Application of modified rock-mass classification systems to blasting assesment in surface mining operations

Mining Science and Technology, 8 (1989) 285-296

285

Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

APPLICATION OF MODIFIED ROCK-MASS CLASSIFICATION SYSTEMS TO BLASTING ASSESSMENT IN SURFACE MINING OPERATIONS M.Z. Sunu and R.N. Singh Department of Mining Engineering, University of Nottingham, Nottingham NG7 2RD (U.K.) (Received June 14, 1988; accepted November 9, 1988)

ABSTRACT Rock-mass classification systems are applied with special reference to blast-induced problems in surface mining. Two field investigations at Croft granite and Whitwick basalt quarries, in the East Midlands (U.K.), are reported. The primary objective of these field investigations was to determine the nature of discontinuities and intact rock properties and to apply rock-

mass classification systems to evaluate blasting efficiency and the stability of newly exposed pit walls. These case studies included the mapping of joints, the laboratory investigation of intact rock properties and field observations in surface mines where the production was carried out by bench blasting.

INTRODUCTION

which all lead to adverse economic consequences. Demand is increasing for more control and predictability in the blasting of rock because of the increasing degree of complexity required in the extraction process, increasingly stringent environmental requirements and the increasing public awareness of blast-induced vibration and noise control. Blast-induced problems become more noticeable particularly in countries, such as Britain, where surface mining operations are frequently carried out near or in towns. This work presents case studies in which

Frequent blasting is often required in surface mining projects. If this is not carefully performed, the physical and mechanical properties of rock are weakened. As a result of blasting-induced stresses, discontinuities are opened and new cracks develop. Adjacent abandoned underground workings and slope faces may be subsequently damaged. Additionally, inadequate and inefficient blasting results in production of oversized rock, difficult digging and loading, increased secondary blasting and reduced slope stabilities,

286 modified rock-mass classification systems have been applied for efficient blasting in Croft granite and Whitnick basalt quarries. In each case study, data from discontinuity mapping, shear and triaxial test results, engineering properties of intact rock samples together with rating adjustment parameters developed in this study and the results of the application of rock-mass classification systems are given. At the end of each section, the results are evaluated and a new blast design is proposed.

RESEARCH GRAMME

APPROACH

AND

PRO-

It is an established fact that rock is rarely homogeneous or isotropic. Hence, rock structure and the presence of geological discontinuities affect blasting to a great extent and can help or hinder the blasting results as defined by the degree of fragmentation [1-7]. If blasting is to become a highly accurate practice in mining operations then the relevant rock and structural properties for the design of efficient blasting should be utilised. The research approach for the evaluation of blasting efficiency in surface mines is based on the following steps: (1) The establishment of the geomechanical properties of discontinuities and the intact rock and their importance in blasting. (2) The evaluation of rock data by means of graphic techniques in assessing blasting efficiency. (3) The establishment of rating adjustment parameters for the rock-mass classification systems and the proposal of modified rockmass rating (RMR) and rock-mass quality (Q) systems in order to assess and optimise current blasting practices in surface mining operations.

Mapping of joints Much emphasis has been placed on the importance of mapping joint systems and the

determination of joint sets. For structural geological considerations, the orientation of joint sets is of major importance as this enables the analysis of the excavation design and selection of the blasting pattern. From an engineering viewpoint, joint orientations are of importance if they present a surface or a combination of surfaces along which blasting takes place. Their orientation in space will determine the efficiency of blasting [1,8]. Detailed line mapping has been used in order to record the information precisely, to avoid any possible errors and to prepare data which are suitable for analysis by stereographic methods.

Stereographic projection techniques An important aspect in surface mining is the systematic collection and presentation of geological data in such a way that they can be easily evaluated and incorporated into fragmentation analysis in order to create efficient blasting. The spherical projections provide a convenient means for the presentation of geological data. The techniques have been discussed by many authors [9,10]. In this research study preference is given to the equalarea projection method for the analysis of discontinuity data.

The effect of intact rock properties on blasting efficiency The physical and mechanical properties of rock that affect blasting have been investigated by many researchers [11-161 and the most important of these properties are compressive strength, tensile strength, shear strength, Young's Modulus, Poisson's Ratio, density and groundwater and moisture content. The expected degree of fragmentation in a blast must be related to the physical properties of the material to be tested. The influence of rock properties can be separated into those

287

of strength parameters and the elastic response to the applied stress, each having separate effects. The compressive, tensile and shear strengths are related to the largest stress level that the rock can withstand before failure.

The rock-mass rating system (RMR system) The rock-mass rating system was originally developed by Bieniawski [17] for jointed rocks and was initially used for tunnel design and subsequently applied to rock slopes. An attempt has been made in this study to correlate blasting efficiency with rock-mass classification systems. The classification system, TABLE 1 Rating adjustment parameters ( R A P ) for blasting efficiency Description of parameters

RMR system rating value

Q system rating value

Blasting with the dip Blasthole planes are parallel to the predominant joint planes First joint set - 40 Second joint set - 20 Third joint set - 10

Rock-mass quality system (O system) 2.1 0.73 0.43

Blasting against the dip Blasthole planes are parallel to the predominant joint planes First joint set 0 Second joint set - 10 Third joint set - 5

0.25 0.43 0.33

Blasting against the strike Blasthole planes are normal to the predominant joint planes First joint set 15 Second joint set - 10 Third joint set - 5

10 7 4

The Q system of rock-mass classification is based on a numerical assessment of the rockmass quality using six different parameters which can mostly be estimated from surface mapping. It was initially used for tunnel design [19] and modified in this study to correlate it with blasting efficiency of jointed hard rock slopes. The six main parameters are as follows:

RQD -- rock quality designation, 0.12 0.43 0.33

Blasting with dip at an angle between 30 and 60 ° First joint set Second joint set Third joint set

under certain conditions, can effectively combine the findings from observation, experience and engineering judgement to provide an assessment of the rock-mass condition [18] and incorporates the following parameters: rock quality designation (RQD), uniaxial compressive strength of intact rock, spacing of joints or bedding planes, state of weathering and condition of the joints, groundwater conditions and the rating adjustment parameters (RAP) for joint orientations. The approach is such that the rock mass should be assigned an in-situ value regardless of its position in space [18]. In order to determine the rating adjustment resulting from discontinuity orientation, i.e., to assess whether strike and dip orientations are favourable, reference should be made to Table 1. To quantify the rating adjustment values, each joint set ranging from most to least predominant should be analysed and corresponding rating values should be summed up. Negative values indicate favourable conditions whereas positive values are unfavourable.

0.15 0.17 0.2

Nj

= joint set number, = joint roughness number, Aj = joint alteration number, Wj = water reduction factor RAP = original stress reduction factor in the Q system (it has been modified as a rating adjustment parameter to be used for blasting purposes (Table 1)). Rj

288

The rating adjustment parameter (RAP) should thus be determined from Table 1. At this stage, the influence of the strike and dip orientations of the discontinuities is included in the Q system. Since the rating values and the Q system itself are logarithmic, in order to establish the final rating, the values for each joint set should first be calculated. Thereafter, the final RAP value is found by using the following equations: For a rock mass having three joint sets: Q ( RAPtotal ) =

e ( l n R A P 1 + I n R A P 2 + l n R A P 3 + 52/19)

(1) For a rock mass having four joint sets: = e ( l n R A P 1 + l n R A P 2 + l n R A P 3 + l n R A P 4 + 78/19)

(2)

BLASTING QUARRY

CASE

STUDY

AT

CROFT

Croft Quarry is situated 11 km southwest of Leicester (U.K.) and is one of the largest quarries in the East Midlands. In this quarry, the determination of rock-mass classification systems was intended to provide an engineering assessment of rock mass based on a rating system of the most significant geological parameters. This led to formulation of direct practical guidelines for assessing efficient blasting.

(100 mm) create less damage to pit walls and fewer detrimental effects on slope faces. The b u r d e n and spacing between adjacent blastholes was 3 - 4 m. For charge initiation, an electric blasting cap was inserted into one end of the dynamite (primer) just prior to its being loaded with ANFO; detonation takes place at the b o t t o m of the blasthole. The unloaded collar section of the borehole is then completely filled with stemming material consisting of a damp mixture of granite dust from the quarry. Care is taken to ensure that the water in the hole (in general, two out of ten holes have water present) did not extend above the top of the explosive charge, thus avoiding saturated stemming. Bench height varied between 15 and 20 m, with an average back inclination of 5 ° - 1 0 ° . In order to minimise detrimental effects on newly created walls and to reduce vibration from blasting, fifteen holes in one line were blasted and 25 ms delay timing was used between consecutive holes. The production is carried out by the bench blasting method in which the borehole is situated parallel to the free face. Some observations regarding the influence of the rock structure on bench blasting were obtained from the work performed by Larson and Pugliese [81. This research studied the effect of joints and bedding planes on the breakage of limestone with small-scale blasts. Experiments were performed in a dolomitic limestone containing two geological structures of importance, namely vertical joints and horizontal bedding planes.

Current blasting practice at Croft Quarry The explosive selected for use in the production of hard rock was ANFO. In boreholes where water was present, slurry explosives were used. The explosive could be loaded easily, safely and uniformly in a continuous column because of its granular form. In this quarry, because the blasting takes place in hard rock, small-diameter blastholes

Blasting damage and its influence on slope stability Damage to pit walls at the site of a blast is caused when borehole pressure exceeds the compressive strength of the rock. The nature, orientation and frequency of structures can weaken a rock type, and hence damage occurs. The rock can also be weakened by

289

weathering, groundwater or fracturing due to earlier blasting. An effective approach is to control the effect of blasting so that the inherent strength of the walls is not destroyed [13]. The basic types of damage which can result from surface blasting can be summarised as follows [14]: (1) Damage to the pit wall immediately adjacent to a blast (backbreak, crest fracture, toppling failure, face-loose rock, etc.). (2) Damage to pit walls not adjacent but still close to a blast (shaking and dislodgement of loose or weathered rock). (3) Damage to underground openings or buildings close to a blast (cracking of foundations, spalling and weakened pillars, etc.). These problems can be minimised or eliminated by controlling the blasting variables (discontinuity orientations and accounting for rock properties).

TABLE 2 Orientation ( ° ) of discontinuity planes and slope faces (Croft Quarry) Structural region A First predominant joint set 67/266 Second predominant joint set 36/262 Third predominant joint set 82/202 Bedding plane 37/260 Current slope face 84/355

B

C

D

82/172

86/024

60/330

80/144

84/165

84/325

32/296

36/176

72/225

-

-

86/138

25/260

85/009

83/240

from the standpoint of rock-mass classification systems and the results of calculations are presented in Table 3.

Structural geological mapping TABLE 3

In order to define the orientation, type and location of discontinuities and to use the relevant data for blasting and to analyse the possible modes of blast-induced problems, an extensive field mapping programme was initiated and 800 discontinuities, in four different structural regions of the quarry, were recorded. The discontinuity measurements were taken over a considerable area of the slope faces and these measurements form the basis of the analysis. The orientation of discontinuity planes and the slope faces were derived from discontinuity mapping values and the results are presented in Table 2, Statistical distribution of dip angles for structural region A is given in Fig. 1, which indicates the high percentage of steeply dipping discontinuity planes. The information regarding the characteristics of discontinuities within a rock mass is vital

Discontinuity frequency, (Croft Quarry)

RQD and spacing values Structural region A

B

C

D

Discontinuity frequency (per m) First predominant joint set Second predominant joint set Third predominant joint set Bedding plane Total discontinuity (Vj per m 3)

4

5

5

5

3

4

4

4

2

3

3

3

1

-

-

1

10

12

12

13

97 82 96

91 75 88

91 75 88

72 85

330

250

250

250

RQD value (%) From borehole readings From joint survey Adjusted

Spacing value (ram)

290

80

60

40 I,L

20

o 10

20

30

40

50

60

70

80

90

Dip Angle

Fig. l. Statistical analysis of discontinuity dip angles (Croft Quarry, structural region A).

D i r e c t s h e a r tests

Laboratory direct shear tests are commonly employed in order to establish the shear strength properties of the natural discontinuities of rock. Direct shear tests for natural discontinuities were carried out on Croft Quarry granite samples. Figures 2 and 3 illustrate the shear stress versus shear displacement for 100, 200, 500, 1000 and 2000 kN normal loads and the linear shear strength envelope respectively. From the above figures, cohesion and the internal angle of friction of the samples were calculated as 37.8 kPa and 39 o, respectively. The angle of fric-

tion value was used in the stereographic projection methods in order to evaluate the blasting efficiency. T r i a x i a l test results

The purpose of this test is to establish the shear strength of a natural discontinuity on a cylindrical specimen under triaxial loading. Triaxial tests were conducted on the cylindrical samples from Croft Quarry. The internal angle of friction and shear strength, which is the interblock shear strength parameter for Croft Ouarrv Samples 2000

Linear Relationship Y=B+MX Y = 37.8 + 0.8105 X Cohesion -? 37.8 kPa =

2000

~" v

1500

.

~

'

~2000

1500

I000 1000

500

500 O~ 0

~-----"3

.

-

-

-

,

.

~ ~ "T ~ ,

6

9

2oo 100 12

Shear Displacement(mm)

Fig. 2. Shear stress versus shear displacement (Croft Quarry samples).

0 I

0

500

I

I

I

1000

1500

2000

Normal Stress (kPa) Fig. 3. Linear shear strength envelope (Croft Quarry samples).

291 TABLE 4 Engineering properties of intact rock samples (Croft Quarry) Physical properties of the intact rock

Structural regions A, B, C and D

Uniaxial compressive strength (MPa) UCS derived by Schmidt Hammer Test (MPa) Point-load strength, diametrical (MPa) Point-load strength, axial (MPa) Tensile strength (MPa) Poisson's Ratio Elastic modulus (aPa) Cohesion (MPa) Internal friction Angle ( o ) Density

(kg/m3)

128 113 5.4

Results of the application of the rock mass classification systems

5.5 13.1 0.28 46.7 38 39

2867

the Q system, were found to be ~5 = 39 o and R j / A j = 0.81, respectively.

Engineering samples

should be in quantitative terms. The suggested values in Table 1 are based on the combined ratings of four different situations for a given discontinuity set. Rating adjustment parameters for each discontinuity set and structural region were determined by analysing each discontinuity plane dip and dip direction relative to the slope face.

properties of intact rock

A summary of the most important intact rock properties which were investigated in dry conditions is given in Table 4.

Determination of rating adjustment parameters (RAP) at Croft Quarry In order to apply the RMR and the Q rock-mass classification systems for blasting purposes, it was necessary to develop a rating adjustment chart for determining the importance of each discontinuity set. A crucial requirement of any classification or rating is that it should be based on the most relevant parameters. Additionally, these parameters

The best method of testing rock-mass classification systems is to check their validity and reliability in actual case studies. Therefore, modified rock-mass classification systems have been applied to blasting in order to understand the effect of structural discontinuities and rock properties on blasting at Croft Quarry [20]. On the basis of structural differences the quarry was divided into four regions. The R MR system results for the four regions are given in Table 5. In structural region A, the present blasting arrangement is very unfavourable owing to the fact that blasting was against the strike. The first and second predominant joint planes and bedding plane are normal to the slope face. Open joints were oriented at 90 o to the rock face; hence backbreak and undercut were unavoidable due to the cross jointing. By adjusting the slope face to 800/275 ° and changing the blasting method to downdip, better fragmentation and stability of newly formed walls could be achieved. Structural region B of the quarry consisted of three joint sets of which the most predominant one lay obliquely to the slope face, creating unfavourable and inefficient blasting conditions. Steeply dipping joints were oriented diagonally to the slope face. This structure resulted in an overhang of collar rock with some backbreak and face-loose rock. By orienting the slope face to 7 0 ° / 1 6 5 ° , efficient blasting and stable remaining slopes could be created.

292 TABLE 5 Rock-mass rating (RMR) classification results (Croft Quarry) Parameter

Structural region A Current slopes, 84/353

Strength of intact rock Drill core quality (RQD) Spacing of discontinuities Condition of discontinuities Groundwater Rating adjustment parameters (RAP)

Structural region B

Proposed Current slopes, slopes, 80/275 86/138

Structural region C Structural region D

proposed Current Proposed Current slopes, slopes, slopes, slopes, 78/135 85/009 79/009 83/240

Proposed slopes, 78/240

12

12

12

12

12

12

12

20

20

20

20

20

17

17

10

10

10

10

10

10

10

20 15

20 15

20 15

20 15

20 10

20 15

20 15

- 6

- 29

- 38

- 1

-61

71

48

34

73

13

4

-75

Total rating

81

2

Description

Very unfa- Very favourable vourable

Unfavour- Fair able

Structural region C of the quarry incorporated three joint sets, the predominant one being parallel to the slope face while the second and third sets were against the dip. The blasted slope face corresponding to major jointing oriented parallel to the slope; a clean and smooth surface consequently results. In this region of the quarry, no adjustment in the current slope face was found necessary. In structural region D, the first and second predominant jointing is perpendicular and the near horizontal bedding is parallel to the slope face. Due to the vertically dipping joints which are almost perpendicular to the blasted slope face, serious backbreak occurred. It was advised that consideration should be given to changing the slope direction, and to change from blasting against strike to change from blasting with dip. BLASTING EFFICIENCY AT WHITWICK QUARRY

ASSESSMENT

In order to optimise blasting practices in this quarry, an extensive programme of field and laboratory work was carried out. The

Favourable

Unfavour- Very favourable able

findings, with reference to the rock-mass classification results, were analysed. Structural mapping of the quarry Some 440 discontinuity readings were taken at two different slope faces at the quarry. Structural regions B and C are represented in the same slope face but present different groundwater problems. The values shown in Table 6 are the orientation of discontinuities

TABLE 6 Orientation of discontinuity planes and slope faces (Whitwick Quarry) Structural region First predominant joint set Second predominant joint set Third predominant joint set Fault plane Current slope face

A

B and C

72/025

45/264

64/043

84/028

74/123 68/052

83/144 70/225

293 TABLE 7 Discontinuity frequency, RQD and spacing values (Whitwick Quarry) Structural region A

BandC

Discontinuity frequency (per m) First predominant joint set Second predominant joint set Third predominant joint set Fault plane Bedding plane Total discontinuity (Vj per m 3)

7

5

6

5

4 -

4 -

17

14

59 69

69 81

154

200

Triaxial tests

R QD Value (%) From borehole readings From joint survey Adjusted

Spacing value (mm)

termined. From the above-mentioned information, cohesion and the angle of friction of the samples were calculated as 48.3 kPa and 34 ° , respectively. The angle of friction value was used in the stereographic projection of planes of the concentration of discontinuity sets in order to evaluate the blasting efficiency.

and the slope face and were derived from the discontinuity survey in the field. Table 7 presents the discontinuity frequency, rock quality designation (RQD) and joint spacing values for this quarry. Since borehole cores have not been supplied for this site, RQD values were extrapolated from discontinuity survey results and a 85% correction factor was applied in order to eliminate the effect of blast-induced fractures on slope faces.

Direct shear tests Direct shear tests for natural discontinuities were carried out on Whitwick Quarry samples containing a suitable discontinuity. The shear stress versus shear displacement for 100, 200, 500, 1000 and 2000 kN normal loads, the power curve, the linear shear strength envelope and graph of vertical displacement versus shear displacement were de-

Triaxial tests under confining pressures of 5, 10 and 15 MPa were conducted on cylindrical rock samples which contained single geological discontinuities. Test data were used to determine the angle of friction, which was found to be 35 o.

Engineering properties of intact rock samples at Whitwick Quarry The important engineering properties of intact rocks examined under dry conditions are given in Table 8 and these were used in the rock-mass classification systems as input data.

TABLE 8 Engineering properties of intact rock samples (Whitwick Quarry) Physical properties of the intact rock Uniaxial compressive strength (MPa) UCS derived by Schmidt Hammer Test (MPa) Point-load strength, diametrical (MPa) Point-load strength, axial (MPa) Tensile strength (MPA) Poisson's Ratio Elastic modulus (GPa) Cohesion (MPa) Internal friction angle ( ° ) Density ( k g / m 3)

Structural regions A, B and C 118 105 5.26 5.6 11.56 0.31 35 48.3 34 2725

294

Evaluation of the rock-mass classification systems at Whitwick Quarry

quarry, some b a c k b r e a k problems occurred which were believed to be due to inaccurate drilling (drillhole deviation) in the hard rock. In the structural regions B and C, classification ratings for current slope faces were generally found to be unfavourable owing to the blasting with dip ( 4 5 0 / 2 6 4 ° ) at an angle of 39 ° . Intense crest fracturing was directly caused b y the natural tendency of the predominant joint plane to break out towards the free face. Some of the adverse problems in this region of the quarry m a y be attributed to the incompetent and highly fractured structure of the slope face. In order to change the blasting practice into a more efficient operations, the slope should be changed to 70 ° / 2 5 8 ° . In this case, b y applying downdip blasting, favourable results could be achieved.

The engineering classification of rock masses at this quarry, for the investigation of blast-induced problems, were found b y employing the results obtained from field and laboratory studies. The R M R classification results are given in Table 9, which also shows rating adjustments in relation to the current and proposed slopes. As discussed previously, according to the information obtained from the investigations, the quarry was divided into three structural regions. In structural region A, the R M R and Q ratings were found to be fair for the current blasting practice. This is considered as being due to the favourable orientation of the secondary predominant joint sets and the fault planes with respect to the slope face, even though the first predominant joint set is situated obliquely. In structural region A, b y creating downdip blasting to the first predominant joint set ( 7 2 ° / 0 2 5 o ), it is believed that very favourable blasting results could be achieved. At this side of the

DISCUSSION OF THE RESULTS F r o m the modification of rating adjustment parameters ( R A P ) and consequent ap-

TABLE 9 Rock-mass rating (RMR) classification results (Whitwick Quarry) Parameter

Strength of intact rock Drill core quality (RQD) Spacing of discontinuities Condition of discontinuities Ground water Rating adjustment parameters (RAP) Total rating Description

Structural region A Current Proposed slopes, slopes, 68/052 70/025

Structural region B Current Proposed slopes, slopes, 70/225 70/258

Structural region C Current Proposed slopes, slopes, 70/225 70/225

12

12

12

12

12

12

13

13

17

17

17

17

8

8

10

10

10

10

20 15

20 15

20 15

20 15

15 10

15 10

- 15 53

- 65 3

- 5 69

- 38 36

- 5 59

- 38 26

Fair

Very favourable

Unfavourable

Favourable

Fair

Favourable

295

100

= ,~ ~3

RMR System = 1 3 . 4 8 + Correlation Coefficient

18.79 =

In

Q

System

0.97

/

80 60

/

or'a::

40

o/

20 very

0 10-3

'1

g Z ' rable ....

favourable '

'

unfavou

fair

rable

10-2

10-1.

Fig. 4. Relationship between the

100

101

unfavourable ,

102

,

, =,,,,

103 Q

RMR and Q rock-mass classification system.

plication of rock-mass classification systems to blasting efficiency a good correlation has been found between the considered parameters. A logarithmic relationship has been established between the R M R and Q system rating adjustment parameters and is given in eqn. (3). (The equation has a correlation coefficient of 0.99): RMR(RAp ) = 19 in Q(RAP) + 26

(3)

Similarly, the relationship (Fig. 4) between the R M R and Q system values is also found to be logarithmic with a correlation coefficient of 0.97 as shown in eqn. (4). R M R = 13.48 + 18.79 In Q

very ,°,,,i

' '''"1

(4)

CONCLUSIONS Detailed geological investigations were carried out in these case studies, enabling the accurate determination of all the R M R and Q classification parameters. In addition, extensive laboratory studies were undertaken to provide input data for analysing blasting efficiency. Furthermore, the quarry slopes were

observed and slope surveys were conducted; thus, an invaluable opportunity to correlate classification predictions with field observations was taken. It is expected that the work presented in this paper will provide the necessary techniques to create efficient blasting in surface mines and thus to reduce the damage to newly opened slope faces and old abandoned underground workings in close proximity to working quarries. Subsequently, improvements in blasting will reduce air overpressure and flyrock problems, will optimise fragmentation, and as a result profitability and productivity will be improved. In order to improve on the uses of classification systems, it is necessary that information is well documented. However, the classification systems are only a means to an end and cannot fully substitute for the final engineering design [18]. They primarily represent an empirical approach and must be enhanced during mine production by suitable field measurements. If classification systems are integrated with monitoring, careful site observations and finite element studies, their use can be extended to include mine design.

296

REFERENCES I Belland, J.M., Structure as a control in rock fragmentation, Carol Lake iron ore deposits. Can. Min. Metall. Bull., 59 (1966): 323-328. 2 Ash, R.L., The influence of geological discontinuities on rock blasting Ph.D. Thesis, Univ. Minnesota (1973), 289 pp. 3 Bhandari, S., Rock fragmentation in blasting. Ph.D. Thesis, Univ. New South Wales (1975), 201 pp. 4 Hagan, T.N., The effects of some structural properties of rock on the design and the results of blasting. In: Aust.-N.Z. Conf. Geomech., 3rd (Wellington, 1980). Vol. 2 pp. 205-213. 5 Bergmann, O.R., Effect of explosive properties, rock type and delays on fragmentation in large model blasts. In: Int. Symp. Rock Fragmentation by Blasting, 1st. Univ. Lule~, (Sweden, 1983). Vol. 1, pp. 71-77. 6 Dick, R.A., Fletcher, L.R. and D'Andrea, D.V., Explosives and blasting procedures manual. U.S. Bur. Mines Inf. Circ. 8925 (1983) 95 pp. 7 Singh, R.N., E1-Mherig, A.M. and Sunu, M.Z., Application of rock mass characterization to the stability assessment and blast design in hard rock surface mining excavations. In: U.S. Rock Mech. Conf., 27th (Alabama, 1986). pp 471-478. 8 Larson, W.C. and Pugliese, J.M., Effects of jointing and separation on limestone breakage at a reduced scale. U.S. Bur. Mines Rep. Invest. 7863 (1974), 13 PP. 9 Hock, E. and Bray, J., Rock Slope Engineering. Inst. Soc. Min. Metall., London (1981), 358 pp. 10 Priest, S.D., Hemispherical Projection Methods in Rock Mechanics. George Allen and Unwin, London (1985), 124 pp.

11 Singh, D.P. and Appa Rao, Y.V., Influence of physico mechanical properties and geological discontinuities on rock blasting. Colliery Guardian, Nov. (1979): 631-635. 12 Hagan, T.N. and Just, G.D., Rock breakage by explosives--theory, practice and optimisation In: Proc. Congr. Int. Soc. Rock Mech., 3rd (Denver, Colo., Sept. 1974). pp. 1349-1358. 13 Hagan, T.N. and Harries, G., The effect of rock properties on the design and results on blasting. In: Workshop Course Manual. Adelaide (1979), pp. 16-60 (Unpubl.). 14 Calder, P., Perimeter blasting. In: Pit Slope Manual. Can. Cent. Miner. Energy Technol. Rep. 77-14 (1977), 82 pp. 15 M~ki, K., On the applicability of the tensile strength as an index to rock fragmentation. In: Symp. Rock Fragmentation by Blasting, 1st. (Univ. Lule~, Sweden, 1983). Vol. 1, pp. 79-95. 16 M~tki, K., The influence of discontinuities on rock fracturing and damage from blasting. Licentiate Thesis, Univ. Lule~, Sweden (1985), No. 008 L, 139 PP. 17 Bieniawski, Z.T., Engineering classification of jointed rock masses. Civ. Eng. S. Afr., Dec. (1973): 335-344. 18 Bieniawski, Z.T., Rock Mechanics Design in Mining and Tunnelling. Balkema, Rotterdam (1984), 272 pp. 19 Barton, N., Lien, R. and Lunde, J., Engineering classification of rock masses for the design of tunnel support. Nor. Geotech. Inst., Oslo (1974), 48 pp. 20 Sunu, M.Z., Application of rock mass classification to blasting induced problems in surface mining. Ph.D. Thesis, Univ. Nottingham (1988), 252 pp.