Geomechanical impact on subway tunnels beneath open-cut tunnel excavation pits under long-distance overlapping conditions

Abstract

In urban locales characterized by high population density, tunneling activities frequently entail extensive spatial overlap with pre-existing subway infrastructure. Thus, the geomechanical impact of open-cut excavation pits on subjacent subway tunnels is highly significant. Drawing upon the empirical data from the Tunnel Project of Erqi Square in Zhengzhou City, China, a suite of three-dimensional numerical models was formulated to scrutinize the interplay of three salient variables—excavation depth, excavation width, and vertical clearance between subway tunnels and excavation pit floors—on subway tunnel deformation. The findings elucidate that: (1) the predominant deformation mode of subway tunnels is vertical uplift, with the maximum vertical displacement exhibiting an almost linear correlation with both excavation depth and vertical clearance, yet diminishing in rate with incremental excavation width; (2) among the variables, excavation depth exerts the most pronounced impact on vertical deformation, followed by vertical clearance, whereas excavation width plays a comparatively marginal role; (3) Predictive model for estimating maximum vertical displacement in the silty clay strata of Zhengzhou City was derived through multiple linear regression analysis, and its efficacy was corroborated through juxtaposition with extant measured data, thereby validating its applicability for preliminary prediction of the maximum vertical displacement of subway tunnels in long-distance excavation above the subway tunnels.