12 October 2015
Progress report
The works to the slope downhill of the road are continuing and surface drains and
ditches are being constructed.
Downslope drainage construction
Work is continuing with piling installation and approximately three quarters of the
required 436 piles are now installed. Progress is good and it is anticipated that piling
will be complete shortly. See photograph below.
Piling at west end of scheme
At the east end of the site piling is complete and efforts are concentrating on
construction of the reinforced concrete capping beam and installation of ground
anchors. The photo below shows about half of the beams cast, but at the time of
writing (12 October) three quarters of the beams are now complete.
Capping beam construction at east end of the works.
The road opening date is forecast as early 2016.
Technical report
The concrete piles (columns up to 27metres deep with the lowest 3 metres
embedded in rock) are being varied in length to suit the depths of rock encountered
by the drilling rigs. Additional boreholes are being sunk to confirm the rock profiles
ahead of the progress of the piling rigs but, where the rock has been found to be
exceptionally low, the contractor has to install longer piles to meet the design
requirements.
At the west end of the site, the sandstone being used to toe-in the piles has been
found to be very weathered and resembles dense sand rather than the expected
weak sandstone. The piles have had to be lengthened and extra drainage installed
to assure the assumed design margins.
Ground anchors are now being installed at the east end of the site where the ‘free
length’ is drilled through the superficial layers of sand, gravel and clay, and the
anchor end secured to competent sandstone. There are 128 anchors in total that tie
back the capping beam to resist ground and water pressures.