Deformation analysis for an immersed tunnel considering cyclic degradation of substratum soil

Abstract

This paper presents a new approach for estimating the deformation of an immersed tunnel by considering the cyclic degradation of the substratum soil during the maintenance period. The long-term effects of cyclic loads, such as tides and siltation, reduce the stiffness of substratum layers, which further affects the tunnel deformation. An improved analytical model is proposed that considers the mechanical behavior of the joint and foundation. This model simplifies the immersed tube tunnel on soft soil as a Timoshenko beam on a Kerr foundation model (KTM). The proposed model was validated through a case study in the field. The measured trends in the degradation of substratum soils and deformation characteristics of the tunnel were analyzed by the proposed model. The estimated deformation from the proposed KTM model showed a higher accuracy (more than 10%) compared with the Timoshenko beam on the Vlazov foundation model. The results showed that the deformation of the immersed tunnel under the tidal load increased from 18 mm to 20 mm after 1000 days. Under the back-silting load, the deformation reached 16 mm after seven years. This study can be useful in the preliminary design and analysis of immersed tunnels.