What are the characteristics of soil nails?

The impact of small buildings adjacent to the building. As the soil nail construction using a small step by section excavation, and in the excavation after the timely provision of soil nail and surface structure, so that the surface layer and the excavation slope close integration. Soil nails and the surrounding soil firmly bonded to the soil slope of the soil less disturbed, the impact of adjacent buildings.

Construction tools are simple and flexible construction. The equipment used for the provision of soil nails and the spraying of concrete equipment are all mobile small machinery, mobile and flexible, the required space is also small. Such machinery vibration is small, low noise, in the urban area construction has obvious superiority. Soil nailing construction speed, in the excavation process easier to adapt to different soil conditions and construction procedures.

Good economic returns. According to Western European statistics, soil nailing support than the anchor wall support program can save 10% to 30% investment in the United States, according to its soil nailing excavation patent report can save about 30% of investment. According to statistical analysis of the domestic economy 9 soil nailing works that investment can save 30% to 50%.

What is the mechanism of soil nailing?

The shear strength of the soil is lower than the tensile strength of the soil is almost negligible, but the soil has a certain structural integrity. After the soil nails with certain length and density are placed in the soil, the soil nails work together with the soil to make up the deficiency of the soil’s own strength to form the composite soil. Soil nails in the role of composite soil are:

  1. Hoop beam skeleton effect. This is determined by the stiffness of the soil nail itself, its strength, and its spatial distribution in the soil. It has the effect of restraining the deformation of the soil, and make the composite soil to form a whole.
  2. Share the role. In the composite soil, the soil nail and the soil shared the external load and soil self-weight stress, soil nails play a role in sharing. The proportion of soil nails is determined by the relative stiffness ratio of soil nail to soil, the spatial position of soil nail and the stress level of composite soil.
  3. Stress transfer and diffusion. Under the same load, the strain level of the soil nail wall is lower than that of the soil slope, thus delaying the formation and development of the cracking field.

What are the types of soil nails?

According to different construction methods, soil nails can be divided into drilling grouting soil nails, soil nails into the soil type and nail-type three categories:

  1. Drilling grouting soil nail: first drill 100 ~ 200mm diameter horizontal hole in the soil slope, and then insert the steel bar, steel bar or steel wire rope and other small diameter rod, and then fill the holes with pressure grouting to form and And the soil nails are tightly adhered around the soil nails. Finally, the connecting members connected with the end portions of the soil nails are arranged on the slope surface of the soil slope, and the shotcrete is used to form the surface layer structure, thereby constituting a self- supporting ability and capable of supporting the later- . This is the most widely used form of soil nails and can be used for permanent or temporary support works.
  2. Driven soil nails: ZSTD-150 soil nailing machine (pneumatic impact bolt machine) will steel directly into the soil. The length generally does not exceed 6m. With pneumatic soil nailing machine can enter 15 per hour. Which provides a lower friction, which requires the nail rod surface area and set density are greater than drilling grouting soil nails. However, due to anti-corrosion problem is difficult to solve, therefore, more for temporary support engineering.
  3. Injection-type soil nail: by the use of compressed air nailing machine at an arbitrary angle of choice will be 25 ~ 38mm in diameter, length 3 ~ 6m straight steel rod (or hollow steel pipe) into the soil. Soil nails can be galvanized or epoxy coated, soil nail head is usually equipped with threaded to attach the panel. This form of construction fast, economical, suitable for a variety of soil, has great potential for development.

(This article comes from 建设工程教育网 editor released)

What is Soil Nailing? Construction Guidelines and Tips

What Is Soil Nailing

Soil nailing is a technique used to bring soil stability in areas where landslides might be a problem. Soil nail can prevent landslides by inserting steel reinforcement bars into the soil and anchoring them to the soil strata. It is called Soil Nail, because it’s like having a nail being hammered into the soil, where the nails, are the steel bars.

Soil Nail Installation Process

Soil nail provides a resisting force against slope failures. Its construction process is faster than other similar methods. The construction procedure starts, drilling into the soil, where the nail, steel bar, is going to be placed. After the drilling has been completed, exact depth must be provided by the geotechnical engineer, the nail must be inserted into the drilled hole.

Then, it must be grouted into the soil to create a structure similar to a gravity wall. After placing the nail, a shot-Crete layer is usually placed as a facing material, to protect the exposed nail, and then other architectural options are placed over the shot-Crete, creating an aesthetic finish to the project.

Steel tendons typically used for drill-and-grout soil nails usually consist of 0.8 to 2.0 inch bars with a yield strength in the range of 60 to 72 Ksi. Drainage is a critical aspect of soil nail wall construction. Face drainage is virtually always used with permanent walls, and very commonly used with temporary walls.

Face drainage usually consists of synthetic drainage elements placed between the shot-Crete and the retained soil, and may be typically 8 to 12 inches wide synthetic strips or perforated pipes.

The grouted soil nail hole typically has a minimum diameter of 4 inches. Centralizers are placed around the soil nail to maintain an even thickness of grout around the bar. For permanent applications, nails may be epoxy-coated or provided with a protective sheath for corrosion protection.

Soil Nailing is not recommended to use on clayey soils, and or clean sands where the cohesion of the soil is minimum.

(This article comes from construction.about.com editor released)

Soil Nail Advantages

Soil nail walls exhibit numerous advantages when compared to ground anchors and alternative topdown construction techniques. Some of these advantages are described below:

  • Requires smaller right of wat than ground anchors as soil nails are typically shorter;
  • Less disruptive to traffic and causes less environmental impact compared to other construction methods.
  • Provide a less congested work place, particularly when compared to bracedexcavations.
  • There is no need to embed any structural element below the bottom of excavation as with soldier beams used in ground anchor walls.
  • Soil nail installation is relatively rapid and uses typically less construction materials than ground anchor walls.
  • Nail location, inclination, and lengths can be adjusted easily when obstructions (cobbles or boulders, piles or underground utilities) are encountered. On the other hand, the horizontal position of ground anchors is more difficult to modify almost making field adjustments costly.
  • Since considerably more soil nails are used than ground anchors, adjustments to the design layout of the soil nails are more easily accomplished in the field without compromising the level of safety.
  • Overhead construction requirements are smaller than those for ground anchor walls because soil nail walls do not require the installation of soldier beams (especially when construction occurs under a bridge).
  • Soil nailing is advantageous at sites with remote access because smaller equipment is generally needed.
  • Soil nail walls are relatively flexible and can accommodate relatively large total and differential settlements.
  • Measured total deflections of soil nail walls are usually within tolerable limits.
  • Soil nail walls have performed well during seismic events owing to overall system flexibility.
  • Soil nail walls are more economical than conventional concrete gravity walls when conventional soil nailing construction procedures are used.
  • Soil nail walls are typically equivalent in cost or more cost-effective than ground anchor walls when conventional soil nailing construction procedures are used.
  • Shotcrete facing is typically less costly than the structural facing required for other wall systems.

(This article comes from Deep Excavation editor released)