◤ Description

Slope stability depends on the following factors:

• slope angle
• characteristics of the soil
• the presence of groundwater
• loads from structures on the slope
• retaining structures

A slope or retaining wall may require strengthening in the following cases:

• construction of a building on a slope
• slope cutting during road construction at the bottom of the slope
• deterioration of soil characteristics under the impact of natural processes (strong wind, water)
• destruction of old retaining walls and other engineering structures

All this reduces the slope stability; therefore, some extra engineering solutions are required.

For slope stabilization, the following engineering structures may be used:

• concrete retaining walls
• piled retaining walls
• ground anchors
• soil nails
• soil stabilization in the sliding area
• installation of the drainage system
• gabions

Below, we discuss slope stabilization using ground anchors or soil nails in more detail.

A ground anchor is an inclined pile, which prevents the failure of a retaining wall or a slope. The ground anchor has the free length and the root.

In the free length part, the anchor rod is isolated from cement and enclosed in a plastic pipe. In the anchor's root, special bell-outs ensure good adhesion of the strand to cement. Due to the free length, the load is transferred directly to the anchor's root, without affecting the risky sliding of the slope.

First, pre-drilling of a borehole is performed with flights augers or using casing pipes for protection. Then an anchor rod is run in the borehole. Then the borehole is filled with cement grout through a grouting lance.

The anchor rod consists of several strands (steel seven-wire ropes). The number of strands is selected depending on the load on the ground anchor. Each strand can withstand a force of about 20 - 22 tons. Usually, anchors have from 3 to 7 strands, which enables them to withstand a load of 60 - 150 tons.

◤ _metods

Unlike ground anchors, a soil nail does not have a pronounced free length. The soil nail takes load along its entire length.

The most common practice is to install soil nails in a grid-like pattern with an interval of 1.5 - 2 m over the entire area to be stabilized. The length of the nails must be greater than the slope sliding triangle. The measures above are designed for reinforcing the slope soil and improving its overall stability. Usually, nails are made using Titan technology.

A soil nail with a Titan threaded rod is installed within a single stage, where drilling, reinforcement and soil grouting occur simultaneously. When drilling is completed, the tubular threaded rod is left in the soil nail.

Drilling is performed with tubular threaded rods. Due to their knurled screw-like surface, the rods show excellent adhesion to the cement. Threaded rods may be 1, 2 and 3 meter long. The rods are connected to each other by couplings. So, the soil nail can be of any length.
After 7-14 days, the nails are fixed with an anchor plate and a nut.
Sometimes the nails are connected with a wire mesh.
Geotextile mats with grass seeds are laid on top of the mesh to reduce surface erosion and make the slope look aesthetically pleasing.

Concrete cantilever retaining walls are usually used to form a new slope. Retaining walls of this type have a footing, which makes them stable.
That's why a cast-in-place retaining wall is first erected, and after that, the angle necessary for the slope stability is filled and formed.
Cantilever retaining walls are not suitable for stabilizing the existing unstable slopes, because their installation would require additional excavation of slopes. However, they are a good option when forming a new slope.

In case of a slope consisting of homogeneous loose soils, rotational failure is usually observed. If there are stable semi-rocky soils, the collapse can occur following a straight-line or broken-line pattern.

Stability analysis is performed using various methods in the software

• GeoStab
• Plaxis
• Slope Stability, Nailed Slope (Geo 5)

Slope analysis takes into account the seismic, loads and stages of construction.

Slope stability analysis is performed by several methods and then the smallest stability factor value is selected:

• Fellenius method
• tangential force method
• Janbu method
• Bishop method
• Morgenstern-Price method
• Spencer's method
• Shahunyants method

We are ready to perform slope stability analysis in state-of-the-art software. If the analysis shows that the slope is unstable, we will select the engineering solution required for slope stabilization and develop the respective design documentation.
We are ready to perform initial slope stability analysis for one section free of charge.

Feel free to contact us!