How to Design Soil Nailing Walls? Common Arrangements of Soil Nails.

Time:2023-12-09From:sinorock View:

Introduction

Soil nailing wall is a prevalent supporting structure in foundation support and slope engineering. The soil nailing wall needs to be reasonably arranged to have a good supporting effect. The layout of soil nailing walls is related to geology and slope gradient. The spacing between the soil nails, tilt angle, length, and material of soil nails are also crucial. This article aims to examine the design of soil nailing walls, exploring their advantages, disadvantages, applications, layout requirements, common arrangements, construction procedures, and precautions.

self drilling anchor bolt in soil nail

What is Soil Nailing Walls?

Soil nailing walls are a form of geotechnical construction where reinforcing elements, typically steel bars or steel pipes, are installed within a slope or excavation. These elements, referred to as soil nails, work in conjunction with the soil mass to create a stable structure. The soil nails are installed at a specific angle, depth, and spacing to counteract external forces and prevent slope failure.

Advantages and Disadvantages of Soil Nailing Walls

Advantages

1. Cost-Effective: Soil nailing is often more cost-effective than traditional retaining wall methods, especially in challenging terrains.
2. Versatility: Suitable for a wide range of soil types and slope gradients.
3. Minimal Disruption: Construction is typically less disruptive compared to other methods, making it ideal for urban areas.
4. Quick Installation: Soil nailing walls can be constructed quickly, reducing project timelines.
5. Adaptable to Existing Structures: Can be used to retrofit existing structures facing slope stability issues.

Disadvantages

1. Limited Height: Soil nailing walls are suitable for moderate to high slopes but may not be appropriate for extremely high retaining walls.
2. Corrosion Concerns: Steel elements may corrode over time, requiring proper corrosion protection measures.
3. Geotechnical Challenges: Success is highly dependent on accurate site evaluation and understanding of geological conditions.
4. Specialized Construction: Requires skilled labor and specialized equipment.

Application of Soil Nailing Walls

Soil nailing walls find extensive application in various engineering scenarios:

1. Slope Stabilization: Prevents slope failure in hilly or mountainous terrains.
2. Retaining Walls: Provides support for excavations and retains soil masses.
3. Tunnel Portals: Stabilizes tunnel entrances in hilly regions.
4. Bridge Abutments: Offers stability to embankments supporting bridge structures.
5. Excavation Support: Provides lateral support during deep excavations.

How to Design Soil Nailing Walls? Layout Requirements

1. Soil Nailing Wall Slope Gradient

The height, length and wall conditions of the construction project will affect the design of the soil nailing wall. The slope is generally 1:0.2-1:0.5, and should not be greater than 1:0.1. It is also necessary to consider whether the soil nailing wall needs to be segmented. If the excavation is stratified, it is usually 300-500mm below the soil nailing position.

2. Soil Nails Spacing

The spacing between soil nails includes vertical and transverse spacing. The vertical spacing of soil nails should correspond to the excavation depth of each layer, and the lateral spacing is generally 1.2m-2.0m. The spacing in soft soil can be set less than 1.2m, or 1.5m in most cases.

3. Shape of Soil Nail Arrangement

The arrangement of soil nails, usually in squares, rectangles, triangles, or irregular patterns, but depends on site constraints and project requirements. Staggered arrangements are common in limited locations, providing enhanced distribution of pressure.

4. Tilt Angle of Soil Nail

The angle of the soil nail is to ensure that slurry can flow from the drill hole to the bit. If the bit is in a hard, deep soil layer, the angle of the soil nail should be increased. The angle between the soil nail and the horizontal direction is usually 10-20°, and the general inclination Angle is 15°. Too small an inclination angle will result in voids in the grouting and insufficient protective layer thickness.

5. The Length of the Soil Nail

The length of soil nails should be 0.5-1.2 times the height of soil nailing wall support, according to the rock and soil density and rock hardness appropriately adjusted or reduced; For soft plastic adhesive, the top soil nail should be appropriately lengthened, generally 9m, 12m.

6. Material Type of Soil Nail

Soil nails are usually made of steel or steel pipes. Steel bars are generally used in 16-32mm diameter of the second, and third-class steel bars. The steel pipe diameter is generally not less than 48mm, wall thickness is not less than 3mm.

7. Geological Characteristics

It is necessary to conduct a comprehensive evaluation of geological conditions, soil shear resistance, groundwater position and level, and then the design of the soil nailing wall and the selection of the soil nailing anti-corrosion process.

Common Arrangements of Soil Nails

1. Square Arrangement

Square arrangement refers to the arrangement of soil nails at the corners of the square. This arrangement facilitates the construction of vertical joints in shotcrete surfaces or the installation of precast concrete panels. In addition, the square pattern facilitates continuous vertical installation of composite drainage strips. In engineering applications, the square arrangement is usually used.

2. Stagger Arrangement

Staggered placement of soil nails can make the distribution of earth pressure in the soil more uniform, and enhance the arch effect of soil, which is conducive to support. The triangle-shaped arrangement of soil nails can reduce the load of soil redistribution on the slope. However, for the high soil nailing wall, it is difficult to establish a vertical and continuous drainage system corresponding to the foundation drainage ditch, which needs to be selected according to the actual situation.

self drilling soil nail

Soil Nailing Wall Construction Procedure

The construction process of the soil nailing wall must be stratified from top to bottom, and the steel mesh shotcrete panel is formed to constrain the deformation of soil between soil nailing walls. The construction process of soil nailing wall is usually as follows:

1. Lay out the construction survey cable
2. Excavation
3. Trim the slope
4. Drill holes, insert anchor bars or rebars, and then grout.
5. Hang steel mesh and shotcrete
6. Curing of concrete surface
7. Dig and repair the slope to the lower level, and then repeat the above steps until to the foundation bottom.

Precautions in the Construction of Soil Nailing Walls

1. Slope Construction: Earthwork excavation and soil nailing support processes should be closely coordinated, and construction should be carried out in strict accordance with the principle of stratified and segmented excavation. After excavation of a section, the slope should be repaired manually in time, and timely support should be provided after achieving the flatness required by the design.
2. Soil Nailing Construction: After the grouting pipe is pulled out, if there is cement slurry overflow at the empty mouth, the hole should be filled in time and the grouting stopper should be set at the hole mouth.
3. Shotcrete: The thickness of shotcrete is 100mm. Spray should be from bottom to top, and spray head and spray surface should maintain vertical.

Conclusion

In conclusion, the successful design and construction of soil nailing walls require a combination of a correct support scheme, advanced design concepts, and a well-trained construction team. Careful consideration of geological and hydrological conditions, along with thorough site investigations, is paramount. Soil nailing walls, when designed and executed meticulously, offer a reliable and cost-effective solution for slope stabilization and excavation support.

With a commitment to providing systematic solutions, Sinorock brings rich experience in geotechnical anchoring services. Sinorock offerings encompass application technology consultation, project investigation, product selection, construction equipment support, sample testing, and more. By focusing on improving construction efficiency and reducing overall costs, Sinorock contributes to the success of geotechnical projects.

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