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West Country Aggregates: Quarry Design

2016

Blasting and Production scheduleJAMES DUNFORD

Camborne schol of mines | Penryn campus, Cornwall

ContentsIntroduction...........................................................................................................................................2

Quarry Parameters................................................................................................................................3

1.1 Bench Height.........................................................................................................................3

1.2 Bench Angle...........................................................................................................................3

Vibration Prediction...............................................................................................................................4

Blast Parameters...................................................................................................................................4

3.1 Number of Blasts per Month.......................................................................................................4

3.2 Hole Diameter..............................................................................................................................5

3.3 Burden.........................................................................................................................................5

3.4 Spacing........................................................................................................................................5

3.5 Sub Drill.......................................................................................................................................5

3.6 Stemming.....................................................................................................................................5

3.7 Hole Volume................................................................................................................................6

3.8 Column Charge............................................................................................................................6

3.9 Blast Ratio....................................................................................................................................6

Explosive Parameters............................................................................................................................6

2.1 Explosive properties....................................................................................................................6

2.2 Primer..........................................................................................................................................6

2.3 Detonation system.......................................................................................................................6

Calculation Results................................................................................................................................7

Timing Design........................................................................................................................................9

Production...........................................................................................................................................10

6.1 Fragmentation (KUZ RAM).........................................................................................................10

6.2 Excavator...................................................................................................................................10

6.3 In-Pit Crusher.............................................................................................................................10

6.4 Front end Loader.......................................................................................................................11

6.5 ADT............................................................................................................................................11

6.5 Productivity Cycle......................................................................................................................11

Conclusion...........................................................................................................................................12

References...........................................................................................................................................12

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IntroductionThe aggregates sector in the UK is showing strong growth coupled with rise in infrastructure projects. Many companies

West Country Aggregates (WCA) have been asked to form a comprehensive design for the blasting and production sequence for a proposed limestone quarry on behalf of the Camborne school of Mines (CSM). Provisional projections show a reserve of material to a depth of 900m with planning permission limiting the depth of the site to 90m below surface elevation. 2m of overburden has already been stripped away to begin production. Regulations permit that bench height be no greater than 15m and for safety overall slope angle must not exceed 47 degrees. Bench widths are set 10m to accommodate the width of one ADT, with all levels having an access ramp to the next. Any changes to access ramp design can be planned and constructed during production.

The geology of the deposit is a limestone with three joint sets confirmed through logging (See Table 1). A horizontal zone of weakness of 1.5m thickness was intercepted through investigation work at a depth of 36m. Investigation work anticipates that the workings will be below the water table.

Joint set Dip ° Direction Persistence Spacing (m)1 32° NNE High 0.92 89° SSE Medium 2.53 18° WSW Low 6.0

Table 1: Geotechnical data for joint sets from site investigation

To the North-West of the site there is a domestic property approximately 250m from the proposed workings. The excavation will be predominately oval shaped.

The quarry has been asked to produce 20,000 tonnes of limestone aggregate per month for the aggregates industry. This results in an annual production of 240,000 tonnes. The quarry is small to medium scale. Rock pile mucking will be achieved through one 35 tonne track mounted swing shovel feeding into the primary in pit mobile crushing unit. The crushed pile will be mucked by one front end loader and fed into a 45 tonne ADT to be transferred to the secondary crushing plant. 500m is the approximated average distance the ADT will cover in one cycle.

The rock mass properties for the site are as follows:

UCS = 170 MPa

Specific Gravity = 2.65 t/m3

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Quarry Parameters

1.1 Bench HeightRegulations impose a limit of quarrying to a depth of 90m. A 2m overburden strip has already been completed. This leaves 88m of mineral depth to be quarried. With a maximum allowable bench height set at 15m it is proposed that the quarry be split into 6 benches with the first being 13m and the following benches 15m in height.

Bench No. 1 2 3 4 5 6Bench start height

from surface (m)0 -13 -28 -43 -58 -63

Bench height (m) 13 15 15 15 15 15Bench finish height

from surface (m)-13 -28 -43 -58 -63 -88

1.2 Bench AngleMost UK quarries operate a bench angle between 5-15 degrees depending on the rock type and stability (assumed value through work experience). Vertical benches present too many issues with drilling and do not support slope stability. WCA recommend a 10 degree bench angle as the most efficient for drilling blast holes and aiding slope stability. For 6 benches this gives an overall slope angle of 37 degrees.

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Figure 1: 2D side view for quarry bench parameters

Vibration PredictionBefore the timings for the holes can be established, first it is important to predict the vibration of the blast. A domestic property is situated 250 meters from the quarry boundary. BS 6472 part 2 dictates that no blast should exceed a peak particle velocity (PPV) of 6mm/s. PPV can be affected by the geology, the Maximum instantaneous charge (MIC) and the amount of explosive detonating at the same time. The main cause of increased PPV is the MIC. MIC is the square of separation distance between blast and receiver i.e. the property divided by the scale distance corresponding the vibration level required. The equation is shown below:

MIC=( ssd )2

To work out the scaled distance in mKg-0.5 requires the following equation:

PPV=α ( sd )β

α and β represent dimensionless site factors. They permit for the use of local geology influencing the attenuation of blast vibration. They are the result of specific site investigation and are resultant from the least squares regression method. [4]

No data has been provided for the dimensionless site factors. WCA assumes that further vibrational analysis will be conducted at the site in order to change the blast design to fit within the allowable limits of vibration. Using previous experience working in limestone quarries, WCA assumes that the value of α for this limestone quarry at a 95% confidence level is 180.00 (for programmable detonation) and β has a value of -1.1.

With this information calculated it’s possible to determine the scaled distance.

6.0 (PPV )=180.00 (α )× ( sd )−1.1 ( β )

Therefore scaled distance = 22.02 m

From this MIC can be calculated:

MIC=( 25022.02 )2

This gives an MIC of: 128.9 Kg

Blast Parameters The following section outlines the key parameters for every blast to be undertaken at the quarry. A breakdown for individual benches can be seen in Chapter 4.

3.1 Number of Blasts per MonthAs there is a limitation on equipment availability it’s the recommendation of WCA that the quarry operates one blast per calendar month. This should maximise the utilisation of the equipment and ensure minimal over break and back break through larger scale blasting.

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3.2 Hole DiameterHole diameter is chosen to suit the blast ratio for the rock type and to supply sufficient yield. In the UK it is common to find quarries blasting with a 110mm drill hole. WCA recommends a 110m drill hole with numerical calculation in this section providing evidence for the choice.

3.3 Burden Burden is calculated through the following equation:

B=(30¿45)D

Where:

B= Burden in meters

D= Hole Diameter in meters

30 to 45 is a value represents the type of rock. Where 30 is hard rock and 45 is soft rock.

For lime stone the value is typically chosen as 37.

With this information the burden is calculates as:

37×0.110=4.07m

3.4 SpacingSpacing is calculated through the following equation:

S=B× (1∨1.25 )

Where:

S = Spacing in meters

1 or 1.25 is the multiplier chosen based upon the geology of the rock. If the jointing preferable then the spacing can calculated with a 1.25 multiplier but in most cases the multiplier is 1 resulting in a square pattern. For this design and geology a multiplier of 1 is sufficient.

Therefore spacing is also: 4.07m

3.5 Sub DrillSub drill is calculated as: U=0.3B

This would give a sub drill of: 0.3×4.07=1.221m

This isn’t a practical value for sub drill for the drill operator. To ensure a clean bench floor and removal of the toe it is recommended that the sub drill value be rounded to 1.0 meters.

3.6 StemmingStemming at the top of the hole is used to avoid fly rock by ensuring the gas pressure of the blast does not vent out the top of the hole. Stemming will be made of 6-10mm graded aggregate. The stemming value is equal to the calculated burden for the hole diameter which is 4.07m practically this is harder to achieve therefore values between 4.0 and 4.2 meters are allowed.

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3.7 Hole VolumeThe volume allocated to one hole is equal to the burden multiplied by the spacing and the height of the hole. The height of the hole includes sub drill, therefore each hole will be 15+1 which is 16 meters. For this design that would result in:

4.07×4.07×16=265.04m3

3.8 Column Charge The column charge is the height of the explosive in the hole. This is equal to the hole height minus the stemming height. For this design it is equal to 16m – 4.07 m which is 11.93 m.

3.9 Blast RatioThere are typical blasting ratios for hard rock, soft rock and medium strength rock based on ANFO. These are:

Hard rock – 4t/Kg

Medium rock – 6t/Kg

Soft rock – 10t/Kg

Explosive ParametersThe following section outlines the explosives and detonation system used for all blasts.

2.1 Explosive propertiesThe chosen explosive is Orica’s CentraTM Gold 70 bulk emulsion. The technical data for this explosive is outlined in Table 2.

Product CentraTM Gold 70Density (Kg/m3) 1200Minimum Blast hole Diameter (mm) 45Hole Type Wet & DryDelivery System PumpedTypical VOD (m/s) 3600Relative Weight Strength (%) 70Relative Bulk Strength 102Gassing time 20 minutes between loading and stemming

Table 2: Explosive technical data [1]

2.2 PrimerThe chosen primer is Brexco’s T-500 Booster.

Colour Red – outer sleeve VOD 6800 m/sMass 500g (+/- 20g)Density 1500 kg/m3

Sensitivity – impact/friction 14.7 J / >353 NTable 3: Primer technical data [2]

2.3 Detonation systemWCA recommends and will calculate the blasting schedule based upon a programmable system provided by Orica. The system is known as IKON. It has been used by Nordkalk in Finland and

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Glendenning in the UK. The system has a high accuracy with delays programmed as low as 1ms. The optimum delay time is considered 8ms.

Figure 2: Simple layout of programmable detonator [3]

Calculation Results Taking the information above WCA has created a table for optimum blast designs for this limestone quarries bench blasts.

Burden (m) 4.07 4.10 4.20 4.30Spacing (m) 4.07 4.10 4.20 4.30Total column charge for 16m hole length (inc sub drill) (m)

11.93 11.90 11.80 11.70

Volume (m3) 265.04 268.96 282.24 295.84Hole tonnage (t) 662.60 672.40 705.60 739.60Required explosive (based on 6t/Kg ratio) (kg)

110.43 112.07 117.60 123.27

Explosive Bulk Strength (%)

102 102 102 102

Explosive Density (t/m3) 1.2 1.2 1.2 1.2Loading rate (Kg/m) 9.83 9.83 9.83 9.83Loaded hole (Kg) 117.28 116.98 116.00 115.02

Table 4: Blast design parameter calculation results

From the table it’s the recommendation of WCA that the parameters highlighted in blue be implemented in the general blast design. The holes are slightly overcharged by 4.91 Kg but this is manageable with the slight expansion of Burden and spacing. Each hole theoretically will yield 672 tonnes of rock. For 20000 tonnes per month target this will mean one blast with 30 holes. The total yield will be 20172 tonnes per month. The extra tonnage can be stockpiled or used for construction of ramps. Each blast will consist of three rows with 10 holes per row in a square pattern. (See figure 3)

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Crest

Bench face

Toe

Drill hole diameter 110mm

Spacing 4.1 m

Sub Drill 1.0 m

Column Charge 11.90 m

4.1m stemming

Burden 4.1m

Burden 4.1m

Figure 3: Design drawing not to scale

Figure 4: Blast Design for starter bench, Delay timings and blast direction

FREE FACE

Timing DesignBench 1 will have the same design as benches 2,3,4,5 and 6 despite being shallower. The design calculations show that the same burdens and spacing’s and all the holes will contain less explosive which will not affect the MIC calculation. The blasting pattern for the starter bench will begin from the middle and propagate outward. The design is derived from Dyno Nobel’s shot firing guide [5].

The designs incorporates a central starting blast with the 5th hole from the left initiating after 0ms delay. From there the blast fires from the left first with a 8ms delay, to the right there is a delay of 16ms for the 3rd hole. There are a total of 15 delays for the 30 hole blast. There are 10 holes per row and each row will initiate 16ms after the first blast from the previous row. See figure 4.

For the all other blasts that aren’t starter bench blasts the design will be shown in figure 5.

Figure 5: Blast pattern for Nonstarter blasts

This pattern is double row to minimise risk of back break. The starter hole fires from the middle similar to the starter bench design. However this design has even holes either side of the middle. The resulting throw will be similar to the starting benches but over a greater distance in width. The blast is based off information passed down via Orica. Timings between holes are set at 8ms as this is shown to be optimum time delay. 16ms delays between rows.

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Production This section will outline the production schedule for the quarry with recommended in pit vehicles and crusher choice.

6.1 Fragmentation (KUZ RAM)It is possible to model the fragmentation using the crushed zone model (defined from Kuz-ram). This would generate a predicted distribution curve for the blast. WCA is interested in looking at the 80% average size from the blast calculated through spreadsheet software. Assumptions on block spacing and other factors have been made [9]. Figure 6 is a table showing the percentage oversize and undersize based upon a maximum oversize aloud by the jaw crusher selected.

Figure 6: Kuz Ram predicted fragmentation

Figure 7: Fragmentation distribution predicted by Kuz Ram for blast parameters.

6.2 ExcavatorThe chosen excavator is the Komatsu PC360LC-10 Hydraulic Excavator with a 2.66 cubic meter bucket attached. The operating weight is 35.6 tonnes. [6]

6.3 In-Pit CrusherThe chosen crusher will be a 200 t/h MC 100 R EVO Kleeman primary jaw crusher. This crushers is mobile track mounted. [7] Maximum size feed is 0.9mX0.5m.

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0 0.2 0.4 0.6 0.8 1 1.20%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Size (m)

Perc

ent P

assi

ng

6.4 Front end LoaderThe chosen front end loader will be a CAT 926 M with a 5 cubic meter bucket.

6.5 ADTCat’s 745C is the ADT of choice with a rated payload of 41.0 tons.

6.5 Productivity Cycle

Assumptions made:

- 2.5% moisture content in rock- 25% swell factor- 4 days a week operating, 1 day maintenance and hammering oversize- 9 to 5 working day with 1 hour lunch break.- 60 second cycle time

For a 7 hour shift, the crusher can process 1400 tonnes per shift. Assuming a 90% utilisation of the crusher this would result in 1260 tonnes crushed per shift. 4 days a week operating equated to 5040 produced per week. Per month this produces 20160 tonnes of crushed material.

The bucket has a capacity of 2.66 cubic meters. The following equation works out the tonnes per cycle of the excavator to crusher. Where 2.65 is the specific gravity of the rock, 1.25 represents the swell factor and 0.9 represents the 90% fill factor.

( 2.651.25×2.66)×0.9=3.96 tonnes per cycle

A shift length is 420 minutes or 25200 seconds. With one cycle taking 60 seconds this will result in a total of 420 cycles per shift. This works out as 60 cycles per hour.

Maximum throughput to the crusher works out as: 3.96×60=237.6 tonnes per hour

This is slightly larger than the 200 tonnes hour that the crusher can achieve but assuming some down time in the day and extended breaks this will match up.

The CAT 926M with its 5 cubic meter bucket will take 4 passes to load the 41 tonne CAT 6745C. it will take 7 minutes for the ADT to load and travel 500m to the secondary plant with a 20kmh average speed and a 60 second cycle per pass for loading. This means that the loader can load 200 tonnes in 35 minutes this will leave 25 minutes per hour where the loader isn’t operating. However factoring in the time it takes to get the pile large enough to begin loading (taken as 3 hours to gain a pile of 600 tonnes). The loader driver’s shift can be cut to 4 hours a day. A 4 hour shift will result in 1400 tonnes an hour being transported to the processing plant. With the last hour just removing the final ends of the crushed pile of 840 tonnes.

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Conclusion- Use of square blast pattern with 4.1 meter spacing and burden.- Programmable detonators with minimum 8ms delay- 30 holes per blast, triple row of ten for starter bench blasts and double row of 15 for

standard blasts- Centra Gold 70 bulk emulsion explosive used- Ikon detonator system for precision timing- 20172 tonnes blasted per month in one blast- 88% of material within crushable size- 12% oversize to be reduced by hammer attachment during maintenance day- 4 day operating week- 8 hour shift with 1 hour break for excavator and crusher- 4 hour loader and adt shift- Crusher 200t/h- Roughly 1300 tonnes crushed per day- Equates to just over 20000 tonnes per month

References

[1]: "Centra™ Gold 70". Oricaminingservices.com. N.p., 2016. Web. 21 Apr. 2016.

[2]: "T 500 Data Sheet". Brexco. N.p., 2016. Web. 21 Apr. 2016.

[3]: Wetherelt, Andrew. "Surface Excavation Design Part 2". 2016. Presentation.

[4]: Wetherelt, Andrew. "Surface Excavation Design Part 5". 2016. Presentation.

[5]: "Shot Pattern Guide". Dyno Nobel. N.p., 2001. Web. 20 Apr. 2016.

[6]: "Excavators | Komatsu | PC360LC-10 Tracked Hydraulic Excavator". Marubeni-komatsu.co.uk. N.p., 2016. Web. 20 Apr. 2016.

[7]: "MC 100 R EVO - Kleemann Gmbh". Kleemann.info. N.p., 2016. Web. 21 Apr. 2016.

[8]: "Cat | 926M Wheel Loader | Caterpillar". Cat.com. N.p., 2016. Web. 21 Apr. 2016.

[9]: "Block Volume Estimation From The Discontinuity Spacing Measurements Of Mesozoic Limestone Quarries, Karaburun Peninsula, Turkey: Table 1". Hindawi.com. N.p., 2016. Web. 24 Apr. 2016.

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