Structural Behavior of Connections between Tunnel Roof and Diaphragm Wall: FE-analysis of the connection in Korsvägen, part of the West Link Project in Gothenburg
Typ
Examensarbete för masterexamen
Program
Publicerad
2022
Författare
Altoubah, Tarek
Philipsson Franzén, Rebecka
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Due to densification of cities and strict demands regarding material use, permanent
Diaphragm walls (D-walls) have become a more common option to use as support ing structures of underground tunnels. D-walls require less construction space than
more traditional foundation methods and is currently being used in the West Link
Project in Gothenburg. The tunnel is only connected to the D-walls through the
tunnel roof and thus, the connections become a critical part of the structure. The
aim of this project was to investigate a certain connection used in the West Link
Project, the load effects on the connection and its behavior regarding cracks.
To study the behavior of the connection, three types of analyses were carried out:
two global analyses (one elastoplastic and one elastic) and one local non-linear anal ysis. An idealized case of the structure in the sub-project Korsvägen in the West
Link Project was chosen as a case study. First, a finite element model using plane
strain-elements of both the surrounding soil and the structure was analyzed. This
model was then compared to a beam model where the effect of the soil was modeled
as applied loads. Section forces and moments from the beam model was inserted
into a detailed local model, of the critical connection. The local model was analyzed
to study the cracks and inelastic behavior of the concrete.
The results showed that the cracking in the connection was extensive, and a large
crack developed in the upper corner between the D-wall and the tunnel roof. It was
concluded that:
• A tunnel located at a large depth, built with a top-down method results in a
critical situation with respect to the connection. The situation in Korsvägen
is thus more critical than the other sub-projects in the West Link project.
• The earth pressure developed in the plane strain model, including the non linear behavior of the soil, showed less mobilization of passive earth pressure
than the analyses using a simplified beam model. One reason may be because
the soil-structure interaction was included in the plane strain model.
• The assumption of elastic structure, and not including the soil-structure inter action in the simplified beam-model analyses result in too high mobilization
of passive earth pressure, and thus the crack widths in the connection were
overestimated.
• The FE-analyses indicated that the design of the connection at Korsvägen is
not sufficient regarding allowable crack widths. Additional measures such as a
haunch, additional struts or lighter backfill, may be used to reduce the crack
widths.
Beskrivning
Ämne/nyckelord
D-walls, tunnel, connection, The West Link Project, FE-analysis, ABAQUS, Non-linear FE-analysis, Concrete damage plasticity