The engineering challenges faced in a foundation pit:
A foundation pit is an excavation that is made below the surrounding ground level. Digging an excavation alters the stress state and groundwater regime of the ground and can also affect neighbouring structures, roads and services.
Common problems requiring engineered support include:
The type of support system required is determined by excavation depth, ground and groundwater conditions—not necessarily by product type.
Steel bars and accessories are just pieces of the puzzle. Other parts of a deep- excavation support system can include:
| System function | Typical purpose |
| Earth retention | Prevent the sides of the excavation from collapsing |
| External reinforcement | Transfer loads into reinforced ground outside the pit |
| Internal bracing | Restrain retaining walls from inside the excavation |
| Water control | Limit seepage, piping, uplift and loss of ground |
| Foundation protection | Control movement affecting neighboring structures |
| Surface protection | Prevent localized ravelling or erosion |
| Monitoring | Detect wall movement, settlement, water pressure and support loads |
| Access protection | Maintain safe routes for workers and equipment |
Wanfeng provides reinforcement and connection elements that can be included in engineered excavation-support systems when designed by a professional engineer. Threaded soil nail bars can be used to reinforce appropriate soil during staged top-down excavation. Threaded anchor bars can be utilized in an engineered tieback system where ground conditions and property lines allow. Rock bolts can be used to reinforce stable or jointed rock masses. Bearing plates, nuts, couplers and welded wire mesh can be used to connect reinforcement to an approved facing.
Subject to the project specification, these products can be part of:
The foregoing systems are not Wanfeng products unless specifically confirmed.
Component Functions
Depending on the engineered design, products supplied by Wanfeng can be used to:
Engineering Professional Services
Excavation dimensions, retaining-wall style, support spacing, length of soil nails or anchors, batter, bond length, level of prestress applied, internal brace type and spacing, depth of wall embedment, drainage and sequenced construction must be engineered by a licensed geotechnical engineer and civil/structural engineer where appropriate.
The engineering should consider:
Wanfeng does not design excavation supports. Components are provided based on specified requirements. We do not replace the engineer’s design of excavation support, groundwater control or temporary works.
| Support system | Typical application | Principal components | Important limitation |
| Sloping or benching | Where sufficient space and suitable ground are available | Excavated slope geometry and surface protection | May be impractical in restricted urban sites |
| Soil nail wall | Ground capable of temporary staged exposure | Grouted nails, drainage, reinforced facing and nail heads | Generally requires top-down staged excavation |
| Ground-anchored wall | Deep excavation with suitable external bond zone | Retaining wall, prestressed anchors, walers and anchor heads | Requires property rights and specialist testing |
| Internally braced wall | Restricted site or anchors not permitted outside boundary | Wall, walers, struts and connections | Struts can restrict excavation operations |
| Cantilever pile or wall | Moderate depth with sufficient wall stiffness and embedment | Sheet piles, soldier piles, secant piles or diaphragm wall | Deflection can govern design |
| Rock excavation support | Competent or fractured rock | Rock bolts, dowels, mesh and shotcrete where designed | Geological discontinuities control performance |
| Underpinning system | Excavation close to existing foundations | Underpinning piles, beams, jacks or transfer structures | Requires structural and geotechnical coordination |
| Ground improvement system | Weak ground, basal instability or seepage concerns | Deep mixing, jet grouting or other approved methods | Not replaced by steel bars alone |
This comparison is conceptual and should not be used to select a system without site-specific design.
1. Threaded Soil Nail Bars
Steel bars used as soil nails in project designed soil nail walls and certain staged excavations.
Important Specification Fields
Other Specification Fields
2. Coupled Soil Nail Bars
Threaded bars sectioned and assembled with compatible couplers when access or nail length prohibits single-piece bars.
Important Specification Fields
Other Specification Fields
Application Note
The entire coupled connection will be required to meet the specified tensile requirement. Capacity of the coupler should be validated separately from the bar material.
3. Threaded Ground-Anchor Bars
Specialty high strength threaded bars that can serve as the tendon of a project designed ground-anchor assembly.
Important Specification Fields
Other Specification Fields
Application Note
Ground anchors are typically designed as complete prestressed systems. Ground anchors are not simply threaded bars. Ground anchors may require:
Only include yourself in the supply of a complete ground-anchor system if you have verified the production, installation and testing of every component.
4. Rock Bolts and Dowels
Steel bars used to reinforce rock sections that may be encountered through or around a foundation excavation.
Important Specification Fields
Other Specification Fields
5. Bearing Plates
Steel bearing plates used to connect bars to approved facing or structural connection details.
Important Specification Fields
Other Specification Fields
6. Nuts and Washers
Fasteners used in soil nail heads, threaded anchors and other drawing based connections.
Important Specification Fields
Other Specification Fields
7. Centralizers and Spacers
Spacing components used to support bars within drilled holes at the correct position and grout coverage.
Important Specification Fields
Other Specification Fields
8. Welded Wire Mesh
Steel mesh that may be used to reinforce the first layer of shotcrete or retain localized loose material where specified.
Important Specification Fields
Other Specification Fields
Application Note
Mesh does not independently define the capacity of a facing. Shotcrete thickness, concrete compressive strength, reinforcement, construction joints, and connections to nails should be designed together as a complete facing system.
9. Nail-Head and Connection Components
Steel items used to connect bars to a facing based on construction drawings.
Possible Components
Important Specification Fields
Hollow or Self-Drilling Bars
Bars with a hollow center may be used when conventional boreholes are disturbed or otherwise difficult to maintain.
Important Specification Fields
Other Specification Fields
Availability Note
Only include hollow bars or self-drilling bars if you have confirmed Wanfeng has actual production capability, load data, coupling strength, and familiarity with all required components for these bars to be installed.
| Typical site condition | Typical requirement | System or products that may be relevant |
| Suitable stiff soil with staged face stability | Top-down reinforcement | Soil nails, drainage and reinforced facing |
| Rock or weathered-rock excavation | Discontinuity reinforcement | Rock bolts or dowels with mesh or shotcrete where designed |
| Mixed soil-and-rock profile | Support adapted to changing ground | Hybrid soil nail, anchor, pile-wall or rock-support system |
| Deep urban excavation | High wall stiffness and controlled movement | Pile or diaphragm wall with anchors or internal bracing |
| Limited property rights | Support without external anchor encroachment | Internal struts, slabs or other internally supported system |
| Adjacent sensitive building | Low-deformation support and monitoring | Stiff retaining wall, staged support and possible underpinning |
| Loose granular ground | Control of face stability and ground loss | Pile wall, ground improvement, controlled excavation or specialist drilling |
| Soft clay | Control of wall movement and basal heave | Embedded wall, bracing and possible ground improvement |
| Water-bearing sand | Seepage cutoff and piping control | Cutoff wall, dewatering, recharge or ground improvement |
| High groundwater | Water pressure and uplift control | Engineered dewatering, cutoff and base-stability measures |
| Weak ground below pit base | Basal stability | Ground improvement, deep embedment, struts or other designed measures |
| Temporary excavation | Construction-stage capacity | Components and coatings suitable for the actual exposure period |
| Permanent basement wall | Long-term durability and structural integration | Permanent retaining system with verified corrosion protection |
| High surcharge near pit edge | Increased wall and support load | Project-specific wall, anchor or bracing design |
| Seismic condition | Verified temporary and permanent seismic response | Project-specific geotechnical and structural analysis |
Disclaimer: Items included on the following list may only be applicable when utilized as components of a system.
Example:
| Characteristic | Soil nail | Prestressed ground anchor |
| Structural behavior | Generally passive | Actively prestressed |
| Load development | Develops resistance as the ground deforms | Load applied and locked off during installation |
| Typical grouting | Commonly full-length grout | Defined free and bond lengths |
| Typical spacing | Relatively closely spaced | Often wider spacing |
| Facing connection | Nail head connected to reinforced facing | Anchor head connected to wall or waler |
| Field testing | Verification and proof testing as specified | Performance, proof and lock-off testing as specified |
| Property boundary | Nails may still require external rights | External anchor bond zone commonly requires property rights |
Project documentation should identify the intended element correctly. Marketing content should not use “soil nail,” “ground anchor” and “rock bolt” as synonyms.
Systems Potentially Provided by Wanfeng
Assuming availability has been confirmed:
Systems That May Be Necessary
DO NOT list as systems provided by Wanfeng until confirmed available:
Typical Soil Nail Construction Sequence
Typical Anchored Wall Construction Sequence
Typical Internally Braced Excavation Construction Sequence
The above interfaces are examples only. Lift heights, lengths of time between excavation and support, support levels, prestress and removal sequences must be in accordance with the approved design and Method Statement.
Wanfeng can evaluate production schedules and approved drawings to determine manufacturability.
Examples of customizable items are:
All dimensions, tolerances, materials, loads and coatings should be verified on approved drawings or technical specifications prior to manufacturing.
1. Incoming Material Inspection:
2. Beam, Bolt, and Thread Details
3. Mechanical Property & Connection Tests (Specify as required by contract)
4. Dimensional Acceptance
5. Surface Preparation and Coating
6. Identification and Release for Shipment
Factory testing verifies supplied component properties. It does not verify excavation stability or installed ground resistance.
| Test or inspection | Typical location | Purpose |
| Bar tensile test | Factory or laboratory | Verify steel mechanical properties |
| Coupler tensile test | Factory or laboratory | Verify connection capacity |
| Nut proof-load test | Factory or laboratory | Verify nut performance |
| Plate inspection | Factory | Verify material and dimensions |
| Mesh weld test | Factory or laboratory | Verify specified weld capacity |
| Coating inspection | Factory | Verify protection requirements |
| Soil nail verification test | Site | Assess installation method and ground bond |
| Soil nail proof test | Site | Check selected production nails |
| Ground-anchor performance test | Site | Evaluate load–displacement behavior |
| Anchor proof test | Site | Verify production-anchor performance |
| Wall survey | Site | Monitor lateral wall movement |
| Settlement monitoring | Site | Monitor surrounding ground and structures |
| Piezometer monitoring | Site | Assess groundwater pressure |
Factory tensile strength must not be presented as proof of soil-nail pullout resistance, ground-anchor bond capacity or foundation-pit stability.
Water- Control Considerations
The plan should consider:
Consideration should be given to effects of dewatering on settlement of adjacent ground and structures.
Monitoring Should Include
Warning Signs
Warning criteria and subsequent actions should be established by the engineers in charge prior to excavation.
Q: What is foundation pit support?
A: Foundation pit support refers to temporary earth retention systems designed and installed to manage soil or rock movement, groundwater pressures and provide safety to workers, nearby structures and utilities. Supports can include retaining walls, anchors, soil nails, struts, drainage and monitoring instrumentation.
Q: What is the difference between foundation pit support and trench shoring?
A: Foundation pits tend to be wider, deeper and more influenced by nearby structures and groundwater conditions. Trench shoring is used for narrow, subterranean excavations. Both systems require appropriate support design based on anticipated loads and ground conditions.
Q: Can soil nails be used for deep foundation pits?
A: In some cases where staged excavations can be temporarily exposed, bond resistance can be achieved and legal rights exist for installation, soil nails could be used in deep excavations. Soil nails are not a panacea for every deep project.
Q: What is the difference between a soil nail and a ground anchor?
A: Conventional soil nails are normally passive and fully grouted. Ground anchors are generally prestressed with specified free length and bonded length. Testing and connections are different as is structural behavior.
Q: Can rock bolts be used in a foundation pit?
A: Rock bolts/rebars/dowels can be used to help reinforce rock sections. However they will not inherently stabilize soil above or help manage groundwater. Deep mixes of competent rock and weaker materials may require hybrid support designs.
Q: Can Wanfeng review complete ground anchors?
A: Wanfeng can evaluate threaded bars, plates, nuts, couplers and any components manufactured based on 2D drawings. Only if the anchor head, tendon, protection of free-length, bond zone, corrosion compatibility and testing records can be verified should “complete ground- anchor” representation be claimed.
Q: Why is groundwater important when designing deep excavations?
A: Improper groundwater management can result in seepage forces, piping, base heave, uplift, loss of soil from the bottom of the pit and movement of soil outside of the pit. Trying to lower groundwater can result in settlement of nearby ground. Control of groundwater usually requires project specific evaluation.
Q: Can Wanfeng fabricate from excavation-support drawings?
A: Yes. Wanfeng can review any material, dimensions, threads per inch, design loads, coatings, test and production methods to verify if we can supply any approved components. Responsibility for overall support design belongs to the project team.
