3D Modeling of Ripping Process
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Hakan Basarir1; Celal Karpuz2; and Levent Tutluoğlu3 Abstract: Due to environmental constraints and limitations on blasting, ripping as a ground loosening and breaking method has become more popular than drilling and blasting method in both mining and civil engineering applications. The best way of estimating the rippability of rocks is to conduct direct ripping runs in the field. However, it is not possible to conduct direct ripping runs in all sites using different dozer types. Therefore, the utilization of numerical modeling of ripping systems becomes unavoidable. A complex ripping system can better be understood with three-dimensional 共3D兲 models rather than two-dimensional models. In this study, 3D distinct element program called 3DEC was used to investigate the ripping process. First, the ripping mechanisms were investigated and then the individual factors that affect the rippability performance of dozers were reviewed. The rippabilities of rocks depend not only on the rock properties, but also machine or dozer properties. Thus, ripper production and rock rippability with D8 type of dozers were also determined by direct ripping runs on different open pit lignite mines within the scope of this research. Production values obtained from numerical modeling were compared with field production values obtained from the case studies. This comparison shows that the model gives consistent and adequate results. Hence, a link has been established between the field results and the 3D models. DOI: 10.1061/共ASCE兲1532-3641共2008兲8:1共11兲 CE Database subject headings: Mining; Numerical models; Rock mechanics; Construction equipment; Three-dimensional models.
Introduction When equipment for a trial test is not readily available for the assessment of rippability, indirect methods can be used to obtain estimates of ripping production. Seismic velocity-based methods, which are solely based on the P-wave seismic velocities of rocks, were suggested and used for rippability classifications in Caterpillar 共1988兲, Komatsu Ltd. 共1987兲, Atkinson 共1971兲, Bailey 共1975兲, and Church 共1981兲. Another indirect rippability classification is by grading methods. In grading methods, different rock properties are graded separately, and according to the total grade, the rippability classes of rocks are determined. Weaver 共1975兲, Kirsten 共1982兲, Müftüğlu 共1983兲, Smith 共1986兲, Singh et al. 共1987兲, Karpuz 共1990兲, MacGregor et al. 共1994兲, and Basarir and Karpuz 共2004兲 are all examples of grading methods. A field trial test is the method preferred for the assessment of rippability; however, performance of field trials of rock ripping with different dozers is not cost effective. Even if a dozer is available, it is difficult to dedicate the dozer just for ripping action. For these reasons, it is necessary to build a model as a representation of the ripping operation and study it as a surrogate for the actual ripping trial. Mainly, three types of modeling methods are available; these are physical, analytical, and numerical 1 Assistant Professor, Dept. of Mining Engineering, Inonu Univ., 44280 Malatya, Turkey. E-mail:
[email protected] 2 Professor, Dept. of Mining Engineering, Middle East Technical Univ., 06531 Ankara, Turkey. E-mail:
[email protected] 3 Associate Professor, Dept. of Mining Engineering, Middle East Technical Univ., 06531 Ankara, Turkey. E-mail:
[email protected] Note. Discussion open until July 1, 2008. Separate discussions must be submitted for individual papers. To extend the closing date by one month, a written request must be filed with the ASCE Managing Editor. The manuscript for this paper was submitted for review and possible publication on February 22, 2005; approved on August 1, 2006. This paper is part of the International Journal of Geomechanics, Vol. 8, No. 1, February 1, 2008. ©ASCE, ISSN 1532-3641/2008/1-11–19/$25.00.
modeling methods, respectively. To prepare the physical model of a ripping system is too costly and time consuming. A ripping system involves 3D action and a combination of several different mechanisms. Thus, analytical modeling of ripping systems becomes too complex and may preclude the possibility of using analytical solutions. For the reasons mentioned above, 3D numerical modeling was utilized to model the ripping system. This paper describes the results of the 3D modeling and direct ripping trials carried out at Tunçbilek and Kangal surface mine districts. Ömerler, 34 Makina, 18PH, and Kuşpınar panels belong to Tunçbilek, and 305 and 310 panels belong to Kangal districts. Direct ripping runs were carried out with a CAT D8N dozer and its nearly equivalent Komatsu D155A type dozers to obtain hourly ripper production. All necessary laboratory tests and field studies were completed to determine the input parameters for numerical modeling 共Basarir 2002兲. The laboratory tests conducted were uniaxial compressive strength tests, triaxial compression tests, deformability tests, indirect tensile strength tests, and unit weight tests. Field studies include determination of discontinuity properties, i.e., number of discontinuity sets, discontinuity spacing. All laboratory tests and field studies were conducted in accordance with the International Society for Rock Mechanics 共ISRM兲 suggested methods 共ISRM 1981兲. The ripping operations at these sites were then numerically modeled in 3D. The hourly ripper productions from direct ripping runs and numerical modeling results for a CAT D8N type dozer were compared with each other, and it is seen that the model developed gives consistent results. By realizing the consistency of the model for a CAT D8N type dozer, the model is extended for different and heavier types of dozers.
Rock Mass Descriptions and Rock and Discontinuity Properties for Numerical Modeling In Tuncbilek district, at 34 panel, slightly weathered grey marl unit is observed. There is slight discoloration on the main discon-
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Table 1. Rock Properties Used in 3DEC
Panel
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34 Makina Omerler 18 PH Kuspinar 305 310
Rock type
Density 共kg/ m3兲
Young’s modulus 共MPa兲
Bulk modulus 共MPa兲
Shear modulus 共MPa兲
Marl Marl Marl Marl Clayey Marl Marl
2,020 2,100 2,090 2,270 1,530
1,184 583 411 665 217
704 323 175 308 93
485 242 185 291 98
2,410
867
425
373
tinuity surfaces. Mainly, two discontinuity sets were identified. Discontinuity spacing ranges from 0.8 to 2.0 m, with an average of 1.5 m. The bed thickness is approximately 2 m for the panel. A fresh and highly strong marl unit is observed in Omerler panel. There is no sign of weathering on discontinuity surfaces. There are two sets of discontinuity, perpendicular to the bedding planes. Spacing is, in the range of 1.5– 2.5 m, with an average of 2.0 m. The average thickness of the bedding is again 2.0 m. In 18 PH panel of Tuncbilek mine, fresh to slightly weathered and slightly strong light gray marl unit is present. There is slight discoloration on major discontinuity surfaces. Two main discontinuity sets were distinguished, having spacing in the range of 0.5 to 1 m, and average spacing is 0.7 m. The average thickness of the layer is 1.0 m ranging from 0.5 to 1.5 m. In Kuspinar panel, a slightly weathered but strong marl unit of gray color is observed. There are two main discontinuity sets. The spacing of those sets is in the range of 0.5 to 2 m, with an average spacing of 1.0 m. The thickness of the layer is about 1 m. In Sivas Kangal district, in 305 panel, fresh soft clayey marl unit is composed of light green to grey in color. Two main discontinuity sets are distinguished with mostly 0.4 m spacing. The thickness of the beds is in the range of 0.5 to 1 m, the average spacing dominantly was around 1 m. Generally slightly weathered, white strong marl unit exists in 310 panel. Two main discontinuity sets perpendicular to bedding plane are observed. Discontinuity spacing is 1 to 2 m with an average of 1.25 m. Bed separation changes from 1 to 2 m, with an average layer thickness of 1.5 m. The input rock mass and discontinuity properties are presented in Tables 1 and 2, respectively.
Numerical Method and Modeling of Ripping Process In this section, details of the simulation of the ripping process by using a 3D discrete element are presented.
Numerical Method Several types of numerical methods are available for the analysis of stress, deformation, fracture, and breakage of materials in mechanical systems. The most popular methods are finite element method, finite difference method, boundary element methods, hybrid methods, and distinct element method. Apart from distinct element methods, programs developed for the other methods have interface elements or sliding lines that enable them to model the discontinuous material only to a limited extent. Finite element and boundary element programs can successfully characterize and model the behavior of rock material and rock mass in the elastic and limited plastic range, but they are limited in modeling the discontinuous media. A 3D discrete element program called 3DEC 共Itasca 1998兲 developed by Itasca Consulting Group was used here, since ripping is a 3D dynamic process involving a combination of different excavation mechanisms and ripping medium is discontinuous. 3DEC, which is based upon a dynamic 共time domain兲 algorithm, solves the equations of motion of a blocky system by an explicit finite difference method. The basic equations used in 3DEC are force-displacement laws. At each time step, the law of motion and constitutive equations are applied. The constitutive laws applied to the block contacts are written below ⌬n = kn⌬un
共1兲
⌬n = ks⌬us
共2兲
In these equations, kn and ks = normal and shear stiffness, respectively, per unit area of the contact in MPa/m; ⌬n, ⌬n, ⌬un, and ⌬us = normal and shear stress increments and normal and shear displacement increments, respectively. For blocks, subcontact force-displacement relations are prescribed and the integration of the law of motion provides the new block positions, and thus the contact displacement increments. The subcontact force-
Table 2. Discontinuity Properties for 3DEC
Panel 34 Makina Omerler 18 PH Kuspinar 305 310
Rock type Marl Marl Marl Marl Clayey Marl Marl
Cohesion c 共MPa兲
Friction angle 共MPa兲
Normal stiffness kn 共MPa/m兲
Shear stiffness ks 共MPa/m兲
0.641 0.511 0.212 0.351 0.041
28 22 19 30 21
766 708 615 481 267
314 295 277 211 120
0.442
23
948
408
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Fig. 1. Calculation cycle of 3DEC program Fig. 2. Sketch showing the major structure of the blocky model
displacement law is then used to obtain the new subcontact forces, which are to be applied to the blocks in the next time step 共Itasca 1998兲. The cycle of mechanical calculation is illustrated in Fig. 1. Generation of Ripping Model Initially, simple models were developed for program verification and to test the abilities of the program. A more complex model was then generated to simulate the ripping action of a D8N type dozer manufactured by Caterpillar Tractor Co. and mechanical behavior of in situ rock as closely as possible. The structure of the model is formed according to the field observations and properties of the rock mass. Although in the field the ripping length was taken as 50 m during direct ripping process, this length was taken as 5 m in the computer model for the following reasons: • Number of blocks limitation of the program 共7,500 rigid blocks maximum兲; • Similarity of joint pattern that is in the form of horizontal bedding all along the ripping length; • Homogeneity of the material between the bedding along the ripping length; and • Site observations indicating that 5 m is enough to simulate typical ups and downs of a trial ripping cycle. One of the main and important tasks of modeling is the model generation in 3DEC. A 3DEC model can be generated in two ways, splitting a polyhedron into separate polyhedral blocks or creating separate polyhedrons and joining them together. To create a model ripping ground, the first step is to create a single main block. By splitting this main block into gradually smaller movable blocks towards the point of ripping action, an overall blocky simulation of the rock mass is then completed. In order to do this, boundaries of the smaller blocks inside the main block are formed by a series of commands normally used in the generation of joint sets in rigid blocks of the 3DEC program. Therefore, movable block boundaries are treated like joint sets, and these interfaces are assigned joint set properties, such as normal stiffness 共kn兲, shear stiffness 共ks兲, cohesion 共c兲, and friction angle 共兲 presented in Table 2. These properties were estimated based on the laboratory experiments on the samples taken from the field and rock mass classification results following the field investigations.
Incorporation of the Ripping Action of the Dozer into the Model To simulate the ripping machine, three major block arrangements were used. A simplified sketch in Fig. 2 illustrates the major structure of the model and related dimensions. Track blocks represent dozer tracks on which the main body of the dozer is supported. In the model, these blocks are treated as fixed blocks in all directions. They are connected to the main ground block, and the contact between the ground and track blocks undergoes no movement, since both main ground block and track blocks are fixed in all directions 共Fig. 3兲. In the shank and ripping head block arrangement, ripper tyne block is attached to the shank body block firmly, which means that they move together during the ripping action. Shank block stands over the track blocks, and the contacts between the shank block and the track blocks are frictionless so that shank and ripper tyne arrangement freely moves through ripping section during the ripping process. Ripper tyne block, part of which penetrates into the ripping ground, does the ripping operation by moving in the ripping section of the main ground block. The main ground block is composed of two sidewall blocks and a bottom block, which remains fixed during the ripping action. In the 3 m wide 1.5 m deep ripping section, ripping blocks, which are relatively smaller compared to the blocks in the other sections, are free to move, and thus to be excavated as the ripping tyne moves through them. Small ripping blocks can move freely in all x, y, and z directions. Tracks of dozer on the right and left stand over the sidewall blocks. It is assumed here that these tracks remain in contact all along the ripping length of the 3DEC model. A view of a typical real dozer is illustrated in Fig. 4. The real track length being around 4 m is consistent with the numerical model, where the length extends to 5 m along the model section. Tyne located between the two tracks has a thickness of 0.5 m, a width of 0.5 m and a length of 1.6 m. This simulates the ripper tyne, which moves in the center between the two tracks in the field. Shank body with a tyne attached provides the connection between the main dozer body and the ripper tyne. Since the ripping equipment arrangement has a certain weight in field applications, this was introduced into the model by turning on the gravity in the 3DEC model for the shank body and ripper tyne arrangement. This also helps to prevent undesired rotations of the rigid ripper shank body and ripper tyne system, in general.
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Fig. 3. 3DEC model cross section and top view
Boundary Conditions The boundary conditions in a numerical model consist of the values of field variables 共e.g., stress, displacements, and the combination of them兲 that are prescribed at the boundary of model. In this model, external block boundaries and tracks have fixed displacement boundary conditions in all directions, since they are sufficiently away from the point of action of the ripping operations. The typical values of normal and pull forces applied by a D8N type dozer are taken from the manufacturer’s catalogue, and presented in Table 3, together with the forces applied by the other dozer types. Loads in a distributed form were applied as horizontal force Fs on the back of the tyne 共pull force兲 to simulate the shearing action of the ripping head, and normal force Fn on the top of the shank block that simulates the thrust applied by the hydraulic systems of the dozer body. Normal force, pull force,
and ripper shank dimensions are shown in Fig. 5. These forces were kept constant during the simulation of the ripping process. Under these constant forces, ripping head penetrated into the ripping section about 1.1 m; however, penetration depth changed with different input ground conditions of the panels studied. Ripping Section and Details of Numerical Simulation of Ripping Process In the ripping section of the numerical model developed, the moving model block dimensions around the ripping end are very important with respect to the depth of penetration or the ripper tyne length, since this directly effects the ripping velocity, and thus the production. All practical movable block sizes, starting from the smallest 共5 ⫻ 5 ⫻ 10 cm兲 to the average discontinuity spacing, are
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Fig. 5. Normal and pull force application in 3DEC model
Fig. 4. Top and side view of real dozer and ripper tyne dimensions
tried in this model. Since the situation where block sizes are greater than the shank length is meaningless, the maximum block size is limited to the shank length. The trial runs show that the ripping velocity is greater when block sizes are smaller, and the velocity decreases, as block sizes become larger. Finally, the velocity approaches zero when the block sizes become equal to the shank length. These results are compatible with the observations of the field runs. For these reasons, the analyses were concentrated on an effective block size of 30⫻ 30⫻ 40 cm around the ripping end. According to the observations, this is also the average representative block size of a typical ripping process in the field. The running length of the model is restricted to a 5 m ripping length, mainly due to the limitations in the capacity of the 3DEC program with respect to the number of blocks. The number of
Table 3. Normal and Pull Forces for Different Dozer Types Dozer type D8 D9 D10 D11
Normal force 共kN兲
Pull force 共kN兲
127 154 205 280
222 302 429 657
blocks in some models was around 4,000 for a 5 m ripping length, while the maximum block capacity of 3DEC is 7,500 blocks. After initializing the numerical model by applying force boundary conditions to represent the action of CAT D8 type dozer forces, dozer movement was initiated. The velocity and displacement at the vertex of the shank body and ripping head arrangement were continuously monitored and logged during ripping through the model section. By knowing the velocity and displacement of the vertex of the shank body, the time spent on ripping can be estimated. Using a program written in FISH programming language of 3DEC to detect the moving blocks, it was possible to calculate volumes of displaced or ripped rock. After the application of ripping loads, blocks affected by the ripping action moved and changed position with continuing program time steps or cycles, as the tyne moves in the ripping section. When the difference between the initial and final coordinates of the blocks exceeded a specified value, the blocks were assumed to be ripped, and their volumes were recorded, and taken into account in the ripping production estimations. Ripping Mechanisms To estimate the rippabilities of rocks, it is important to understand the mechanisms of ripping. There are four main types of ripping mechanisms described in the literature. These mechanisms are ploughing, crushing, lifting, and breaking, respectively. The type of mechanism that dominates the ripping process mainly depends on the rock type and rock properties. Rock types and ripping mechanisms are outlined by Darcy 共Darcy 1971兲 as presented below: • Ploughing: In dense marl without bedding planes, a narrow road is plowed, displacing only a small amount of material; • Crushing: In fractured rocks with small defect spacing 共0.1– 0.3 m兲 material is easily crushed, disorganized; • Lifting: In horizontally stratified rocks, slabs are lifted by ripper causing breaking by traction, bending, and shearing; and • Breaking: In inclined stratified rocks, breaking takes place by shearing at the point of the ripper by bending and lateral traction. Ripping is usually the best in the direction of the dip of the beds, as a regular ripping depth can be maintained. The ripping failure mechanisms observed in the field were similar to the ones reported by Darcy 共1971兲, as mostly crushing, then ploughing, lifting, and breaking. Failure was first observed as the cracks growing through the rock mass, and chips and slabs forming. The cracks then propagate and form the blocks, and these blocks are crushed and/or pushed by the fresh slabs and
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Fig. 6. Beginning of a typical run
chips in the back around the ripping head. Some were drawn out from the rock mass upward as the fresh blocks push them. In the numerical simulation, an individual moving block ahead of the ripping head cannot be broken, crushed and/or sheared through, since these blocks are introduced as rigid blocks to the models. However, these actions are simulated by the failure of the contact and separations at the joint like interfaces of the blocks. When all these blocks are combined in a properly dimensioned region around the ripping head, breaking mechanisms described above can be simulated. The illustrations to show the ripping mechanisms observed in the numerical simulation of the ripping process are presented in Figs. 6 and 7. Fig. 6 shows the beginning of a typical run where a ploughing mechanism dominates. The 3D modeling failure mechanisms were then observed to be mixed in the form of dominantly crushing, ploughing, and slabbing as seen in Fig. 7.
Ripper Productions Ripper productions were obtained by two different methods. These methods involve runs simulated by the 3D numerical models and direct field ripping runs.
Fig. 8. Velocity and displacement of the vertex of the shank and ripper body for panel 305
Productions from Numerical Modeling After applying force boundary conditions to represent the action of CAT D8 type dozer forces, the dozer movement was initiated to simulate the production. The velocity and displacement of the vertex on the shank body were monitored, as seen in the typical example in Fig. 8 for panel 305. Initially velocity increases, and the tyne penetrates into the ripping section to a point where now the blocks moving and accumulating in front of the tyne causes a jamming, as seen in Stage I in Fig. 8. At this point, tyne velocity decreases until the tyne breaks this jam by overcoming the resistance of these blocks to move ahead for another cycle. This process is repeated in Stage II. After a sufficient penetration with around 1 m into the ripping section, the ripping head moves smoothly ahead with higher velocities, and this Stage III was assumed to be characterizing the typical advancement stage of the dozer for the production computations. Here, the velocity keeps on increasing to higher values. However, in the production computations, the velocity values corresponding to a displacement of around 1 m were used as the average velocities to represent the typical ripping cycles. For all panels studied, this penetration amount was accepted to be the standard for consistency in the production computations. This way, in the production computations, the volume of blocks detected as changing positions during ripping made the real differences in the estimated productions of different panels. The average ripping cycle time to be used in the production computations was found by dividing the displacement value around 1 m with the corresponding average velocity of the ripping. Average velocities corresponding to the displacements of 1 m, average ripping times, volume of ripped rock produced, and hourly ripper productions of the sites modeled are presented in Table 4. Ripper productions here were estimated by using Q=
Fig. 7. Numerical modeling of ripping by using smaller blocks
3,600q t
共3兲
Where Q = hourly production, m3 / h; q = volume of ripped rock, m3; and t = time spent during ripping, s.
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Table 4. Calculated Productions Obtained from the Simulation of the Ripping with 3DEC for a D8 Dozer Rock type
Panel
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34 Makina Omerler 18 PH Kuspinar 305 310
Marl Marl Marl Marl Clayey Marl Marl
Average velocity 共m/s兲
Average displacement 共m兲
Average time 共s兲
Volume of ripped rock 共cm3兲
Production 共m3 / h兲
4.30 4.06 3.80 3.31 1.80
1.02 1.04 0.96 1.00 1.05
0.24 0.26 0.25 0.30 0.58
40,933 41,094 80,138 80,416 281,783
614 569 1,154 965 1,749
3.27
0.95
0.29
40,358
501
Direct Ripping Production Direct ripping runs are very important for determining the ease of ripping and measurement of hourly production. Observations such as measurement of ripper depth and hourly ripper production during direct ripping trials play an important role in assessment of the ease of ripping. Caterpillar D8 and its equivalent Komatsu D155 type dozers were utilized during direct trials in all studied panels. The weights and horsepower ratings of these dozers are similar. The measured and recorded parameters during ripping trials are: • Tr: Ripping time, s; • Tm: Maneuvering time, s; • L: Ripping length, m; • W: Ripping width, m; and • D: Ripping depth, m. Ripping time and maneuvering times were recorded during a direct ripping trial. Ripping length was chosen as 50 m for all studied panels. Ripping width was measured after each direct ripping trial to calculate the volume of the ripped material. To measure the width of ripping, the material ripped and removed by the dozer blade and the distance between the cracked edges on both
sides due to the ripping were measured. To measure ripping depth, the ripper tyne was continuously observed during a direct ripping trial throughout a profile. For easy measurement of depth of tyne involved in ripping, tyne is painted with different colors every 10 cm. The direction of ripping was selected as perpendicular to the strike of main discontinuity sets in the selected mine panels to obtain the most favorable crushing conditions with respect to the discontinuity orientations. During a typical direct ripping trial, continuous observation of the depth of ripper shank allowed an assessment of the ease and efficiency of each ripping trial 共Basarir and Karpuz 2004兲. A simple sketch regarding the ripped section geometry and ripping parameters is presented in Fig. 9. The shape of the ripping cross-sectional area mainly depends on the rock type. Based on the field studies by Bozdag 共1988兲 and observations of this study for marl type rocks, the dominant ripping section is triangular. The hourly production of the ripper is found by using the following formula 共Bozdag 1988兲: Qr = qr
60 Er Cr
共4兲
Where Qr = hourly production, bank m3 / h; qr = production in a cycle, bank m3 / cycle; Cr = cycle time, min; and Er = efficiency of ripping, %. Quantifying the operator efficiency is a difficult task and includes some personal bias. For example, it can be stated that the productivity of an average operator can be 15% higher than the poorer operator 共Caterpillar 1994兲. In this study, using the site engineers’ opinion, and the field observations of different dozer operators, the operator efficiencies were assessed quantitatively and presented in Table 5. Cycle time Cr consists of two time periods 共5兲
Cr = tr + tm Fig. 9. Simplified geometry of a typical ripped section
Where tr = ripping time, min; and tt = maneuvering time, min.
Table 5. Ripping Process Parameters Measured and Recorded in the Field for D8 and Equivalent Dozers Panel name 34 Makina Omerler 18 PH Kuspinar 305 310
Rock type
Dozer type
Operator eff. 共%兲
Ripping time 共s兲
Man. time 共s兲
Ripping depth 共m兲
Ripping width 共m兲
Ripping length 共m兲
Marl Marl Marl Marl Clayey Marl Marl
D155A D8N D155A D155A D8N
80 90 95 95 95
89 90 88 79 50
17 15 12 5 23
0.75 0.65 0.90 0.80 1.10
0.70 0.50 1.30 1.05 1.03
50 50 50 50 50
D8N
90
109
25
0.65
0.85
50
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Table 6. Computed Direct Ripping Production Values for D8 and Equivalent Dozers
Panel
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34 Makina Omerler 18 PH Kuspinar 305 310
Rock type Marl Marl Marl Marl Clayey Marl Marl
Cross-sectional area 共m2兲
Production in a cycle 共m3兲
Hourly production 共m3 / h兲
Ripper depth percentage 共%兲
0.26 0.16 0.59 0.42 0.57
13.13 8.13 29.25 21.00 28.33
357 251 1,000 855 1,327
63 54 75 67 92
0.28
13.81
334
54
Production in a cycle is found by multiplying the crosssectional area and the ripping length qr = Car ⫻ L
共6兲
Where qr = production in a cycle, bank m3 / cycle; Car = cross-sectional area, m2; L = ripping length, m; and Car =
DW 2
共7兲
Where D = ripper depth, m; and W = ripping width, m. The measured parameters are presented in Table 5 for the estimation of ripping productions of different dozer types at different sites. The direct ripping productions of studied panels are calculated and presented in Table 6. The results of direct ripping runs in this table were compared to the production values in Table 4 computed from the 3D modeling. The results of the comparisons are plotted in Fig. 10. A linear fit with an added point at origin was preferred, since the ideal model was supposed to simulate the ripping process one to one in the form of a line y = x. As seen in Fig. 10, the coefficient of correlation is quite high for the CAT D8 type dozer used in the investigations. Three-dimensional modeling work is concluded to be successful, considering the variations and uncertainties in input rock and discontinuity parameters, limitations of the 3D modeling and the program used, heterogeneity of the rock in the field, and the scale of the field work. Thus, it is decided that the numerical modeling approach
developed for the estimation of production values for the CAT D8 type dozer can be quite confidently extended to the estimation of productions for other types of dozers at different sites. The production values computed using numerical models for the other panels were all calibrated using the regression relationship obtained from the results plotted in Fig. 10. To calculate the ripping production values for other types of dozers, input rock properties were left as the same. However, the normal and pull forces of dozers were changed according to dozer types and force values provided in their sales catalogues, as summarized in Table 3. The calculated and calibrated productions of studied panels are all given in Table 7. This table also includes the attempts to assess the ease of rippability of different dozer types at different panels with the objective to introduce a rippability classification system for the sites investigated.
Conclusions and Recommendations A simulation of the ripping process is conducted by using threedimensional distinct element code 3DEC. Using a large number of rigid blocks connected by the interfaces with discontinuity properties in the field, a ripping section was generated around the ripping head. As the ripping head was moved through the ripping section, ripped blocks changed positions, and these were used in the estimation of model ripping productions. Dominant failure
Fig. 10. 3DEC model production results versus direct ripping productions of the field trials 18 / INTERNATIONAL JOURNAL OF GEOMECHANICS © ASCE / JANUARY/FEBRUARY 2008
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Table 7. Estimated Production Values and Ease of Rippabilities for Different Types of Dozers Dozer types
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D8
D9
D10
D11
Panel name
Rock type
Prod. 共m3 / h兲
Ease of ripping
Prod. 共m3 / h兲
Ease of ripping
Prod. 共m3 / h兲
Ease of ripping
Prod. 共m3 / h兲
Ease of ripping
34 Makina Omerler 18PH Kuspinar 305
Marl
440
Difficult
513
Difficult
1,931
Easy
2,136
Very easy
Very difficult Easy Moderate Very easy
1,137 4,374 2,544 8,932
Difficult Very easy Very easy Very easy
1,790 6,642 4,676 9,228
Easy Very easy Very easy Very easy
Difficult
1,791
Easy
3,664
Very easy
310
Marl Marl Marl Clayey Marl Marl
402 890 732 1,386 346
Very difficult Easy Moderate Very easy Difficult
472 921 814 7,239 564
mode of the ripping process in the models was crushing. The moving block sizes used in the model greatly affect the ripping velocity. This velocity increases dramatically as the block sizes decrease. Based on this realization, modeling work for ripping action and production estimations involved the use of an optimum 3DEC block size of 30⫻ 30⫻ 40 cm, which is very compatible with the block sizes in the field. Three-dimensional modeling of the ripping process was concluded to be successful, considering that the computed production values were in reasonable agreement with the measured values obtained from the direct field trials with D8 type of dozers. Hence, with 3D models calibrated using the field results, it was possible to make estimates and suggestions for ripping productions in other sites with heavier capacity dozers without any need to run field trials.
References Atkinson, T. 共1971兲. “Selection of open pit excavating and loading equipment.” Trans. Inst. Min. Metall., Sect. C, 80A, 101–129. Bailey, A. D. 共1975兲. “Rock types and seismic velocity versus rippability.” Proc., Twenty-Sixth Highway Geology Symposium, 135–142. Basarir, H. 共2002兲. “Rippability assessment based on direct ripping, specific energy concept and numerical modeling.” Ph.D. thesis, METU, Ankara, Turkey. Basarir, H., and Karpuz, C. 共2004兲. “A rippability classification system for marls in lignite mines.” Eng. Geol. (Amsterdam), 74, 303–318. Bozdag, T. 共1988兲. “Indirect rippability assessment of coal measure rocks.” MS thesis, METU, Ankara, Turkey.
Caterpillar. 共1988兲. Caterpillar performance handbook, 19th Ed., Caterpillar Inc., Peoria, Ill. Caterpillar. 共1994兲. Caterpillar performance handbook, 25th Ed., Caterpillar Inc., Peoria, Ill. Church, H. K. 共1981兲. Excavation handbook, McGraw-Hill, New York. Darcy, J. 共1971兲. “Application of rock mechanics to rock excavation.” Reveue de I’industrie minerale-mines, June, 455–482. ISRM suggested methods. 共1981兲. “Rock characterization testing and monitoring.” E. T. Brown, ed., Pergamon Press, New York, 211. Itasca. 共1998兲. 3DEC user’s manual, Itasca Consulting Group, Inc., Minneapolis. Karpuz, C. 共1990兲. “A classification system for excavation of coal measures.” Min. Sci. Technology, 11, 157–163. Kirsten, H. A. D. 共1982兲. “Efficient use on construction of tractor mounted rippers.” Civil Engineer in South Africa, 24, 293–308. Komatsu Ltd. 共1987兲. Specifications and application handbook, 10th Ed., Komatsu Ltd., Akasaka, Minato-ku, Tokyo, Japan. MacGregor, F., Fell, R., Mostyn, G. R., Hocking, G., and McNelly, G. 共1994兲. “The estimation of rock rippability.” Q. J. Eng. Geol., 27, 123–144. Müftüoğlu, Y. M. 共1983兲. “A study of factors affecting diggability in British surface coal mines.” Ph.D. thesis, Univ. of Nottingham, England. Singh, R. N., Denby, B., and Egretli, I. 共1987兲. “Development of new rippability index for coal measures excavations.” Proc., 28th US Symp. on Rock Mech., Tucson, Ariz., 935–943. Smith, H. C. 共1986兲. “Estimating rippability of rock mass classification.” Proc., 27th US Symp. on Rock Mech., Univ. of Alabama, 443–448. Weaver, J. M. 共1975兲. “Geological factors significant in the assessment of rippability.” Civil Eng. In South Africa, 17, 131–136.
INTERNATIONAL JOURNAL OF GEOMECHANICS © ASCE / JANUARY/FEBRUARY 2008 / 19
Int. J. Geomech., 2008, 8(1): 11-19
