Geotechnology in Construction
The problem of Civil Engineering has generally been seen either to relate to
"Design" or to "Construction". Research in Civil Engineering Design
has often been taken to mean the study of some static scenario so as to eliminate unwanted
behaviour. Research in Civil Engineering Construction has often been taken to mean the
study of management techniques for the control of construction activities.
The new challenge is to relate Design to Construction, which requires a study of the Technology used to create some facility. Spin-off should include the optimisation of construction processes, and the development of new technology, including:
The construction of Civil Engineering facilities is transient in space and time, by
definition. Furthermore, the ground is sensitive to the whole history of its deformation:
its fundamental properties can be transformed by the construction process itself. It
follows that the study of Geotechnology - the technologies and processes used in ground
and foundation engineering to make insertions, extractions, injections, abstractions,
compactions, excavations and other necessary modifications - must encompass change as a
central issue.
The simulation of transient processes such as tunnel construction, both in centrifuge
models and in finite element computations, has led to strong involvement with leaders in
the industry. Analyses of the successful New Austrian Tunnelling Method (NATM) trial at
Heathrow, and the subsequent collapse of the Heathrow Express tunnels in the Central
Terminal Area, were carried out for W.S. Atkins by Dr Ganesh Dasari.
Compensation grouting - the injection of grout during tunnel construction, at an
intermediate level between ground surface and tunnel crown, to eliminate subsidence and
collateral surface damage - has been under investigation. The basic mechanism of
hydro-fracture, widely used for compensation grouting, is under ongoing study, together
with the global plastic mechanisms which control subsidence at the ground surface. This
research has now moved into the field following a BRITE Euram project, COSMUS, inspired by
Bachy-Soletanche Ltd with involvement from Tractabel, CEA-LETI, EPFL, and Glötzl. This
allowed us to study real-time data analysis which is the essential pre-cursor to the
automatic control of any construction process. The Cambridge team was led by Dr Kenichi
Soga and myself.
Other aspects of tunnel construction include the influences of soil grouting on newly
constructed tunnel linings: this was studied by Dr Siew Wei Lee in conjunction with Nishimatsu
Construction. London Underground Ltd are also interested in tunnel linings. We recently completed an
EPSRC project supported by LUL, to measure the actual earth and water pressures being
exerted on the lining of a 75 year old tunnel in London, and to consider how construction
activities followed by ground-water changes might have brought these about. In addition to myself,
the work was steered by Prof Robert Mair and Dr Kenichi Soga, and conducted by Dr Susan Gourvenec.
Tunnel machines fall into a much wider class of technologies for soil extraction, including drilling, boring and straightforward digging. "Diggability" is notoriously difficult to predict.
Since, in every case, these technologies depend on the creation of a dis-continuum it
seems essential to undertake a proper study of fracture, the cracking and disintegration
of a soil body. Our understanding of the micro-mechanics of plastic deformation and flow
must also be improved.
Insertion is just as open to future research as is extraction. Dr David White and I are collaborating
with Giken
Seisakusho Ltd on the hydraulic pressing-in of piles, as contrasted with driving by
hammer for example. The degree to which there is soil disturbance, or the transmission of
damaging vibrations, is obviously of interest. Construction in the urban environment
demands the consideration of neighbours as a prime concern. Equally, the prediction of the
bearing capacity and settlement of piled foundations has very much been a matter of
creating an empirical database. There is now an opportunity to establish databases of
piles inserted by other means, and to describe properly the micro-mechanisms of pile
penetration and subsequent service behaviour. Boring and driving are found to result in
completely different end-bearing behaviour, and it may be anticipated that variations
within these contrasting techniques also lead to appreciable differences, especially in
settlement.
Geotechnical construction off-shore has been researched mainly in the context of
pile-driving, but other technologies are also of interest. Coflexip Stena Offshore,
Fugro, Boreas and BP have been supporting work on the modelling of shallow deformation mechanisms
in soft muds, such as those involved in laying sub-sea pipelines. Pipelines may be buried partly to
provide thermal insulation, and partly to isolate them from possible damage from shipping. One
concern is the possible upheaval buckling of such pipelines under the influence of internal pressure and
high temperature, and the principal uncertainty lies in the mobilisation of uplift resistance of the soil
above: centrifuge tests have already helped clarify this. Much more work is needed on the characterisation
of shallow sea-bed soils, the possible entrainement of water during ploughing and back-filling, and the
behaviour of such back-fills after construction and in service. Other mechanisms such as pipeline snaking
when laid on the sea bed at 2 km depth in the Gulf of Mexico, are also under investigation. This
work forms part of a collaboration with Professor Andrew Palmer.
Those with an interest in the research and development of construction technology and processes in geotechnical engineering are encouraged to contact me. You may
Let me know, by e-mailing me with
the subject geotechnology.