The first sheet piles go in
We're installing sheet piles along the boundary to hold back the excavation and protect the neighbour's fence footing. I didn't manage to film the very first pile, but I caught the second. In this clip, the piling rig's vibratory hammer drives a 7 m long, 5 mm thick steel sheet into the sandy soil.
As they go, the crew stops to check the sheet is plumb and straight, and nudges the rig slightly sideways to keep it in line. The aim is to get each sheet as true and square as possible to the one before.
Once the sheet is mostly in, the crew removes the safety chains so it can be driven further down.
Each sheet has a hooked edge (an interlock, or clutch) that slides into the next one, a bit like fingers locked together in a "monkey grip".
Driving down to the reduced level (RL)
In the next video, the excavator drives the sheet piles down to the required reduced level (RL), a height measured from a survey datum.
A couple of sheets went lower than the others, so they were pulled back up to about 600 mm higher than shown.
The lower position is the height we'll need for the external works later, but we've left the sheets higher for now to protect the fence footing line. It also gives us a small path across the site. Once we add road base and level it, people can get from the front to the back without walking through the work area.
At the external works stage, we'll cut off the extra height with an oxy torch and bring everything down to the final RL.
Working in tight access
In this last video, you can see the end of a 30-tonne excavator fitted with a vibratory piling head.
We used this setup because the normal piling rig's head and hydraulic lines would have fouled on the brick columns and capitals, the fence line and the gardens. It couldn't get past them safely.
The curved head gives the clearance and alignment needed to grip the sheet properly and drive it down to the required RL.
Before the head lets go of a sheet, the operator can vibrate it up and down. Once a sheet sits still, friction from the soil builds up, so when they start again they need enough force to overcome it. That's why the first burst of vibration is usually the loudest.
If you've got vibration work happening near neighbours, get a dilapidation survey of nearby structures beforehand and ask whether vibration will be monitored.
How these piles were planned is in Post 21, and the full install sequence is in Post 28.
