Rock Fragmentation: By handling the Rock

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Rock Fragmentation

By handling the Rock

From Quarry to Breakwater

Tom J.A. Korevaar

06-05-2015

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Introduction

Potential breakage of armour stone could be a problem when it is exposed to many rough handling events after it is purchased and before it is permanently placed in the breakwater. This could be a significant problem when the rock is intended for a dynamically stable structure, for example berm breakwaters. Especially the grading of the rock material could be influenced by a negative way due to breaking and fragmentation of the rock. In this research the process of the rock from the quarry until the final positioning at the breakwater has been tried to simulate as much as possible. During this process tests are executed and the losses will be determined. Eventually it should a more clear view of the breakage of armour stone during the construction stage.

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Scope

Project

The research is done for the project Constanta Beach Rehabilitation in Romania. The project aims on the rehabilitation of beaches by constructing breakwaters and sand nourishment of the beaches. An overview of the project can be seen in Figure 1 and Figure 2.

Figure 1: Overview rehabilitation beaches Tomis

Figure 2: Overview rehabilitation beaches Efori North

With the construction of the breakwaters a lot of armour stone has been used. This armour stone has been delivered from a quarry a distance away from the project. The project includes the construction of 8 emerged breakwaters and 5 submerged breakwaters. In Figure 3, Figure 4 and Figure 5 typical cross-sections of the several breakwaters are shown. Visible is that the quantity of core material is relatively small compared to the armour layer, in comparison to a larger breakwater.

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Figure 3: Typical Cross-Section with 1-4 T armour layer

Figure 4: Typical Cross-section with 1-4 T and 300-600 kg as armour layer

Figure 5: Typical cross-section with 300-600 kg and AccropodeTM II as armour layer

Research Question

The goal of this research is to obtain an understanding about which quantities of what grading are lost during the time between purchase and the final positioning of the rock in the structure. Because of this lost an additional volume has to be purchased or a higher grading has to be taken into account during the design phase. The main research question will be:

 What is the percentage of rock that is lost between purchase and final positioning?

A side aspect of the research will be to compare an image analysing software (IAS) to do a grading test to a physical grading test. If such software could be applied in earlier stages of a project it could have a major value. The functioning of such software will be explained in the chapter of theoretical framework.

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Theoretical Framework

Breakage

If a rock breaks two types of breakage can be identified that will have different effect on the degradation. These two types are major breakage and minor breakage. Major breakage refers to breakage of individual armour stones along pre-existing defects. In practice this means that the broken part of the stone has a mass of at least 10 % of the initial stone mass. If major breakages takes place on a significant number of stones, this may significantly affect the mass distribution of the armour stone and consequently the value of the design parameters such as and . The

resistance to major breakage is named integrity. Minor breakage refers to breakage of asperities. Often this happens when stone edges or small corners are broken off. The phenomenon has a limited impact on the mass distribution and the value.

Rock Grading

In Figure 6 the standard grading according to the Rock Manual are shown. In the project as mentioned earlier the armour layer grading used are 1-4 ton and 300-600 kg. In the figure is also the

shown, the is defined as “the average mass of the sample heavier than a fragment” [1]. So

the will differ from the .

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By blasting rock from a quarry the percentage fine rocks is significant higher than the fraction of armour stone. [1] When small breakwaters are constructed the ratio between small material (core and filter) and larger material (armour stone) is more equal than is acquired from the quarry. What means that with every tonnage of produced armour stone the residual of small material will be significantly higher than when a large breakwater is constructed. Therefore the focus of this research will be done on the grading 1-4T, which is the grading of armour stone used on the breakwaters. Because rock of the grading 1-4 T is unavailable 1-3 T is used. This will not have any effect on the research that is going to be done. In Table 1 the lower and upper limits of the 1-3 T according to the rock manual are stated. [1]

The sample that is used has to exist of at least 90 pieces of rock to be able to execute a proper grading test during the different stages of the process. [1] A standard sampling method shall be used as described in the EN13383. [2]

Lower and Upper Limits of 1000-3000kg Grading

kg kg min % max % ELL 650 650 0 5 NLL 1000 1000 0 10 W50 1800 2300 50 50 NUL 3000 3000 70 100 EUL 4500 4500 95 100 Wmax 4500 100

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Intrinsic properties

Intrinsic properties of the rock relate to the properties of the rock source, its geological history or the industrial process. [1] The intrinsic properties are determined using laboratory tests. The relevant intrinsic properties for this experiment are the single axis compressive strength, the resistance to wear and the density of the rock. All properties have been determined by previously performed tests. The resistance to wear has been determined by using a Los Angeles method. The rock used in the research is coming from different quarries and therefore the sample inlcudes multiple kinds of rock. The sample will exist of rock from 3 quarries: Nicolae Balcescu (Limestone), Ben-Ari Negev (Basalt) and Hidromineral (Granite). The intrinsic properties can be found in Table 2.

Property Basalt (Ben-Ari Negev) Granite (Hidromineral) Limestone (Nicolae Balcescu) Minimum density (saturated dry surface [kg/m3] 2986 kg/m3 2820 kg/m3 2833 kg/m3 Maximum water absorption [% of the weight] 0.13% 0.20% 2.56% Minimum compression stress [N/mm2] 158 N/mm2 140 N/mm2 116 N/mm2 Resistance to abrasion (Los Angeles) – maximum weight loss 12% 19.70% 23.30%

Table 2: Intrinsic Properties Stone

Image Analysing Software

The image Analysing software (IAS) determines a size grading on base of a picture taken from the sample. When the picture is taken 2 objects with known dimensions have to be placed in the stockpile (1 in the front and 1 in the back). The software will identity the individual blocks from the image and will make a size distribution based on the 2 reference objects.

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During the tests the process as executed in reality has been tried to simulate as much as possible. During the process from the quarry until the final position in the breakwater there will be some critical stages in which the rock is handled by excavators and other equipment. These stages will be elaborated in this paragraph and the critical points will be indicated.

 Loading trucks at the Quarry: The first crucial point is when the graded rock is loaded into trucks at the quarry for transport to the construction site. The rock stone is loaded by an excavator with a bucket and drops into the trailer of the truck, during this process the rocks will not be protected. The stage before the grading of the rocks is not relevant for this investigation.

 Dumping at the Stockpile: During the transport from the quarry to the construction site the rocks are not exposed to major external forces and the fragmentation during the transport will therefore be negligible. The next critical point in the process will be the dumping of the rock from the quarry on the stockpiles on site. The trucks will tilt their trailer and the rock slides out and will make impact with the rock from the stockpile.

 Stockpiling: When the rock is in the stockpile it is occasionally moved by an excavator to maintain the accessibility of the stockpile, during this procedure the excavator will drive over the stockpile using his steel caterpillar tracks. Rock under the tracks will be exposed to an larger force.

 Loading from Stockpile: When the rock is transported to the breakwater it will be loaded into dump trucks by an excavator. Again the rock will be exposed to an additional impact.  Dumping at/in Breakwater: When the rock arrives at the breakwater the rock will be

dumped directly in the water or on the already constructed part of the breakwater.

 Positioning/profiling Armour Layer by Excavator: After the dump the final step will be the positioning of the armour layer of an excavator with a bucket. When this step is completed the armour layer will be in its final position and will no longer be exposed to major impact forces caused by handling.

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Test Phase

In Appendix A: Test Phase a more detailed description of the process executed during the test phase is given. During the test phase has been tried to simulate the process as described above as much as possible. In this chapter a small summary will be given. The following steps were executed:

 Acquiring Sample

In this step the sample has been acquired according to methods of the EN13383. The number of stones used is 90.

 Initial Grading Test

During this step the initial grading test was executed. Also were the individual stones numbered and the dimensions were measured.

 Loading/Dumping

The first loading and dumping step simulated the rock brought from the quarry. During this step the rock was loaded on a dump truck and after that dumped on a different place.

 Stockpiling

After the first dump the stockpiling has been done by a wheel loader. In this step the wheel loader piles the stones into a more compact pile.

 Loading Trucks/ Weighing Bridge

The next step is the loading of the trucks which passed over the weighing bridge to determine the intermediate mass loss

 Dumping

The trucks dump the sample again, which simulates the stage in which the dumpers dump the material on the breakwater.

 Profiling

An excavator profiles the individual stones as it should be done on the breakwater.  Final Grading Test

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Results

This chapter will describe the results obtained during the tests. For images of breakage is referred to Appendix A: Test Phase. In Figure 7 the grading curve is shown as a result of the grading test. Also the obtained values shown in Table 3. The of the sample is 1879 kg which falls within the limits

of 1700 kg and 2100 kg. [1]

Figure 7: Grading Initial Grading Test

Weight Criteria [kg]<

Weight retained [kg]

Cumulative

weight [kg] % Retained % Cumulative

650 0 0 0 0 1000 10620 10620 6.3 6.3 1800 57326 67946 33.9 40.2 2300 29365 97311 17.4 57.5 3000 32590 129901 19.3 76.8 4500 39227 169128 23.2 100 > 4500 0 169128 0 100

Table 3: Results Initial Grading Test

0 10 20 30 40 50 60 70 80 90 100 500 5000 M a s s per c e nt a ge li ghte r than (% ) Weight [kg] 1000 - 3000kg

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Intermediate Weighing Moment

The intermediate weighing moment shows the weight of the rock as measured on the weighing bridge. 2 trucks are used from which the several weights are shown in Table 4 Including the empty weights as a reference value. The losses in this stage are only losses by fragmentation (minor breakage). The leftovers will also be left over at the

Truck Empty Weight [kg] Weight Trip 1 [kg] Weight Trip 2 [kg] Weight Trip 3 [kg] Weight Trip 4 [kg] Total Weight Rock [kg] CT13KON 14300 34720 34640 35140 24460 71760 CT36KON 14900 37400 37220 37620 34460 87100 Total Weight [kg]: 158860

Table 4: Results Truck weighing

Final Grading Test

During the final grading test the weight of every single rock has been determined again. This time dimensions of the rock are disregarded. The individual results can be found in. In Figure 8 the grading curve is shown as a result of the grading test. Also the obtained values shown in Table 5

Cumulative

650 6933 6933 4.4 4.4 1000 15796 22729 10 14.4 1800 54339 77068 34.3 48.7 2300 24288 101356 15.3 64 3000 33664 135020 21.3 85.3 4500 23335 158355 14.7 100 > 4500 0 158355 0 100

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The number of blocks measured in this test increased from 90 pieces till 105 pieces. Also pieces below 650 kg were weighted and later used as fragments in the determination of the grading curve. As shown in the curve and the table the percentage of stones smaller than 1000 kg is larger than the tolerated amount. The grading shown in Figure 8 is no longer a 1000-3000 kg grading.

Figure 8: Grading Curve Final Grading Test

Cumulative

650 6933 6933 4.4 4.4 1000 15796 22729 10 14.4 1800 54339 77068 34.3 48.7 2300 24288 101356 15.3 64 3000 33664 135020 21.3 85.3 4500 23335 158355 14.7 100 > 4500 0 158355 0 100

Table 5: Results Final Grading Test

The determined is 1701 Kg which is just in between the limits of 1700 kg and 2100 kg. During

the final grading test has been tried to identify the single blocks. For an amount of blocks this was successful. The results from this comparison are shown in Table 12 in Appendix C: Final Grading Test. In the table also the initial L/T value is shown.

0 10 20 30 40 50 60 70 80 90 100 500 5000 M a s s per c e nt a ge li ghte r than (% ) Weight [kg] 1000 - 3000kg

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In Figure 10 the image shown as used for the image analysing software. The stock shown on the picture is similar to the stock on which the final grading test has been executed. In Figure 9 the image is shown after the software has processed it.

To converse the size distribution to a mass distribution the formula [1]:

With [1]:

= the sieve size which is used by the software. In Table 6 the conversed limit values are shown. The density used is the average of the intrinsic properties which is 2880 kg/m3.

Kg [m3] [m] [m] 650 0.23 0.61 0.72 1000 0.35 0.70 0.84 1800 0.63 0.85 1.02 2300 0.80 0.93 1.10 3000 1.04 1.01 1.21 4500 1.56 1.16 1.38

Table 6: Limit Values Size Distribution Figure 10: Image from Stockpile

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Weight Criteria [kg] < % Cumulative (Grading

Test) % Cumulative (IAS)

650 4.4 62.3 1000 14.4 78.3 1800 48.7 92.7 2300 64 95.8 3000 85.3 99.1 4500 100 100.0 > 4500 100 100.0

Table 7: Results Image Analysing Software

Table 7 shows the results of the IAS compared to the result of the final grading test. Figure 11 shows the comparison of the grading curves retrieved from both the grading test and the IAS.

Figure 11: Grading Curve Final Grading test & IAS

0 10 20 30 40 50 60 70 80 90 100 500 5000 M a s s per c e nt a ge li ghte r than (% ) Weight [kg] 1000 - 3000kg Grading Test Grading Curve IAS Grading Curve

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Conclusion

Fragmentation

From the test results can be concluded that the lost due to fragmentation (minor breakage) of this process is the difference between the total mass of the both grading tests:

However the final grading test shows a grading that is no longer representative for a 1000-3000 kg grading. See Figure 12. To make the sample a proper 1000-3000 kg grading again stones from the lower weight regions have to be removed (degraded). Removing the stones smaller than 750 kg will bring the grading back within the limits of the 1000 – 3000 kg. Table 8shows the new parameters of the sample.

Figure 12: Grading from Final and Initial grading test

0 10 20 30 40 50 60 70 80 90 100 500 5000 M a s s per c e nt a ge li ghte r than (% ) Weight [kg] 1000 - 3000kg Final Grading Test Initial Grading Test Final Sample without degraded rock

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17 Weight Criteria [kg] < Weight retained [kg] Cumulative

650 0 0 0.0 0.0 1000 14440 14440 9.6 9.6 1800 54339 68779 36.2 45.8 2300 24288 93067 16.2 62.0 3000 33664 126731 22.4 84.5 4500 23335 150066 15.5 100.0 > 4500 0 150066 0.0 100.0

Table 8: Final Grading After Degradation

The lost due to degradation (major breakage) will be another 8.3 tons. The percentage of lost due to degradation will be:

This brings the total of losses at 11.3 %. It should be kept in mind that 4.9 % can be reused in a other grading. From Figure 12 can be concluded that even if you grade your grading back to a proper 1000-3000 kg grading the grading curve will always be more steep than was in the initial state. It should be kept in mind during this conclusion stage that the sample used for the test is already exposed to breakage a couple of time compared to “fresh” rock from the quarry.

The results from the Image analysing software are not accurate as shown in Figure 11. The strange grading curve can be explained by the fact that most of the stones are covered by other stones and therefore the software only sees a part of it. The grading is therefore much smaller as it supposed to be. The software will probably function much better on a sample with a smaller grading, because the dimensions of the rock are more similar.

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Recommendation

Fragmentation Test

The location of the test could be improved to receive a more realistic value. The rock used in the sample during this test was already handled multiple times and therefore it was already exposed to breakage. In reality the quarry would be a better location to execute the test.

After the test some aspect could be improved for similar next tests. By acquiring the sample the stockpile existed of different kinds of rocks which gave a completely general result. To achieve a more specific result rock of 1 single kind should be used.

During the initial grading test the number of the blocks should be done by putting more numbers on 1 single block, because of the breaking an scratching a lot of numbers were already unidentifiable after the first dumping step. At the end only 30% of the blocks could be identified again. This way also the L/T-ratio can be checked with the breakage.

Another point that could be improved is the intermediate weighing moment. To see if every dumping moment gives the same fraction of losses the process of dumping, stockpiling and loading could be done an additional time. This also matches the reality in which the stone is often picked more times than described above.

To improve the results achieved by the image analysing software the picture should be taken from a bird point of view or at least perpendicular to the sample. This way the major part of the stone will not be hidden behind the stone in front of it as happened in this research. The pictures used in this research were taken from a to flat angle.

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Literature

1. CIRIA, CUR, CETMEF, 2007. The Rock Manual, second edition. The use of rock in hydraulic engineering. CIRIA, London.

2. British Standard Institution (BSI), 2002a. Armour stone - part 1: Specification. BS EN 13383-1. BSI, London.

3. British Standard Institution (BSI), 2002b. Armour stone - part 2: Test Methods. BS EN 13383-2. BSI, London.

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Appendix A: Test Phase

This Appendix will describe the process that has been followed during the test phase. The process existed of several steps with several measuring moments, these steps will here be described in more detail.

1. Acquiring Sample

The first step was the acquiring of the sample. The sample should exist of at least 90 pieces, according to the rock manual. [1] To guarantee the randomness of the sample, the rock has been picked from different locations from the stockpile. [2] To select the rock an excavator is used as shown in Figure 13. After the sample had been established the initial grading test could be executed.

Figure 13: Acquiring the sample

2. Initial Grading Test

The grading test is executed with a weighing cell as shown in Figure 14. Before the blocks were separately weighted they were numbered and measured. The measurements determined were the length and the thickness. With these the L/T ratio was defined in a later stage of the process. The length of the rock has been defined as the longest side of the rock, the thickness is the side perpendicular to the length. The blocks are lifted using a steel sling and special trained riggers to handle the sling.

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3. Loading/Dumping

The first step of the simulation is the loading and dumping of the sample. The sample has been loaded into dump truck, transported to a different location and dumped again. During this process some significant damage has been observed. The loading has been done by an excavator using his bucket. The dumping of the material has been executed by dump trucks as shown in Figure 18. In Figure 19 and Figure 20 results of the breakage after the dumping are shown.

Figure 17: Loading the Dump trucks Figure 15: Measuring the individual rock Figure 16: Numbering of the individual rocks

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4. Stockpiling

The next step in the process is stockpiling the sample. The stockpiling has been done by a wheel loader as shown in Figure 22. The result of the stockpiling is shown in Figure 21.

Figure 22: Stockpiling sample using Wheel loader Figure 21: Result of the Stockpiling

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5. Loading Trucks

The next step is loading trucks to put them on the weighing bridge to get a first intermediate result. Before the trucks were loaded they were weighted empty to have a reference level. In the initial method an intermediate measuring moment was planned between the first dumping and the stockpiling. However after a conversation with the superintendent on site he explained that both steps are not executed separately and therefore the measuring moment between the two steps in not relevant for this research.

Figure 24: Truck on the weighing bridge

Figure 25: Minor Breakage Due to Stockpiling

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6. Dumping

After the trucks have been on the weighing bridge the dump the sample again. This step simulates the dumping of the rock on the final position/at the breakwater as shown in .

7. Profiling

The final stage of the simulation is the profiling. In this stage the excavator placed the blocks in a similar as it should be done at the breakwater. In this final stage also an image has been made for using the Image analyzing software. The sample as is placed in the current state will be used for the final grading test as well.

Figure 28: Profiling of sample by an excavator _{Figure 29: Result of the Profiling Phase}

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8. Final Grading Test

After the positioning the final grading test was executed in the same way as described by the initial grading test. The results of the test are compared with the initial results and the results of the intermediate weighing moment. The results will me elaborated in more detail in the chapter results. In Figure 30 a stone is shown that is still without breakage however has a high probability to break in a next handling step.

Figure 31: Final Grading Test Figure 30: Stone with Potential Breakage

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Appendix B: Initial Grading Test

Nr Stone

Weight (kg)

Length (cm)

Thickness (cm)

L/T

1 2293 120 70 1.7 2 1496 163 58 2.8 3 1024 133 62 2.1 4 3956 200 100 2.0 5 2454 173 89 1.9 6 2741 215 88 2.4 7 1236 116 69 1.7 8 3007 176 112 1.6 9 3744 170 100 1.7 10 2690 180 105 1.7 11 2550 172 101 1.7 12 2210 198 58 3.4 13 3452 152 97 1.6 14 3076 183 112 1.6 15 2213 129 77 1.7 16 2081 183 83 2.2 17 3335 171 112 1.5 18 2620 159 67 2.4 19 1777 152 68 2.2 20 839 120 63 1.9 21 1496 153 79 1.9 22 3494 215 115 1.9 23 1651 192 53 3.6 24 3090 177 81 2.2 25 2843 195 113 1.7 26 1738 129 80 1.6 27 2290 201 85 2.4 28 926 131 81 1.6 29 1129 139 53 2.6 30 3198 192 75 2.6 31 1308 134 72 1.9 32 2604 163 105 1.6 33 1944 155 66 2.3 34 2989 158 93 1.7 35 1974 112 88 1.3 36 1248 118 51 2.3 37 2013 134 60 2.2 38 1499 128 40 3.2 39 1009 138 85 1.6 40 1642 120 60 2.0 41 1983 210 101 2.1 42 2072 215 80 2.7 43 1693 134 60 2.2 44 1738 160 74 2.2 45 1230 90 78 1.2

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Nr Stone

Weight (kg)

Length (cm)

Thickness (cm)

L/T

46 1690 131 87 1.5 47 872 90 83 1.1 48 2096 138 99 1.4 49 1511 132 62 2.1 50 938 134 52 2.6 51 1454 125 52 2.4 52 2063 138 85 1.6 53 1012 102 68 1.5 54 4461 160 110 1.5 55 1281 199 85 2.3 56 1120 141 65 2.2 57 2463 118 102 1.2 58 2953 138 70 2.0 59 1675 127 90 1.4 60 1568 162 45 3.6 61 2222 218 82 2.7 62 1412 153 71 2.2 63 2861 190 97 2.0 64 1218 164 84 2.0 65 1705 175 62 2.8 66 830 129 40 3.2 67 4414 155 98 1.6 68 1254 121 40 3.0 69 1621 131 73 1.8 70 860 128 99 1.3 71 1523 110 90 1.2 72 1096 101 72 1.4 73 1490 145 94 1.5 74 947 135 56 2.4 75 1224 142 98 1.4 76 830 110 56 2.0 77 905 120 40 3.0 78 1460 105 90 1.2 79 1406 164 69 2.4 80 1221 177 101 1.8 81 830 130 80 1.6 82 914 175 76 2.3 83 1081 133 99 1.3 84 1054 145 60 2.4 85 1541 150 55 2.7 86 1911 140 87 1.6 87 1260 165 77 2.1 88 1535 148 66 2.2 89 2822 189 67 2.8 90 929 110 74 1.5

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Appendix C: Final Grading Test

Weight of Individual Blocks [kg]

2251 245 1030 242 343 1451 2646 726 803 1935 1511 2893 2123 2030 1732 1678 735 2687 2890 3102 1523 982 988 788 2604 3443 702 1484 1645 3213 152 1505 1221 1696 833 1612 469 881 806 517 1863 806 1275 1168 896 654 1212 1445 1403 950 2287 1457 3291 1496 1977 600 343 600 2308 1439 896 1732 794 2401 1627 1194 624 1899 1535 863 3114 1478 3941 340 1018 1998 2720 621 1672 3231 1597 1182 1669 305 302 618 1254 2637 1347 1311 1511 2520 1132 1051 2598 746 1672 2314 947 1374 2048 2075 2446 612 1802 Number of Blocks: 105

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Number of Block Initial Weight [kg] Final Weight [kg] Weight Loss [kg] L/T

1 2293 2123 170 1.7 2 1496 1478 18 2.8 4 3956 3941 15 2.0 7 1236 1221 15 1.7 9 3744 3231 513 1.7 10 2690 2687 3 1.7 13 3452 3291 161 1.6 16 2081 2030 51 2.2 17 3335 3213 122 2.6 19 1777 1612 165 2.2 21 1496 1496 0 1.9 22 3494 3443 51 1.9 23 1651 988 663 3.6 25 2843 2646 197 1.7 26 1738 1732 6 1.6 31 1308 1182 126 1.9 32 2604 2604 0 1.6 34 2989 2893 96 1.7 35 1974 1899 75 1.3 43 1693 1678 15 2.2 44 1738 1696 42 2.2 48 2096 2075 21 1.4 49 1511 1051 460 2.1 53 1012 982 30 1.5 57 2463 2287 176 1.2 58 2953 1977 976 2.0 59 1675 1672 3 1.4 60 1568 1511 57 3.6 65 1705 1627 78 2.8 78 1460 1347 113 1.2 81 830 726 104 1.6 82 914 788 126 2.3 83 1081 803 278 1.3 85 1541 1505 36 2.7 86 1911 1863 48 1.6 88 1535 1535 0 2.2

Rock Fragmentation: By handling the Rock