Having got the equipment, heavy plant etc on site, and the bridge crossing finished, work on the piles to support the aqueduct each side of the river channel could start.
But first, sheet piling had to be installed to support the platform for the drilling rig.
Then to bore 12 metres down for each of the 26 piles on the west bank.
The huge bit, or auger, is being guided to the correct place to start the bore.
The drill is now down the full extent of 12 metres. At this depth the bottom of the pile is only 900mm above sea level!
A temporary steel tube, or sleeve is then driven into the bore hole. This sleeve is necessary in order to prevent water ingress into the bored hole from layers near the surface.
In the foreground are the points circled in yellow paint where the piles are to be drilled. The orange metal frame will be welded to the sheet piling to hold it in place whilst the sleeve is driven down.
It is vitally important that the concrete used for the piles is of the right strength and quality. As each batch of concrete is taken on to the site, three test cubes are made. These cubes are taken to Portsmouth University where they are crush tested at 7 days and 28 days to verify the strength of the concrete.
Having put the reinforcing into the borehole the concrete is fed in using a skip, a tremmie having been placed in the top of the steel sleeve to ensure there are no air pockets in the mix.
When the concrete has been poured, the 6m steel sleeve is pulled out.
Several layers were encountered whilst drilling. The top layer was clay, then a black sludge alluvium, then dry granular clay (as seen here) and finally blue weald clay.
Next, into the river to remove the spoil from the drilling. It was to be used to build up the bank on the east (right hand) bank for the drilling platform on that side.
The sheet pile at extreme right had been used to probe through the foundations of the former aqueduct still under the site on the east bank.
After one week on site, 12 piles had been bored on the west bank out of the 26 required on that side.
[digital pictures: Eric Walker]
