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In the process of blasting excavation of rear tunnel with mall clear distance and large section, it is very important to ensure the safety of front tunnel exposed to blasting vibrations. Based on the six-lane Xiaoyu Tunnel of Beijing-Qinhuangdao Expressway, a blasting vibration velocity distribution law of the longitudinal and transverse sections of the front tunnel was monitored and analyzed during the excavation of the rear tunnel. The blasting parameters of the rear tunnel were dynamically adjusted and optimized, and the safety control measures of blasting vibration were put forward according the monitoring results. The results showed that the vibration velocity on the radial direction of the side wall of the front tunnel was the largest when the rear tunnel was excavated, and it is mainly caused by cut hole blasting. The vertical vibration velocity is slightly lower than the transverse vibration velocity. However, there is little difference between them, and the blasting vibration energy is mainly concentrated in the frequency band of 30~100 Hz. For the vibration distribution on the longitudinal section of the front tunnel, the peak vibration velocity decays with distance, but the vibration velocity on the unexcavated direction is relatively higher, which is 1.2~1.6 times of the vibration velocity on the same excavated distance. For the vibration velocity distribution on the cross-section of the front tunnel, the vibration velocity on the front side is 5~10 times higher than that on the back side. Multi-stage cutting was adopted to optimize the distribution of the holes.12 different delays were adopted to reduce the charge per delay, and the delay interval was increased to 60 ms to control the blasting vibration. The field practice shows that the optimized blasting design can reduce the vibration velocity of the side wall of the front tunnel by about 50%.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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