Impact of high-altitude environments on the motion and settling characteristics of wet-mix shotcrete dust in tunnels

Abstract

The wet-mix shotcrete process is a major source of dust during tunnel construction. Here, to investigate the influence of the plateau environment on particle motion equations, a combination of on-site investigations in a high-altitude tunnel and laboratory characterization of collected dust samples was used to establish a CFD model of wet-mix shotcrete to study the dispersion characteristics of dust particles in the tunnel. The results showed that: 1) wet-mix shotcrete dust primarily consists of cement particles rich in elements such as Ca, Si, and O, with particle sizes ranging from 1 to 100 μm. The particles are relatively regular in shape, being spherical or blocky; however, their surfaces possess numerous burrs and pores, resulting in poor wettability. 2) With increasing altitude, the vertical force on the particles decreases, resulting in a higher settling velocity and greater particle sedimentation. 3) For particles of a given size, the settling ratio increases at higher altitudes, but this effect is not significant for particles below 5 μm. Based on these results, it is recommended that the minimum dust exhaust wind speed in high-altitude tunnels should be higher than that of low-altitude tunnels, all other things being equal.