Rock Bolt is one of effective supporting methods to reinforce foundation of civil construction. It relies on bonding strength between soil layer and rock bolt structure to provide bearing capacity. It is widely applied in engineering structures which needs stress to transfer in stable soil body.
The fundamental principle of geotechnical anchoring is to transfer tension of structures or keep self stability of excavation face in stratum, relying on shearing strength of self drilling rock bolt’s surrounding stratum.
As self drilling bolt’s raw material, seamless steel tube’s quality must be completely inspected according to product standard and technical specification. Specific inspection includes steel tube’s chemical component analysis, geometric dimension inspection, surface quality inspection, physical and chemical properties inspection, processing property inspection, metallographic analysis, thread inspection and measurement. The purpose is to ensure quality of steel tube and meet relevant standard code or technical condition requirement.
During tunnel construction, deformation often happens. Observing from tunnel surface, there are cracks, shedding phenomenon or underground water dropping appearing. If reason doesn’t get analyzed and maintained timely, worse deformation will happen.
Self drilling anchor system’s inclination should be 15°~25° horizontal downward, no large than 45°. With increase of inclination, horizontal component of self drilling anchor system decreases. Too large inclination will reduce anchoring effect and increase vertical component on supporting structure, which will also cause settlement of retaining structure and surrounding foundation. To use self drilling anchor system’s pulling resistance effectively, self drilling anchor system should parallel with direction of side pressure effect.
The TBM boring the Los Condores Hydroelectric Power Plant has completed the 900m access tunnel and is working on the first section of the headrace tunnel. The machine, a 4.56m Robbins double shield, has so far excavated 1,300m.
The 6.7km long, 9.9m diameter twin Bolaños rail tunnels have been completely bored on the Madrid-Galicia High-Speed Line for client in Spain.
During urban engineering construction, loose stratum with scree and gravel has often been encountered and mortar rock bolt is often used. But it is easy to happen hole collapse, difficult to insert and other problems, then casing pipe should be needed, which reduces construction efficiency. On the other hand, slurry will not full and supporting effect is poor. While SDA bolt can overcome problems during installation and grouting of urban loose stratum.
In soft rocks or soil, the fiction force of self drilling bolt’s hole wall is less than the bond stress of slurry, so the ultimate load of self drilling bolt depends on the biggest fiction force of anchorage section’s stratum.
Hollow anchor bolt’s designed tension is mainly depended by possibility, reliability and convenience of construction technique.