressure, and can safely deliver an 80-ton steady force. It so happens that this photo was taken, exactly as the force was 80 tons.
The pile itself is about 11 metres long, and readers will see that it still has about 1.5 metres to go.
This particular section of the wall was proving more difficult than the piles in the distance, because, despite lots of pre-survey work, the bottom of the pile was encountering a harder layer. Whether it was large shingle, hard core, consolidated ballast, or something else - we’ll probably never know.
Talking to the operators, it seems that this problem (i.e., when the Giken is on its limit of force) is dealt with in one of three ways as follows.
A high-pressure water hose is attached to a nozzle welded to the bottom of the pile; this softens the ground around and below the pile. However, if this doesn’t work, then the engineering calculations permit a certain number of piles to be cut short.
And if the resulting underground gap in the steel is deemed too large, then grouting can be forced in under high pressure.
Readers may also be wondering how the machine positions itself for the next pile. Simple. More hydraulic rams are used to move the whole assembly along horizontally. And then yet more rams then grip tightly on a given number of piles already driven in, thus providing an anchoring force to resist that of the main piling ram.
Finally, it is worth noting how unusual it is for a member of the public to be able to get near enough to take this photo.
Normally (excessive?) health and safety rules would keep them well away.
But because the flood wall is being constructed adjacent to the public footpath, which also provides the only means of access to the adjacent houseboats, the construction team have decided to keep the path open, but for residents only. Given the adequate supervision, the arrangement seems to be working well.
Editor’s note: We have been contacted by Angela Spinks, stakeholder communications and liaison officer at Team Van Oord, which is carrying out the work, who has asked us to remind readers that they should not attempt to visit the construction site. The Riverbank path is closed to the general public during the work and access is for Riverbank residents only.
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