Västlänken E02-Centralen – Large excavation pit in Gothenburg's soft clay retained by diaphragm walls

Abstract

Currently, comprehensive construction works are ongoing within the West Link Project in Gothenburg, whereby a railway tunnel is built below central Gothenburg, consisting of five construction lots including three underground stations. The purpose of the Centralen lot is to connect the commuter traffic to Nils Ericson terminal and to Gothenburg's Central Station by a new four-track underground station with two platforms. Designed as an underground structure, the new station was built by NCC Infrastructure (NCC) as a cut-and-cover tunnel. As the ground consists only of very soft clay down to great depth, the design and construction of the underground station was particularly challenging. Additionally, the complexity of the site conditions is enhanced by limited space, adjacent buildings and existing infrastructure crossing the site. Swedish Transport Administration, Trafikverket (TrV) decided for an early contractor involvement (ECI) contract to overcome the challenges of the Centralen lot. In the first phase, a multidisciplinary project team defined the construction methods, logistical constraints, general design and set a target price. Wayss & Freytag Ingenieurbau AG (W&F) was appointed as a subcontractor for heavy special foundation works. The team developed a solution using diaphragm walls (D-Walls) to create the excavation pit for the new station, which is up to 18 m deep and 50 m wide. S&C Consult GmbH (S&C) served as a consultant during the planning and construction phase and in the quality assurance of the D-Walls. It should be emphasised that this was only the fifth D-Wall project in Sweden. Thanks to the constructive and open cooperation of all parties, the work was successfully completed on schedule in July 2023.