Surface settlement of subway station construction using pile-beam-arch approach

This paper illustrates the surface settlement characteristics of subway station construction in the shallow-buried soft ground using the pile-beam-arch (PBA) approach of the shallow tunnelling method. The geological conditions, cross sections and measured surface settlements of 30 subway stations constructed by the PBA approach in Beijing are presented. The total surface settlements of the strip foundation station and the pile foundation station using the PBA approach mainly range from 40 mm to 80 mm and from 30 mm to 40 mm, respectively. The superposition of the surface settlements in Stage 1 and 3 of the PBA approach accounts for about 90% of the total surface settlement, and that in Stage 2 and 4 accounts for about 10%. The mean of the surface settlements produced in silty clay is smaller than that in silty sand, and is approximately 1.4 times as large as that in gravel. The surface settlement generally decreases with the increase of the overburden depth. The surface settlement could more than double due to the effect of groundwater. The surface settlement induced by the excavation of the latter level of drifts is commonly larger than that of the former level of drifts. In addition, the quality of workmanship has significant impacts on the surface settlement. This research is conducive to update the database of the world subway projects and can serve as a practical reference for future similar projects.