ASSESSMENT OF THE INFLUENCE OF ADJACENT EXCAVATION STEP LENGTH ON SHIELD TUNNEL DEFLECTION
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Abstract
Protecting existing underground structures in urban areas from adverse impacts caused by surface construction activities is a significant challenge, especially when applying the open-cut sequential excavation method. This paper proposes a simple analytical method to determine the deflection of the tunnel axis induced by the sequential excavation of the overlying excavation pit segments. The method is based on identifying the changes in soil stress at the tunnel cross-section during each construction stage, followed by using analytical techniques to determine the corresponding tunnel deflection. The tunnel-soil interaction is modeled by an Euler-Bernoulli beam on an elastic foundation represented by the Winkler model. Furthermore, the paper investigates the influence of segmental excavation length on the tunnel deflection. The results show that with excavation step lengths of 3.6 m, 7.2 m, and 14.4 m, the maximum tunnel deflection increases by 135% and 193%, respectively. These results provide a basis for optimizing construction methods, minimizing risks, and effectively protecting underground structures.
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