A303 Stonehenge
The stones at the Stonehenge have stood their
ground for thousands of years but the needs of
the those travelling to and from the south west
of England mean that a road upgrade is now deemed
necessary. Soil Mechanics were selected in their
bid to carry out the investigation of an 11km
section of the A303 around this nationally important
site to enable planners and designers to develop
the scheme to construction.
The projected bypass of the stones and the village
of Winterbourne Stoke will be either in cutting
or tunnel and to enable Mott MacDonald to complete
their design, the specification called for the
detailed logging of nearly 700m of core from the
boreholes and deep trial pits. Detailed logging
meant that each and every fracture in the rock
had to be recorded - bad enough when the geologist
has to sit hunched over a core box and even more
daunting proposition when they have to carry out
the work in situ, actually standing in a 5m deep
trial pit, with four faces visible and a requirement
to systematically record thirteen specific measurements
of each feature.
In modern investigation, it is relatively uncommon
for man entry to deep pits to be contemplated,
since there are serious health and safety issues
which have to be overcome making the work relatively
costly. At Stonehenge, which sits on the Chalk,
it was essential since examination of the mass
of the soft rock is the only reliable way of revealing
the true scale of its jointing pattern. The best
technical solution having been derived, appropriate
arrangements were made and a safe method of working
evolved and put into practice.
The work was completed by a number of field geologists
augmented by others who were logging the borehole
samples and core. In addition a core storage facility
housed a photography set up and a site-lab, set
up by ESGL's Dorset based resources, to carry
out index testing of the Chalk whilst still fresh.
A new data management software system was also
used on site to allow the transmittal of digital
data to Mott MacDonald. With over 150,000 fracture
measurements made at the end of the first phase,
most were highly relieved that the data would
not have to be re-entered into the Clients computer
system as a result of the site staffs efforts.
The initial factual reports, when submitted for
review, led to compliments as to the high quality
of the report and commendation of the staff for
the considerable effort that had clearly been
made.
The job has been carried out in a tremendous
team spirit, despite the technical difficulties
and the disruption as a consequence of the foot
and mouth crisis which imposed restrictions on
movement in and about the area. Perhaps the only
disappointment is that we did not find any "old
bluestone" workings which might have resolved
the problem as to how the stones were dragged
to the site from mid Wales.
|
