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

Time:2022-09-24From:sinorock View:

Soil nailing wall is a very common supporting structure in foundation suppport and slope engineering. The soil nailing wall needs to be reaonably arraged 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 will introduce the design and layout of the soil nailing wall.

self drilling anchor bolt in soil nail

Soil Nailing Wall 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 nailing arrangement is usually a staggered arrangement of squares, rectangles, triangles, or in the case of limited locations, irregular arrangements, which are described in detail below.

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 soil nailing wall and the selection of 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.

Considerations

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.

Self-drilling soil nailing construction - grouting while drilling

1. Earthwork excavation and drainage

2. Mix the cement slurry and send it to the drilling zone

3. Install the first anchor bolt. After the bolt is drilled, install the coupler and centralizer.

4. Install the next self-drilling anchor bolt and continue drilling until the designed drilling depth is reached

5. Seal the drill hole.

6. Install the plates and nuts

Conclusion

A successful foundation project must have at least three conditions: a correct support scheme; an advanced design concept; a well-trained construction team. At the same time, attention should be paid to the geological, and hydrological conditions of the construction site and the surrounding environment of careful investigation, according to the ground characteristics of the site and the surrounding environment to work out an economic and reasonable targeted support scheme.

With rich experience in geotechnical anchoring service, Sinorock is committed to providing customers with systematic solutions including application technology consultation, project investigation, product selection, construction equipment supporting, sample testing, etc., to improve construction efficiency and reduce the overall comprehensive costs.

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