A field test on spray dust suppression in large-section tunnel excavated by roadheader

Spray dust suppression is one of the effective dust suppression methods during the excavation of tunnels with the small cross-section. To investigate its suitability in large-section tunnels, a full-section spray dust suppression field test was performed in one railway tunnel with an excavation area of 120 m 2 . The standard solid cone nozzles with a 0.9-type specification were used in the filed test, and four different water pressure (i.e 4.0, 5.0, 6.0 and 7.0 MPa) were set to highlight the effect of water pressure on dust suppression. The dust concentration was measured by the oven-drying method. An average dust suppression rate, defined as the mean value of dust suppression rates at all measurement points under the same water pressure, was proposed to quantitatively evaluate the efficiency of dust suppression. Additionally, the effective dust suppression space under different water pressures was analyzed. The cross-section area effect on spray dust suppression was finally discussed. The results show that the average dust suppression rate initially increases and then decreases with the increase of water pressure, reaching a maximum value of 68.7% at 6.0 MPa. As the water pressure increases, the effective dust suppression range decreases. In summary, spraying is suitable for dust control in large-section tunnels excavated by roadheader, but its dust suppression efficiency is approximately 10%–20% lower than that in small-section tunnels.