The connection between subway stations and tunnels in subway systems is a critical consideration in the design of underground transportation systems. Expansion joints may be introduced between the station and tunnel to reduce the stress and deformation transmitted to the structure and mitigate the potential structural damage. However, adverse conditions such as large deformations in liquefiable sites and extreme earthquakes can severely impact the integrity of this connection. This study employs three-dimensional finite element numerical models of dynamic soil-structure interaction in liquefiable sites to investigate the seismic response of the subway station-tunnel connection structure under different distributions of liquefied soil layers and considering various structural connection methods. The results demonstrated that subway station-tunnel structure placed in liquefied interlayer sites experiences greater seismic damage compared to structures with their upper parts embedded in homogeneous liquefiable sites. In addition, using expansion joints between the station and tunnel can indeed reduce the seismic stresses and deformations transmitted to the structure, which can mitigate the extent and severity of its damage. However, the expansion joint can lead to misalignment between the subway station and the tunnel. The findings provide theoretical references for seismic design and disaster mitigation measures for subway structures in liquefiable sites.

The integral abutment bridge concept allows removal of expansion joints, bearings, piles for horizontal earth loads, and other uneconomical details. These details not only add to construction costs but also increase the maintenance work and expenses. When expansion joints are eliminated from a bridge, thermal stresses must be accounted for in the design. This paper describes the design challenges for a 45.6 m one-span integral abutment bridge, nearby Gatineau, Quebec, Canada. According to the geotechnical report, the soil under the foundation of the bridge consists of a 1.0-5.4 m granular embankment mixed with organic material and layers of wood chips, 15 m layered deposits of granular and cohesive soils, and a 35.7 to 40.8 m thick clay that is laid on a till layer. Because a 5.3 m granular backfill of abutments would lead to remarkable consolidation settlement and maintenance issues, it was decided to substitute 3.7 m of the granular backfill with a lightweight material to minimize the long-term settlement problem. A 3D bridge model in CSiBridge was used to simulate the construction stages and nonlinear behavior of soil around the piles to predict the induced efforts in the bridge due to different loads, including thermal and deck shrinkage loads. Structural design of piles was accomplished by taking into account the plastic hinge at the top of the piles and estimating the buckling free length of piles based on analysis of pile under lateral load in L-PILE software. While some Canadian provinces have developed standard details for approach slab joints, Quebec's ministry of transportation (MTQ) does not propose any standard expansion joint detail for integral bridges. Therefore, the typical strip seal expansion joints detail of MTQ was adapted for this project to reduce water infiltration inside the joint even though it is away from the deck and is located at the end of approach slab. During the construction, the result of test piles revealed that excess pore water pressure due to pile driving operation needs some time to disappear. Thus, minimum waiting times for the main stages of construction were defined. [GRAPHICS] .