Civil Engineering Reference
In-Depth Information
The use of SN anchors, resin anchors, friction pipe anchors and expansion shell an-
chors requires that the boreholes in which they are to be installed are stable. Figure
20.12, for example, shows the working steps for the installation of a SN anchor.
In unstable boreholes, injection drill bolts are used consisting of a drill bit and an
anchor pipe made of threaded high-strength steel bar with sleeve connections (Fig.
20.11). After the bolt is drilled to the desired depth (Fig. 20.13, upper), the bond
between the bolt and the rock mass is accomplished by injecting cement-based
suspension via injection openings in the drill bit and the anchor pipe (Fig. 20.13,
lower). In this way, the loosened rock mass surrounding the borehole is grouted
and stabilized.
Figure 20.13
Installation of an injection drilling bolt (Wittke et al. 2002)
Anchor rods made of steel and glass-fiber-reinforced synthetics with different
strengths and cross-sections are provided by manufacturers. The advantages of glass
fiber anchors over steel anchors lie mainly in the fact that they can be cut as well as
bent.
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