UNDERGROUND ENGINEERING - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 249

Moving underground
Decisions about infrastructure policy form an integral process where political
and social consensus should be achieved at an early stage on issues related to
planning and procedures, finance and economy, environment and construction
techniques. Underground construction is usually conceived as relatively expensive,
but if for above ground construction additional costs related to environmental
impact and traffic congestion during construction are taken into account, the
difference between the aboveground and underground alternatives is significantly
reduced. Moreover, when the potential for dual use of the ground in urban areas is
considered, the underground option even becomes attractive.
Relevant conditions for the decision-making process for large-scale
infrastructural projects are usually not clearly formulated and the selection and
rejection of alternatives is generally not based on well-defined procedures. In this
respect, three main issues are important: transparent information about advantages
and disadvantages of underground construction for the short term and the long
term, a methodology to weigh all 'hard and soft' aspects in an integral manner, and
an inventory of missing knowledge with a corresponding research agenda.
There are many parties involved: governmental institutes, authorities, research
institutes and universities, engineering and consulting companies, contractors and
manufacturers, and research-coordinating offices and professional organisations.
The disciplines relevant to realising the underground infrastructure are manifold:
civil engineering (construction, geotechnics, dynamics, hydraulics, building
physics, materials, traffic technology, planning), mining engineering (rock
mechanics, geology), mechanical engineering (excavation technology, ventilation,
aerodynamics, control technique, vehicle/rail technology, installation technique),
electrical engineering (light/signal technique, safety-monitoring, air condition),
mathematics (informatics, risk analysis), chemical engineering (soil chemistry,
ground freezing), economy (transport, finance, logistics, management and
exploitation), equity and law (deprivation, allowances, labour inspection, contract,
liability, insurance), planning (city planning, architecture, aesthetics, landscape),
cultural technology (history, archaeology, social development), social science
(public relations, psychology, sociology, media technique), and environmental
sciences (ecology, biology, natural history). The geotechnical engineer needs skills
beyond his technical education (see Chapter 8 and Annex III) to play a proper role.
Ground movements due to excavations and tunnelling
In geotechnical engineering the induced deformations in the surroundings of
construction sites due to building activities is referred to as undesired
environmental effect. For large projects where deep excavations are used or where
tunnel machines are used, environmental effects are almost inevitable. The removal
of ground causes a change in the soil stresses in the neighbourhood. Artificial
groundwater lowering is sometimes used to create a safe building ground in the pit
(bottom heave), but it causes settlements due to consolidation of soft soil layers in
the adjacent areas. Building pit walls either strutted or anchored will deflect and in
unfortunate cases loss of soil by seepage through improper wall plate connections
may occur. During tunnelling an oversize drilling compared to the lining is applied