SLOPE STABILITY Table 1
Table 1 - Description of Geotechnical Categories, with examples and requirements for monitoring and evaluation.
stitutive laws into numerical codes such as for better modelling of under-water slope stability.
Geotechnical monitoring
Geotechnical monitoring is an essential part of geotechni- cal engineering and the actual doing is described in ASTM (American Society for Testing and Materials) standards and the philosophy e.g. in Eurocode 7.
Monitoring is used as a tool to:
- validate geotechnical design and trigger pre-defined courses of actions on time when accelerations in deformation or absolute values of deformation exceed trigger limits (limits defined in advance).
- analyze the behavior of geotechnical structures for which no design is available. In those cases the data generated by monitoring is the input for a subsequent geotechnical design.
Monitoring is not performed for its own sake. Monitoring is
a part of the design process (key words: observational method). Therefore, the frequency of monitoring, the type of monitoring and the reactions to monitoring by operations are part of the same design and geotechnical management process.
The type of monitoring depends on the design, geotechni- cal category, mining method and geotechnical environment. Monitoring of slopes in hard rock operations is different from monitoring of slopes in clay quarries or monitoring of slopes under water in dredging operations. The parameters that are monitored in our mines and quarries (Figure 1) vary from local deformation monitoring on the object itself (e.g. over a single rock discontinuity), to large scale monitoring of defor- mations on the scale of a mine and quarry (e.g. using inSAR,
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Interferometric Synthetic Aperture Radar), to monitoring of stresses in hard rock operations. As is described in the text monitoring can be done to verify slope design but can also be used to deduce the rock mass properties to be used as input parameters for the design process itself.
The following overview (more details can be found in
Schmitz (2020)) shows geotechnical monitoring done in house (only InSAR and fracking, and the installation of load cells and Lidar scans are hired-in). Geotechnical monitoring methods can be grouped as:
deformations/velocity/accelerations:
- deformation measured in surface mines with e.g. inclinometers (applied in Sibelco clay pits, hard rock open pit mines, quarry walls) or tachymeters or simple tell-tales (surface mines),
- satellite based radar interferometry (used to monitor surface mines, tailings facilities and subsidence above underground mines),
- Special dredging sensors have been developed to moni- tor the behavior of slopes under water.
stresses: absolute values and changes in mine and quarry morphology (topography):
- photogrammetry with drones provide topography (nearly all our quarries use drones),
- LIDAR drones have been used for a new surface mine development in a forested area,
- bathymetry for dredging operations, and 3D laser scanning to map geotechnical features in under- ground mines.
Oct.Nov.Dec 2020 • TPG 29
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