The Application of the Self-drilling Soil Nail in Railway Slope

Soil nailing is a new technology used for foundation pit excavation and slope reinforcement. Economical, reliable, quick, and easy construct, it has been rapidly promoted and used in many countries. Except as temporary support when excavating the foundation pit, it can also be used as a permanent earth retaining project with reliable performance.

Anti-corrosion

For permanent support, soil nail rust resistance and durability should be considered.

Increase the section of soil nail reinforcement. That is, according to the site conditions, predict the corrosion rate of the steel bar, determine the possible maximum corrosion depth according to the specified service life, and add it to the diameter of the soil nail steel bar.

Apply zinc or epoxy to the rebar surface to increase rust resistance. However, this method also needs to consider the corrosion rate and increase the cross-section, and this coating is easily damaged by impact, and it is also difficult to handle at the joint.

A protective layer of cement mortar. That is, general grouting nails are used, and the thickness of the protective layer is not less than 30-40mm. Since the soil nails will cause the mortar protective layer to crack, the corrosion rate still needs to be considered, and the cross-section of the steel bars should be appropriately increased.

Use envelope anti-rust nails. Add plastic corrugated casing outside the steel bar, the wall thickness of the casing is not less than 1mm, leave a gap of not less than 5mm between the casing and the steel bar, and inject cement slurry, and the casing and the drill hole are still filled with grouting. This method is the most reliable.

Drainage Facilities

(1) Remove the loose earth and stone on the top of the slope and make a gutter.

(2) In order to facilitate the seepage of water from fissures in the mountain, PVC drainage pipes (2/3 of the pipe wall are opened at a certain interval, with a diameter of 10mm and a spacing of 50cm are arranged in a staggered manner, and covered with permeable geotextiles). The camber angle is 5°, and the hole diameter and hole depth are determined according to the stratum conditions and the height of the slope.

(3) The surface should be trimmed and sealed to prevent surface water from infiltrating into the ground or flowing into the slope.

Excavation

(1) During construction, excavate in layers from the top of the cutting, each layer of soil slope excavation is controlled at 2-3m, and the rock slope can be appropriately increased. When the rock slope is excavated to 2m from the design slope surface line, small blasting is used, supplemented by manual trimming of the slope surface.

(2) When excavating according to the design slope rate, try to make the excavation surface as flat as possible. After the earthwork excavation is completed, the slope surface shall be repaired in time, and the slope collapse and over-excavated large pits shall be embedded in time with rubble, and the flatness deviation shall be controlled within ±20mm.

(3) When the composite support of soil nails and row piles is used, after the concrete strength of the pile body reaches more than 70% of the design strength, the pile body should be inspected for no damage at 40%.

(4) During mechanical excavation, it is strictly forbidden to over excavate or cause the slope to loosen. The slope should be cut with small tools or shovels and shovels.

(5) Minimize the exposure time of the slope, spray the first layer (5cm) of concrete after the slope is formed, and carry out support construction immediately.

The following measures are taken for the soil layer that is prone to collapse: spray the concrete surface layer immediately after excavation, drill holes, and set soil nails after solidification; Smaller segment length segment jump excavation and support; advance steel pipe or a steel bar in advance before excavation.

As a permanent project, soil nailing support has not only been applied in highway, water conservancy, and urban construction but also has been successfully applied in railway construction. In the past, the railway slopes were mainly constructed with materials such as stone or concrete and were used to use gravity retaining walls. The structural reliability was low, and there were many diseases after delivery and operation. The new technology of soil nailing is adopted to reduce the amount of engineering and material consumption, and can well achieve the goal of slope reinforcement. The combined application of soil nailing support technology and other support technologies is feasible for the support of high slopes and has a wide range of application values.