An experimental study on the anchoring characteristics of an innovative self-swelling Split-set

Abstract

In order to improve the anchorage performance of conventional Split-sets, an innovative self-swelling Split-set is proposed in this paper. The structure of the rockbolt is introduced and the anchorage mechanism discussed. The self-swelling roll length, position and spacing are optimized based on laboratory pull-out tests. The experimental results indicate that the maximum load capacity and the energy absorption capacity at 200 mm displacement of the self-swelling Split-set are 92 kN and 16.8 kJ respectively when five 10 cm long self-swelling rolls with a 10 cm spacing are placed at the tail of the rockbolt. The time-dependent characteristics of the rockbolt using the optimized structure parameters show that the anchorage force of the rockbolt reaches 74.2% and 96% of the load capacity 12 and 24 h after installation respectively and the corresponding energy absorption capacity is 73.8% and 100% of the maximum energy absorption capacity respectively. The field pull-out test results show that the self-swelling Split-set provides an anchorage force of 92 kN 24 h after installation and the rockbolt can slide with a constant resistance. For comparison, a conventional Split-set of the same size provides only a maximum load capacity of 43 kN and its anchorage force decreases gradually once it slides. The results from the long-term monitoring of the surface displacement and axial force of the rockbolt in an experimental tunnel show that the rockbolt has a better anchorage performance than conventional Split-sets. The self-swelling Split-set takes the advantage of the radial expansion pressure induced by the hydration reaction of the self-swelling rolls to increase the contact force between the rockbolt and the borehole walls, which greatly improves the anchorage force and the energy absorption capacity. In addition, it is simple to install and the unit cost is low.