As the need for caverns and large
underground spaces increases, Mott MacDonald is at the forefront
when it comes to planning and executing the design and construction
of such facilities. Our experience to date includes large span
caverns for hydropower projects, storage facilities of all types,
underground stations and turnouts for metros and railways, major
highways requiring three- and four-lane tunnels, together with the
conceptualisation of underground cities.
Cross-over cavern
on London’s Heathrow Express rail link, looking towards the
airport’s central terminal area
Creating large underground spaces is a major challenge and demands
experience and good judgement as well as a wide range of technical
and engineering expertise. It is also perceived to be a high risk
activity and, in accordance with current best practice, we ensure
that an effective risk management strategy is put in place at all
stages of a project. Our systems, procedures and processes are
implemented right from the planning stage through to the design,
construction and operational phases in order to ensure the safety
of personnel and the integrity of the works.
The systems we employ during design range from state of the art
numerical modelling of cavern excavations through to fire life
safety assessments using the latest computational fluid dynamics
applications. Numerical modelling of the multiple headings used for
large span excavations is critical in terms of controlling the
works during construction.
Ground modelling
We specify detailed site investigations on the basis of developing
sophisticated ground models that allow us to accurately predict the
performance of the excavations at all stages using either 2 or
3-dimensional finite element or finite difference methods.
Dinorwig pumped
storage scheme in Wales features nine inter-connected caverns, the
largest 50m high covering 4500m2
The predicted ground support interaction from the modelling help to
mitigate design and construction risks and to identify residual
risks that should be carried forward to construction. To manage
residual risks control limits are now routinely specified to assist
engineers during construction to monitor and continuously assess
the progress of the works.
Designs need to relate to construction and we are familiar with all
methods including drill and blast and all mechanical methods of
excavation. Good site supervision is essential not only to minimise
safety risks but also to ensure the best possible performance of
the excavations during operation. We understand how to manage
construction and the benefits of an effective management and
decision making process that can respond quickly to the need of the
project. Our range of roles – from traditional site supervision to
independent checking or assisting contractors in there
self-certification role – ensures that we can respond easily and
effectively to a project’s needs.
Operation and maintenance
Creating underground space is also about operation and maintenance
(O&M) and our expertise in this field, particularly the
management of highway tunnels and establishing O&M procedures
for railway tunnels, has enhanced our capability. Emergency and
evacuation procedures as well as the comfort and perceptions of
users are given a priority. Lining systems and finishes all assist
in this process and we continuously strive to improve and innovate
to develop effective and economic management systems.
Notable cavern projects engineered by Mott MacDonald include:
- Channel Tunnel – UK cross-over
- ‘Muela hydropower, Lesotho
- Dinorwig pumped storage project, UK
- Heathrow Express cross-over, UK
- Kárahnjúkar hydropower project, Iceland
