Ground deformation induced by a shallow-buried twin-tunnel with small spacing: a case study of Guangzhou Metro Line 18 excavated by earth-pressure balance TBM

During tunneling in urban areas, ground deformation may cause damage to surface and sub-surface structures and buildings, especially the shallow-buried twin-tunnel. In the present study, a 3D numerical simulation and field measurements are adopted to study the ground deformation and stress characteristics of the segment of Guangzhou Metro Line 18. Two measures are adopted to reduce the ground deformation, i.e., grouting from the middle shield and compressed air assistance. The results indicate that the ground surface does not have a settlement as the TBM passes, but an upheaval as the two measures are adopted properly. The maximum upheaval values of the advance tunnel and second tunnel are approximately 45 mm and 5 mm, respectively. As the buried depth of the tunnel increases, the ground upheaval decreases gradually. When the advance tunnel is excavated, soils adjacent to the tunnel have an outward horizontal displacements. The maximum horizontal displacement is approximately 40 mm at the turning of the tunnel. As the tunnel is excavated along straight line, the maximum horizontal displacement is approximately 20 mm. The second tunnel excavated has similar effect on the soils, rendering a slight squeezing effect on the advance tunnel. The maximum horizontal displacement of soils between the two tunnels is approximately 25 mm. While the squeezing effect has a slight effect on the deformation and force distribution of the segments of the advance tunnel. The grouting from middle shield and compressed air assistance can well control the ground deformation of the shallow-buried twin-tunnel with small spacing.