Tips and excavation

The construction of excavations, tips and lagoons should be set out in the tips and excavation rules. The rules covering tipping and excavation must be clear. Many incidents occur from falling rock off faces and from falling equipment off tips. These are all matters that should be addressed in the design of the quarry and will involve the geotechnical specialist who can advise on the strength and stability of the tip and tipping point. For example how close to an edge the equipment can tip, the thickness of the layers and compaction needed. From this the suitability of the equipment can be determined. The direction of faces being excavated to minimise cost, maximise fragmentation and stability will also help productivity as well as maximise safety. Again face heights and suitability of equipment will be determined. Too many drivers are killed and injured while working on stockpiles and tips. Look closely at your procedures and make sure that this danger is eliminated.
Layered Compacted Tip
These tips are inherently more stable than end tipped tips. The material is tipped and compacted into layers by the earth moving machinery or by vibrating rollers. The selection of equipment is important. Often dozers and dump trucks are not correctly sized and the material is tipped in too thick layers to be effective and the tip becomes an advanced face tip. The rules will embrace the recommendations set out in the design report. It is important that the tip is properly drained, that the distance equipment can approach edges and the position and size of the edge protection is set out. The maximum height of each bench and the extent of the tip must be set out and what to do if a defect is found. The supervision requirements must be set out. The inspection and maintenance scheme will be monitoring the rules and how the tip is built.
Advancing face tips
These tips are constructed by a vehicle or conveyor tipping material away from the edge of the tip and the material pushed forward by a dozer. The design of the tip will stipulate the foundations and drainage requirements, heights of benches or tipping layers, how close the tipping vehicles can approach the edge of the tip, typically at least 8m and therefore where the edge protection should be positioned.
Typically rear dump trucks and wheel loaders go over the edge of the tips due to the inherent instability of the outer edge. The rules should stipulate the type of vehicle that can use the tip.
Even dozers should not push the edge of the tip clear. The rules should set out how the tip is to be constructed, the type of equipment that can be used, the supervision and the inspection and maintenance required for the tip. This will form part of the inspection and maintenance scheme for the quarry.
These tips are less compact than layered tips and therefore potentially less stable. The material creates natural slip lines as it is built and any failures will occur on these lines, which can combine with poor foundations. These tips must not be left with block tipped materials on top as water will drain down the potential slip plains. Note edge protection must be maintained around the tip when vehicles use them.
Face heights
The heights of faces must be stable in themselves but also within the reach of the equipment that is being used to load from them. In sand and gravel quarries then the equipment should reach the face tops. This may be done by splitting the faces. Operators will need to justify by means of a geotechnical report the stability of the faces where this is not done.
Tips and stockpiles
Stockpiles are now treated as tips. Because of the way in which they have been built they will have inherent planes where sliding may occur
Tipping near tip and excavation edges
The distance that vehicles can approach edges and position of edge protection must be clearly stated in the rules. Tip edges will collapse during the day or overnight and must be a specific part of the maintenance and testing scheme. The rules must state what to do it defects are found. Drainage and foundations are particularly important as are the presence of relic structures and bedding in the material.
Tipping and excavating the same stockpile
This is one of the most hazardous operations in a quarry. Where ever vehicles approach the edges of tips and excavations the operator has to ensure that the material will not fail under the vehicles weight. In the case of stockpiles there will be inherent failure planes from the way the stockpile was built. The loading machine may undercut the face and cause failure
Special precautions should be taken and identified in the rules and supervision should be appropriate. The maintenance and testing schemes will also have to address these issues
Working near water
Draglines
The faces of excavations have to be kept stable even though you cannot see them, for example under water. In this case the slopes will be saturated and the rules should take account the stability assessment that will have been made in the design. Draglines may over steepen the slope on which they stand and cause failure. These slopes should be treated as a significant hazard. Edge protection should be placed around any water filled excavation and rescue facilities provided.
Long reach hydraulic excavators
Hydraulic excavators have the capability to over steepen the slope on which they stand. The rules must address the issue of what they may dig based on the geotechnical assessment. These excavators may dig 10-15m below water level. The slopes must be treated as significant hazards. Edge protection should be placed around any water filled excavation and rescue facilities provided
Quarries should be designed to avoid overhangs.
Faces should be dressed prior to work activity taking place below.
This face collapsed onto the loading excavator while the operator had gone to a meal break.
Here the face collapsed onto the loader and dump trucks while loading was taking place following a blast.
This excavator was crushed after being left under a face overnight.
This Hydraulic back actor excavated under the platform on which it was standing causing it to fall into the workings. This incident is common with drag lines and excavators excavating beneath water. The excavation rules must cover the face profile to be left so that the machine has firm foundations to stand on
This face is showing obvious signs of movement, and the geotechnical specialist was contacted to redesign the slope. In these circumstances careful consideration has to be given to letting vehicles still load on the faces below.
This face is showing obvious signs of movement, and the geotechnical specialist was contacted to redesign the slope. In these circumstances careful consideration has to be given to letting vehicles still load on the faces below.
This face is showing obvious signs of movement, and the geotechnical specialist was contacted to redesign the slope. In these circumstances careful consideration has to be given to letting vehicles still load on the faces below.
Here the face height is being lowered so that the it is within the reach of the loading equipment.
Lagoons need special consideration and regular inspection should be carried out to ensure that they remain safe. This lagoon is over full. Water is seeping over the top and running down to the industrial estate below. Every lagoon has to have an emergency overflow which is 1m below the minimum bund wall.
A typical lagoon wall. Note the drains, edge protection and access arrangements. You must be able to get to draw off points and pumps.
Down stream method of raising lagoons. Note that drainage must be extended before the lagoon wall is raised and access maintained.
A Christmas tree lagoon built in thin layers again with good access and edge protection.
Good access should be provided for inspection and maintenance, with edge protection on the top and access road beneath.
While it is a good idea to have vegetation it should be controlled so that the inspections can be easily and speedily carried out. The brambles on this lagoon prevent adequate inspections of the site.
Burrowing animals will severely affect the integrity of the lagoon and should be discouraged or taken into account in the design
The excavation of lagoons should be done as part of the geotechnical specialists design criteria. Here an excavator was buried while extracting settled materials when the material it was excavating failed.
Good access to the draw off points should be provided. Here some one has to walk the plank! How do operators get out to floating pontoons, and submersible pumps.
The rules will need to address the means of access in cases such as this for maintenance and recovery purposes.
Here good access is provided out to the draw off point but how do people get down the bank?
This lagoon has started to leak water onto the main road. Because it is readily accessible it was possible to detect and put remedial measures in place.
In this clay quarry extensive after care has had to be installed to ensure the integrity of the road above. This should be taken into account in the original design.
The drainage of water is essential to the stability of all tips and lagoon bunds. There should be internal drainage of the tip, and this is usually provided by under tip drains, with the soils removed.
Tips must be adequately drained, and the drainage systems maintained. Here is a typical drainage system
Water should never be allowed to accumulate against the toe of a tip.
This tip showing signs of distress on the outer faces, slips and bulges subsequently failed.
A 6 metre high tip failed and for its height flowed further than the Abervan failure, it crossed a main road and engulfed a house.
All its stored energy ceased as it reached a bungalow on the other side of the road. Failure was due to incomplete drainage construction at the base on this part of the tip when it was landscaped. Landscaping should only be done as part of the design of the tip and under the supervision of the geotechnical specialist
A tip which was registered as closed for approximately 10 years failed after a prolonged period of rain and flowed into an adjacent wood.
Investigation established that only livestock had used this tip since completion, but their movements had ruptured the clay cover allowing water to lubricate the waste causing failure.
Failures of excavated slopes and tips are reportable under RIDDOR. The test is if anyone would have been killed or injured if they were there at the time of the slip. This means even if they occurred at the weekend when no one was on site they are still reportable.
Barrier (fencing) should be suitable for the environment. The type of fencing will depend on location of the quarry. Lagoons should always be fenced