Slope Monitoring movement - e-library WCL



Slope Monitoring movement

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Slope Failure in opencast mines will result in loss of men, machine or both. It takes quite sometime to return normalcy, to remove material that has collapsed, reform benches etc., Geotechnical teams are employed to assess the safe pit slope .Slope monitoring equipments that provide data. Slope monitoring includes monitoring the surface and subsurface movement in the underlying rock strata and the relationship of this to the known geological structure.

The selection of equipment for slope monitoring will depend on a number of factors, including the perceived or known geotechnical risk and the feasibility of the equipment. Mines with geotechnical risks need multiple types of monitoring equipment as no single technique can provide all the information necessary. Using of multiple types of monitoring equipment is based on the needs of a mine at any given time; for example, very shallow mine walls may only require simple, long-term measurements of movement, whereas with steep walls the risk of failure is much higher. Production plans have an impact on the level of information required regarding slope stability - active production areas that are in the vicinity of mine slopes where stability problems exist will require close monitoring. Warning of impending failure can prevent injury, and also equipment damage.

Monitoring methods used on the surface fall into three main categories: radar and laser systems; prism-based; and visual survey and extensometers.

Radar is now widely used by the majority of open-pit mines. The main advantages of radar systems are that they can penetrate dust and fog while optical devices cannot. This consist of a dish that scans horizontally and vertically, usually mounted on a mobile trailer. There are two basic types of slope monitoring radar commercially available: real-beam radar such as Ground Probe's Slope Stability Radar (SSR) and synthetic aperture radar, such as IDS Australasia's IBIS-M, both of which have advantages and disadvantages, depending on the requirements of each mine. These similar in measuring of displacement, but differ in the way in which they locate and map the displacements.

A real-beam, slope-monitoring radar offers a more precise instrument for monitoring rock wall movements that is necessary. It provides full coverage of the slope, and independent measurements in horizontal and vertical dimensions, near real-time measurements, sub-millimetre accuracy and it can detect rapidly developing failures. However, it is heavy to move around and may be affected by atmospheric changes. Synthetic aperture radar gives scope for high azimuthal resolution at long range, but vertical resolution depends on converting range information into elevation using a digital terrain model. It gives full coverage, but only in its deployment area, and offers near real-time measurement and sub millimetre accuracy. However, it requires a fixed installation and is not mobile.

The range includes: the MSR 200, which can detect slope failures at an operational range of 1,200m; and the MSR 300, with an operational range of 2,500m.They generate their own electrical power. The newest member of the MSR family is the MSR 060 V, which is a fully fledged MSR system, mounted on a standard pick-up vehicle and capable of operating at distances of up to 600m. MSR systems are used altitudes from sea level to 4,800m elevation.& temperatures ranging from -30°C to +55°C

Ground Probe . This system remotely measures the movement of wall surfaces, and uses visual images to confirm and display the results. The dual-measurement system enables geotechnical engineers and mine personnel to track slope movements confidently, and set alarms to improve safety and optimize productivity.

The Work Area Monitor (WAM), launched in 2011, was developed for operation by a mine production crew with no specific technical skills. The system comprises sensitive, fast-scanning radar, coupled with a high-resolution camera, all built into a mine-standard, light vehicle. The primary function of the WAM is to sound a local area alarm to warn workers of slope movement in their vicinity, as opposed to the broader pit-monitoring and long-term deformation measurements of the known slope-stability radars.

Ground Probe also offers Geo Seer, a software application that provides secure local and remote access to geotechnical information from the SSR.

IDS Australasia IDS manufacture two products for slope stability monitoring: IBIS-L, which was designed specifically for landslide monitoring; and IBIS-M, which is used for monitoring walls in open-pit mines.

IBIS-L uses microwave interferometer to offer real-time, 2D mapping of simultaneous displacements over large areas, with an accuracy of up to 1/10mm. It operates autonomously, samples movements every five minutes, and is suitable for use by day or night in any weather.

IBIS-M is based on small, horn antennas that are moved along a linear scanner, making the product more flexible than parabolic dish antennas, which have to be moved mechanically. IDS say this allows it to achieve higher performance in terms of accuracy, resolution, scan time, reliability, capital and operational costs.

LASER: Laser scanning is a remote sensing technique that involves sweeping a narrow laser-beam pulse along a direction characterized by lateral and vertical angles relative to the scanned slope. The method gives accurate discontinuity measurements by generating. a 'point cloud' or 3D representation of each reflecting point of the target slope.

Laser scanners are ideal for capturing baseline data and for visualizing changes in surfaces. Apart from the obvious benefit of being able to capture accurate survey data from a safe distance, laser scanning creates an immediate record of structures such as undercuts

Laser-based techniques are popular for larger mines as they do not have the same distance limitations of other techniques such as radar. Modelling and analysis software enables to interpret the data.

Some advantages of laser surveying include full coverage of the target area, near real-time results and no need to physically access the slope.

Disadvantages include less accuracy than other methods, a fixed installation and the fact that systems need to be protected from environmental conditions.

Site Monitor Slopes

Site Monitor Slopes has been developed for periodic or continuous monitoring of unstable high walls in open pit mines.

Site Monitor is a state-of-the-art laser measurement-based system to measure and monitor the stability of rock faces and landslips. It has been developed in partnership with mining surveyors to provide a simple-to-use, reliable solution that has the flexibility and performance to function in a wide range of monitoring applications. Using non-contact laser hardware, Site Monitor will make range measurements on a pre-defined grid at a selected interval. The software suite incorporates an Analysis module for displaying and analysing time-series monitoring data.

Key advantages

• No requirement for prisms to be placed in the survey area

• Rapid monitoring of thousands of points rather than single prism locations

• Complete coverage of visible surface

• Portable system can be moved into areas of limited access

• Up to 6km measurement range

• Competitive cost

• Data can be taken into Volumes module

COMPANIES 3D Laser Mapping 3D Laser Mapping provides Site Monitor Slopes; a monitoring system that uses advanced laser-scanning technology with powerful, simple-to-use software. Site Monitor is a flexible, modular system that can be tailored to suit clients' needs.

The data generated by Site Monitor Slopes is high resolution and takes advantage of waveform analysis. This is a complex feature, but in essence provides the facility to 'see more'; for example, through vegetation or protective wire meshes.

Maptek Maptek's I-Site laser-scanning technology collects and models detailed survey data. Maptek makes the I-Site 8800 and 8400 scanners. Cut and fill volumes can be calculated, and the model can be used to model slope stability over time. I-Site point data can also be imported into hydro-dynamic models and used to estimate shear stresses on slopes."

PRISM·BASED SYSTEMS: Automatic prism-monitoring systems using motorized total stations have been used in mines since the early 1990s. Prisms are mounted on each of the points to be monitored, together with one or more stable reference points, with their observation controlled by a software application. The total station measures horizontal and vertical angles and slope distances to each prism, from which easting, northing and height values and, subsequently, displacements are computed.

"Usually, the total stations are installed at a permanent location and levelled to align their main axis with the direction of local gravity. Attention is paid to select only very stable sites to ensure the co-ordinates computed from the station will remain in a consistent reference frame to simplify the detection of movement in the monitoring points.

"In mines, the total stations are usually placed at the top of the pit. At least one stable point is needed to orientate the total station, and account for rotations due to uneven heating and cooling of the monument and instrument. If the instrument cannot be located on a stable pillar then a free-station calculation, using measurements to multiple stable control points, can be used to account for movements of the total station."

Total stations are often referred to as robotic because once the station and prisms are installed in the mine no manual input is needed as the instrument movements are managed by software.

Advantages of prism-based systems include sub-millimeter accuracy, measurement in real-time, the ability to measure long-term deformation changes, 3D co-ordinates and a long measurement range. Compared with radar, the initial cost is low. However, it is restricted to localized measurement only, requires a fixed installation and can be affected by atmospheric changes.

Technological advances in total stations include faster speeds and the ability to find and lock on to targets over long distances. Improvements in communications technology, such as wireless mesh radio networks, also allow remote placement and control of total stations and global navigation satellite systems (GNSS) receivers.

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