ISSN 1062-7391, Journal of Mining Science, 2016, Vol. 52, No. 2, pp. 226–232. © Pleiades Publishing, Ltd., 2016. Original Russian Text © F.K. Nizametdinov, A.A. Nagibin, V.V. Levashov, R.F. Nizametdinov, N.F. Nizametdinov, A.E. Kasymzhanova, 2016, published in FizikoTekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, 2016, No. 2, pp. 26–33.

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Methods of In Situ Strength Testing of Rocks and Joints F. K. Nizametdinov*, A. A. Nagibin, V. V. Levashov, R. F. Nizametdinov, N. F. Nizametdinov, and A. E. Kasymzhanova Karaganda State Technical University, Blv. Mira 56, Karaganda, 100000 Kazakhstan, *e-mail: [email protected] Received July 11, 2015

Abstract—The article offers in situ test methods for cohesion and internal friction angle in rocks and at joints. Technologies and instrumentation for shearing of rock wedges in an open pit mine and for laser scanning and digital imaging of local falls and breaks of inaccessible rock blocks in pitwalls have been developed and approved for constructing a limit equilibrium equation and for calculation of strength properties of rocks and joints. Rock wedges for the tests are prepared using various design drill rigs, the rock wedges are sheared using a 40-t jack placed in a special metal housing with an electric hydraulic pump. Exploration of inaccessible local falls in pitwalls uses electronic tachometers and 3D mine scanner. The tests and approval of the described exploration techniques have been carried out in open pits in Kazakhstan and Kirgizia. Keywords: In situ testing, cohesion, rocks and joints, internal friction angle, rock wedge, fall, hydraulic jack, shear, limit equilibrium equation. DOI: 10.1134/S1062739116020357

INTRODUCTION

Efficient open pit mining expects that mineral reserves are extracted in full and at minimum amount of stripping, based on reliable geomechanical evaluation of slope stability. Reaching the goal requires geological knowledge of a deposit, accuracy of strength characterization of rocks and joints, as well as description of structural features and jointing of rock mass. The strength characteristics included in slope stability estimation are density γ , compressive strength σ c and tensile strength σ t , cohesion and internal friction angle for rocks and joints [1, 2]. The most accurate values of strength characteristics of rocks are found in in situ testing of rock wedges cut directly in a rock mass [1, 3–7]. There are many schemes of in situ shearing tests of rock wedges using hydraulic jacks and hydro-cushions [6, 7]. Rock wedges are cut using round-pointed shovels, chisels, pneumatic hammers and drill rigs, and when prepared the wedges are sheared by a calibrated hydraulic jack. During shearing, the maximum and minimum shearing forces Qmax and Qmin are registered using the hydraulic jack manometer. Linear parameters and angles of a wedge are measured using a rule and a dip compass. The post-testing calculations include the shear surface area S, actual Qmax and Qmin in terms of hydraulic jack calibration coefficient and the wedge weight P. Based on the in situ testing data, the shearing τ and normal σ N stresses are found and a rock strength rating is plotted to estimate the cohesion K and internal friction angle ρ [2]. The flat shearing test (see Fig. 1) can be carried out with an edged wedge on a pit terrace. The induced stresses are found from the formulas [8–10]:

σN =

P , S

τ= 226

Qmax , S

(1)

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Fig. 1. In situ flat shear testing of rock wedges.

Fig. 2. Beveled shearing of a rock wedge.

The cohesion can be given by [9]: Κ=

Qmax − Qmin , S

(2)

and the internal friction angle—by: tanρ =

Q min . P

(3)

The beveled shearing test (Fig. 2) can be carried out at the bottom of a trench or at a bench toe. The beveled shearing-induced stresses are calculated from the formulas: Q cos β + P cos δ , τ = Qmax sin β − P sin δ , (4) σ N = max S

S

where β —the angle between the shearing force orientation and the shear plane; δ —the incline of the shear surface. In the beveled shearing test, the cohesion is found from the formula (2), and the internal friction angle is given by: Q (sin β − 1) − P sin δ − Qmin . (5) tanρ = max Qmax cos β + P cos δ The instrumentation of the in situ shearing testing includes a 40-t hydraulic jack bolt-fixed in a metal housing and shearing metal plates (Fig. 3a). Shearing force in the hydraulic jack is created using an electrical oil plant (Fig. 3b), and granodiorite and marmorized limestone wedges are cut using a drill rig [5]. The shearing test schematic is given in Fig. 4.

Fig. 3. In situ shearing testing instrumentation: (a) shearing installation: 1—hydraulic jack; 2—metal housing; 3—thrust plates; (b) electrical oil plant. JOURNAL OF MINING SCIENCE Vol. 52 No. 2 2016

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Fig. 4. Rock wedge: (a) preparation scheme; (b) prior to shearing.

Table 1. Shearing of rock wedges in Bozymchak open pit mine, Kirgizia

Rock

Rock Manometer wedge readings, kPa Shear area, 3 volume, m m2 Shearing force, Weight, N Width Length kPa 0.136 24517 0.50 0.66 0.330 3797.5 379.85 0.214 11964 0.55 0.900 0.504 6019.2 185.08

Rock wedge parameters, m Height

Marmorized limestone

0.412

Granodiorite

0.425

Internal friction angle, deg

Cohesion, MPa

25

1.17

25

0.36

Parameters of prepared and sheared rock wedges in Bozymchak open pit mine are given in Table 1 together with the calculated values of cohesion. When preparing hard rock wedges (granodiorites and marmorized limestone), it was found that first a wedge should be delineated using a small size rock-drill, or should be pre-cut with a diamond disk and then delineated using a drill rig [5]. The calculation cohesions in Table 1 illustrate combination conditions of the tested rock wedges, taking into account jointing. Table 2 presents generalized shearing test data for rock wedges at actual Kazakhstan deposits. The experimental–analytical method proposed in [11] for estimating stability of underground excavations is based on numerical calculations of stress state of rocks and uses data of in situ monitoring of behavior and parameters of damaged zones in adjacent rock mass. It is worth noticing that cohesion and friction angle can be reliably obtained at rock joints (fractures, faults and bedding) by the method developed by the present paper authors and based on “inverse calculations of failure and falls in highwalls” (e.g. [12]). This has become possible with the modern electron laser equipment (tacheometers, scanners, GPS transducers) and software products (Surpac, Datamine), which enable accurate surveying and determination of sizes and volumes of rock falls (see Fig. 5 and Table 3). In such case, the mechanism of dislocation of a rock block (see Fig. 6) is accurately enough described by the limit equilibrium equation: Pi sin δ av = Pi cos δ av tan ρ ′ + K ′S + σ t S shear ,

(6)

where Pi —the weight of a dislocated rock block, N; δ av —the average angle of weakened surface (slide surface), deg; ρ ′ —the friction angle at the joint, deg; K ′ —the cohesion at the joint, MPa; σ t —the tensile strength, MPa; S shear —the shear surface area, m2. JOURNAL OF MINING SCIENCE Vol. 52 No. 2 2016

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Table 2. In situ test data on rocks and joints at actual deposits in Kazakhstan Strength characteristics Deposit

Rock

Number of sheared wedges

Cohesion K, MPa

Internal friction angle ρ , deg

Argillaceous deposits Argillaceous deposit in landslide body Weathered argillaceous shale (red) Weathered argillaceous shale (yellow)

0.022 0.010 0.056 0.076

18 15 26 29

18

Argillaceous deposits Coaly–argillaceous shale Weathered argillaceous shale

0.037 0.052 0.042

22 26 23

10

Neogene gypsum-bearing clays Speckled clays Speckle coal clays

12 12 15 21 18 18 15 15

40

Footwall clays

0.043 0.0125 0.087 0.122 0.127 0.044 0.054 0.113

Kachary

Argillaceous deposits Creeps of argillaceous deposits

0.0104 0.0109

10°20′ —

10 3

0.03 0.07

20 30

0.04 0.06

22

Chiganak

Argillaceous shale: Weathered Cleaved Jasper quartzite, fine slabs: Jointed (interface) Jointed, folded (interface) Jasper quartzite, solid: Weakly jointed (rock mass) Rare joints (rock mass) Argillaceous shale, cleaved: Interface Folded Interface compaction zone (heavily broken up to the state of gouge)

Toparsky

Alekseevsky

Turgai

Bauxitic clays (along jointing) Footwall clays (along jointing)

22 15 0.11 0.17

34 34

0.02 0.07 0.06

20 3 30

Fig. 5. Surveying of local rock falls in an open pit: (a) layout (1—V = 662 m3, S = 406.805 m2; 2—V = 1180 m3, S = 692.444 m2; 3—V = 886 m3, S = 393.704 m2); (b) photo of local rock falls in southern pitwall. JOURNAL OF MINING SCIENCE Vol. 52 No. 2 2016

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NIZAMETDINOV et al. Table 3. Data on dislocations in the southern wall of Bozymchak open pit mine Characterization Level, m Sliding surface incline δav, deg Sliding surface area S, m2 Volume V, m3 Granodiorite density γ, t/m3 Sliding block weight Р, t Joint friction angle ρ′, deg Calculated joint cohesion K′, MPa

No. 1 Planar

No. 2 Planar

No. 3 Planar

2370–2350 36.5 394 886 2.89 2542.8 25 0.014

2340–2350 42 692.4 1180 2.89 3386.6 25 0.016

2320–2310 42.5 406.8 662 2.89 1899.94 25 0.016

No. 4 Volumetric (creep wedge) 2240 65.5/43.0 96.5/61.0 168/209 2.87 482.1/599.8 25 0.035

Fig. 6. Schematic showing a sliding block.

The revealed sliding of three granodiorite blocks over the inclined surface allows constructing a limit equilibrium equation for each case, in accordance with the expression (6). For the first rock block: 1 ; (7) Ρ1 sin δ 1 = Ρ1 cos δ 1 tanρ1′ + Κ 1′S1 + σ t S shear for the second rock block: 2 ; (8) Ρ2 sin δ 2 = Ρ2 cos δ 2 tanρ 2′ + Κ 2′ S 2 + σ t S shear for the third rock block: 3 . (9) Ρ3 sin δ 3 = Ρ3 cos δ 3 tanρ 3′ + Κ 3′ S 3 + σ t S shear If a rock joint is a single fracture with the presence of ferric hydroxide, it is acceptable that K1′ ≈ K 2′ ≈ K 3′ ≈ K ′ and ρ1′ ≈ ρ 2′ ≈ ρ 3′ ≈ ρ ′ , σ р ≈ 0 . Considering the geometrical data of creep rock blocks (see Table 3) and sliding surfaces, the formulas (7)–(9) take on the form: K 1′ = 3.839 − 5.188tanρ1′ , K 2′ = 3.273 − 3.635tanρ 2′ , K 3′ = 3.155 − 3.442 tanρ 3′ . For equal conditions of creep blocks, it is possible to write the system of equations for the first and second sliding case, first, and, then, for the second and third. The first system of equations: ⎧ K ′ = 3.839 − 5.188 tanρ ′, ⎨ ⎩ K ′ = 3.273 − 3.635 tanρ ′;

(10)

⎧ K ′ = 3.272 − 3.635 tanρ ′, ⎨ ⎩ K ′ = 3.155 − 3.442 tanρ ′.

(11)

the second system of equations:

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The solution of (10) yields K ′ = 0.02 MPa and ρ ′ = 20° , the solution of (11)— K ′ = 0.01 MPa and ρ ′ = 31° . Accordingly, the averaged cohesion and angle of friction at joints in granodiorites will be: K ′ = 0.015 MPa and ρ ′ = 25.5° and can be used to estimate slope stability of the southern wall in Bozymchak open pit mine. The cohesion and angles of friction at joints and fractures in different rocks are generalized and compiled in Table 4, based on the ample research [2, 5, 13–16]. Apparently, the further analysis of standard slope stability designs may accept the following ranges of the strength characteristics of rock joints: K ′ = 0.01–0.10 MPa, ρ ′ = 10–30° [8]. The reported values of the strength characteristics of rock joints are usable for the comparison, first, or for the assessment of slope stability in jointed rock masses, second. CONCLUSIONS

The authors have developed and trialed the in situ shearing test procedure aimed to assess strength characteristics of rocks using a shearing installation including a standard hydraulic jack and an electrical oil plant. The article describes the proposed shearing schemes for rock wedges and the analytical formulas to find cohesion and internal friction angle of rocks. Table 4. Averaged values of strength characteristics of rock joints Cohesion K ′ , MPa Rock Phyllite Clay Coal Shale Argillite Diabase Coaly clay Limestone Magnetite Secondary quartzite Quartz porphyrite and granodiorite porphyrite Skarn deposits Syenite Diorite Granodiorite Siltstone Serpentine Breccias Coaly diorite Porphyry Hornfels Jaspilite Sandstone Gaze Weathered porphyrite Marble Peridote

Range from — 0.02 0.011 0.075 0.095 — 0.030 — — —

to — 0.3 0.185

— — — 0.40 0.50 — 0.182 0.30 0.011 — 0.50 — 0.185 — 0.242 — 0.42

Friction angle ρ′, deg

Average

Range

Average

0.030 — — —

from 9.0 8.0 13.0 9.0 12.0 21.0 13.0 16.0 16.0 17.0

to 25.0 27.0 25.0 28.0 28.0 — 30.0 27.0 27.0 28.0

—

—

17.0

28.0

22.5

— — 0.70 — — — — 0.024 — 0.70 — 0.100 — — — 0.86

— — 0.55 0.50 — 0.182 0.30 0.018 — 0.60 — 0.592 — 0.242 — 0.640

17.0 17.0 17.0 17.0 17.0 24.0 24.0 23.0 20.0 20.0 20.0 20.0 25.0 31.0 36.0 36.0

28.0 28.0 28.0 28.0 30.0 — — 27.0 31.0 31.0 31.0 33.0 37.0 — — —

22.5 22.5 22.5 22.5 23.5 24.0 24.0 25.0 25.5 25.5 25.5 26.5 31.0 31.0 36.0 36.0

0.140 — — — — —

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— 0.16 0.098 0.075 0.118

17.0 17.5 19.0 18.5 20.0 21.0 21.5 21.5 21.5 22.5

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Also, the proposed estimates of cohesions and angles of friction at joints (fractures) are based on laser scanning of creep blocks and on the constructed and solved equations of limit equilibrium, and are trialed in Bozymchak open pit mine. The reported generalized data on the strength characteristics of rocks and joints from actual deposits of Kazakhstan and Kirgizia are used in the slope stability assessment in open pit mining. REFERENCES 1. Fisenko, G.L., Ustoichivost’ bortov kar’erov i otvalov (Slope Stability of Open Pits and Dumps), Moscow, 1965. 2. Popov, I.I., Nizametdinov, F.K., Okatov, R.P., and Dolgonosov, V.N., Prirodnye i tekhnogennye osnovy upravleniya ustoichivost’yu ustupov i bortov kar’erov (Natural and Technological Principles of Slope Stability Control in Open Pit Mines), Almaty: Gylym, 1997. 3. Wittke, W., Rock Mechanics, Springer–Verlag, Berlin, 1984. 4. Bieniawski, Z., Engineering Classification of Joined Rock Masses, Trans. South Africa Inst. Civ. Eng., 1973, vol. 15, pp. 335–344. 5. Nizametdinov, F.K., Ozhigin, S.G., Dolgonosov, V.N., et al., Upravlenie ustoichivost’yu tekhnogennykh gornykh sooruzhenii (Stability Control of Man-Made Mine Structures), Karaganda: Kaz.-Ross. Univ., 2014. 6. Babello, V.A., In Situ Study of Rock Mass Strength in Urtui Open Pit Brown Coal Mine, GIAB, 2004, no. 10, pp. 203–206. 7. Babello, V.A., Krivorotov, A.P., and Fedoseeva, L.V., Results of Determining Strength Characteristics of Rocks by Wedge Failure Method, Izv. Vuzov, Stroit., 2006, no. 1, pp. 98–103. 8. Il’nitskaya, E.N., Teder, R.N., Vatolin, E.S., et al., Svoistva gornykh porod i metody ikh opredeleniya (Properties of Rocks and Determination Methods), Moscow, 1969. 9. Bondarik, G.K., Komarov, I.S., and Ferronsky, V.N., Polevye metody inzhenerno-geologicheskikh issledovanii (Field Measurements), Moscow, 1967. 10. Lomtadze, V.D., Metody laboratornykh issledovanii fiziko-mekhanicheskikh svoistv gornykh porod (Laboratory Testing of Physico-Mechanical Properties of Rocks), Leningrad, 1972. 11. Kurlenya, M.V., Baryshnikov, V.D., and Gakhova, L.N., Experimental and Analytical Method for Assessing Stability of Slopes, J. Min. Sci., 2012, vol. 48, no. 4, pp. 609–615. 12. Nazarov, L.A., Nazarova, L.A., Usol’tseva, O.M., and Kuchai, O.A., Estimation of State and Properties of Various-Scale Geomechanical Objects Using Solutions of Inverse Problems, J. Min. Sci., 2014, vol. 50, no. 5, pp. 831–840. 13. Popov, I.I., Shpakov, P.S., and Poklad, G.G., Ustoichivost’ porodnykh otvalov (Stability of Overburden Dumps), Alma-Ata, 1987. 14. Popov, I.I., Shpakov, P.S., and Yunakov, Yu.L., Upravlenie ustoichivost’yu kar’ernykh otkosov (Slope Stability Control in Open Pit Mines), Moscow: Gornaya Kniga, 2008. 15. Bagdasar’yan, A.G., Lukishov, B.G., Rodionov, V.N., and Fedyanin, A.S., Detection of Features of a Rupture Structure in Walls of an Open Pit in Terms of the Muruntau Open Pit, J. Min. Sci., 2008, vol. 44, no. 1, pp. 73–81. 16. Kartashov, Yu. M., Matveev, B.V., and Mikheev, G.V., Prochnost’ i deformiruemost’ gornykh porod (Rock Strength and Deformability), Moscow, 1979.

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