Experimental study on degradation behaviors of rock bolt under the coupled effect of stress and corrosion

The corrosion of rock bolts buried in rock and soil layer is obviously different from that of general ground structure. The main corrosion sources of the latter come from the air and the corrosion sources of rock bolts are not only from the air, but also the rock-soil body and groundwater. At the same time, the corrosion of rock bolts is under the stress state in practical engineering. To study the stress-corrosion effect of grouted rock bolts, using a self-developed rock bolt stress corrosion device, corrosion tests were conducted under different working stresses (10 kN, 35 kN and 60 kN), corrosion environments (5% Na2SO4, 1.5% NaCl + 2.5% Na2SO4 and 3% NaCl) and corrosion times (3 d, 7 d and 14 d). The results show that the NaCl solution is more corrosive than the Na2SO4 solution for the grouted rock bolts with more rust productions. The maximum tension of rock bolts under the condition of no corrosion reaches 60.16 kN, and under the T-60-A-14d working condition, the maximum tension of rock bolts is only 3132 kN. Compared with the condition of no corrosion, the maximum tension of grouted bolts is lowered by 25%-50% under the different working stresses and corrosion conditions. The maximum difference values of the relative bonding strength of rock bolts is 14.9% under corrosion time, 13.1% under working stress and 9.4% under corrosion environment. It shows that the corrosion effect of the rock bolt under the corrosion time is the most significant, and the working stress is second. The influence of the corrosion environment on the bonding strength of the grouted rock bolts is the least important The slip curves of the rock bolts under the environment of no corrosion have an obvious rising stage, and uplift of tension accounts for about 62.9% of the maximum tension. The final residual tension is stable at approximately 25 kN. The bonding slip curves of corroded rock bolts, of which the "initial tension rising stage" almost disappears, demonstrate a trend of steady decline. The minimum final residual tension is less than 10 kN (T-35-B-144). The larger the working stress is, the more significant the degradation effect of anchor tension is. It is shown that the current test and study on the corrosion of anchor bolts can not accurately reflect the corrosion law of rock bolts in practical engineering if only the material or the axial force with small value is applied. The influence of stress on the corrosion test of rock bolts can not be ignored. (C) 2019 Elsevier Ltd. All rights reserved.