This section describes:

• risks and suggested control measures for tips and tipping
• inspection processes for tip heads and tip conditions.

Incidents can occur for various reasons when tipping or dumping, mainly because of unsafe tip head conditions or design, unsafe dumping or tipping practices, or some combination of these.

Tipping risks include:

• no windrow or restraint, or an inadequate windrow or restraint, which makes the edge location difficult to judge, and offers inadequate restraint to keep a vehicle from going over the edge
• inadequately compacted tip edges that may not support the weight of mobile plant using the tip
• a tip that runs downgrade to the windrow, which gives drivers less control while reversing, and can soften the dump area from poor drainage
• inadequate lighting for night operations, or poor visibility during inclement weather, which may impact driver judgement and detection of unsafe conditions
• inadequate clearance between equipment and overhead power lines, in particular when truck trays are raised at dump points and when tips get larger so clearance may be gradually reduced
• congestion around the tip head where dump trucks or other mobile machinery crowd the tip head due to operational delays or unplanned events.

On this page

• 11.1 Dumping and tipping methods
• 11.2 Controlling end-tipping risks
• 11.3 Suggested control measures
• 11.4 Procedures for examining tip heads
• 11.5 Tip maintenance and inspection
• 11.6 Other considerations for stockpiles
• 11.7 Reworking or reshaping tips

11.1 Dumping and tipping methods

There are three methods of offloading material from a truck:

• Paddock dumping where loads are dumped close to each other and, if another layer is to be built on top, the surface is levelled and prepared for the next lift using mobile plant.
• Dump short and push off where loads are dumped and pushed off a tip edge while leaving the windrow in place.
• End-tipping where loads are dumped down a free face and the load slides down requiring regular maintenance and re-building of windrows.

Paddock dumping or dumping short and pushing off are the preferred options for all tips. This is because these methods generally reduce the risk of vehicles driving off an edge or the edge collapsing due to increased weight from vehicles. Under carefully managed circumstances end-tipping can be done safely.

11.2 Controlling end-tipping risks

Whenever heavy vehicles are operated near the edge of a slope, there is a risk that the edge material will not support the vehicles. This is especially relevant on tips or stockpiles where the material is normally in a relatively loose condition.

In a tip or stockpile the material is typically at its ‘angle of repose’. The angle of repose is the angle at which the material rests when dumped in a pile. This angle will vary depending on the size and shape of the constituent particles, how the material is dumped and the amount of moisture in the material when it is dumped.

For a pile of material at its angle of repose, the edge of the pile is marginally stable. When dumped or pushed over the edge, the material tends to slide until it comes to rest at an angle where it can barely support its own weight. This is why it is hazardous to bring the heavy weight of a truck close to the edge of an angle of repose slope. When this occurs, the slope material has to support not only its own weight, but also the additional weight of the loaded truck. If the additional weight of the truck causes the material’s shear strength to be exceeded, the edge of the slope will give way under the weight of the truck. This risk is increased when the load is raised, and additional weight is transferred onto the rear wheels. This is why serious incidents keep happening at uncontrolled tip heads. For an example of tip design, see Figure 46.

The edge of a pile can also become unstable if the foundation cannot support the weight of the material and begins to give way. Especially in a tip of overburden, the edge may become unstable because of a zone of weak material in the tip. Sliding may occur on a layer of the material.

Because the tip head must be capable of supporting the weight of the vehicles being used, usually a truck, and withstand the other dynamic forces imposed in stopping and dumping near the edge, competent engineering advice may be required to design the tip.

End-tipping should therefore only be done where the following risk mitigation measures are in place and maintained:

• A geotechnical assessment of every tip with a minimum factor of safety (FOS) of 1.2 (see Section 6.7 for more information).
• Tips and tip heads (including windrows) should be designed (with drawings, see figure 46 for an example); formed from consolidated layers; and terraced or stepped back to minimise fall risks.
• The edge and windrows should be systematically maintained while end-tipping.
• The windrow should be used as a visual guide only. The windrow should not be used to help stop the truck but only as a visual guide to judge where to stop.
• There is adequate supervision of dumping operations to make sure unsafe conditions are being corrected and safe practices are being followed.
• There are specified intervals for reviewing the end-tipping and auditing of the processes.
• Unusual material (for example weaker or wetter) should always be treated differently than standard overburden. Unusual material should always be paddock dumped in an area where it will not compromise tip stability.

Track-dozers are preferred for maintaining tip heads because they distribute the weight of the mobile plant over a greater area than a rubber-tyred dozer, which decreases ground pressure.

When dumping short, a good rule of thumb is to dump one truck-length back from the edge. The benefit of using this method is that the truck drivers are not exposed to the risks at the edge of the tip.

To prevent trucks reversing into water, only backfill water-filled areas by the dump short and push off method.

Tip construction procedure

All tips should have a construction procedure to follow when dumping. This procedure should:

• describe how the tip design, from the geotechnical assessment, will be implemented by the workers
• specify the overall slope angle, maximum heights of batter slopes and minimum bench widths
• consider the type of material being dumped and the dumping method
• consider the size and type of vehicles being used
• include windrow specifications (see Section 8.3 for more information)
• be easily understood by workers.

Workers should be trained in the procedure and dumping should be monitored, to ensure the procedure is being followed.

Using diagrams is a good way to communicate the procedure to workers. Figures 47 and 48 are examples of easily understood tip construction procedures that describe how the tip design from the geotechnical assessment will be implemented.

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These are only two potential dump construction methods. The procedure that the mine follows should be based on the geotechnical assessment.

Dumping methodology

Loads should be dumped in phases according to the design to ensure stability and to allow the tip face to be built out uniformly. A phase is a series of dumps whereby progressive loads are dumped adjacent to the previous one (see Figure 49).

At the end of each phase the tip surface, edge and windrow should be reformed (taking into consideration any compaction or movement of the windrow that is required) before the next phase starts.

There should be communication between the mobile plant operators and the truck drivers to advise when the next phase can start.

When reversing close to the edge of a tip, drivers should reverse slowly and come to a gradual stop at the tip head. As a truck reverses up and the brakes are applied, dynamic forces are produced which push down and out on the tip. The more abruptly a vehicle stops, the higher these forces are. These forces can make a stable edge give way.

Drivers should reverse perpendicular to the edge, or with the driver’s side tyres leading just slightly (see Figure 50). In many tip head accidents, the tyre tracks have revealed the truck was reversing at an angle, with the rear tyres opposite the driver leading. In these cases, the driver’s side mirror would have indicated the driver still had a distance to back up, while the opposite side rear tyres were already contacting the windrow or going over the edge.

Construction of windrows at tip heads

A critical function of a windrow at a tip head is to keep the heavy load on the rear tyres of the truck from getting too close to the edge. In this respect the height of the windrow is important because the higher the windrow, the wider the base of the windrow. It is this wide base that is critical in keeping the load back from the edge.

Windrows should be seen as an extra safety control measure and should not be used as a brake or even an indicator that the edge has been reached. They should be designed, constructed, installed and of sufficient height to offer definite restraint in the event a vehicle accidentally contacts them. While traditional rules of thumb for windrow heights (half the height of the wheel) may be useful, they are often not supported by design calculations and could be inadequate as a safety barrier.

Design parameters for windrow construction should be followed. Design parameters include:

• using material to construct the windrows that is non-uniform in size, to allow interlocking of particles for greater cohesion and strength
• sloping the outer face of the windrow to its natural angle of repose. The slope should be pushed up steeper on the inner face (but must maintain adequate width)
• the width and distance should be enough to keep the heavy loading on the rear tyres of trucks from getting too close to the edge where the material could give way.

Construction of stop-blocks (or wheel back-stops) at permanent tip heads

When a truck (or loader) dumps off a permanent tip head (for example, into a hopper) adequate stop-blocks should be in place. The stop-block should be designed, constructed, installed and of sufficient height to offer definite restraint. The stop-block should be adequate for the largest vehicles that will use the tip head. Remove spills (including gradual build-up) that accumulate in front of the stop-block as these will reduce the height of the block.

11.3 Suggested control measures

Overhead hazards

Carry out dumping operations clear of overhead hazards such as power lines, pipework and so on. Continuously check for overhead hazards. If a tip or stockpile increases in size, vehicles may gradually begin working closer and closer to overhead hazards that were too far away to be a concern when the tip or stockpile was started.

Visibility of a dump site

Adequate lighting should be provided. The area should be illuminated well enough to allow signs of tip head instability, such as cracks, to be detected. If visibility is poor (for example, due to bad weather), dumping should be stopped or other control measures implemented to maintain safety (for example, trucks should dump back from the edge).

During bad weather (for example, fog), a trigger point should be established that will determine when operations will need to be modified or stopped due to reduced operating parameters. This can include visibility, temperature (freezing), traction on pavements (rain) and wind.

Vehicle manoeuvring

It will usually not be possible to completely avoid reversing trucks where dumping has to happen. However, you should reduce the amount of reversing to as little as possible. For more information on reversing, see Section 14.5. Tip heads should be of sufficient size to permit manoeuvring by the largest equipment that is intended to be used.

Dump-point surfaces

The horizontal surface at the tip head should be kept level from side to side so trucks will not tip on their sides when the tray is raised (see Figure 51).

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The surface of the tip head should be kept sloped a small amount so, when reversing to the tip head, trucks will be going up a slight grade (see Figure 52). This gives the driver better control. It also provides a better opportunity to get
the truck out if any shifting of the ground occurs, as well as keeping the tip head better drained.

Communication

There should be a clear and effective system that allows communication between anyone entering the stockpile or dump area, such as two-way radio.

A protocol should be established to define who is coordinating the tip head. If a dozer is present at the tip head, it is good practice to assign this to the dozer driver. If a dozer driver is not constantly present, then other arrangements should be made where multiple trucks may be present at the same time.

If an excavator is used, position the boom to allow visibility between the operator and trucks.

Using spotters

A spotter is someone who guides a truck into the dumping position, either from a safe viewing platform protected from the elements, or in a stationary vehicle.

A spotter should always ‘spot’ the truck from the driver’s side. Where spotters are used, radios should be provided.

Spotting platforms should be highly visible to all vehicles.

For more information on spotting practices see our guidance Safe reversing and spotting practices

Using technology

Make use of technologies such as proximity sensors and vehicle-mounted cameras that can improve both tip head safety and efficiency. See Section 14.10.

A rearward facing camera can assist a truck driver in backing up square to the tip head and determining how close to the windrow the vehicle is positioned. They should be provided at all times where end-tipping is undertaken.

Trucks can be fitted with hoist cut-out features if sensors detect that the truck is tipping at an angle that is too steep.

Traffic flow

Consider the types of vehicles entering the tip head when determining a direction of travel (for example, driver cabs may be on the left or the right-hand side). Approaching with the tip head to the driver’s cab side gives the driver the best opportunity to check the condition of the tip head just prior to dumping.

Drivers should stay back from the edge a minimum of one truck length on their approach and in making their turn.

Toe exclusion zone (prohibited zone)

A toe exclusion zone should be established at a safe distance from the toe of all working tip and stockpile slopes. Barricade fencing, windrows or traffic cones and warning signs should be erected where there is a risk of harm.

Restricted access for light vehicles and workers on foot

To make sure no additional traffic hazards are introduced there should be restricted access to operational areas of a tip for light vehicles and workers on foot. Signs should be erected indicating restricted access areas.

Where light vehicles are required to access the tip head you should establish dedicated light vehicle parking areas and have protocols in place to eliminate pedestrian and heavy vehicle interaction, stopping operations until pedestrians have left the tip head.

Segregation of vehicles at the tip head

Demarcated routes, for use during night or day, should be provided. This should ideally separate access to and exit from the dumping areas. One-way routes are preferable. By restricting movement to defined routes grading and watering requirements are reduced.

Vehicles in the dumping area should always remain in the view of the driver of a reversing vehicle; that is, on the cab side. Vehicles should remain at least one truck width apart from other vehicles while dumping (see Figure 53). This leaves room in case a truck tips over on its side while attempting to dump. Truck drivers should never drive within the reversing path of another vehicle.

Do not reverse a vehicle blindly in a dumping area. Drivers should make full use of visibility aids and should not reverse until they are certain the path is clear and only if protection is in place adjacent to any edge of a hazard. Safe operating procedures should outline the protocols and rules when working at a tip head.

Light vehicles should go to the designated area if there is one. If not, they should stay a nominated distance away from the trucks dumping or queued to dump, similar to having a loading clearance zone. Trucks should queue in a location that ensures they will be safely separated from the dumping truck and in clear view of that truck’s operator.

Dumping the load

Drivers should be trained on how to safely handle sticking material (hang-ups). Sticking material can make the truck tip over as the tray is raised or cause a more critical loading condition on the edge of the tip.

If the tray gets to about two-thirds of the way up and material is still sticking, the driver should lower the tray and find another means of getting the material out (using a backhoe).

This risk is more prevalent with road trucks and trailer units. Operators should consider wet weather conditions changing a normally free-flowing load to one that sticks together due to the rain.

When material sticks in the tray, on no account should drivers try to jar it loose by jamming on the brakes as they reverse. The truck could tip over, the tray hoist could fall causing sudden extreme movement, or if this is done near the edge of a tip, the added force could cause the edge to collapse.

A safe system of work should be established for dumping loads. When the truck is positioned, the driver should apply the park brake before putting the transmission into neutral. When the hoist or tray is rising, the truck driver should use the mirrors to watch the material flowing from the tray to ensure there are no side spills or uneven flow (which may indicate a hang-up). Check for cracking or slumping of the tip head.

Raised trays and alignment of articulated vehicles

The vehicle should stay level if it is moved forward during dumping. Driving with the tray raised should be restricted to short distances, and only where it is required to fully discharge a load. Raised tray alarms and built in speed controls can reduce the risk of vehicles being driven with the tray raised.

Always align the tractive unit and trailer of an articulated vehicle when dumping (see Figure 54). Provide enough space for a vehicle to manoeuvre the trailer and cab so they are lined up.

Never jackknife a trailer unit so that there is a risk of the trailer overturning onto the truck.

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Removing material from a stockpile

The removal of material from the toe of a stockpile can have a significant effect on the stability of the edge.

In the case of loose, free-flowing material, loading out at the toe may have little impact because the material tends to slide back to its angle of repose. Once material has become tightly packed from vehicles on the stockpile, or from sitting for a period of time and settling in, the area where material is loaded out will generally stand at a steeper angle. Material standing at about 35° when dumped over the edge can typically stand at 45° once loaded out.

In some cases, such as when material has been sitting for a long time, the material may stand even steeper or may even stand in an overhanging condition. With these steepened conditions, there is less slope material to support loadings on the stockpile, and a sudden failure could occur.

Mobile plant operators should be trained to continuously trim the face so that it does not overhang and collapse (see Figure 55). Faces should be worked in a straight line so that wings do not develop and create a crescent face which can be self-supporting in the short term but fail suddenly.

Barriers should be installed to restrict access to the top of the tip above the area which is being loaded out. The purpose of the barriers is to isolate the potentially dangerous edge (which could be undercut) from drivers and to eliminate material being dumped onto the loader.

Water saturation of a stockpile can lead to failures and vehicle access should be restricted if this is a factor.

11.4 Procedures for examining tip heads

It is critically important to examine a tip head for unsafe conditions on a regular and on- going basis. Tip head conditions can change due to new material being dumped, the effects of equipment near the tip head, weather conditions, or even just the settling-in of material with the passage of time. In stockpiles, a big factor affecting the tip head condition is the loading-out of material from the toe of the pile.

If the PHMP for tips, ponds, and voids at a mining operation requires regular inspections to be carried out then the PHMP must specify how often inspections occur and a competent person for supervising both tipping operations and inspections.

Operators and supervisors should be trained to identify unsafe conditions and practices at tip heads. They should routinely check for hazards such as cracks, inadequate windrows, unstable material on the slope below the tip head, or a loaded-out slope. Any unsafe conditions should be reported immediately, with operations suspended if required. If defects are found during an inspection, they must be recorded in writing, reported to the operations manager if urgent action is needed, and the relevant operator must ensure that a written record of the defect and action taken are kept as part of the HSMS.

11.5 Tip maintenance and inspection

Regular maintenance of tip surfaces should be undertaken, as well as the access and exit routes. This helps to make sure vehicle hazards due to spillage, wheel ruts, potholes and water ponding are minimised. Windrows or backstops should be maintained in height and profile.

Control dust using water trucks or spray systems to reduce dust nuisance and poor visibility hazards. Dust control in dumping areas should be at least equal to that in loading areas.

When completing inspections look for indications of inherent failure mechanisms or defects due to poor operational practices.

These can include:

TENSION CRACKS OR SETTLEMENT

A tension crack or settled area near the edge of a tip or stockpile is a warning sign of an unstable, or marginally stable, slope. Cracking is an indicator that some movement has already taken place. If movement has occurred, then the slope material is unable to support its own weight, and it should not be relied on to support additional weight, such as a truck.

If there is a tension crack in the dump area, vehicles should not travel over or near the crack. The additional weight of the vehicles may trigger the slope to fail. Loads should be dumped a minimum of one truck-length away from the crack or in an alternative area.

Cracked areas should be clearly marked and isolated so the area is not used, or the condition should be immediately corrected by flattening that area of the tip. This can be done by dumping material at the bottom as a buttress, and carefully pushing material down from the top using a track-dozer.

Tension cracks will tend to run parallel to the edge of the slope. In some materials, other types of surface cracking may occur as a result of the material drying out. Drying cracks tend to be randomly oriented.

MOVEMENT OF SLOPE MATERIAL

A crack or a scarp (a steepened area where the material has slid) on the slope is an indication of instability. Bulging of the slope material is not always as apparent as cracks, but it is another sign the slope material is moving.

Bulging can be detected by looking along the slope of the tip, especially the area near the toe, and paying particular attention to any material that is not at the normal angle of repose.

Bulging of the ground next to the tip is an indication the foundation underneath the tip is too weak to support the weight of the tip. A failure through the foundation could cause a portion of the tip to slide.

Where any signs or movement of bulging material is recognised, dumping operations should be immediately stopped. Dumping operations may resume after a risk assessment and consequent control measures (including re-forming the tip) have been completed and actioned.

SOFT AREAS

Ruts and accumulations of water may indicate soft areas. The hazard in this situation is that as a truck starts to dump, the tyres may sink into the soft area. In the worst case this could result in the truck tipping over, especially if combined with material hanging up in the tray.

Soft areas should either be clearly marked so the area is not used, or the condition should be immediately corrected by re-grading and sloping the area to promote better drainage.

Drivers should stop dumping and move to a firmer area if they feel the tyres sinking into the ground and immediately report such occurrences to their supervisor.

INADEQUATE WINDROWS

Inspections should include checking windrows are adequate to prevent vehicles getting too close to the edge. Windrows must be designed, constructed, installed and of sufficient height to offer definite restraint in the event a vehicle accidentally collides with them.

It is important vehicles do not reverse forcibly into a windrow. As the tyres sink into the windrow, the heavy loading on the rear tyres gets closer to the edge, which can cause the edge to give way. Inspections should include checking for tyre marks on the windrow material. If you notice tyre marks, the potential hazard of this practice should be discussed with drivers immediately and appropriate action taken.

For more information on construction of windrows, see Section 8.3.

UNDERMINED SLOPES

When material is loaded out from the toe of a slope, it makes the slope less stable and more prone to sliding. In this weakened condition the material at the edge of the slope may not be able to support its own weight and the additional weight of a truck. An undermined slope is especially hazardous at a tip head because the additional weight of the truck, if positioned too close to the edge, can cause the edge to suddenly give way.

Because of this hazard, even without cracks or other signs of instability, dumping at or near the edge, where the tip has been loaded-out and undermined, should be strictly prohibited. If your examination identifies an undermined area, it should be cordoned off and rectified.

11.6 Other considerations for stockpiles

Walls or other supports provided to contain stockpiles should be designed by a competent engineer to ensure their stability. If stockpiles grow to an extent that was not anticipated, they should be subject to a design review to ensure safety. In windy conditions, spray water on the stockpiles to minimise the dust hazard.

Engulfment

Engulfment can occur where loaders (or other mobile plant) are removing material from a stockpile that is substantially higher than the loading equipment. Hazard control measures (benching, height restrictions, and continuously collapsing the face so it does not overhang) and emergency procedures (in the case of an engulfment) should be established.

Where using draw down points, such as reclaims, there is a risk mobile plant will fall or inadvertently drive into a draw down hole. Major contributing factors include:

• the suitability of mobile plant for the stockpile design and operating environment (for example mobile plant operating alongside relatively steep stockpiles with heights above the safe limits of mobile plant)
• the operator not being aware of the location of draw down points and either driving into the hole, or sliding into the hole
• the operator driving over the top of a bridged hole that suddenly collapses
• insufficient surface structures or other navigational aids that could be used by the operator to identify the location of draw down points.

Where there is a risk of engulfment, mobile plant should be designed to protect the operator and provide for prompt recovery of the operator. Consideration should be given to the rescue of people in the event of an emergency. Recovery systems and methods should be developed and tested.

Control measures for engulfment at draw down points

The stockpile mobile plant should be designed to withstand engulfment forces of at least 40psi (280kpa). This assumes a safety factor of 2:1 and is based on USA stockpile dozer incidents and investigations.

Devices, such as flags or lights, to assist the mobile plant operator in determining whether draw points are operating.

Pedestrians should be prohibited from the hazardous area at all times, for example draw down points.

Provide communication devices, such as radio telephones and mobile phones, so mobile plant operators can communicate with the control room in the event of an emergency.

Safety equipment should ensure the operator is in a safe atmospheric environment if the mobile plant cab is engulfed to help with rescue. Equipment includes breathing apparatus, rescue harness, emergency lighting and mats or portable bridges (to bridge the gap between stable ground and the engulfed mobile plant).

Position indicating devices should be used to assist mobile plant operators in determining the location of draw down points in high-risk zones. Audible or visual alarms should be provided to alert the mobile plant operator. Devices you could use include GPS, cameras over draw down points, proximity detection and fixed structures to provide a reference point.

11.7 Reworking or reshaping tips

Tips may be re-worked or re-shaped for landscaping or for operational requirements (for example, forming roads over dumped material). A geotechnical specialist should be consulted when planning rehabilitation to ensure the stability of the tip at all times. For more information on rehabilitating tips, see Section 7.6.