The effects of the pressure outlet's position on the diffusion and pollution of dust in tunnel using a shield tunneling machine

Abstract

In order to gain a more in-depth knowledge of a shield machine's dust-suppression ventilation system, this paper uses the shield region on the south side of the No. 8 Subway from Jiaodong International Airport, Qingdao, China, as a case study, and conducts field measurements and numerical simulations for examining dust concentration distributions in a tunnel when the ventilation system is not in operation (i.e., under single-pressure conditions) and when the air pressure cylinder is in operation (specifically, the distance between the pressure outlet-2 and the cutter, denoted as Lp, was set at different values within a range of 30∼75 m). The results reveal that under single-pressure conditions, dust was diffused throughout the entire tunnel and caused serious pollution. After the ventilation system was opened: when Lp < 50 m, the use of a ventilation system could not control the diffusion of dust effectively, and its dust-suppression performance was enhanced with the increase of Lp; when 50 m ≤ Lp ≤ 55 m, its dust suppression performance was relatively optimal, but some dust still spread to the operating region; when Lp > 70 m, a low-velocity airflow belt was formed in the operating range of 25∼30 m, i.e., the ventilation requirements could not be satisfied; and when 60 m ≤ Lp ≤ 70 m, both the ventilation and optimal dust suppression performance could be achieved simultaneously.