Abstract
The rock load acting on the lining of an underground excavation is influenced by multiple factors, including rock type, rock mass condition, depth, and construction method. This study focuses on quantifying the magnitude and distribution of the radial loads on the lining of a deep shaft constructed in hard rock by the so‐called short-step method. The blasting‐induced damage zone (BDZ) around the shaft was characterized using ultrasonic testing and incorporated into the convergence‐confinement method (CCM) and 3D numerical analyses to assess the impact of BDZ on rock loading against the liner. The results show that excavation blasting of shafts is an important controlling factor for the degradation of the rock mass, while the orientation and magnitude of the principal stress had a minimal influence on the distribution of blast‐induced damage. The analysis shows that increasing the depth of blast damage in the walls can increase the loads acting on the lining, and the shear loads acting on the liner could be significant for shafts sunk by the short‐step method in an area with anisotropic in situ stresses.
Highlights
Vertical ventilation shafts are passages widely used in mines and tunnels to provide fresh air underground and to remove exhaust or smoke in case of a fire [1,2,3,4]
In some extralong tunnels constructed in China, such as highway tunnels in Nibashan (10 km), Mi Cangshan (13.8 km), and Zhong Nanshan (18 km), vertical ventilation shafts were set in the middles of the alignments. ese vertical shafts, extending hundreds of meters deep, are often constructed in mountainous terrain; such shafts and shafts constructed in soft ground differ greatly with respect to the construction method and lining design
E ultrasonic test results are shown in Figure 9. e results illustrate that the rock mass surrounding the shaft can be divided into two different zones according to the P-wave velocity (Vp). e region with P-wave velocity values on the order of 2.8 km/s is referred to as the blasting-induced damage zone (BDZ)
Summary
Vertical ventilation shafts are passages widely used in mines and tunnels to provide fresh air underground and to remove exhaust or smoke in case of a fire [1,2,3,4]. As the shaft excavation advances and the shaft bottom moves close to the section under consideration, the radial ground displacement increases and the effective support pressure (associated with three-dimensional face advance effects) decreases. Verma et al [37] carried out field investigations at different tunnels to study blast-induced damage for a wide range of rock mass qualities. Previous studies investigating the loads acting on shaft linings consider the displacement and stress distribution around the shaft, but the impact of the blast-induced damage is not taken into account [38,39,40]. The excavation and lining design for a vertical shaft at this depth relies heavily on empirical methods that consider the mechanical properties of the rock masses along the shaft alignment.
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