The karst development of National Highway G5 Gujia Mountain Tunnel is strong. It is characterized by many deep and narrow vertical karst fissures, karst troughs, and karst ditches. Such measures as backfilling, reinforcement, and bridging were adopted for this project, and advance support with T75mm large diameter self-drilling IBO rock bolts were widely applied in the construction of this tunnel.
The 2084 m long highway tunnel has 2 lanes. The maximum buried depth is 191m.
The tunnel had to pass through over 80 karst caves since they are strongly development.
Small Diameter IBO rock bolts are normally used as advanced support. But its strength is limited, and total laying length is less than 6m. Moreover, the grouting effect is not as good as bigger diameter ones. If the gouge is big, the small diameter anchoring support can’t ensure safety, collapse might occur.
After investigation and test on site, we decided to use T75 Large diameter self-drilling IBO Rock Bolts in the application of tunneling. The IBO rock bolts were assembled with alloy drill bits, high strength plates and nuts. Since the big diameter and higher strength, the T series IBO rock bolts can prevent the mass of earth-rock from gliding.
Fig. Anchoring and grouting of T75 self-drilling IBO rock bolts
2). Water-Cement Ratio W/C=1:1, cement-water glass volume ratio=1:0.5.
3). Cement Grade:32.5.
4). Glass water baume degrees=35, module=2.4.
Large diameter self-drilling IBO rock bolts were widely used in the construction of karst tunnels. With the reinforcement support by T75 big diameter IBO anchor bolts, the tunnels can across through the 10-20m karst caves successfully. The big diameter self-drilling IBO anchors have features:
Now the highway has been opened to traffic. And Gujia Mountain Tunnel also functions well. It has been approved that large diameter self-drilling IBO rock bolt anchoring is a kind of reliable solution for tunneling.