1. State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China 2. China Railway Southwest Research Institute Limited Company, Chengdu 611731, China 3. Zhaotong Zhaolu Expressway Investment and Development Limited Company, Zhaotong 657000, China
Numerical simulation and on-site testing methods were used to analyze the diffusion law of dust and CO during the ventilation process of high-altitude tunnel construction by relying on the Mangkang Mountain Tunnel Project of the Sichuan Tibet Railway in order to analyze the diffusion law of pollutants during the ventilation process of high-altitude tunnel construction. Results show that dust mainly diffuses towards the outside of the tunnel in the form of wall-adhering flow, and it accumulates into ‘dust clusters’ during this process. Dust diffusion is mainly influenced by gravity and causes sedimentation. Excessive wind speed in the tunnel is not conducive to reducing dust mass concentration. CO migrates in the form of ‘air masses’ from the vicinity of the palm face to the entrance of the cave. The volume of CO air masses gradually expands during the migration process, and the mass concentration peak continuously decreases, gradually forming a ‘U-shaped’ distribution trend. The on-site test results of CO mass concentration basically accorded with the numerical simulation results. The CO mass concentration in the tunnel will increase as the altitude increases, and the time it takes for the CO mass concentration at the same location in the tunnel to meet the standard requirements will increase. A formula for calculating the correction coefficient of CO mass concentration during tunnel ventilation was derived based on altitude, which is a good supplement to the altitude correction coefficient of CO in the current specifications.
Fig.5Schematic diagram of blasting throwing distance
边界条件
设定值
入口边界风速/(m·s?1)
20.8
风筒直径/m
1.8
湍流强度/%
2.8
出口边界
Pressure-out
空气密度
由海拔高度具体确定
操作压力
由海拔高度具体确定
壁面粗糙度
与掌子面距离小于65 m的区域内为0.08 m， 其余区域为0.01 m
Wall边界
无滑移
Tab.1Setting of boundary conditions for simulating carbon monoxide diffusion
计算模型
模型设定
求解器
Pressure-Based
时间子步/s
0.05
湍流模型
Standard k-ε两方程
近壁处理
Standard Wall Functions
能量方程
On
组分输运模型
On
压力速度耦合
Piso
梯度格式
Green-Gauss Node Based
离散格式
Second Order Upwind
Tab.2Setting of carbon monoxide diffusion calculation model
边界条件
设置
风筒入口
根据计算需求设置
风筒水力直径/m
1.8
风筒出口
Interior(内部面)
风筒壁面粗糙度/m
0
湍流强度/%
2.8
空气密度
由海拔高度具体确定
操作压力
由海拔高度具体确定
隧道壁面粗糙度
与掌子面距离小于65 m的区域内为0.08 m， 其余区域为0.01 m
隧道壁面
无滑移
Tab.3Setting of boundary conditions for simulating dust diffusion
离散型模型
设置值
相间耦合
选择
相间耦合频率/Hz
50
最大计算步数
500 000
长度/m
0.02
喷射类型
Surface
粒径分布
Rosin-Rammler
分布指数
2.543
粉尘质量浓度/(kg·m?3)
2 320
粉尘质量流量/(kg·s?1)
0.228
粉尘最小直径/μm
1.00
粉尘中间直径/μm
19.99
粉尘最大直径/μm
100.00
粉尘释放初速度/(m·s?1)
20.0
Saffman升力
选择
隧道壁面
地面为trap类型 除地面以外的其他壁面为reflect类型
Tab.4Parameter setting of discrete phase model
计算模型
设置
求解器
Pressure-Based
时间子步/s
0.001
湍流模型
Standard k-ε两方程
壁面
Standard Wall Functions
能量方程
Off
离散型模型
On
压力速度耦合
PISO
梯度格式
Green-Gauss Node Based
离散格式
Second Order Upwind
Tab.5Setting of dust diffusion calculation model
Fig.6Flow stream line distribution of air flow field around tunnel face
Fig.7Wind speed distribution of tunnel section at different distances from tunnel face
Fig.8Three-dimensional cloud diagram of tunnel dust diffusion at different time
Fig.9Dust distribution of tunnel section at different distances from tunnel face
Fig.10Variation of dust mass concentration with time at different distances from tunnel face
Fig.11Cloud diagram of CO mass concentration distribution in tunnel at different time
Fig.12Cloud diagram of CO mass concentration distribution at different time in different sections
Fig.13Cloud map of CO distribution in typical section of tunnel
Fig.14Distribution of CO mass concentration at respiratory zone height in tunnel
Fig.15Carbon monoxide measuring instrument
仪器设备名称
仪器功能
仪器精度
DECEMLDD260 激光测距仪
测量隧道相关尺寸和标记后续测试点位置
最小分度为0.001 m，测试范围为0.05~60 m
MOT500-CO-Y（红外3%）CO测试仪
测量隧道内断面不同位置的CO质量浓度
最小分度为0.000 1%，测试范围为0~0.5%
Tab.6Field test equipments and their functions
Fig.16Comparison of CO diffusion numerical simulation and field measurement results in tunnel
工况
H/m
pa/kPa
ρa/(kg·m?3)
1
0
101.325
1.225 7
2
1 000
89.870
1.112 2
3
2 000
79.490
1.007 0
4
3 000
70.106
0.909 6
5
4 000
61.642
0.819 6
6
5 000
54.028
0.736 6
Tab.7Condition parameters at different altitudes
Fig.17Variation of CO mass concentration at different altitudes
距掌子面距离(m)
ρ/(kg·m?3)
H = 0 km
H = 1 km
H = 2 km
H = 3 km
H = 4 km
H = 5 km
50
0.000 204 9
0.000 226 5
0.000 250 3
0.000 276 6
0.000 305 7
0.000 337 9
55
0.000 222 1
0.000 245 5
0.000 271 4
0.000 299 9
0.000 331 4
0.000 366 3
60
0.000 243 0
0.000 268 6
0.000 296 8
0.000 328 1
0.000 362 5
0.000 400 7
65
0.000 273 3
0.000 302 1
0.000 333 9
0.000 369 0
0.000 407 8
0.000 450 7
70
0.000 294 0
0.000 324 9
0.000 359 1
0.000 396 8
0.000 438 6
0.000 484 7
75
0.000 294 7
0.000 325 8
0.000 360 1
0.000 397 9
0.000 439 7
0.000 485 9
80
0.000 368 7
0.000 407 6
0.000 450 4
0.000 497 8
0.000 550 1
0.000 608 0
85
0.000 486 5
0.000 537 7
0.000 594 3
0.000 656 7
0.000 725 8
0.000 802 2
90
0.000 524 6
0.000 579 8
0.000 640 7
0.000 708 1
0.000 782 6
0.000 864 9
95
0.000 530 9
0.000 586 8
0.000 648 5
0.000 716 7
0.000 792 1
0.000 875 4
100
0.000 584 3
0.000 645 8
0.000 713 7
0.000 788 8
0.000 871 7
0.000 963 4
105
0.000 712 2
0.000 787 1
0.000 869 9
0.000 961 3
0.001 062 5
0.001 174 3
110
0.000 834 0
0.000 921 7
0.001 018 7
0.001 125 7
0.001 244 2
0.001 375 1
115
0.000 970 2
0.001 072 3
0.001 185 1
0.001 309 6
0.001 447 4
0.001 599 7
120
0.001 140 5
0.001 260 4
0.001 392 9
0.001 539 4
0.001 701 3
0.001 880 3
125
0.001 310 2
0.001 448 1
0.001 600 3
0.001 768 5
0.001 954 6
0.002 160 2
130
0.001 435 0
0.001 585 9
0.001 752 7
0.001 936 9
0.002 140 7
0.002 365 9
135
0.001 472 7
0.001 627 6
0.001 798 7
0.001 987 8
0.002 196 9
0.002 428 1
140
0.001 407 9
0.001 555 9
0.001 719 6
0.001 900 4
0.002 100 3
0.002 321 2
145
0.001 275 3
0.001 409 4
0.001 557 6
0.001 721 4
0.001 902 5
0.002 102 6
150
0.001 112 1
0.001 229 1
0.001 358 3
0.001 501 1
0.001 659 1
0.001 833 5
155
0.000 922 0
0.001 018 9
0.001 126 1
0.001 244 5
0.001 375 4
0.001 520 1
160
0.000 692 8
0.000 765 7
0.000 846 2
0.000 935 2
0.001 033 6
0.001 142 3
Tab.8Variation of CO mass concentration at different altitudes
H/km
K
H/km
K
0
1
3
1.343
1
1.123
4
1.482
2
1.201
5
1.623
Tab.9Average value of CO mass concentration correction coefficient at different altitudes
Fig.18Fitting curve of CO mass concentration altitude correction coefficient
Fig.19Time required for CO mass concentration at different altitudes to reach specified concentration
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