Common installation and usage issues of wire mesh in mine support

Rolled mesh is widely used in mine support (commonly used as roadway surface protection and isolation of gravel) due to its good strength, flexibility, and relatively easy installation. However, in complex underground environments, its installation and use often face a series of challenges, directly affecting the effectiveness and safety of support. The following is a systematic analysis and response strategy for common problems.

1、 Typical issues in the installation process

Poor fit with the contour of the tunnel, forming an "empty roof" or "net pocket"

Problem description: The mesh fails to tightly adhere to the rock wall or the previous support surface, resulting in suspended areas at the top or shoulder corners. This will result in uneven load transmission, and the mesh is prone to tearing when subjected to impact locally. Additionally, the voids behind it are prone to accumulate gravel, further increasing the load.

Root cause analysis:

The excavation section of the tunnel is irregular, and the mesh is a regular rectangle, so there will inevitably be gaps when directly laid.

The installation sequence is improper, as it did not unfold from the center of the arch towards the two sides and gradually fix.

The fixed point (such as anchor rod tray) is not tightly pressed and compacted with the mesh.

Key points for solution:

Pre deformation treatment: Before installation, the mesh can be moderately arched and pre bent to better adapt to the curvature of the tunnel arch.

Segmented splicing and overlapping: It is allowed for the mesh to have a certain overlap (usually ≥ 10cm) during laying, and to be fully tied with iron wire or connecting rings to form a flexible whole, rather than rigid tension.

Compulsory compaction: Confirm that the tray size of the anchor rod (cable) is large enough, the stiffness is strong enough, and the mesh can be firmly pressed against the rock surface (or sprayed layer) during fastening, eliminating the gap.

Insufficient connection strength, integrity compromised

Problem description: Only sparse point tying is done between adjacent mesh pieces, or connection methods with insufficient strength are used. Under the deformation of the surrounding rock or the impact of gravel, the connection point first fails, causing the mesh to "fight on its own" and lose its overall bearing capacity, with fragments escaping from the connection.

Root cause analysis:

In order to achieve installation speed, the connection quality was ignored.

The use of ordinary thin iron wire for binding has insufficient shear and tensile resistance.

The connection points are arranged in the stress concentration area, but have not been reinforced.

Key points for solution:

Standardized full connection: It is stipulated that all intersecting warp and weft wires of adjacent mesh must be firmly twisted with a pair of galvanized iron wires or high-strength connecting rings.

Key areas should be strengthened: In stress concentration areas, tunnel intersections, and fault zones, double-layer mesh or heavier type (thicker wire diameter) rolled mesh should be used, and anchor rod support should be strengthened.

Collaborative failure with anchor rod (cable) support system

Problem description: The anchor rod tray failed to effectively press down on the mesh, or the mesh size did not match the anchor rod position, resulting in the need to cut and tear the mesh during installation, seriously weakening its strength. The "point" support provided by anchor rods and the "surface" protection provided by rolled mesh have not been effectively combined.

Root cause analysis:

When designing the support, the specifications and spacing of the mesh and anchor rods were not integrated into the design.

The deviation of the drilling position on site was large, causing the anchor rod to be unable to pass through the mesh hole, and the workers forcibly damaged the installation of the mesh.

Key points for solution:

Design collaboration: During the design phase, the spacing of anchor rods should match the length modulus of the rolled mesh, and the mesh size should allow the anchor rods to pass through smoothly.

Using a positioning net or large tray: A layer of lightweight positioning net can be laid first to assist in drilling and positioning. Using large arched trays or W-shaped steel strips can effectively compress the mesh and achieve load distribution.

2、 Common problems during use

Fatigue damage and stress corrosion cracking

Problem description: Under the continuous or periodic action of ground pressure in mines, the rolled mesh is in an alternating stress state for a long time. In addition, the environment underground is humid and contains corrosive ions (such as sulfides), which can easily generate fatigue microcracks at the wave bending points (stress concentration points) and accelerate their propagation, leading to brittle fracture of the mesh.

Root cause analysis:

The material itself has insufficient corrosion resistance (based on actual reports) and fatigue performance (such as using ordinary carbon steel galvanized mesh instead of stainless steel or higher anti-corrosion (based on actual reports) grade materials).

The deformation of the roadway has not been stable for a long time, and the mesh continues to withstand deformation stresses beyond the design range.

Key points for solution:

Material upgrade: In highly corrosive or important long-term tunnels, consider using polymer coated embossed mesh (such as PE immersion) or stainless steel embossed mesh to significantly improve corrosion resistance (based on actual reports) and fatigue life.

Strengthen monitoring and maintenance: conduct regular inspections and reinforce or replace areas that have undergone significant deformation or corrosion.

Wear and detachment of surface protective layer

Problem description: Under the collision of ore loading and transportation equipment or high-speed airflow (dust) erosion, the galvanized layer or plastic coating on the surface of the mesh is worn out at a suitable speed, losing its anti-corrosion protection (based on actual reports), and the substrate is corroded at a suitable speed, resulting in a sharp decrease in strength.

Root cause analysis:

In areas with frequent mechanical activities such as transportation tunnels and loading points, no additional protection was taken for the mesh.

The coating quality or thickness does not meet the standard.

Key points for solution:

Partial innovation service protection: In areas prone to wear and tear, waste conveyor belts, rubber pads, etc. can be added as buffer layers on the inside of the embossing net.

Choose wear-resistant (based on actual reports) coating: specify the use of thickened immersion treatment, which has much better performance than ordinary galvanizing.

Backwater pressure and frost heave caused by poor drainage

Problem description: When there is water seepage in the tunnel, the tightly laid rolled mesh and sprayed layer may hinder the natural discharge of groundwater. The accumulation of water behind the back forms static water pressure, deteriorating the stress state of the support body. In cold regions, repeated frost heave can directly damage the connection between the mesh and the surrounding rock.

Root cause analysis:

The support design is fully enclosed and no drainage channel is provided.

Key points for solution:

Design an active drainage system: Before laying the rolled mesh and shotcrete, install permeable hoses or set up blind drainage ditches in advance to guide water to the roadway drainage system. Confirm that the support system is' sparse 'rather than' blocked '.