How to reduce the output of fines rate during block stone extraction by drilling and blasting?

At many quarries for the extraction of building stone there is a problem of increased output of fines after all stages of crushing and grinding, which leads to a decrease in the economic performance of mining enterprises. The fine fraction is formed by the crushing / grinding of prefractured rock mass. Reducing the intensity and size of the prefracture zones will lead to a solution to the problem at hand. It was established that the greatest influence on the shape and duration of the blast pulse is exerted by the velocity of explosive detonation. As the detonation velocity decreases, the peak pressure of the head part of the pulse decreases, and the duration of its rise increases, while a low-amplitude pulse of long duration contributes to better crushing of a rock mass with the least effect of prefracture. Using explosives with a reduced detonation velocity allows reducing the “surplus” impact on a rock mass and thus reducing the intensity of prefracture in the zone of controlled crushing during a blast. This is because the individual pieces will be weakened to a lesser extent after a blast and as a result, the yield of undersize when crushing rock into crushed stone will be reduced.

For more information, see the article:

📌 Khokhlov S.V., Vinogradov Yu.I., Makkoev V.A., Abiyev Z.A. Effect of explosive detonation velocity on the degree of rock pre-fracturing during blasting. Mining Science and Technology (Russia). 2024;9(2):85-96. https://doi.org/10.17073/2500-0632-2023-11-177

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How to estimate the modulus of deformation of a block rock masses using discrete element simulations?

The deformation modulus of rock mass is a fundamental parameter in the geomechanics of tunnels, mining, and other geotechnical rock-supported facilities. The mechanical properties of a rock mass, seen as a fractured medium, are determined by the intact rock, the pattern of relative joint-sets, the geometrical arrangement of the joints, and their mechanical properties. Joint sets, acting as planar discontinuities, confer scale and direction-dependent mechanical properties. The critical factor influencing the deformational behavior of a rock mass is the stiffness of its fractures and discontinuities. The present study investigates the anisotropic deformation modulus of blocky rock masses formed by three intersecting joint sets, including two orthogonal sets. This was achieved through discrete element simulations of representative volumes of blocky rock masses. These studies facilitate the estimation of the blocky rock mass deformation modulus in different directions without the need for laboratory and in-situ tests or empirical relationships.

For more information, see the article:

📌 Ahrami O., Javaheri Koupaei H., Ahangari K. Determination of deformation modulus and characterization of anisotropic behavior of blocky rock masses. Mining Science and Technology (Russia). 2024;9(2):116-133. https://doi.org/10.17073/2500-0632-2023-08-143

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💥 How does the detonation velocity of explosives affect rock fracturing?

In quarries for building stone extraction, up to 30% of the rock turns into fines after blasting and crushing, reducing economic efficiency. One of the key factors is the prefracture zones formed during explosive detonation.

🔬 What was studied?

1️⃣ Explosive detonation velocity (ranging from 2 to 5.2 km/s).
2️⃣ Stresses in the rock mass during blasting.
3️⃣ Microfracturing using X-ray microtomography.

📊 Results:

✔️ The size of the prefracture zone increases from 33R to 77R (where R is the charge radius) as detonation velocity rises.
✔️ Microfracture density (N) depends on the distance from the charge:
• Near zone (10R): from 5,000 to 13,800 pcs/cm³ (exponential growth).
• Far zone (70R): from 0 to 200 pcs/cm³ (linear growth).

💡 Practical conclusions:

➡️ Using explosives with reduced detonation velocity minimizes prefracture zones and decreases fines yield.
➡️ Optimizing blasting parameters allows controlled rock fragmentation and increases the output of marketable fractions.

For more information, see the article:

📌 Khokhlov S.V., Vinogradov Yu.I., Makkoev V.A., Abiyev Z.A. Effect of explosive detonation velocity on the degree of rock pre-fracturing during blasting. Mining Science and Technology (Russia). 2024;9(2):85-96. https://doi.org/10.17073/2500-0632-2023-11-177

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How to determine the deformation modulus and anisotropy in blocky rock masses?

🔹 In a study published in Mining Science and Technology (Russia), the authors investigated the anisotropic behavior of blocky rock masses. They employed the discrete element method to model and analyze the deformation modulus as a function of loading direction, joint properties, and intact rock characteristics.

🔹 Key Findings:
✔️ The deformation modulus depends on the Joint Roughness Coefficient (JRC) and the Uniaxial Compressive Strength (UCS) of the intact rock.
✔️ The influence of joint roughness on the deformation modulus is three times greater than that of intact rock strength.
✔️ The degree of anisotropy in the deformation modulus ranged from 1.6 ≤ Rₑ ≤ 2.5, with an average value of 1.88.
✔️ During joint sliding failure, the yield strain (0.2–0.4) is independent of the loading angle (θ) and the orientation of the third joint set (α).

🔹 Practical Applications:
The results enable the prediction of rock mass behavior without costly field tests, which is crucial for designing tunnels, boreholes, and other geotechnical structures.

Read the full study in Mining Science and Technology (Russia):

📌 Ahrami O., Javaheri Koupaei H., Ahangari K. Determination of deformation modulus and characterization of anisotropic behavior of blocky rock masses. Mining Science and Technology (Russia). 2024;9(2):116–133. https://doi.org/10.17073/2500-0632-2023-08-143

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How to Assess Rock Mass Stability at Deep Mine Levels?

Geomechanical rating classifications are key tools for designing underground mining operations. A new study presents a detailed assessment of rock mass conditions at deep levels of the Udachny mine using RMR and Q systems.

🔹 Key Findings from the Study:
• RMR: Range of 32–62 at Q = 1, median values:
o kimberlites of the Zapadny Ore Body (ZOB) — Class III stability;
o kimberlites of the Vostochny Ore Body (VOB) — Class IV;
o host rocks — Class II (average RMR = 54).
• Q-Index: Logarithmic range of 0.18–105.6, median values:
o VOB — Class D (poor condition);
o ZOB — Class C (fair condition);
o Host rocks — Class B (Q ~ 4–10).
• Rock Strength (UCS):
o kimberlites: 2.15–119.48 MPa (variability due to heterogeneous composition)
o host sediments: 28.14–71.73 MPa (average: 41.05 MPa)
• Jointing:
o host rocks — Class I (monolithic, >2 m spacing);
o ZOB — Class III (0.5–1 m spacing);
o VOB — Class IV (0.1–0.5 m spacing).

🔹 Practical Recommendations:
• for permanent workings: rockbolting (2 m length, 1–4 m spacing) with 5–6 cm shotcrete;
• for excavation junctions: reinforced support (2.5 m rockbolts, 9–12 cm shotcrete);
• moderate correlation between RMR and Q due to differing parameter sensitivities (e.g., RMR ignores rockbursts, Q omits strength).

The study highlights the need for integrated approaches: ratings require continuous updates as mining progresses.

📌 Read the full paper:
Serebryakov E.V., Zaytsev I.A., Potaka A.A. Assessment of rating parameters of the rock mass conditions at Udachny underground mine deep levels. Mining Science and Technology (Russia). 2024;9(3):206-220. https://doi.org/10.17073/2500-0632-2023-12-192

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