Slope stability is important for three principle reasons. Firstly
those excavating and recovering raw materials need to be safe,
secondly slopes need to be suitable for their intended future
uses and thirdly slopes need to fit into the local landscape.
All quarry slopes have to be excavated (or constructed) safely
and in accordance with the Quarry Regulations 1999. It is a
necessary part of any major quarry that the proposed slopes
at each stage of excavation, or restoration, have been properly
designed. Failure to do so can lead to a variety of ground
movements, some of which may be large and extend beyond the
quarry boundary. Ground movements of any kind can jeopardise
the safety of people nearby.
The factors that affect the stability of slopes may be summarised
These factors will determine where ground movements are likely
to occur, and their size (in three dimensions). To assess the
stability of a slope it is necessary to consider how any ground
movement might occur. For example, is there the risk of a block
sliding down an angled bedding plane, or toppling forward as
a result of joint cracks? The presence of water in a bank of
soil may cause a landslip.
- Geological structures such as bedding planes (contact
surfaces between rock layers), joints and faults (naturally
- The properties of the rocks and soils, which determine
how well they hold together.
- Ground water conditions, because water pressure behind
a slope will create instability.
- Operational controls such as the height of faces, width
of benches , whether the quarry
faces are angled or vertical and the excavation methods
Once ground conditions are understood, it is usually possible
to design slopes using appropriate benches, slope angles, or
drainage, to avoid large scale movements. Monitoring should
still be carried out on any artificial slope and rockfall may
remain a hazard requiring long-term management ( rockfall
Wedge failure in a limestone quarry.
of a rock column in basalt workings.