DESCRIPCIÓN DEL GASTO POR EL USO DE SERVICIOS DE SALUD

Monitoring plays an important role in surface mining. It is a well-known tool that has been used to manage the hazards associated with unstable slopes. Slope

monitoring helps mining companies to prevent loss of production, equipment and lives. However, slopes failure sometimes occurs without any warning. By monitoring pit slopes, mining companies are able to anticipate the failure (Cawood & Stacey, 2006).

In surface mining, some risks are associated with slope instability. One of the main objectives of any mining companies is to make a profit. When extracting the ore, mining operations expand production and the pit gets larger and deeper; which can increase the frequency of hazards associated with slope instability.

According to (Kayesa, 2005), the main reasons for monitoring slopes are:  To verify slopes in terms of the design;

 To assist mine management team in terms of slope stability;  To provide early warning when pits are not stable;

 To measure displacements of unstable areas; and  To manage the risks.

Jonny confirmed that the main three reasons for monitoring are (Sjoberg, 1996):  To maintain safe operations;

 To give advance warning of instability; and

 To give additional geotechnical information in terms of slope behaviour.

In slope monitoring process, five major steps exist (Cawood & Stacey, 2006). These steps include:

 1. Monitoring Requirement

This includes the safety and economic advantages.  2. Project Requirement

It is based on risk assessment and pit design.  3. Design the Monitoring System

This is to implement the monitoring system and consider instrumentation.  4. Measure the Actual Displacement and Record of Field Date

This involves the responsibilities of personnel, precision and accuracy. In this stage, the measurement of frequencies and techniques are vital.

In this stage, the outcomes are reported. Some decision can be reviewed in terms of design. In addition, the analysis of cost-benefit also plays a vital role.

Slope monitoring system is divided into four sections. These sections include surface measurements, remote monitoring, subsurface measurements and visual monitoring. These sections have also subsections that will be discussed below.

2.6.1 Remote Monitoring

2.6.1.1 Time Domain Reflectometry

Slope movement can be monitored using time domain reflectometry (Kane & Beck, 1999). It is used to monitor slope failures around excavations (Kane & Beck, 1999). To monitor slope failures, the instrument uses both cable tester and coaxial cable. This means the two cables are connected. Therefore, the first mentioned sends an electrical pulse to the second one, which is grouted in a borehole and detects the break zone.

The advantages of Time Domain Reflectometry (TDR) over inclinometers include:  Coaxial cable is cheaper than inclinometer casing;

 Reading for TDR takes several minutes while reading for inclinometer can take over an hour;

 The coaxial cable can be placed in any location on the slope;  It is easy to automate the reading for TDR; and

 Slope movement can be determined during data collection.

2.6.1.2 Laser Scanner

The Laser scanner operates with a battery and requires no levelling. However, a camera has been used to take photographs at the beginning of scanning (Little, 2006). When the scan is done, the data collected is transmitted by radio to a computer in the survey office (Little, 2006).

In this office, the data should be downloaded into Polyworks and Site Monitor Analyse software where it would be analysed (Little, 2006). The software can detect slope deformation and pit movement by comparing against base measurement. This system cannot give early warning of failures. Therefore, it is used to identify high-risk areas.

This system is able to record and analyse up to 8000 measurements per second (Osasan, 2012). It has been successfully implemented in the South African mining industry. For example Kumba Iron Ore and De Beers Kimberley both located in the Northern Cape Province, South Africa use this system for slope monitoring purposes (Osasan, 2012). Figure 12 shows how a laser scanner is installed in an open pit mine.

Figure 12: Laser Scanner Installation in an Open Pit Mine (Little, 2006)

2.6.1.3 Slope Stability Radar

This device is used in surface mining for monitoring slopes instability (Figure 13). It is used when failure may occur. However, its effectiveness is based on its capacity to work. It is able to scan 10000 square metres in one minute and give warning before any failure (Little, 2006). In addition, it is able to work in all-weather conditions, and 24 hours a day. A digital camera is used and has a capacity to scan 120 degrees vertically and 360 degrees horizontally.

Figure 13: Slope Stability Radar (Little, 2006)

The Slope Stability Radar (SSR) consists of a 0.92m diameter dish that is controlled by gears and motors for vertical and horizontal movement. At the back of the parabolic dish, a camera is set up for the photographs purpose (Figure 13). After taking the photographs, a 2D scan area is selected by the operator and scanning commences (Figure 14). On this mobile, there are orange and red alarms. The red alarms indicate the evacuation of workers from the risky area while the orange alarms alert workers to a potential problem (Little, 2006). For example, at Potgietersrust Platinum Open Pit Operation in Limpopo, South Africa the red alarms were set for two hours at 10mm of movement and an area of 80 square metres. The distance of the SSR from the slope determines the area (Little, 2006). Little concluded that the SSR provides early warning and equipment and people have been successfully evacuated from the risky area.

Figure 14: Radar Set Up in an Open Pit Mine (Little, 2006)

2.6.2 Surface Monitoring 2.6.2.1 Total Station

Total station surveying is used in open pit mines to measure vertical and horizontal angles. In addition, it allows surveyors to measure coordinates of points as well as distances. This system is also used to monitor slope movement. One of the advantages of this system is that it can provide 3D position solutions of the monitoring points (Little, 2006). Reference points are needed when monitoring slopes movement using total station. These points help to determine the coordinates of the monitoring points.

Total stations and prisms collect and store data during the operating process. This data is sent to the survey office via a computer. The data is then analysed by the geotechnical engineer for the purpose of identifying slope movement, and report potential areas of failure to the mining team (Little, 2006). Figure 15 shows the installation of prism and total station in an open pit mine.

Figure 15: Installation of Prism and Total Station in an Open Pit Mine (Little, 2006)

2.6.2.2 Tension Crack

The presence of cracks in pit areas is one sign that can notify geotechnical engineers of slope instability. To monitor cracks, geotechnical engineers need to measure crack width and distance (Jami & Ed, 2000). As reported by Jami (2000), geotechnical engineers can identify new cracks during regular inspections if existing cracks are painted or flagged. To measure the displacement of cracks, a pair of pins is installed on either side of the crack and a steel tap is used to measure the distance.

A portable-wire-line extensometer is another system that is used to monitor displacement around tension cracks. In this method, a wire anchored is set up around the unstable area. A weight suspended from one side tensions the wire which moves over the upper side of the pulley as shown in Figure 16. The displacement is recorded either electrically or manually when the weight moves due to the movement of the unstable portion (Jami & Ed, 2000).

Figure 16: Portable Wire-Line Extensometer (Jami & Ed, 2000)

2.6.2.3 Global Positioning System (GPS)

Global Positioning System (GPS) is also used to monitor slope stability because of the GPS’s high accuracy in terms of displacement measurements. The GPS is used to measure displacement of slopes in surface mines (Sakurai & Shimizu, 2003). It simultaneously measures the 3D displacements of several points over a large area and many authors have shown that this system plays a vital role when monitoring displacements of slopes (Sakurai & Shimizu, 2003).

This tool is used for the purpose of monitoring slope stability because it is less labour intensive (Ma, et al., 2001). Furthermore, a large number of points are required to be monitored when monitoring a slope and the GPS can monitor a large number of points and has the ability to measure distances and coordinates or angles (Gili, et al., 2000).

2.6.3 Visual Monitoring

Visual monitoring is conducted by regular inspections in the pit areas. These inspections are conducted to discover any significant cracks that can lead to slope failures.

According to Kayesa (2005), visual monitoring can be done by the production team during the shift.

Therefore, the team can record any changes in the production area. In the same context, every morning before starting any shift, it is required that the geologist or the geotechnical engineer walks around the pit looking for any visible sign of slope displacement (Kayesa, 2005).

According to Little (2006), visual inspection is grouped into four categories.  Daily inspection which is done by the geotechnical assistant in pit areas;

 Detailed inspection which is done by the geotechnical Engineer when an unstable slope is identified;

 Monthly inspection which is done by the geotechnical Engineer at the end of each month; and

 Presplit inspections, which is done by the geotechnical assistant after any blasting process.

2.6.4 Subsurface Measurement 2.6.4.1 Piezometers

Piezometers are used in surface mining to measure pore pressures and are useful tools assisting in mine dewatering programmes (Gerard, 2001). Water infiltration is responsible for many slope failures. Resisting forces decrease due to the presence of groundwater while driving forces increase which can lead to slope failure. In addition, the effect of groundwater can be critical to the stability of pit slopes. It is required to control pore pressure. The process of controlling water level will assist in the design process. In this context, information such as water level is required when monitoring pit slopes (Gerard, et al., 1998). Piezometers should be open on the top and bottom sides to provide accurate information when controlling the level of water in order to have safe pit slopes (Morton, et al., 2008).

2.6.4.2 Inclinometers

Slope inclinometers are used to measure horizontal displacements along several points on a borehole in order to establish the rate of slope movement (constant, accelerating or decelerating) (Gerard, et al., 1998). An inclinometer casing is placed into a borehole in the purpose of monitoring displacements. It consists of many components as listed in Figure 17.

Figure 17: Inclinometer, Readout Device and Cable (Bennett, 2008). Information collected from inclinometers can help to:  Locate shear areas;

 Determine if shearing is rotational or plan; and  Determine if movement is constant, slow or fast.

2.6.4.3 Seismic Monitoring

The seismicity in rock indicates the development of new cracks (Stacey, 2007). To anticipate these cracks, it is necessary to monitor the slope using seismic monitoring. Seismic monitoring helps in terms of providing early warning of developing slope instability (Wesseloo & Sweby, 2008). In addition, it detects movement that cannot be recognized by surface measurement. However, this system has the ability to predict the occurrence of micro-seismic events in rock mass before the formation of macroscopic fractures (Xu, et al., 2012). This monitoring strategy uses geophones installed near to the surface into borehole where the slope is unstable. They are used to measure seismic vibration and function like a microphone. When the sensors detect the micro seismic activities, the information collected is transmitted to a computer via radio link on surface. Furthermore, the seismic monitoring involves the uses of geophones installed in the pit area. These geophones record micro seismic movement down to 0.001mm (Little, 2006). After collecting data, the seismologists have to interpret them and combine a report.

2.7 Mine Planning 2.7.1 Overview

In the mining industry, mine planning is the process used to determine the exploitation of mineral resources with the purpose of maximising its intrinsic value (Arteaga, 2014). Mine planning is a critical field in the mining industry as it creates the organisation plan that must be followed (Rupprecht & Grobler, 2016). One of its main objectives is to select the best exploitation strategy that will minimise both the mine capital and operating costs. Mine Planning is also used to schedule mine production during the mine life (Runge, 2012).

Mine planning is a critical discipline in the mine business. It is considered a roadmap that provides future direction when mining. Slope stability is one of the modifying factors used in mine design and impacts on the overall strip ratio and thus the extraction schedule, equipment selection and cost components. Mine planning plays an important role when dealing with slope stability in open pit mines - pit slopes that are well designed should prevent unexpected failure of the rock mass during the mining operations. The design of slopes and mine planning are interchangeable elements and are complementary aspects for the engineering method.

The mine planning process plays a vital role while designing slopes in open pit mines. It is taken into consideration by any mining operation because of the level of accuracy. Economics and safety are considered the first priority in dealing with any mining project. Their failure can lead to severe consequences. For this reason, slopes should be well planned and designed. However, at these stages of evaluation, pit slope and inter-ramp angles suffice. In fact, appropriate information needed for operating considerations and the configuration of bench are required during the feasibility stage (Stacey & Read, 2009a). Therefore, it is required that at all stages, the mine planner and the geotechnical engineer deal with different aspects to understand the level of accuracy. Furthermore, Communication between the two parties is critical and should be taken into account for a well-designed slope to be fully documented.

2.7.2 Mine Planning Process

The mine planner and geotechnical engineer must follow the relevant steps as described below during the design process (Table 3).

Table 3: Steps in the design process (Whittle, 2011).

Steps Action Details

1 General preparation Assign roles. Perform stakeholder analysis. Determine purpose and scope.

2 Preparation of inputs for the study

Prepare the following:

 Information about exploration and mining rights in the area of interest.

 Resource information, including reports, maps, drill-hole data, and block models for the area of interest.

 For existing mines, information about the mining operations and equipment, processing facilities, and infrastructure (Include data for operational performance, variability, and capacity and costs.).

 Information about alternate mining and environmental laws and details of exploration and mining rights.

 Forecasts of future commodity demand and price.  Forecasts of future costs.

3 Framing Determine the set of decisions and alternatives to be tested as part of the study.

4 Assessment Conduct the modelling, optimization, and economic evaluation of alternatives. Conduct risk assessment on main candidates for selection.

5 Selection Select the best alternative plan(s). Select the actions to preserve future options.

2.7.3 Pit Slope Design and Optimisation

Mining companies aim to make profit by maximising ore recovery at the lowest cost while maintaining safe operating conditions. In terms of pit slope stability, pit slope angle must be well designed and optimised to prevent any slope failure due to under or over design. Poor or inadequate pit slope design impacts on the operations of the mine and creates dilution, increasing loss, as well as affecting the profitability of the operation.

In open pit mining, planning commences with a geological block model that will determine whether a given block in the model is mineable or not. The planning process is usually used to find an optimal annual schedule that will give the highest Net Present Value while meeting pit slope constraints such as planned pit slope angle (Appianing & Mireku-Gyimah, 2015)

In order to have a stable pit slope, the pit slope angle must be well designed and optimised during the mine-planning phase. Pit design and optimisation is hard work that requires the use of mining software. In this context, Appianing, (2015) argued that pit design and optimisation could be carried out by using Surpac and Whittle software (Appianing & Mireku-Gyimah, 2015)