⚡ electrical engineering

Rockburst proneness evaluation and borehole pressure relief technology for deep heterogeneous rock masses: A case study of Sanshandao Gold Mine

This study integrates theoretical modeling, laboratory testing, and PFC2D simulations to evaluate rockburst proneness and optimize borehole pressure relief parameters for deep heterogeneous rock masses at the Sanshandao Gold Mine, ultimately identifying a 0.10 m borehole diameter as the most effective solution for mitigating rockburst hazards.

Original authors: Shang Hu, Qinzheng Wu, Yang Liu, Hanwen Jia, Yantian Yin, Anran Yin, Peng Chao

Published 2026-10-22

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CC BY 4.0

Original authors: Shang Hu, Qinzheng Wu, Yang Liu, Hanwen Jia, Yantian Yin, Anran Yin, Peng Chao

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Deep underground, where the earth's crust presses with immense force, mining operations face a hidden and violent threat known as a rockburst. This is not a slow collapse but a sudden, explosive release of energy stored in the rock, capable of shattering tunnels and endangering workers. The danger is greatest in deep mines, where the weight of the rock above creates extreme pressure. Complicating matters is the fact that the rock itself is rarely uniform; it is a heterogeneous mix of different minerals and cracks, making its strength vary wildly from one spot to another. This unpredictability makes it difficult for engineers to know exactly how much pressure a specific piece of rock can handle before it fails, or how to safely release the built-up energy without causing a disaster. Without a way to accurately measure this hidden strength and manage the stress, mining deep resources becomes a gamble with high stakes.

Researchers at the Sanshandao Gold Mine in China have tackled this challenge by developing a new way to predict rock strength and a tested method to relieve the dangerous pressure. Instead of guessing how strong a rock sample is, the team first measured its density and the speed at which sound waves travel through it. They discovered a reliable mathematical relationship between these easy-to-measure properties and the rock's actual crushing strength. This allowed them to calculate the exact breaking point for each individual rock sample, rather than relying on an average that might be too high for weak spots or too low for strong ones. With these precise predictions, they could safely perform controlled tests where they loaded the rock to the brink of failure and then unloaded it, mimicking the stress changes that happen during mining. These tests revealed that the deep rock at the mine is prone to moderate-to-strong rockbursts, a finding that demanded immediate action to prevent disaster.

To manage this risk, the team turned to a technique called borehole pressure relief, which involves drilling holes into the rock to create space for the stress to escape. However, drilling the wrong size hole could either do nothing or make the rock too weak to support the tunnel. The researchers used a sophisticated computer simulation that accounted for the natural, uneven strength of the rock to test four different hole diameters, ranging from 5 centimeters to 20 centimeters. They found that the smallest holes failed to release enough pressure, while the largest ones damaged the rock so severely that it lost its ability to hold the tunnel together. The sweet spot was a hole with a diameter of 10 centimeters. This specific size created a zone of relieved stress that connected perfectly with neighboring holes without destroying the rock's structural integrity, effectively balancing the need to release energy with the need to keep the tunnel stable.

The team then took this computer-optimized design into the real world, drilling 10-centimeter holes spaced one meter apart in a test roadway. They monitored the tension in the support bolts holding the tunnel together for a week after the drilling. The results confirmed the simulation: the force on the bolts dropped steadily and consistently, indicating that the stress was successfully being redirected away from the tunnel walls. The bolts did not bounce back, suggesting the pressure relief was permanent and effective. This study provides a clear, quantitative path forward for deep mining, proving that by understanding the unique strength of every rock sample and choosing the precise size of relief holes, engineers can safely manage the violent energy of the deep earth.

Technical Summary: Rockburst Proneness Evaluation and Borehole Pressure Relief Technology for Deep Heterogeneous Rock Masses

Problem Statement
Deep mining operations face severe rockburst hazards driven by high in-situ stress. A critical challenge in mitigating these hazards is the pronounced heterogeneity of deep rock masses, characterized by variable mineral compositions and developed joints. This heterogeneity causes significant fluctuations in rock strength within the same mining area, rendering conventional loading-unloading tests difficult to calibrate due to the inability to accurately determine peak loads. Furthermore, existing rockburst evaluation methods often rely on single indices or assume homogeneous rock properties, failing to account for the uncertainty and discreteness inherent in deep heterogeneous rock masses. Consequently, there is a lack of integrated frameworks that address strength prediction, comprehensive risk evaluation, and optimized pressure relief technologies specifically for deep heterogeneous conditions.

Methodology
This study employs a multi-faceted approach combining theoretical derivation, laboratory testing, numerical simulation, and field monitoring, utilizing the Sanshandao Gold Mine as a case study.

Strength Prediction Model: A physically constrained power-law model was developed to predict uniaxial compressive strength ( $S$ ) using non-destructive parameters: density ( $\rho$ ) and P-wave velocity ( $v_p$ ). The model, expressed as $S = A(\rho v_p^2)^b$ , was calibrated against 30 heterogeneous rock specimens and validated using leave-one-out and five-fold cross-validation. This model was used to determine individualized peak loads for subsequent loading-unloading tests, avoiding the errors associated with using a mean-strength design.
Multi-Parameter Evaluation: Six rockburst proneness indices were integrated: impact energy index ( $W_{cf}$ ), brittleness coefficient ( $B$ ), elastic strain energy index ( $W_{et}$ ), deformation brittleness index ( $K_u$ ), ground stress index ( $S$ ), and tangential stress index ( $T$ ). A game-theory combination weighting method was used to fuse subjective weights (from Analytic Hierarchy Process) and objective weights (derived from entropy and coefficient of variation to account for heterogeneity). These weighted indices were processed through a standard normal cloud model to quantify the fuzziness and randomness of the evaluation, generating a comprehensive certainty degree for rockburst grades.
Numerical Simulation (PFC2D): A 2D Particle Flow Code (PFC2D) model was established with a Weibull random field to simulate the heterogeneous strength distribution of the Sanshandao rock mass. Simulations were conducted for boreholes with four diameters (0.05 m, 0.10 m, 0.15 m, and 0.20 m) under 40 MPa hydrostatic stress. A new metric, the Pressure Relief and Surrounding-rock Stability Efficiency Index (PRSEI), was proposed to balance stress relief ( $\eta_S$ ) against normalized damage ( $D_n$ ).
Field Verification: Based on simulation results, an industrial test was conducted in a roadway using 0.10 m diameter boreholes with 1.0 m spacing. Vibrating wire stress meters on resin anchor bolts monitored axial force changes over seven days to verify stress relief effectiveness.

Key Results

Strength Prediction: The power-law model achieved a high fitting accuracy ( $R^2 = 0.958$ ) and successfully predicted individual specimen strengths, enabling the design of safe and reliable loading-unloading tests. Cross-validation confirmed the model's generalization ability ( $R^2 = 0.951$ ).
Rockburst Evaluation: The multi-index evaluation using the cloud model and game-theory weighting indicated that the deep rock mass of the Sanshandao mining area possesses a "moderate-to-strong" rockburst proneness. The regional risk score was calculated as 3.2. The analysis highlighted that the impact energy index ( $W_{cf}$ ) held the highest combined weight (0.318) due to its high discreteness caused by heterogeneity.
Pressure Relief Optimization: PFC2D simulations revealed a unimodal relationship between borehole diameter and the PRSEI.
- 0.05 m boreholes provided insufficient relief (PRSEI = 0.283).
- 0.15 m and 0.20 m boreholes caused over-relief and excessive damage, reducing stability (PRSEI = 0.173 and 0.000, respectively).
- The 0.10 m borehole achieved the maximum PRSEI of 0.466, creating a critically connected plastic zone (radius = 0.50 m) without compromising rock integrity.
Field Verification: Field monitoring showed a monotonic decrease in anchor bolt axial forces (reducing to 83.23%–86.97% of initial values) over seven days with no rebound. While the magnitude of reduction was lower than the numerical stress-release coefficient due to system stiffness and measurement location, the trend confirmed the successful transfer of stress and release of elastic strain energy.

Significance and Claims
The paper claims to provide a quantitative basis for rockburst evaluation and pressure relief optimization specifically tailored for deep heterogeneous rock masses. Its primary contributions include:

Individualized Testing: Establishing a non-destructive strength prediction model that solves the problem of peak load determination for heterogeneous specimens, ensuring the reliability of loading-unloading tests.
Heterogeneity-Aware Evaluation: Developing a rockburst proneness evaluation framework that explicitly incorporates rock mass heterogeneity into the weighting process, cloud parameters, and uncertainty intervals, offering a more reliable assessment than conventional single-index or standard fuzzy methods.
Optimized Pressure Relief: Proposing the PRSEI metric to quantify the trade-off between stress relief and rock stability, identifying 0.10 m as the optimal borehole diameter for the studied conditions.
Integrated Framework: Validating a complete technical system that links strength prediction, risk assessment, and engineering control measures, verified through both numerical simulation and field application at the Sanshandao Gold Mine.

The authors acknowledge limitations, noting that the models were calibrated on a single mining area and that the 2D simulation simplifies 3D stress states. They suggest that further validation is required for generalization to other deep mines and that longer-term monitoring is necessary to fully capture the long-term pressure relief effects.

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