Simulation Study on the Effect of Forced Ventilation in Tunnel under Single-Head Drilling and Blasting

Qingsong Pu,Guang Zhang,Xinping Li,Shaohua Hu,Yi Luo,Junhong Huang,Chenhao Pei,Yingwei Zhu,Mohammad Rafiee

doi:10.1155/2020/8857947

Qingsong Pu, Guang Zhang + Show 7 more

Open Access

https://doi.org/10.1155/2020/8857947

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Abstract

Based on the excavation of Yuelongmen tunnel on ChengLan Railway in China, this paper will probe into the forced ventilation effect of harmful gas generated by drilling and blasting construction, simulate the diffusion process of harmful gas generated during blasting operation on the tunnel face by establishing the finite element model of gas turbulent flow and concentration diffusion in the tunnel, and study the spatial-temporal evolution law of CO concentration field under different air pipe layout locations and tunnel excavation methods. The results show that, compared with corner layout, haunch layout, and central layout, the ventilation effect is the best when the air pipes are arranged near the wall at the tunnel vault, and the CO concentration can be reduced to the concentration limit after 588 s of ventilation; compared with the full-face tunneling method and the lower pilot heading method, the benching tunneling method can effectively reduce the retention time of CO near the tunnel face, and the CO concentration on the tunnel face can be reduced to the standard limit after 326 s of ventilation near the wall of tunnel vault.

Highlights

With the continuous construction of the railway network in southwest China, tunnels have become the key works of the railway network in southwest China due to geographical limitation, such as mountainous and hilly areas
If the air pipe is laid near the wall at the tunnel vault for ventilation, the variations of CO concentration on the tunnel face under different construction methods are shown in Figure 9, in which you can see the CO concentration on the tunnel face in the benching tunneling method is decreased to the standard limit of 20 mg/m3 after ventilation for 326 s, while it will take 874 s and 784 s for the full-face tunneling method and lower pilot heading method
(2) It is found after the comparison of air pipe layout methods that when the air pipe is laid near the wall at the tunnel vault, the CO near the tunnel face could reach the standard limit in the shortest time, which will decrease to the standard limit after ventilation for 588 s, but it will take 738 s, 840 s, and 786 s if the air pipe is laid at the corner, haunch, and center, respectively

Summary

Introduction

With the continuous construction of the railway network in southwest China, tunnels have become the key works of the railway network in southwest China due to geographical limitation, such as mountainous and hilly areas. The research methods on the ventilation and discharge of harmful gas from tunnel implosion can be divided into field measurement, model test, theoretical analysis, and numerical simulation [9]. E difference in space structure at the tunnel face caused by different construction methods makes it more difficult to predict the diffusion process and distribution characteristics of harmful gas [22, 23]. 2. Numerical Model of Forced Ventilation for Tunnel Construction with Single-Head Drilling and Blasting. E forced ventilation of tunnel under single-head drilling and blasting construction is a typical turbulent flow problem in fluid dynamics. E control equations of gas turbulent flow and concentration diffusion in the tunnel are as follows:. C∗1ε, C2ε, αk, αε are the model constants, C∗1ε 1.42, C2ε 1.68, and αk αε 1.39

Finite Element Model and Working Condition Design

Initial Conditions of Explosion Gas and Tunnel Boundary Conditions

Operation Condition Design

Numerical Simulation Analysis of Forced Ventilation of Tunnel

Conclusions