Application of hollow bar and solid bar in different formations

Time:2021-04-27From:sinorock View:

Hollow bar and solid steel bar are two different anchoring forms. Therefore, installation procedure depends on the ground conditions and borehole stability, rather than space constraints.

In loose or collapsed formations, self-drilling hollow bar is the best solution. Due to this solution solves casing demand, it can be installed quickly and grouted simultaneously. In water-bearing rock formations, casing can easily get stuck, so self-drilling anchor system is the most practical solution.

Although the variety of drill bits has broadened the range of hollow anchor bar applications, self-drilling rock bolt is not suitable for all geological conditions. Drill bit selection includes clay bit for soil, tungsten carbide button bit for rock formations, and other types of bits.

In tight rock formations, the DTH drilling method is more efficient, and solid threaded steel bars are generally used. The drill bit in self-drilling anchoring system is disposable. Compared with standard bit, it is suitable for rock holes up to 5m deep and not suitable for deeper drilling.

In wet clay formations, solid threaded rebar will be selected because problems can arise when drilling with self-drilling anchor. Under wet clay formation, drill cuttings will get stuck in the hole, resulting in borehole plugging and flushing blocked. Usually using the auger to drill and solid bar for support.

Self-drilling hollow bar can be used in wet clay formations if there is a nozzle on the drill bit. If a high water-cement ratio (w/c 0.9 or similar) is used for high-pressure flushing, jetting fluid will be generated at the drill bit. This causes the clay to liquefy and then wash out of the borehole. The system also requires a high-pressure grouting pump to handle a large amount of rinse fluid at the borehole.

Although self-drilling rock bolt has obvious advantages in loose or collapsed formations, it cannot provide an effective drilling effect in wet clay or tight formations, where the solid bar is more effective.

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