142 X2 Category 2: Civil Structures Background The project Doorstroom (Thoroughfare) Station Utrecht (DSSU) includes optimising the current railway infrastructure on the site of Utrecht Central Station. Part of this plan is a service tunnel, which connects the public road with the southern rail yard. This underpass crosses four tracks and is built with minimum disturbance to normal train traffic. On behalf of ProRail, the DSSU project is designed by Movares and will be executed by the contractors combination U-Central (BAM Rail and Volker Rail). The design phase includes the preliminary design, the final design and the implementation design. Implementation The service tunnel is made up of 8 segments. The tunnel ramps consist of 6 open tunnel segments parallel to the tracks. The junction with the train tracks consists of 2 partially closed segments. The partially closed segments include a section in which the road turns the corner at 90 degrees. Under segment 4 there is a pump basin for rainwater. Due to the high water table a sheet pile pit is needed since lowering of the groundwater level is not permitted. After unearthing of the pit and the pouring of the underwater concrete the pit is drained. For driving the sheet pile along the tracks there is 1 train-free period of 52 hours available. To build segment 5 in its final location there will be approximately 7 months when 2 of the 4 tracks will be out of service. This segment can be built relatively simply without disturbing the rail traffic. On the other hand, segment 4 must be built during a train-free period. To that end, the deck west of the railway tracks will be built on top of the sheet piles and during a 52-hour train-free-period slid on to its final place. The deck is located temporarily on the sheet pile walls, which are part of the building pit. Afterwards, the pit under the deck is unearthed. Then underwater concrete is poured and drained after the concrete has been sufficiently cured and the finishing work can begin. This phase consists of building the pump basin, building the concrete walls and floor underneath the deck, when once again a train-free period in needed. Finally, the sheet piling is disconnected from the newly built segment to ensure that all external forces will be distributed to the new segment. Design During the entire design phase engineering programs such as Allplan (drafting) and Scia (design) were used. The final design consists of a model where fabrication and reinforcement drawings can be generated. It is intended that this data can be transferred completely to the contractors combination U-Central so that information loss in the digital chain is reduced to a minimum. The tunnel floor has both a longitudinal and transverse slope and goes through a bend in the tunnel. The floor reinforcement is orthogonal and follows the upper surface of the floor. The project is designed in accordance with the latest European standards (EC2) and, where possible, the use of standard lengths of rebar. Service Tunnel Station - Utrecht, The Netherlands Software: Allplan Engineering, Scia Engineer
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