# An Investigation into Bol Anchoring Performance during Tunnel Construction in Bedded Rock Mass
## 3 Experimental Results
### Shear Testing  
The shear-displacement curves of different anchoring methods, which were measured by strain gages, are shown in Figure 7. The average maximum shear force values of the no-anchoring specimen, end anchoring specimen, and full-length anchoring specimen were, respectively, 3.55 kN, 15.34 kN, and 17.35 kN, as shown in Figure 8. It is evident that the maximum shear force of the end anchoring specimen was increased by 332.11% while the maximum shear force of the full-length anchoring specimen was increased by 13.10% compared with that of the end anchoring specimen. The shear-displacement curve of the no-anchoring specimen mainly shows the shear deformation process of the joint plane. Figure 7a shows that the specimen develops buckling failures as it is loaded to its ultimate load, resulting in a loss in the bearing capacity and representing a brittle feature. Moreover, the end anchoring specimen develops a \"turning point\" of a sudden drop and then a rise in shear force prior to its full yield to failure, as shown by Figure 7b. This occurrence was not observed in the other two cases. This point can be regarded as the decision point in terms of whether the bolt of the end anchoring specimen engages its shear resistant effect. Before this point, the joint plane mainly bears the shear effect. The extent of its shear stiffness mainly depends on the friction force of the plane and the pre-stressing force of the bolt. At failure, the joint plane suffered shear failures, and the specimen at both sides developed relative sliding, thus mobilizing the shear strength of the bolt itself. Therefore, this point can also be referred to as the \"yield point\" of the joint plane and the \"mobilization point\" of the bolt's shear strength. After this point, the shear strength of the bolt body enhanced the comprehensive shear-bearing performance of the joint plane. Meanwhile, the shear force increased slowly with increasing shear displacement. These are called the plastic phase and plastic strength phase [34; 43]. Others refer to them as the slowly increasing resistance phase [24]. Figure 8: Shear force of the specimens by different anchoring methods. Figure 7: Shear–displacement curves: (**a**) No bolt; (**b**) End anchoring; (**c**) Full-length anchoring. In accordance with the characteristics of the bolt resistance increase, the bolt developed plastic hinges at both sides of the joint plane. When the strength of the bolt or concrete reached its limit strength, the anchored specimen developed buckling failures. It was also observed that the patterns of the full-length anchoring specimen and end anchoring specimen's shear-displacement curves varied somewhat (Figure 7c). The bolt of the full-length anchoring specimen was in tight contact with the concrete via the anchoring agent. It could resist the shear resistance effect immediately under the load effect until the specimen developed buckling failures. The bolt of the full-length anchoring specimen and its joint plane jointly bore the shear load. No \"turning point\" developed. The same occurrence was observed in the end anchoring case. Compared to the no-anchoring specimen, the end anchoring specimen and full-length anchoring specimen represented a larger ultimate load, a more rapid and greater increase of bolt resistance, a longer plastic strength phase, and a stronger residual shear-bearing capacity after buckling. The typical strain distribution curves of the end anchoring specimen and full-length anchoring specimen segments obtained by the test are shown in Figure 9. The following can be observed from the strain distribution curves. * The maximum value of the bolt axial force is near the joint plane and is anti-symmetrically distributed at both sides of the joint plane. * The axial force of the bolt for full-length anchoring is mainly concentrated near the joint plane. It decreases rapidly with increasing distance from the joint plane, and its distribution is relatively uniform.