A soil nail wall is constructed in stages as excavation proceeds. Stability of each stage is affected by the ground conditions, construction sequencing, timing of installation, groundwater conditions and facing performance. Some typical issues encountered are listed below.
Successful soil nail projects take into consideration the overall system. Bar strength does not determine stability of the wall or soil–grout bond strength.
Wanfeng provides steel reinforcement and connection products that can be components of an engineered soil nail wall.
Threaded bars are used as tensile reinforcing elements. Bars are generally placed into drilled holes and grouted throughout the required length. Bearing plates, nuts and nail-head details are used to connect bars to the wall facing. Welded wire mesh can be used to reinforce the initial shotcrete facing if required.
Additional components may include:
Purpose of Soil Nail Systems
Engineered soil nail walls can be used to:
Engineering Disclaimer
Final wall geometry, excavation lift heights, nail diameter and length, spacing, inclination angle, grout-hole diameter, required bond length, nail-head connections, facing details, drainage systems and construction sequence should be designed or reviewed by experienced geotechnical and structural engineers.
Design considerations should include but not be limited to: ground investigation results, groundwater conditions, surcharge loads, overall stability of the system, internal stability of soil nails, facing capacity, pullout resistance, seismic demand, adjacent structures and utilities, and required design life.
While Wanfeng can provide steel reinforcement and connection products to meet specified requirements, we do not assume the responsibility of the engineer’s soil nail wall design or the contractor’s responsibility for drilling and grouting, facing construction and field quality control testing.
| Characteristic | Soil nail | Prestressed ground anchor |
| Typical structural behavior | Generally passive; resistance develops with ground deformation | Actively prestressed to apply load |
| Typical grouting | Commonly grouted along the nail length | Usually incorporates defined bond and free lengths |
| Construction arrangement | Closely spaced reinforcement installed with staged excavation | Often wider-spaced anchors connected to structural facing or walers |
| Load application | Typically not locked off at a high prestress | Tested and locked off at a specified load |
| Facing interaction | Commonly connected to reinforced shotcrete or permanent facing | Commonly connected to walers, beams or structural facing |
| Design terminology | Soil nail bar and nail head | Tendon, bond length, free length and anchor head |
PASSIVE SOIL NAILED SYSTEMS AND PRESSTRESSED GROUND ANCHOR SYSTEMS
(The two systems should not be used interchangeably.) Project drawings should specifically show if a component is to be used as a passive soil nail or a prestressed ground anchor.
1.Threaded Soil Nail Bars
Steel bars used as the primary tension element of the soil nail assembly.
Essential information
Other information
2.Coupled Soil Nail Bars
Threaded bars coupled using approved couplers when bar length requirements for shipping, drill rig access or maximum nail length requires bars to be installed in sections.
Essential information
Other information
NOTE: The coupled connection must be capable of meeting or exceeding the project specified tensile requirement. Do not determine coupler strength by looking at bar strength only.
3. Hollow or Self-Drilling Soil Nail Bars
Bars with a hollow threaded center that can be used to drill, provide reinforcement and inject grout into ground conditions where maintaining a c perl hole is restrictive or not possible.
Essential information
Other information
NOTE: Only include hollow/self drilling soil nail bars if Wanfeng has confirmed production availability and all technical specifications have been confirmed. These bars should not be included just to fill a SEO category.
4. Soil Nail Bearing Plates
Steel plate located at the soil nail head used to transfer load from the threaded bar to the wall-facing connection.
Essential information
Additional information
5. Soil Nail Nuts and Washers
Details used to secure bearing plates or other approved soil nail head details to the threaded bar. Thread must be compatible.
Essential information
Additional information
6.Centralizers and Spacers
Parts used to ensure the correct bar position and grout cover is maintained within a drilled hole.
Essential information
Additional information
7. Welded Wire Mesh
Steel mesh that can be used as part of the initial or final facing if specified within the approved design details.
Essential information
Additional information
NOTE: Mesh reinforcement does not define the strength capacity of a facing. Shotcrete thickness, concrete compressive strength, reinforcement layout, nail-head connection and construction joints need to be engineered together as a complete system.
8.Nail-Head Connection Components
Project specific steel details that connect the soil nail bar to the selected facing. These components can consist of multiple parts.
Essential information
Examples of Components:
NOTE: Only show connection components that Wanfeng has the capability to produce to meet drawing specifications and have tested for approval.
| Typical ground or project condition | Typical requirement | Product or system response that may be relevant |
| Stiff cohesive soil with temporary face stability | Conventional staged installation | Fully grouted threaded soil nail bars with engineered facing |
| Weathered rock or mixed soil and rock | Reinforcement through variable material | Drilled and grouted bars selected for the actual ground |
| Dense granular soil with sufficient short-term stability | Control of ravelling and prompt facing installation | Soil nails with closely coordinated excavation and initial facing |
| Ground prone to borehole collapse | Installation method capable of maintaining or forming the hole | Casing, specialized drilling or verified self-drilling system |
| Variable fill or buried obstructions | Adaptable drilling and verified bond resistance | Investigation, trial nails and project-specific drilling method |
| Groundwater entering the wall | Drainage and controlled construction conditions | Drain strips, outlets, surface-water control and suitable corrosion protection |
| Aggressive soil or groundwater | Increased corrosion protection | Encapsulated, coated or otherwise protected nail system as specified |
| Limited delivery or handling length | Sectional bar installation | Coupled threaded bars with verified connection capacity |
| Temporary soil nail wall | Construction-stage performance | Components designed for the specified temporary exposure period |
| Permanent soil nail wall | Long-term strength, facing and durability | Verified corrosion protection, permanent facing and documentation |
| Significant surcharge behind the wall | Increased structural and global-stability demand | Project-specific geotechnical and structural design |
| Seismic loading | Verified seismic performance | Project-specific analysis and appropriately detailed components |
| Soft clay, organic soil or very loose saturated ground | Potentially unsuitable conventional soil nailing conditions | Specialist assessment or an alternative retaining system |
| Nails extending beyond the property boundary | Legal and geometric constraint | Revised layout or alternative support system approved by the engineer |
Soil Nail Selection Guide
Selection Warning
This guide is intended as a general guide only. It does not determine if soil nailing is applicable to your project.
Where:
Special designs are required and could be considered for an alternative retention system.
A typical soil nail wall construction sequence may involve the following activities:
Construction Sequence Warning
Actual Lift Heights, Unsupported Exposure Time, drilling sequence, Grouting procedures and Timing of Facing installation are to be detailed in the approved design and method statement.
Wanfeng will not specify the amount of soil that can be exposed prior to completion of the next stage of support.
| Design consideration | Temporary soil nail wall | Permanent soil nail wall |
| Service period | Defined construction duration | Full project design life |
| Facing | Commonly temporary reinforced shotcrete | Engineered permanent facing system |
| Corrosion protection | Based on actual exposure and ground conditions | Designed for long-term soil and groundwater exposure |
| Drainage | Required for construction-stage conditions | Must remain functional and maintainable |
| Documentation | Construction and installation records | Permanent works records and compliance documentation |
| Testing | As specified in the temporary works design | Verification, proof and acceptance requirements defined by the permanent design |
| Inspection | Construction-stage inspections | Long-term inspection and maintenance plan |
| Structural contribution | Limited to the approved temporary design | Verified for long-term strength, serviceability and durability |
Temporary nuts/bolts should not be used as part of permanent structures unless the material, installation, corrosion protection and performance meets the requirements for permanent construction.
If provided with approved soil nail schedules and drawings, Wanfeng can determine the manufacturability of the nails.
Items that can be customized:
Dimensions, tolerances, material specifications, stresses, coatings and test documentation shall be clearly defined on an approved drawing or technical specification prior to fabrication.
1. Raw Materials Inspection
2. Bar and Thread Inspection
3. Mechanical Testing and Connection Inspection
Where required and contractually obligated:
4. Dimensional Inspection
5. Surface Treatment Inspection
6. Identification and Final Inspection
7. Certificates and Test Reports
Where standards or third party testing are claimed, the following website information should include:
ASTM, EN, ISO, BS, AS/NZS or project standards should ONLY be referenced if conformance can be provied for the actual product supplied.
Specify the required corrosion protection based on ground conditions, groundwater chemistry, desired service life and project requirements. Possible protection options include:
Important Limitation
The overall corrosion-protection system includes more than the finish on the steel bar. Corrosion resistance may also depend on:
Do not substitute one coating for another that is specifically required by the project without engineering approval. Only publish a “double corrosion protection” claim when the entire assembly and all supporting documentation meet the project definition.
Tests completed during manufacturing will only verify component properties. Field testing verifies available soil–grout bond resistance.
Verification methods may include (and should be included in the project quality plan):
| Test or inspection | Typical location | Primary purpose |
| Steel tensile test | Factory or approved laboratory | Verify bar material properties |
| Coupler tensile test | Factory or approved laboratory | Verify connection capacity |
| Plate dimensional inspection | Factory | Verify drawing compliance |
| Coating inspection | Factory | Verify specified coating properties |
| Soil nail verification test | Project site | Assess installation method and ground bond behavior |
| Proof test | Project site | Confirm performance of selected production nails |
| Grout and installation records | Project site | Document installed construction quality |
1.What is a soil nail wall?
A soil nail wall is a reinforced soil mass typically constructed top down in lifts. Steel bars are placed into drilled and grouted holes and connected to a reinforced facing to support the retained soil.
2. How is a soil nail different from a rock bolt?
A soil nail is used to reinforce soil or weathered material and relies on the surrounding grout and wall facing for resistance. A rock bolt is typically used to reinforce blocks of rock or rock discontinuities. Both can use threaded steel bars but design assumptions and overall system requirements vary.
3. Are soil nails prestressed?
Conventional soil nails are typically passive reinforcement and not stressed to high levels of prestress. Resistance is gained through deformation of the reinforced groundmass. Prestressed anchors are a different type of retaining system.
4. Are soil nail bars typically fully grouted?
Fully grouting conventional soil nail bars along their length is common. However, the method of grouting, hole diameter, required cover and bond resistance should be defined in the project specification and confirmed in the field.
5. Can soil nail bars be coupled?
Yes. Sectional bars can be joined using compatible couplers where allowed by the design. The entire coupler connection should meet the specified load requirement and be installed with the proper thread engagement.
6. Can soil nailing be used where groundwater is present?
Groundwater may have the potential to affect excavation stability, drilling rates, grouting capabilities, corrosion and facing pressures. Assessment may allow for drainage or dewatering solutions to be used or another retaining option may be necessary.
7. What corrosion protection options are available?
Options may include galvanizing, epoxy coating, encapsulation or a combination of systems depending on project requirements and verified manufacturing capabilities. The chosen method should protect the entire nail assembly and not just the exposed portion of the bar.
8. Can Wanfeng produce soil nails from just drawings?
Wanfeng can verify approved bar, plate, nut, coupler, centralizer and nail head drawings for manufacturing feasibility. All final dimensions, loads, coatings, tolerances and tests should be confirmed prior to production.
