PRETEC NC-Bolt and Pc-Bolt
A combination bolt is installed for immediate support of rock, anchored by an expansion shell, to be fully grouted at a later stage, allowing it to be classified as permanent support. The advantage is that a single bolt is effective for immediate work protection at the face after torque tensioning, while later gaining additional corrosion protection by the grouting.
The combination bolt may be used for most ground conditions, but excluding ground subjected to strain bursting and very large contour convergence. The injected grout improves the corrosion protection provided by the plastic grout pipe and the Pc-Coat. Such bolts are therefore highly attractive for very corrosive environments like subsea tunnels. The end-anchorage with tensioning of the rebar, plastic grouting pipe and the cementitious mortar embedment creates a very stiff system offering extended durability. Any tunnel may cross zones of variable need of corrosion protection for bolts, but to classify the exposure level may be difficult. One mitigation strategy may be to use the well protected Combination Bolt along all of the tunnel length.
The NC-Bolt and Pc-Bolt may be used under most ground conditions, except when very high rock stresses may produce large radial deformations or strain bursting.
Pretec produce two types of combination bolts - NC-bolt (rebar bolt) and Pc-Bolt™(tube bolt). Product data sheets and brochures for both bolt types can be downloaded from http://www.chinapretec.com.
Included products in this EPD