Nowadays, the powerful tools for the geometric surveying and

Nowadays,
slop stability accidents are very general in open cast mining. Though several
mines are running safely with slope movement with the help of monitoring to
enable timely warning against dangerous stability conditions of the slope. Many
things are carried out in open cast mines to prevent the slop failures. For
example, slopes can be designed with high factor of safety to prevent injury
and reduce equipment damage. Groundwater, precipitation runoff and surface
water can be managed to decrease the harmful effects on slope stability. Sometimes,
even a well designed and constructed slope may be fail because of unpredicted
weather conditions, unknown geological structures, or seismic activities. That
is why regular examination and monitoring of slopes are necessary for early
detection of the slope failure and related hazards.

 

Always
surveying techniques have played an important role in collecting data for
mapping, but recently new methods and equipment for data capture and processing
have increased the possibility to achieve variety of information. This thesis
gives brief description about monitoring methods such as Surveying, Photogrammetry,
Global Navigation Satellite system (GNSS) and 3D Laser scanning. These all are
the powerful tools for the geometric surveying and modelling. 

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Afterwards, geodetic equipment which are used
for monitoring of open cast mines are also covered in this thesis. Brief
explanation of the GNSS survey equipment, Digital level and Total station is
given in this thesis. At last, geodetic equipment is followed by case study. This
final segment represents the practical application of the monitoring method and
equipment in open cast mine.

In a current scenario, slope
movement is a general issue in open pit mining. Sometimes it is really
dangerous to mankind who are working in the pit. So, slopes must be constructed
with proper planning. Slopes may be constructed with high factor of safety to prevent
injuries and other damages inside the pit. Properties of the rock mass, hydrological
conditions and geological structures are the main elements, which must be taken
into consideration for safe and efficient slope structures. In the opencast
mines, benches are generally used to block the rocks before to fall and occur a
major hazard. There are also some other possibilities to reduce the hazards related
to slope failures. 1. The use of monitoring devices for warning of slope failures
2. Perfect geotechnical designs of slope 3. Rock fall catchment system which
may be used to stabilize the slopes in specific locations 4. Proper scaling of
loose material from highwalls in the pit. 1 But
slopes never fail suddenly. Slope gives a sign in the form of measurable
movement or the creation of cracks prior to failure. So, systematic monitoring
of slope stability is required with respect to time. 2

Nowadays, technological
developments and innovations in the field of information technology, computer
science and satellite technology bring new hopes for surveying and
geoinformatics. Many new methods for monitoring of opencast mines are
available. This thesis gives brief explanation about Surveying, Photogrammetry,
Global navigation satellite system and 3D Laser scanning. These all methods are
very powerful and efficient. To make these methods efficient, modern monitoring
instruments are also required. Geodetic surveying equipment such as GNSS survey
equipment, total stations and digital level are used for monitoring of opencast
mines. These instruments are capable of measuring long distances with the
desired precision. 3

 

 

2. Monitoring methods

 

Monitoring methods most commonly relied on the
slope and displacement monitoring at surface mine sites. This chapter gives
brief explanation about the monitoring methods such as Surveying,
Photogrammetry, Global navigation satellite system and 3D Laser scanning.

2.1 Surveying

 

Sometimes in the pit. where access to the slope
is difficult or hazardous, and there is a need for frequent and accurate
measurements and quickly analyze the results, surveying is very preferable
monitoring method.4
It involves the measurement, representation and management of data related with
a mining operation.

The arrangement of survey system is shown in
figure 1. The EDM (Electronic distance measurement) is very effective and used for
monitoring of slopes in the pit. This method consists of reflector prism which is
fixed on or around areas of expected instability and also non-moving control
points (one or more than one) needed for survey stations. The distance between
prism and survey station is taken into consideration. The angle and distance
are measured constantly to make a record of the slope movement. While taking
measurement, it is very important that control points for survey stations are
placed on stable surface and the target prisms are properly anchored. The
survey can be done by survey team or mine surveyor or can be automated.

Generally, manufactures provide brief information
about accuracy and error limits of their equipment at the time of purchase.
Sometimes, errors in the equipment may occur due to atmospheric variation in
pressure or temperature, and human error can also be a factor. So, the
equipment used for surveying must be well adjusted before to use and properly
calibrated according to instruction provided by manufactures to ensure
equipment accuracy and reliability. Sometimes inconsistency in data is created due
to the errors in the equipment and therefore steps are required to make these
errors remain negligible. 1

Mining companies are monitoring their operations
in the pit regularly. There are many possibilities to do that. However, terrestrial
measurement is a time-consuming technology for monitoring. Absolute precision
of single points is high using terrestrial method, but still it is not economic
to gather many details. By using photogrammetry method, larges area inside the
pit can be measured with details.

1 Girard, Assessing and monitoring open pit mine
highwal

1 Girard, Assessing and monitoring open pit mine
highwalls

2 Slope monitoring : Techniques and Instruments

3 P.P. Bahuguna, D.Kumar, S.Kumar, Modern
survey instruments and their use in mine surveying

4 Slope monitoring : Techniques and Instruments

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