Nailing and Anchorage

Nailing Vs Anchorage: Nailing and anchorage are both soil stabilization methods with a few differences. The difference between these two terms is that in anchorage method we apply a pre-stress to create a tension. This way the anchorage system become more resistant against large deformations.

On the other hand, soil nailing  is  a  common practice  to  stabilize the soil walls by installing some nails. In  the first phase of nailing project, holes  are  drilled. Next, steel bars are placed into drilled holes to be secured by grouting.

The advantages of nailing and anchorage methods:

1. Increase in Shear strength of  the soil mass
2. Limitation and controlling the soil deformations in effect of increase in shear strength on slip surface because of increasing the vertical forces.
3. Decrease in slip forces on failure surface.

Nailing implementation method

Soil nailing operation starts with excavating the soil up to 1 or 2 meters. The depth of this excavation must be small enough to allow the soil remain stable for the next 24 hours. And the scope of excavation must be large enough to provide sufficient space for machinery equipment. Since the diameter and length of each nail may be different from other, the excavation team must be careful not to drill excessively.

When the holes have been drilled, we install the nails along the center line of the holes. In this stage, we need to use spacers along the nail to ensure that grout will be injected properly. By gradually inserting an injection  tube, the holes are grouted under a certain pressure. The earthen wall is covered by a layer of shotcrete to provide a temporarily support. If we leave the nails unprotected the soil pressure might causes a punching shear. As a result we must apply bearing  plate to lower the stresses and prevent punching failure. Finally, a 10 centimeters coating of concrete covers is a good idea to cover the plate and make an even durable surface.

Anchorage and implementation method

We can construct the anchorage system by using either a single bar or with steel strands. The main procedure of implementing a single bar anchorage is similar to nailing. In this method the hole is not filled with grout. Instead a hydraulic jack pulls the bar to create a tensile stress inside it. This tension is the main factor that prevents soil movements. By tightening a nut the end of each anchorage is closed.  Instead of steel bars we can use steel strands that are more suitable for higher lateral soil pressure.