Slope monitoring plays an important role in managing geotechnical risk across mines, roads, rail corridors, embankments and other infrastructure. Changes in ground movement, groundwater conditions and slope geometry can provide engineers with valuable information about how a slope is behaving and how conditions are developing over time.
Engineers can use several types of measurements to monitor these changes. Surveying instruments and remote sensing technologies can track surface displacement, while borehole instruments can detect movement below the surface. In addition, groundwater monitoring can provide context about changes in pore-water pressure and groundwater levels.
The appropriate monitoring method depends on site conditions, the expected failure mechanism and the information engineers need to support their assessment.
What Can Be Monitored on a Slope?
Slope monitoring can focus on several measurable parameters:
- Surface displacement: movement across the visible slope surface.
- Subsurface displacement: movement within the ground or along potential shear zones.
- Crack movement: changes in the width or displacement of known cracks and discontinuities.
- Groundwater conditions: changes in pore-water pressure or groundwater levels.
- Surface geometry: physical changes to the shape and structure of the slope.
Each measurement provides a different perspective on slope behaviour. Therefore, monitoring programs may combine several technologies to understand the development, location and potential causes of movement.
1. Total Stations and Prisms
Total stations provide an established method for monitoring slope displacement. Engineers install prisms at selected locations across a slope and survey them repeatedly to identify changes in position.
Robotic total stations can automate this process and collect measurements from multiple prisms at scheduled intervals. As a result, engineers can track displacement at known locations without conducting every survey manually.
Prism monitoring can provide precise displacement measurements. However, each prism represents movement at a specific location, so engineers need to consider prism placement carefully when designing the monitoring network.
The system also requires clear visibility between the total station and its prisms. In addition, atmospheric conditions, instrument setup and target geometry can influence measurement quality.
Typically useful for: Precise displacement monitoring at selected locations.
2. GNSS Monitoring
Global Navigation Satellite System (GNSS) sensors can continuously track changes in position at selected locations.
Permanent GNSS stations can collect displacement measurements over time and transmit the results to a monitoring system. Therefore, GNSS can support monitoring across large sites or locations where repeated manual surveying would be difficult.
However, the monitoring network only measures movement at the locations where engineers install sensors. The number and position of GNSS sensors should therefore reflect the expected deformation mechanism and the areas considered most important to monitor.
Typically useful for: Continuous monitoring of selected surface locations across geographically distributed areas.
3. Borehole Inclinometers
Borehole inclinometers provide information about deformation below the ground surface.
To collect these measurements, engineers install an inclinometer casing within a borehole and measure lateral displacement at different depths. Repeated surveys can then show how movement develops through the subsurface and help identify potential shear zones or sliding surfaces.
This information becomes particularly valuable when engineers need to understand the depth and mechanism of movement observed at the surface.
Typically useful for: Identifying and monitoring subsurface deformation and potential shear zones.
4. Extensometers and Crackmeters
Extensometers and crackmeters measure displacement across known cracks, joints or other discontinuities.
For example, repeated measurements can show whether a feature is opening, closing or changing over time. These instruments provide highly localized information, so engineers generally install them around features that they have already identified as relevant to the geotechnical assessment.
Engineers can also connect these instruments to automated monitoring systems when they need to track changes in a particular crack continuously.
Typically useful for: Monitoring known cracks, joints and localized areas of movement.
5. Piezometers
Groundwater conditions can significantly influence slope stability because changes in pore-water pressure affect the effective stresses within a slope.
Piezometers measure groundwater levels or pore-water pressure. For example, engineers can install vibrating-wire piezometers in boreholes and connect them to automated data acquisition systems for continuous monitoring.
Engineers often interpret piezometer measurements alongside displacement, rainfall and other geotechnical information. In this way, they can investigate whether changes in groundwater conditions correspond with changes elsewhere in the slope.
Typically useful for: Monitoring groundwater levels and pore-water pressure.
6. Ground-Based Radar
Ground-based interferometric radar remotely measures surface deformation across an area of a slope.
The radar repeatedly scans the visible surface and measures changes in the returned radar signal over time. It can therefore provide spatial information about deformation across many measurement locations.
Frequent scanning also allows engineers to follow how movement develops over time. For example, they can identify areas where deformation is accelerating, expanding or showing other changes that require further assessment.
However, monitoring geometry remains an important consideration. The radar requires suitable visibility of the monitored surface, while the orientation of movement relative to the sensor influences the displacement it records.
Typically useful for: Continuous, area-based surface deformation monitoring.
7. LiDAR and Terrestrial Laser Scanning
LiDAR uses laser pulses to measure distance and create a three-dimensional representation of a surface.
Terrestrial laser scanners can capture dense point clouds containing large numbers of measurement points across a slope. Engineers can then compare surveys collected at different times to assess changes in surface geometry.
Because LiDAR collects measurements across an area, it can help engineers understand how changes are distributed spatially across a slope. Depending on the system and acquisition frequency, engineers can use LiDAR for applications ranging from periodic surveying to more frequent deformation monitoring.
However, site conditions still affect data collection. Therefore, engineers should consider line of sight, surface characteristics, atmospheric conditions and scanning geometry when planning a LiDAR monitoring program.
Typically useful for: Detailed 3D mapping, surface change detection and area-based deformation monitoring.
8. UAV Photogrammetry and UAV LiDAR
UAVs provide another method for collecting spatial information across large, steep or difficult-to-access slopes.
Photogrammetry uses overlapping photographs to generate orthomosaics, digital elevation models and three-dimensional representations of the terrain. Alternatively, UAV-mounted LiDAR can collect dense 3D point-cloud data directly.
By repeating these surveys, engineers can compare slope geometry over time and identify areas where significant surface changes have occurred.
However, the frequency of data collection depends on the survey schedule, weather, site operations and regulatory requirements. For this reason, UAV monitoring commonly supports periodic assessments and broader spatial surveys.
Typically useful for: Periodic mapping and change detection across large or inaccessible slopes.
9. Satellite InSAR
Interferometric Synthetic Aperture Radar (InSAR) uses satellite radar observations from different times to measure changes in ground position.
Satellite coverage allows engineers to investigate deformation across large geographic areas without installing instruments throughout the entire monitored region. Consequently, InSAR can support regional assessments, long-term deformation analysis and the identification of areas that may require closer investigation.
Several factors can affect measurement availability and quality, including satellite revisit frequency, vegetation, atmospheric effects, terrain geometry and the orientation of movement.
Therefore, engineers may combine satellite observations with ground-based instrumentation when critical areas require higher-frequency information.
Typically useful for: Large-area and longer-term deformation monitoring.
Point-Based and Area-Based Slope Monitoring
Engineers can also group monitoring methods according to how they sample movement across a slope.
Point-based instruments collect measurements at specific locations. Prisms, GNSS sensors, extensometers and similar instruments fall into this category. Engineers can position these instruments around known areas of concern or locations that represent important aspects of slope behaviour.
Area-based technologies, meanwhile, collect spatial information across a broader portion of the slope. Radar, LiDAR, UAV surveys and satellite InSAR can provide this type of coverage at different spatial scales and monitoring frequencies.
In addition, subsurface and environmental instrumentation can provide further context. An inclinometer can show how displacement develops with depth, while a piezometer can show changes in pore-water pressure.
By combining these datasets, engineers can develop a more complete interpretation of observed slope behaviour.
Choosing a Slope Monitoring Method
The design of a monitoring system should reflect the conditions and objectives of the site.
Several factors may influence the selection of monitoring technology:
- Expected failure mechanism
- Required measurement precision
- Monitoring frequency
- Size of the monitoring area
- Surface and subsurface conditions
- Line-of-sight availability
- Site accessibility
- Groundwater conditions
- Environmental and operational conditions
- Communication and power availability
- Required alarm or response time
- Integration with existing monitoring systems
The relative importance of these factors will vary between applications.
For example, a large open-pit wall may require broad spatial coverage and frequent deformation measurements. A road cutting may have several localized sections that require dedicated monitoring. Meanwhile, another slope may require extensive groundwater and subsurface instrumentation to understand the mechanisms driving observed surface movement.
Therefore, engineers should design the monitoring approach around the characteristics of the slope and the engineering questions they need to answer.
Where Compact Radar and LiDAR Monitoring Can Fit
Remote monitoring technologies now operate across a wide range of spatial scales.
Some applications require coverage across very large slopes, while others involve smaller critical areas such as access roads, localized sections of mine slopes, infrastructure corridors or underground excavations. In these situations, compact monitoring systems can provide dedicated coverage of areas that require frequent measurements.
Geobotica’s NanoRadar is a compact interferometric radar developed for continuous sub-millimetre deformation monitoring. Engineers can deploy it around localized slopes, access roads, underground excavations and other areas where they require frequent deformation measurements.
GeoLidar uses LiDAR-based monitoring to capture spatial information across a monitored surface and detect millimetre-scale changes over time.
Engineers can incorporate these systems alongside conventional geotechnical instrumentation, including prisms, inclinometers and piezometers. Together, these technologies can provide surface deformation data alongside the subsurface, groundwater and geological information used in geotechnical interpretation.
Building a More Complete Picture of Slope Behaviour
Geology, structure, groundwater, excavation, weather and other site-specific conditions can all influence how a slope behaves. Monitoring allows engineers to observe these conditions and track changes over time.
Surface displacement, subsurface deformation, groundwater conditions and changes in slope geometry each contribute different information. Therefore, engineers often draw on several sources of monitoring data when interpreting developing ground behaviour.
Modern monitoring programs can use a broad range of instruments, from sensors installed within individual boreholes to remote sensing systems that collect measurements across large sections of a slope.
By selecting and combining technologies according to the site’s monitoring objectives, engineers can build a clearer picture of slope behaviour, identify developing changes and support informed geotechnical decisions.
Recent Comments