The tunnel jacking
for Boston's Central Artery project involved jacking three
interstate highway tunnels under an operating communter
railway
Mott MacDonald’s involvement in major tunnelling projects means
that we have extensive knowledge and experience in predicting and
controlling ground movements. This is vital in underground and deep
surface excavations, particularly in urban environments, to ensure
adjacent structures are not damaged.
To assess the magnitude and impacts of ground movement, our
analytical techniques draw together general empirical formulae for
ground movement prediction, a large database of project case
studies as well as state-of-the-art computer software which we’ve
developed in-house.
Predicting ground movement
We have gained considerable expertise in the use of instrumentation
for monitoring both ground and building movement. Our capabilities
include the prediction of ground settlement contours and the
identification of structures at risk.
On London
Underground’s Jubilee Line extension, we undertook settlement
prediction, risk assessment and monitoring for the new station at
Westminster
Using the PROBEA software program, we are able to assess ground
movement resulting from tunnelling, shaft construction and open cut
excavations in any combination and orientation. Further
examinations are then conducted on particular structures with
respect to tensile strains as well as angular distortions. For the
second stage we use our in-house, AutoCad-compatible programs
BREXIS and ANSETTLE.
We’ve worked with both owners and contractors in developing
preventative measures to control and minimise ground movements to
within acceptable limits. Our successes have resulted in avoiding
expensive underpinning works and the minimising costs and delays to
projects.
A selection of the more notable tunnelling projects which required
extensive settlement analyses include:
- settlement predictions for the Docklands Light Railway in the
City of London and the evaluation of measures to prevent settlement
during tunnelling operations near Mansion House
- extensive settlement assessments for the Jubilee Line Extension
and CrossRail projects through central London
- settlement assessment, instrumentation, monitoring and
reporting of data, plus the post-tunnelling defect survey of
surface and subsurface structures and tunnels affected by the
construction of the Heathrow Express rail link
- the specification of protective measures to affected
structures, compensation grouting, monitoring by real-time
electrolevels, inclinometers and precise levelling techniques for
the St Clair River Tunnel between the USA and Canada
