Issue 41

L. Zhang et alii, Frattura ed Integrità Strutturale, 41 (2017) 356-368; DOI: 10.3221/IGF-ESIS.41.47 364 Figure 5 : Surrounding rock release rules. Figure 6 : Largest vault settlement displacement. According to Fig. 6, the largest vault settlement displacement of surrounding rock, shotcrete added with the new liquid accelerator is smaller than that when the shotcrete added with the traditional accelerator interacts with surrounding rock, indicating that the shotcrete added with the new liquid accelerator has better supporting effects for surrounding rock. Take an average of the largest settlement displacements of 8h, 12h, 1d, 3d, 7d, and 28d surrounding rock. This value is 3.59 when the traditional accelerator is used while it is 2.66 when the new liquid accelerator is added, which improves supporting effects by 26%. In the first three days of shotcrete support, the largest vault displacement of surrounding rock keeps growing. That is because the tunnel surrounding rock releases stress and forms new stress equilibrium. The release process is accompanied with vault settlement. From 0 to 72h, the largest vault displacement is 3.17 mm during spraying concrete support added with the traditional accelerator while that is 1.84 mm during spraying concrete support added with the new liquid accelerator, with the change rate decreased by 42%. Three days later, stress release of surrounding rock is reduced, meanwhile, the vault settlement is reduced and surrounding rock tends to be stable due to the support. On the 28th day, the largest settlement displacement is 3.82 mm when shotcrete added with the traditional accelerator, and it is 2.41 mm when shotcrete added with the new liquid accelerator, reduced by 37%. (2) Distribution of surrounding rock plastic zones 12h, 1d, and 3d plastic zones are selected to study the development of plastic zones of surrounding rock supported by different kinds of shotcrete. According to analysis on Fig. 7 to 12, the surrounding rock plastic zones are mainly distributed on the cavern haunch and side wall. With the passage of time, the plastic zone gradually extends to the tunnel deep and arch springing. It also can be seen from the figures that the plastic zone of surrounding rock supported by shotcrete added with new liquid accelerator is obviously smaller than that of surrounding rock supported by shotcrete added with the traditional accelerator. 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 0 18 36 54 72 90 108 126 144 162 180 Surrounding rock stress release rate Excavation time/h