The present study aims to determine the effect of rock bolts on the behavior of a rock joint through physical experiments. A rock analog material and bamboo were selected to simulate the rock material and rock bolts respectively. Considering different anchoring angles, anchoring position and anchoring density, a series of uniaxial experiments were carried out in the laboratory. On the basis of these test results, several laws were found. (1) Installing bolts in the middle of the crack was more efficient in improving peak strength than at the end; (2) It was better to install bolts perpendicular to the loading direction; (3) When the number of bolts reached a certain amount, the anchoring effect would not be further enhanced.
Jointed rock masses are very common in rock engineering [1,2]. With the excavation, the original cracks propagate, coalesce and loosen the rock mass. Therefore, the surrounding rock mass may fail and threaten the safety of engineering structures on and in rock [3-5]. Fortunately, rock bolts can mitigate this problem efficiently. Rock bolts bind the rock mass into an integral unit which interacts through the so called suspension function, combination beam function and dowel function [6, 7]. Besides, the normal stress and shear stress near the cracks provided by rock bolts, they also prevent cracks from propagating [8, 9]. So, the bearing capacity of the rock mass is promoted. Compared to the wide use and efficient anchoring effect observed in practice, mechanistic studies of rock bolts are meager. So far, the anchoring mechanism can not be interpreted very well. To utilize the rock bolts better, it is necessary to make the mechanism clear. In this paper, physical tests were performed to study the characteristic of anchored samples with different anchoring angles and anchoring positions.
To simulate the rock material, several principles should be considered.
The grout material was mixture of barite powder and rosin alcohol solution. The weight ratio was barite: rosin: alcohol=1:0.1:0.2.
Ratio of tensile strength to compressive strength
The sample was in parallelepiped shape. The crack runs through the sample and with an angle of 45 degree to the loading axes.With such consideration, a kind of mixture was chosen, which was developed by Shandong University of China. This kind of material was composed of barite powder, ferrous powder, quartz sand, rosin, alcohol and plaster powder.
The choice of rock bolt material was always a key point, because it was hard to meet all the analogy theory for the mechanical parameters. With reference to literature and trial testing [10-13], a kind of bamboo was selected to simulate the rock bolt. The mechanical parameters of the bamboo were E=10.10GPa,st = 132.05MPa. The diameter of bolt and hole were 2.5mm and 3.5 mm respectively.