ABSTRACT
In stratified ground, entries have roof spans that may be determined by beam analysis, provided the immediate roof separates from the overlying strata. This situation is often the case in softrock mines. Point anchored, mechanical bolts are the least expensive bolt type. Because of tensioning during installation, point anchored bolts provide immediate support to the roof and are also referred to as active support. Examples of distributed anchorage obtained by cementation of steel in a bolt hole are steel rods cemented along the entire bolt length with a resin compound that is mixed as the bolts are spun into holes. Bolts may also be deliberately trimmed or shortened in the course of mining; the portion remaining continues to provide support. Because stress concentration, related strain and associated displacement decay rapidly with distance from a bolt hole collar, most of the bolt load is also concentrated near the collar and diminishes rapidly along the bolt.
