Portal zones are transition areas between surface and subsurface conditions. Common issues at portals include weathering, stress relief, groundwater pressures, variable overburden heights and construction disturbance.
Some typical engineering issues are:
Portal environment conditions may change seasonally, due to rainfall events, blasting, excavation advance or climate/weather events. Regular inspection and monitoring should be continued throughout construction and throughout the design service life.
Our range of products includes reinforcing elements and surface- retention hardware which can be utilized as part of an integrated portal ground-support system. Rock bolts or threaded bar can be installed to reinforce jointed rock masses or stabilize potentially unstable blocks against adjacent sound rock. Bearing plates and steel straps distribute applied loads on the exposed face, and welded wire mesh can be used to retain smaller fragments between points of reinforcement.
When incorporated into a system, these products may interact with:
Systems listed above should not be included as part of a solution unless they are known to be included in Wanfeng’s supply scope.
Functions of a Portal Support System
The correct engineering application of these products can be used to:
Engineering Disclaimer
The final portal position, slope angle, cut-and-cover sequence, scaling requirements, bolt-spacing, length and pattern, drainage details and requirements for temporary and/or permanent support must be designed by a competent geotechnical/geological engineer, tunnelling specialist or qualified structural engineer.
Engineering decisions should take into account geological investigation reports, discontinuity/set-spacing orientation and persistence, groundwater inflow/risk of flooding, degree of weathering, ground-surcharge loads, method of excavation and tunnel geometry, expected rockfall angles/distances, required design-life and any applicable codes of practice, standards or legislation.
Wanfeng does not take responsibility for the engineering design of a project portal, surrounding slopes or support against excavation. Products are supplied based on confirmed specifications only.
1.Rock Bolts / Portal Reinforcement Bolts
Steel rock reinforcement elements which can be used around portal crowns, shoulders, side slopes and rock-cut faces.
Key specification parameters:
Other parameters:
2.Fully Grouted Threaded Anchor Bars
Threaded steel bars that can be used with project specified grout or resin to reinforce fractured rock around portal excavations.
Key specification parameters:
Other parameters:
3.Friction Bolts / Split Sets
Fast-installation rock reinforcement elements that can be used in competent rock and good quality, controlled diameter boreholes.
Key specification parameters:
Other parameters:
Application details:
It should be understood that the load capacity of friction bolts is primarily dependent on borehole diameter, the quality of ground throughout installation and conformance with installation procedures. Confirmation of use in deteriorated boreholes, severely fractured ground, oversized or washed-out holes should be clearly obtained prior to installation.
4.Cable Bolts
Long length rock reinforcement elements which can be used where larger sections of potentially unstable material projects beyond the maximum practical anchorage length of conventional bolts.
Key specification parameters:
Other parameters:
Application details:
Care should be taken to use cable bolts only where their overall length, orientation, bonded length and load capacity have been clearly identified as suitable by the project engineer.
5.Bearing Plates
Steel plates used in conjunction with compatible bolts/nuts to transfer and distribute reinforcement loads into the excavation surface.
Key specification parameters:
Other parameters:
6.Welded Wire Mesh
Surface-retention panels which may be used to help contain smaller rock fragments between reinforcement points.
Key specification parameters:
Other parameters:
Application details:
Engineering evaluations or recommendations should be sought when using welded wire mesh for surface retention applications. Such panels should not be assumed to automatically conform to engineered rockfall meshing or tested barrier systems.
7.Steel Straps
Flat or profile steel elements that can be used to help improve load distribution between bolts and add confinement/restraint across fractured zones.
Key specification parameters:
Other parameters:
8.Nuts, Couplers and Accessories
Hardware that is matched to the selected bolt thread type, installation methods and performance requirements.
Key specification parameters:
Configurations can include:
| Typical portal or excavation condition | Typical requirement | Product categories or systems that may be relevant |
| Competent rock with isolated loose blocks | Localized block reinforcement | Rock bolts with bearing plates |
| Jointed portal crown or shoulders | Reinforcement across discontinuities | Rock bolts or threaded anchor bars |
| Fractured portal face | Reinforcement and surface retention | Bolts with welded wire mesh and suitable plates |
| Closely fractured surface rock | Retention between bolt positions | Mesh with plates and steel straps |
| Weak material around bolt collars | Wider surface load distribution | Larger or stiffer plates and straps, subject to design |
| Unstable rock extending deeper into the slope | Deeper anchorage | Longer threaded bars or cable bolts where verified |
| Weathered or variable boreholes | Anchorage suited to measured hole conditions | Project-approved grouted or alternative bolt system |
| Portal transition into more competent rock | Gradual change in reinforcement intensity | Engineered combination of bolts, plates and mesh |
| Shallow cover above the portal | Pre-support and control of crown deformation | Project-designed canopy, forepoling, spiles or other pre-support |
| Wet portal face or active seepage | Drainage and corrosion resistance | Engineered drainage with galvanized, coated or otherwise protected components |
| Exposed portal subject to rockfall | Stabilization or interception of falling material | Anchored mesh, draped mesh, barriers or canopy selected for the assessed hazard |
| Mixed soil-and-rock conditions | Support compatible with both ground types | Project-designed soil nails, anchors, piles, shotcrete or retaining systems |
| Temporary construction access | Rapid installation and frequent inspection | Approved temporary bolts, mesh, scaling and protective structures |
| Long-term portal support | Durability and maintainability | Permanent products with verified corrosion protection and traceability |
| High deformation or seismic demand | Verified deformation or energy capacity | Only products supported by relevant test data |
Disclaimer
This chart is for preliminary guidance purposes only. While the following products or systems may be appropriate in certain circumstances, they should not be considered as definitive solutions.
Regular welded wire mesh is designed as a surface- retention product. It should not be advertised as an energy-rated rockfall system unless the total assembly has been tested and certified as such.
Portal canopy sizes, bolt spacing, anchor lengths, mesh volume, d/r combinations should be determined on a project-specific basis.
Portal support projects may include products or work outside of Wanfeng’s defined scope of manufacturing. Clearly identify on your website what you supply verses related engineering systems.
Possible Wanfeng Supplies:
(Pending manufacturing confirmation)
Systems Related to Portal Supports:
(DO NOT list as WANFOENG products unless you confirm supply capabilities)
Have your portal or excavation-support drawings reviewed by Wanfeng engineers for manufacturability.
Customization Options Include:
All custom sizes, tolerances, materials and performance criteria must be verified against an approved drawing, purchase specification or technical agreement prior to manufacturing.
Note: Recommended quality-control checks should be scaled to the type of product, approved drawing(s) and project inspection plan.
Raw Material
Measurements & Thread
Yield and Tensile testing
where required and contractually specified:
Inspect Weld Quality
Control of Coating & Painting
Traceability & Sign Off
Certificates
If you claim to have ISO certification, third-party testing, or compliance to ASTM, EN, AS/NZS or any other standard. Please publish:
Please do not post logos of Standards without associated documentation that covers the specific product and scope of supply.
Performance of a support product will be affected by installation parameters as well as the entire engineered system.
Installation considerations on a project may include:
Quality assurance inspections should be conducted during installation to confirm correct installation of products and that support design is followed.
1. What support products are commonly used around tunnel portals?
Rock bolts, threaded anchor bars, bearing plates, welded wire mesh, steel straps, shotcrete, drainage and structural portal protection are some of the many options. Product selection depends on geology, portal shape and the design engineer’s preference. The final system should be selected by the project engineer.
2. Why does a portal often require more support than the tunnel interior?
Weathering, shallow cover, stress relief, open joints, rainfall and surface disturbance commonly affect portal rock. These factors can result in the portal zone being less confined than rock found farther inside the tunnel.
3. How are rock bolts and mesh applied at a portal?
Rock bolts are often used to reinforce blocks defined by joints or fractures. Mesh is installed to help retain smaller rock fragments between points of reinforcement. Bearing plates and straps can help connect components and distribute loads against the surface.
4. Is welded wire mesh considered rockfall netting?
Not necessarily. Welded wire mesh can be used to provide surface retention over limited areas, but engineered rockfall netting and barriers can have specific energy capacities and require certified connections and full-system testing. Engineers should not use these terms interchangeably unless supported by test data.
5. Can friction bolts be installed at tunnel portals?
Friction bolts can be suitable in competent rock with properly controlled borehole conditions. Installation into weathered, highly fractured holes or holes with unstable sides and bottom should be confirmed by engineering analysis and installation testing.
6. How should bolt length and spacing be determined?
Bolt length and spacing depends on many variables including portal geometry, discontinuity orientation, potential failure surfaces or wedges, rock quality designation (RQD), groundwater conditions, bottomhole condition and design load. Determine bolt length and spacing by consulting a qualified geotechnical or tunnelling engineer.
7. What kind of corrosion protection is available for exposed portals?
Options may include uncoated steel, hot dip galvanizing, or another specified coating depending on the manufacturing capabilities of the support supplier. The corrosion protection system should be selected based on exposure to water, salts, atmosphere, potential damage during installation and expected design life.
8. Can Wanfeng produce per portal-support drawings?
Yes. If approved drawings are provided, Wanfeng can confirm material availability, dimensions, threads, tolerances, specified coatings, testing requirements and production feasibility. Production should only occur after technical confirmation.
