Probabilistic Differential Settlement Design for Direct Foundations of the HZM Link Immersed Tunnel

Thomas Kasper

COWI A/S, Parallelvej 2, 2800 Kongens Lyngby, Denmark
e-mail: tkas@cowi.com

Albrecht Lentz

COWI A/S, Parallelvej 2, 2800 Kongens Lyngby, Denmark

Sune Yding

COWI A/S, Parallelvej 2, 2800 Kongens Lyngby, Denmark

Arend Jelmer Boukes

COWI A/S, Parallelvej 2, 2800 Kongens Lyngby, Denmark

Kristian Schmidt Bertelsen

COWI A/S, Parallelvej 2, 2800 Kongens Lyngby, Denmark

Tommy Olsen

COWI A/S, Parallelvej 2, 2800 Kongens Lyngby, Denmark

 

 ABSTRACT

Non-uniform foundation stiffness, non-uniform foundation loads and gravel bed surface tolerances lead to a combination of differential settlements and load redistributions with associated shear key forces in the segment joints and immersion joints of immersed segmental concrete tunnels. The 5.7 km long immersed tunnel of the Hong Kong - Zhuhai - Macao (HZM) Link in the Pearl River estuary in southern China has to be founded on varying soft soil deposits and is subject to large sedimentation loads. This paper presents a probabilistic design approach for differential settlements and shear key forces with focus on the direct foundations with a gravel bed on native ground in the central part of the tunnel. An extensive site characterisation forms the basis for detailed CPTU based settlement (foundation stiffness) calculations and the determination of longitudinal and transverse foundation stiffness variations. Soil-structure interaction models are used to determine shear key forces from longitudinal and transverse foundation stiffness variations as well as from gravel bed surface tolerances. Based on the principles of reliability theory, the different effects are combined to determine characteristic 95 % fractile shear key forces as a basis for the structural design of the shear keys. The method is demonstrated for one segment joint and has proven to be a viable tool for the design of the tunnel.

Keywords: Probabilistic design, Reliability theory, Immersed Tunnel, Foundation design, Differential settlement, Soil-structure interaction.

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