METHOD OF MOVING MATERIAL

Abstract

The invention is directed to a method of strip mining that involves dividing the pit into blocks in a diamond shape arrangement with an angular advancing strike face and removing waste material from each diagonally adjacent block so as to minimize the amount of waste material pushed by dozers and maintain the incline of ramps to gradients of 10% or less so that trucks can take mined ore from the pit.

Claims

1. A method of strip mining to mine an ore seam including dividing the pit into a plurality of blocks where each block is orientated along a mining strike length in a diamond pattern formation to present an angular advancing strike face; moving overlying waste material from a first block of said plurality of blocks to access the ore seam wherein the waste material is divided into an upper cut volume and lower cut volume, the upper cut volume is removed out of the pit and the lower cut volume is moved into a first adjacent pit void; mining the exposed ore seam in the first block; identifying a second block of the plurality of blocks that is diagonally orientated with respect to the first block and along the mining strike length; moving an uppercut volume from the second block to the first block and a lower cut volume of the second block to a second adjacent pit void to expose the ore seam; and mining the exposed ore seam in the second block; wherein the steps of moving waste material and mining the exposed ore as performed with respect to the second block are repeated with the remainder of the plurality of blocks.

2. A method as claimed in claim 1, wherein the first and second adjacent pit voids are behind the advancing strike face and formed from a previous mining operation.

3. A method as claimed in claim 1 wherein the method is carried out to move waste material minimal distances and have inclines with a substantially 10% gradient or less.

4. A method as claimed in claim 1 wherein a front corner of an adjacent block is incorporated into the cut volume to form a roadway to move ore from the pit.

5. A method as claimed in claim 1 wherein a percentage of dozer and truck and shovel operations usage is dependent on topography and geology including direction and depth of the ore seam.

6. A method as claimed in claim 1 wherein the diamond pattern has the plurality of blocks orientated at 45 degrees to the advancing strike face but changes to 90 degrees when a dipping angle of the ore seam increases to substantially 10 degrees and higher.

7. A method as claimed in claim 1 wherein the length of the blocks along the advancing strike face can be extended as a dipping angle of the ore seam increases so as to maintain an inclined ramp with a maximum gradient of substantially 10 degrees.

8. A method as claimed in claim 1 wherein strategic blasting is used to reduce an amount of waste material to be mechanically excavated, facilitate the dozing by casting material in the direction that the dozers will need to push the material, separating and dealing with the upper and lower layers of material differently, and or directing material to a position that allows the formation of a ramp or bridge to transport excavated material from the pit.

9. A method as claimed in claim 1 wherein strategic blasting includes placing explosives at two or more locations, arranging the explosives at each location and coordinating a timing of a detonation of the explosives, wherein the two or more locations can be locations at different depths at a work site, spaced locations to effect casting of site faces in different directions and locations that involve a combination of vertical depth and horizontal spacing positioning, wherein the blasting maximizes the casting of the material to facilitate moving the waste material.

10. A method as claimed in claim 1 wherein the ore seam is a coal seam.

Description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0082] A preferred embodiment will now be described with reference to a three year plan for mining a coal seam in an open cut mine.

[0083] Mining Method Year One

[0084] The mine is an open cut coal mine with a single seam of coal three meters thick. The coal seam is located beneath 21 meters of waste rock material, giving the mine a strip ratio of 7:1. The mine operates as a “dozer push operation”; that is the waste rock is removed with a fleet of high production dozers. The dozers push the waste rock from the area above the coal seam into a waste dump area directly across the pit.

[0085] The mine needs to maintain saleable coal for each year of one million tons for its market. The coal weight is approximately 1.25 tons per cubic meter. That translates to uncovering 800,000 cubic meters of coal per year. The mine has been set up with a strike length of 2 kilometres. The mine will need to advance at a rate of 150 meters per year to uncover the coal needed to supply the market with some safety margin.

1,000,000 ton/1.25=800,000 m.sup.3

[0086] 2,000 meters strike length: 8,000 meters/(2,000 coal m.sup.3/3m thick)=approximately 150 meters advance.

[0087] The mine will need to remove 6.3 million cubic meters of waste rock per year to uncover the coal needed for its markets.

[0088] The advancing blocks will be calculated with a strike length of 2,000 meters and advancing 50 meters at each time giving 150 meters of advancement for the year.

[0089] The mine first began operation as an excavator and truck operation. It was later decided to change to a dozer operation and has operated as a traditional dozer strip mine for the last three years. It has four caterpillar D11 dozers each capable of moving two million cubic meters per year as the primary waste rock removing machines. It was decided that having the dozers as a primary waste rock removal machines that some margin of extra capacity was needed. Having only three dozers would leave no room for any change in circumstances.

[0090] The coal is removed with an excavator and truck fleet. A second excavator and smaller truck fleet is available when needed to increase production after wet weather or other unforeseen circumstances. It is also used as a backup when the primary excavator and trucks are in need of repairs.

[0091] The mine is fortunate not to have hard areas that require drilling and blasting to loosen the waste rock before removal. Ripping is required in some areas but the reduced dozing time needed for ripping with the dozers has been calculated as more cost efficient than blasting.

[0092] The strip mining method has to-date been a direct push from the waste rock cut area into the waste rock fill area. With this mining method the dozers start pushing the waste rock from the top surface of the cut volume and slowly work downwards to the bottom surface of the cut volume. As this is being carried out the dozer must push the waste cut volume into the waste fill volume. The top surface from the cut volume will be placed in the bottom of the fill volume. As the operation progresses, the bottom cut volume will be placed in the top of the fill volume (see FIG. 26).

[0093] It is decided to increase efficiencies of the mining operation and look at other mining methods to make higher profits.

[0094] Three mining methods are considered for this year's mine planning. It is decided to use a diamond pattern method at 45 degrees as this will result in the best mining efficiency's for pit dimensions and geology for this year's mining. It can be used with the excavator and trucks or dozers. It is decided to use the dozer fleet as they will be most effective with this method. From historical mining cost at this mine using excavators and trucks for waste rock removal, a base line cost of between $2.10 to $3.20 per BCM (Bank Cubic Meter) has been established. The dozer historical cost range from $0.90 to $1.80 per BCM for waste rock removal.

[0095] The pit is designed in a diamond pattern in a series of blocks and not in a straight advancing face. The diamond pattern is used to reduce the amount of waste rock being moved into a lower position than the height it was cut from, and reduce the amount of waste rock that is moved into a higher position than the height from which it was cut.

[0096] Another benefit is the distance the waste rock is pushed. In current dozer push methods to lift the waste rock to a certain height it must be pushed a certain distance; this ratio is a limiting factor in designing a pit for dozer push operations.

[0097] The mining engineer's produce a mining plan that will take into account the recovery rates of coal needed throughout the year. The blocks are divided into 50 meter squares in a diamond pattern along the strike of the pit. Some extra design work is needed at each end of the strike to take into consideration of only one half of a block will be used.

[0098] After the mining plan has been established, a dozer push plan is developed for each block. After the first block is established the waste rock from each block will be moved in a more efficient manner (see FIG. 27).

[0099] To maximise the efficiency of the method the first upper cut volume of block 1 is removed out of the pit void by pushing it to the side or removing it with a truck and shovel operation (see FIG. 27).

[0100] With reference to FIG. 28, the lower cut volume of block 1 is now pushed into the void created from the last mining strip or a box cut.

[0101] The upper cut volume of the next block 2 in now pushed across the top of the previous bottom fill volume (see FIG. 29).

[0102] The lower cut volume of block 2 is pushed across the pit into the fill position (FIG. 30).

[0103] Upper cut volume of block 3 (FIG. 31) is now pushed across the top of lower fill volume from block 2. This is repeated across the length of the pit.

[0104] The dozer push plan is developed to take into consideration of the waste rock cut area and the waste rock fill area. Consideration is given to the adjustment needed in the fill area to take into account the swelling of the waste rock as it is removed from the cut area. The waste rock in this mine has a swell factor of 0.30. The rock in the ground before it is disturbed will have a Bank Cubic Meter of 1.00. After it is disturbed with blasting or digging it will have a Lose Cubic Meter volume of 1.30 meters.

[0105] As part of this calculation, allowance for swell factors and material repose angles are used to identify boundaries that material will travel to from the fill area when it is pushed into place to eliminate waste rock flowing onto the exposed coal ready for recovery (FIG. 32).

[0106] As part of the calculation for dozing in this method the dozing distances and dozing angles are a significant cost if they are not contained to shorter lengths and less step angles.

[0107] A dozer pushing up a steep grade can push less material than a dozer pushing along a flat surface or pushing down hill, thus the movement of material up a slope takes longer and subsequently costs more. The cost and time required to move this volume can be calculated using the average push distance and gradient.

[0108] As the angle increases the production rates decrease, as the angle decreases the production rates increase. The graph in FIG. 33 can be used to make the calculation.

[0109] The production rates will increase by 60% for downhill pushing at 30% grade using 0% Grade as the base line and decrease 70% for pushing up a grade of 30% or 17 degrees.

[0110] The cost difference can be explained in the following example. A dozer push rate of 400 m.sup.3 per hour at 0% grade. If the dozer has to push uphill at 30% grade the rate will need to be adjusted by multiplying 400 m.sup.3×0.3=120 m.sup.3 per hour. If the dozer pushes downhill at 30% grade the adjustment will be 400 m.sup.3×1.6=640 m.sup.3 per hour. The difference between the two is 520 m.sup.3 per hour or an increase of 533%.

[0111] To reduce costs and increase the rate at which material is moved the engineers will use the diamond method and reduce the vertical distance that material must be moved by pushing “low dirt” low and “high dirt” high.

[0112] The typical straight push method results in material being pushed from the lowest cut point (top of coal) to the highest fill point (maximum dump height).

[0113] To determine the most efficient dozer push method of a selected cut area and dump area, the surveyed start surface, designed final surface and machine data are inputted to a programmable processor.

[0114] The programmable processor generates a cross section through the start and final surfaces and uses average push length and gradient to calculate an estimated cost and machine production for a range of different push methods. The production estimates for each of the methods can be compared to determine the most efficient method for the selected cross section. A push plan, which the machine operator can follow, is then produced with the software. Straight push block 1 is shown in FIG. 34 while straight push block 2 is shown in FIG. 34.

[0115] In FIG. 36 (45 degree low section push) and FIG. 37 (45 degree high section push), the 45 degree method utilises a diamond pattern to allow the top half of a block to be pushed over the dump of the lower half of the previous block resulting in a shorter less steep push.

[0116] With reference to FIG. 38 (straight push data) and FIG. 39 (45 degree angle push data), there is shown a push length comparison between straight and 45 degree angle pushes. It is shown that the average push lengths and distances are greater for the straight push method. The data is a comparison of 50 m×50 m×21 m blocks.

[0117] As the waste rock is removed from the coal, recovery of the coal can start to take place. Ramps into the pit have been designed as part of the year's mining plan. Once the first 50 m×50 m block is removed and the coal exposed the excavator and trucks can begin to recover the coal. The mining plan has calculated that the dozer fleet should finish the next block as the coal recovery nears completion from the first block.

[0118] To allow access along the strike for the trucks to travel a corner from each block is removed as part of the dozers push plan (see FIGS. 40 and 41).

[0119] Mining Method Year Two

[0120] As the year closes the next year's mine planning is being prepared. From the drill hole samples and logs taken in the advancing area of the mine, it is noticed that the coal is beginning to dip downwards and later in the year it will approach a dip of 11 degrees. To uncover the coal needed for sales a change in mining methods may be needed as costs will increase with the deeper coal.

[0121] Three methods are considered: straight dozing, diamond pattern at 45 degrees and straight diamond pattern at 90 degrees. It is decided that the diamond pattern at 45 degrees will be most efficient until the coal dipping angle increases to 10 degrees. At that point the mining method will change to a diamond pattern at 90 degrees.

[0122] The 90 degree pattern method has the diamond pattern parallel to the advancing mining area with the mining cut areas mined in a diagonal pattern. These usually have the mining area advancing from an end of the pit (FIG. 42).

[0123] The advantages to this method when used on dipping ore bodies is that the sequence can take advantage of downhill pushing. A dozer's efficiency will increase by as much as 60% when the dozer is pushing down hill at 17 degrees. The advantages can only be obtained if the fill area is significantly lower than the cut. Having a dipping coal seam has this advantage if the pit can be designed to take this advantage (FIG. 43).

[0124] One disadvantage of mining steep dipping seams with truck and shovel operations is that the dip may be greater than 10% needed to drive a loaded truck out of the pit with either waste rock or mined ore. Ramps are needed to make roadways for the trucks and must be cut into the waste dumps or the cut volumes above the ore body.

[0125] An advantage of the 90 degree method is the blocks can be arranged so that the diagonal corners from one cut volume to the next lower cut volume are less than the maximum ramp angle for the trucks to drive out of the pit. This will allow the trucks used to recover the ore to use the void created as a ramp out of the pit (FIG. 44).

[0126] This method will give the mining operation some flexibility as the coal dip increases, by using the area behind the blocks as ramps to recover the coal. As the dip increases, the blocks can be lengthened along the strike to maintain a maximum of 5.7 degrees (10%) ramps for coal recovery (FIG. 45).

[0127] The 90 degree diamond pattern will prove higher production rates over the 45 degree diamond pattern as the dip increase by taking advantage of the higher dozer production rate for more downhill pushing. The advantages of this method will rely on setting the pit geometry to having multiple work faces. The engineers have calculated that the excavator and truck fleet will be required to establish the change over from 45 to 90.

[0128] Although this will take some time to complete a schedule has been draw up to have the excavator start at the end of the pit the dozers have completed. The schedule has shown only a small time delay in having coal exposed for recovery and the economic justification shows a cost reduction in operating expenses for the year as compared to continuing with the present 45 degree diamond pattern. There will be some disruption to coal recovery rates with a period of time when no coal will be recovered. It has been calculated that by utilizing the second excavator and truck fleet and increase some work hours that coal recovery will be re-established quickly and the total years coal production will be meet. The marketing department has informed the customers and they are satisfied with the total tonnage being delivered for the year (FIG. 46).

[0129] To take full advantage of this method and to keep the coal recovery rates in line with coal needed for sales, two advancing pit openings are established. The first is opened at one end of the pit and the second is opened in the centre of the strike. This will have the two opening approximately 1000 meters apart. After established, the mining plan will have the dozers working from the bottom side back towards the top side. While this is an advantage for the dozers to be always pushing downhill, the coal cannot be recovered easily until the dozers have reached the last top block. Having two openings will allow the dozers to complete one section and then move to the other opening while the excavator and trucks remove the coal from the section completed. The secondary excavator and trucks will be used to establish the bottom block cut to start the next dozer push sequence. The process will be repeated with the dozers and truck fleets moving from each area as they complete their work.

[0130] The distance between the two openings is not too great and the movement of slow heavy equipment from one opening to the other has been calculated into the cost benefits modelling (see FIG. 47).

[0131] The method also has the cost benefit of reducing the ramps required. The slope down the dip along the path created by the blocks can now be used for the ramp access into the coal recovery area.

[0132] Mining Method Year Three

[0133] In the following year (year three) the coal seam is continuing to dip below 10% but will not exceed 20% for the remaining minable area. The 90 degree diamond pattern will need to be adjusted by adding the secondary excavator and truck fleet to remove the top of the waste rock.

[0134] Adding the extra capacity of removing the waste rock with the second excavator and truck fleet before the dozing begins with the 90 degree diamond pattern has been calculated as the most efficient use of the mines present mining equipment.

[0135] It has been calculated that if the mining depth continues to increase the cost effectiveness of the dozers will decrease. With the added depth now growing to 40 m the dozers will need to push longer distances and at a higher grade. As the dozers are limited to pushing the waste rock into the fill area by the angle they can push up at, this will mean longer push lengths. The fill area is also limited to the previous block dimensions. The dozers will not be able to dump all the cut waste rock into the fill area. The cost will grow using dozers alone. While it will be still cheaper than using excavator and trucks, the dozers are reaching a limit they cannot exceed which is room to push the waste rock. It will be cost effective to use a combination of equipment.

[0136] As the depth of coal increases, the cost of mining will increase. The excavator and truck costs will increase with depth. There will come a time in the future that the cost increase because of increasing ore seam depth will make the mining operation uneconomical. The dependence on efficient mining methods will extend the mine life beyond the original mine plan.

[0137] The original mine plan was developed using excavators and trucks when coal prices were high. The mine had an expected life of 15 years. The cost of infrastructure and other capital was costed out over the 15 year period. The expected mine life would have ended when waste rock removal reached $2.60 per BCM in year 15. The new mining method has maintained cost under $2.60 and will continue for another 4 years past the original mine life.

[0138] The cost of infrastructure and capital can now be spread over more years giving the mine a more return on investment than first calculated. The mine set up cost was $60 million. Over the original life of 15 years equates to a yearly cost of $4 million per year. If the mine can extend its operation for another 4 years than the $60m will be spread over 19 years of operation giving a cost per year of $3.2 million (See the spreadsheet in FIG. 48).

[0139] The preferred embodiment of the method of strip mining involves dividing the pit into blocks in a diamond shape arrangement with an angular advancing strike face and removing waste material from each diagonally adjacent block so as to minimize the amount of waste material pushed by dozers and maintain the incline of ramps to gradients of 10% or less so that trucks can take mined ore from the pit.

Variations

[0140] It will of course be realised that while the foregoing has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is herein set forth.

[0141] Throughout the description and claims of this specification the word “comprise” and variations of that word such as “comprises” and “comprising”, are not intended to exclude other additives, components, integers or steps.