⚡ electrical engineering

Zonal Synergistic Control of Surrounding Rock in Deep Soft-Rock Roadways Based on Strong–Weak Bearing Structures

This paper proposes and validates a zonal synergistic control strategy for deep soft-rock roadways that leverages the residual self-bearing capacity of damaged rock by dividing the surrounding mass into distinct weak, stable, and strong bearing layers, thereby significantly reducing deformation and plastic zone extent through optimized support design.

Original authors: Xinfeng Wang, Yunhui Jiang, Tian Jiang, Chuanqi Zhu, Yimin Deng

Published 2026-08-13

📖 6 min read🧠 Deep dive

CC BY 4.0

Original authors: Xinfeng Wang, Yunhui Jiang, Tian Jiang, Chuanqi Zhu, Yimin Deng

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

The Deep Earth's Tug-of-War

Imagine the Earth's crust as a giant, heavy blanket draped over a soft, squishy mattress. When we dig a tunnel through this mattress to mine for coal, we are essentially pulling a hole through the blanket. The heavy weight of the blanket (the rock above) wants to crush the hole shut, while the soft mattress (the surrounding rock) tries to squeeze inward. This is the daily struggle of deep mining.

In the world of rock mechanics, scientists have long known that when you dig a tunnel, the rock around it doesn't just break and stop; it goes through a messy transformation. It starts strong, then gets damaged and weak, and finally settles into a "residual" state where it's still broken but can still hold a little bit of weight. Think of it like a crumpled soda can: once you crush it, it's not as strong as a new one, but it doesn't instantly turn into dust. It still has some structural integrity left. The big question for engineers is: how do we build a support system that works with this crumpled can, rather than just trying to hold up the entire mountain with a single, giant beam? If we get this wrong, the tunnel roof caves in, the floor pushes up, and the walls squeeze together, making the mine unsafe and unusable.

The "Strong-Weak-Strong" Sandwich

This paper tackles the problem of keeping deep, soft-rock tunnels from collapsing by proposing a clever new way to look at the rock around the tunnel. Instead of treating the rock as a single, messy blob, the authors suggest we think of it as a three-layered sandwich, where each layer has a different job.

The Problem with the Old Way
Traditionally, engineers often tried to support the tunnel by just bolting everything down or pumping in grout (a cement-like paste) everywhere. The authors argue this misses the point. They found that the rock naturally organizes itself into three distinct zones after a tunnel is dug, and treating them all the same is like trying to use a sledgehammer to fix a watch. The rock near the wall is broken and weak, the middle zone is trying to hold things together, and the deep zone is still strong and stable.

The New "Strong-Weak" Model
The authors developed a mathematical model (using some fancy math called complex-variable theory) to prove that the rock forms three specific layers:

The Inner Weak Layer: This is the rock right next to the tunnel wall. It's been crushed and is in a "residual" state—like a crumpled soda can. It's weak and deforms easily.
The Intermediate Stable Layer: Moving a bit further out, the rock is damaged but still holding its shape. It acts as a buffer, transferring stress from the weak inner layer to the strong outer layer.
The Outer Strong Layer: Deep in the rock, far from the tunnel, the rock is still strong and healthy. This is the real "heavy lifter" that holds up the mountain.

The paper argues that the key to stability isn't just shoving more bolts into the weak layer; it's about creating a "zonal synergistic" system. This means using different tools for different layers to help them work together. The goal is to stop the weak layer from getting worse, help the middle layer transfer the load, and let the strong outer layer do the heavy lifting.

What They Found: The Magic of "Residual Strength"
The researchers used computer simulations (MATLAB and FLAC3D) to test how different factors change these layers. They discovered a few critical things:

The "Residual Strength" is Key: Even when rock is broken, it keeps some strength. The more "residual strength" the broken rock has, the thinner and safer all three layers become. It's like if your crumpled soda can was made of a slightly tougher metal; it would hold its shape better and not crush as easily.
Pressure Makes it Worse: The deeper the tunnel (higher in-situ stress), the thicker and more dangerous these layers get. The stress pushes the "weak zone" further out, making the tunnel harder to stabilize.
Support Matters: Adding support (like bolts and grout) doesn't just stop the rock from moving; it actually changes the shape of these layers. It squeezes the weak inner layer back in and helps the strong outer layer take over the load.

The Real-World Test: Dingji Mine
To see if this theory works in the real world, the team tested it in a deep soft-rock roadway at the Dingji Mine in China. They designed a specific support system based on their "three-layer" idea:

Grouting: They pumped grout into the rock right next to the tunnel wall to turn the "weak layer" into something a bit stronger.
Bolts: They installed steel bolts to stitch the "intermediate layer" together.
Cables: They used long steel cables to anchor the shallow rock to the deep, strong "outer layer," effectively letting the deep rock hold up the tunnel.

The Results
The results were impressive. Before this new support system, the tunnel was deforming rapidly. After applying their "zonal synergistic" plan:

Computer Simulations: Showed that roof subsidence (sagging) dropped by about 30%, floor heave (pushing up) dropped by 31%, and the walls squeezing together dropped by nearly 49%. The area of broken rock (the plastic zone) shrank to just about 1 meter.
Field Monitoring: They watched the tunnel for 60 days. The results were even better than the simulations suggested. Compared to an unsupported tunnel, the roof sank 92.46% less, the floor heaved 92.52% less, and the walls converged 90.23% less. The tunnel stopped deforming and stabilized after about 28 days.

The Bottom Line
The paper concludes that we don't need to fight the rock; we need to understand its "personality." By recognizing that the rock forms a weak inner layer, a stable middle layer, and a strong outer layer, engineers can design support systems that help these layers work together. Instead of just holding up the roof, the support system mobilizes the rock's own remaining strength to keep the tunnel safe. It's a shift from brute force to a smart, cooperative strategy that turns a crumbling tunnel into a stable one.

Technical Summary: Zonal Synergistic Control of Surrounding Rock in Deep Soft-Rock Roadways Based on Strong–Weak Bearing Structures

Problem Statement
Deep soft-rock roadways face significant challenges regarding large deformation and progressive failure. Conventional support designs often fail to fully utilize the residual self-bearing capacity of damaged surrounding rock. While previous studies have addressed stress environments, failure evolution, and bearing structures, the specific spatial evolution of strong and weak bearing layers, their synergistic interactions, and their mechanical relationship with engineered support remain insufficiently resolved. There is a need for a mechanics-based framework that links rock damage, stress transfer, and self-bearing behavior to optimize support systems for deep soft-rock conditions.

Methodology
The study employs a multi-faceted approach combining analytical modeling, numerical simulation, and field monitoring:

Analytical Modeling: A layered mechanical model was developed using complex-variable theory, conformal mapping, and elastoplastic mechanics. The rectangular roadway problem was transformed into an equivalent circular problem to derive analytical solutions for stress, strain, displacement, and the radii of the elastic, plastic-softening, and fractured zones.
Zonal Division: Based on strength degradation and stress redistribution, the surrounding rock was theoretically divided into three distinct radial layers:
- Inner Weak Bearing Layer: Corresponds to the fractured zone with residual strength and low tangential stress.
- Intermediate Stable Bearing Layer: Corresponds to the plastic-softening zone where stress is redistributed but remains below a specific threshold ( $K_1$ times in-situ stress).
- Outer Strong Bearing Layer: Comprises the high-stress portion of the plastic-softening zone and the effective elastic range where tangential stress exceeds specific thresholds ( $K_1$ and $K_2$ times in-situ stress).
Parametric Analysis (MATLAB): Analytical expressions were used to quantify the effects of residual strength, in-situ stress, and support resistance on the thickness and evolution of these bearing layers.
Numerical Simulation (FLAC3D): Three-dimensional simulations characterized stress redistribution, roadway deformation, and plastic-zone evolution under varying mechanical parameters and a proposed combined support scheme.
Field Monitoring: A combined grouting–bolt–cable support scheme was implemented in a deep soft-rock roadway at the Dingji Mine. Deformation was monitored at roof, floor, and sidewall locations over a 60-day period to validate the theoretical and numerical findings.

Key Contributions

Strong–Weak Bearing Model: The paper proposes a model that links rock damage states to stress transfer mechanisms, defining a tripartite bearing structure (inner weak, intermediate stable, outer strong) rather than treating the surrounding rock as a homogeneous failure zone.
Analytical Thickness Formulas: The study derives specific analytical expressions for the thicknesses of the three bearing layers, demonstrating how they are governed by rock mass strength, in-situ stress, and support resistance.
Mechanism of Control: It establishes that stability control should prioritize limiting the expansion of the inner weak bearing layer, maintaining an appropriate intermediate bearing range for stress transfer, and preserving the integrity of the outer strong bearing layer.

Results

Parametric Sensitivity:
- Residual Strength: Increasing residual strength (cohesion and internal friction angle) significantly reduces the thickness of all three bearing layers, with the most pronounced effect on the inner weak layer.
- In-Situ Stress: Higher in-situ stress expands the disturbed range and the thickness of all bearing layers, shifting the stress concentration zone deeper and increasing roadway deformation.
- Support Resistance: Increasing support resistance compresses the near-wall weakened range (inner layer) and the peripheral stress-disturbance range (outer layer), enhancing radial confinement without uniformly changing all layer thicknesses.
Numerical Simulation: Under the proposed support scheme, FLAC3D simulations showed reductions in roof subsidence (30.37%), floor heave (30.92%), and sidewall convergence (48.60%) compared to unsupported conditions. The plastic zone extent was reduced to approximately 1 meter.
Field Monitoring: After 60 days of monitoring, the combined support scheme resulted in deformation reductions of 92.46% (roof), 92.52% (floor), and 90.23% (sidewall) relative to unsupported conditions. Deformation stabilized after approximately 28 days. The plastic zone was effectively controlled, and the support system successfully mobilized the residual self-bearing capacity of the rock.

Significance
The paper claims that zonal synergistic support is an effective strategy for deep soft-rock roadways. By explicitly recognizing and targeting the distinct mechanical roles of the inner weak, intermediate stable, and outer strong bearing layers, the proposed support scheme (grouting, bolts, and cables) can mobilize the residual self-bearing capacity of the surrounding rock. This approach offers a mechanics-based framework for designing support systems that improve roadway stability, reduce deformation, and limit the extent of plastic failure in deep mining environments. The study validates that controlling the near-wall fractured zone while ensuring stress transfer through deeper layers is critical for managing large deformations in soft rock.

The Deep Earth's Tug-of-War

The "Strong-Weak-Strong" Sandwich

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