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Ground Stability, Foundations and Substructures 75
Hadley Centre provides information on environmental changes (http://www.metoffice.
gov.uk/climatechange/), which may be of use when thinking about how to detail and construct
buildings to better cope with climate change. It is also necessary to determine the
nature of the subsoil through physical investigation, as described in Barry’s Introduction to
Construction of Buildings.
Landslip
Landslip may occur under natural slopes where weak strata of clay, clay over sand or weak
rock strata may slip down a slope, particularly under steep slopes and where water acts as
a lubricant to the slip movement. Landslides of superficial strata nearest to the surface,
which will be most noticeable and therefore recorded, are those that will in the main cause
land instability, which may affect the foundations of buildings. Landslides of deeper strata
that have occurred, or may occur, generally go unnoticed and will only affect deep excavations
and foundations. The most noticeable landslides occur in cliff faces where the continuous
erosion of the base of the cliff face by tidal movements of the sea undermines the
cliff and causes collapse of the cliff face and subsidence of the supported ground (Photograph
3.1). Similar landslip and subsidence may occur where an excavation is cut into a
slope or hillside. The previously supported sloping strata are effectively undermined and
may slip towards the excavation. Landslip is also common around excavations for deep
coal mining, and around areas of quarrying for metal, stone, chalk and limestone.
Surface flooding and soil erosion
Surface flooding may affect the stability of surface ground, and the seasonal movement of water
through permeable strata below the surface may cause gradual erosion of soils and permeable
rocks that may lead to land instability. For example, the persistent flow of water from fractured
water mains and drains may cause gradual erosion of soil and lead to land instability. The
incidence of surface flooding and erosion by below surface water is, by and large, known and
recorded by the regional water authorities (see Environment Agency for further information).
Surface flooding can be addressed through a combination of strategies. Sustainable
drainage systems (SUDS) provide an alternative approach to surface drainage in built-up
areas. The main approaches are to prevent run-off from hard surfaces and roofs and to
prevent pollution. Run-off can be prevented (or reduced) by the use of surface finishes that
allow water to soak into the ground. For example, monolithic surfaces such as tarmacadam,
concrete slabs and pavers laid in concrete should be replaced with permeable paving (the
joints between the paving units allow the water to drain through the surface), gravel or
lawns. This allows water to infiltrate the ground, helping to maintain groundwater levels
and flows in water courses in dry weather. It also reduces the amount of water running
into piped drainage systems, helping to reduce the risk of flooding downstream. Additionally
the use of green roofs to minimise run-off of water and the use of storm water storage
(for use in the garden or as part of a recycled system) can also help to reduce the amount
of surface water entering the piped drainage system.
For buildings located in areas prone to surface water flooding, it may be possible to
implement flood protection methods. The first step is to improve the surface water drainage,
both around the property and the surrounding area. A variety of proprietary systems
are also available that aim to prevent the entry of surface water to the building (e.g. via a