Interaction Analysis of the Synchronous Excavations of Deep Foundation Pit and Adjacent Underground Channel

Based on FLAC3D finite element analysis and field measurements, this paper studies the synchronous excavation of the deep foundation pit and the adjacent underground channel in the 17th section of the Beijing Metro Line 10 Phase II project. Due to the very tight schedule and deadline, an underground channel has been added between the double-arch tunnel and the deep foundation pit and excavated synchronously with the deep foundation pit. The minimum distance between the two excavations is 5 m. It was found that (1) the underground channel excavation destroys the intact structure of the soil around the channel and foundation pit on a larger scale, which affects the formation of soil arch behind the retaining pile and thus increases the lateral pile displacement, and the addition of anchor cables at the north and south sides of the foundation pit is not necessary; (2) if conditions permit, it is the safest to excavate the underground channel first and then the foundation pit; (3) the primary interaction spacing between the two adjacent excavations is the same depth as that of the foundation pit, and when the spacing increases to twice the depth of the foundation pit, there is basically no interaction; (4) compared with the solid and heavy soil, the adjacent existing underground channel is like a “hollow, elastic, light” tube and more sensitive to the foundation pit excavation, whose uplift and deformation rebound could exert a force on the surrounding soil and then enlarge the lateral displacement of the retaining pile.