Soil Nailing for Slope Stabilization: An Overview
Soil nailing is an in-situ reinforcement technique by passive bars which can withsand tensile forces, shearing forces and bending moments. This technique is used for retaining walls and for slope stabilization. Its behaviour is typical of that of composite materials and involves essentially two interaction mechanisms. The soil-reinforcement friction and the normal earth pressure on the reinforcement. The mobilization of the lateral friction requires frictional properties for the soil, while the mobilization of the normal earth pressure requires a relative rigidity of the inclusions.
A landslide (landslip) is a geological phenomenon that comprises a wide range of ground movements, such as rock falls, deep failure of slopes etc. Landslides can occur in offshore, coastal and onshore environment. It can be controlled by the use of proper slope stabilization techniques. Soil stabilization is a term in which the natural soil is changed in order to meet the engineering purposes by means of physical, chemical, biological and combined method of either two of them or all three. Weight bearing capacity and the performance of the in-situ soil and sand can be increased by soil stabilization techniques . Soil nailing is an advance technique of slope stabilization amongst other techniques. Soil nailing is the technique used in slope stabilization and excavation with the use of passive inclusions, usually steel bars, termed as soil nail. Soil nailing is typically used to stabilize existing slopes or excavations where top-to-bottom construction is advantageous compared to other retaining wall systems . Soil nails are structural reinforcing elements installed to stabilize steep slopes and vertical faces created during excavations. Commonly used soil nails are made of steel bars covered with cement grout. The grout is applied to protect the steel bars from corrosion and to transfer the load efficiently to nearest stable ground. Some form of support, usually wire mesh-reinforced shotcrete, is provided at the construction face to support the face between the nails and to serve as a bearing surface for the nail plates.
ORIGIN OF THE SOIL NAILING TECHNIQUE
The soil nailing technique was developed in the early 1960s, partly from the techniques for rock bolting and multi-anchorage systems, and partly from reinforced fill technique (FHWA, 1998). The New Austrian Tunneling Method introduced in the early 1960s was the premier prototype to use steel bars and shotcrete to reinforce the ground. With the increasing use of the technique, semi-empirical designs for soil nailing began to evolve in the early 1970s. The first systematic research on soil nailing, involving both model tests and full-scale field tests, was carried out in Germany in the mid-1970s. Subsequent development work was initiated in France and the United States in the early 1990s.
• Tunnelling Method in the 1960’s.One of the first applications of soil nailing was in 1972 for a railroad widening project near Versailles, France, where an 18 m (59 ft) high.
• In Germany, the first use of a soil nail wall was in 1975.
• The United States first used soil nailing in 1976 for the support of a 13.7 m deep foundation excavation in dense silty sands.
• In India use of soil nailing technology is gradually increasing and guidelines have been made by IRC with the help of Indian Institute of Science, Bangalore.