关键词: 特长隧道, 多工作面爆破, 横洞交叉口, CO体积分数, 叠加效应, 数值模拟, 三维评价体系

Abstract: During collaborative blasting construction across multiple working faces in extra-long tunnels, the spatiotemporal superposition of carbon monoxide (CO) at cross-hole intersections causes excessive local volume fractions and prolonged exposure. To address these challenges, the correlation among blasting interval, blasting sequence, and pollutant superposition effect is investigated. A case study is conducted in the No. 1 transverse tunnel of an extra-long railway tunnel with a parallel guide working area. A comprehensive method combining field measurement, numerical simulation, orthogonal testing, and evaluation system construction is adopted. Four monitoring sections were arranged on site to obtain CO volume fraction evolution data, and a three-dimensional numerical model was established using Fluent software. A two-factor, three-level orthogonal test was designed, with blasting intervals of 3, 5, and 10 min and blasting sequences of a-b-c, b-c-a, and c-a-b（a, b, and c refer to working face）. Subsequently, a three-dimensional “strength-time-concentration” evaluation system was established to quantify the primary influencing factors using the entropy weight method and range (min-max) normalization. The results show that: (1) The peak superposition coefficient is the dominant factor affecting the superposition effect, whereas the blasting sequence primarily controls the peak volume fraction and the time exceeding the standard. (2) According to the three-dimensional evaluation and entropy weight method results, the c-a-b blasting sequence with a 3-min interval has the best comprehensive score. (3) Considering the cumulative concentration control benefit, the c-a-b blasting sequence with a 10-min interval is recommended. (4) The three-dimensional evaluation system can finely quantify the superposition effect. The proposed synergistic strategy of “prioritizing blasting sequence optimization and blasting interval regulation” can effectively weaken the pollutant superposition effect and provide theoretical support and engineering reference for pollutant safety control in multiface intersection construction of extra-long tunnels.

Key words: extra-long tunnel, multiple working face blasting, cross-hole intersection, carbon monoxide volume fraction, superposition effect, numerical simulation, three-dimensional evaluation system