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The New North-South Underground Line Cologne 

City of Cologne/Koelner Verkehrs-Betriebe AG/Others Cologne, Germany
The North-South Underground Line connects the historical centre of Cologne with the southern parts of the city, providing a fast link to the city centre and the main station. The route has a total length of approx. 3.9 km, including seven underground stations and one station above ground.

The project was divided into four planning and two con­struc­tion lots. CDM Smith led a con­sor­tium in the design and per­mis­sion planning as well as ten­der­ing for the two southern planning lots, in­clud­ing the two Kartäuserhof and Bonner Wall un­der­ground stations.

km
tunnel length
underground stations
m
excavation depth

The northern section involved the Breslauer Platz (main station) stop to be built using the top-down method. The excavation pit was secured using diaphragm, bored and soldier pile walls, some with multiple bracing; the pit intersected with existing structures in places, and included two launching shafts for the tunnel boring machines (TBM) launchs. In addition, an excavation pit at 25 m depth was excavated and secured by diaphragm walls with multiple bracing at Kurt-Hackenberg-Platz as the receiving shaft for the TBMs from the southern lot and launching shaft for compressed air propulsion underneath the philharmonic concert hall. This involved a highly complex process of determining pressure levels due to repeatedly changing dependencies between construction, stability specifications and costs. 

With our engineering services, we contributed to the 1970s born idea of ​​creating a light rail connection from the northern to the southern city centre becoming a reality.
Michael Löffler, Project Manager

CDM Smith was re­spon­si­ble for tech­ni­cal prepa­ra­tions for all of the spe­cialised ex­ca­va­tion en­gi­neer­ing work in the northern section, which involved di­aphragm, bored and soldier pile walls with wood and shot­crete lagging, Jet grouted shafts, in­jec­tion grouting un­der­pin­ning and sealing blocks, el­e­va­tion and pore grouting, and de­wa­ter­ing measures.

The Rathaus, Sev­erin­straße, Chlod­wig­platz und Karthäuserhof un­der­ground stops were partly mined out using piling, in­jec­tion grouting and ground freezing as pro­tec­tion between tunnels ex­ca­vated by TBMs. Wa­ter­tight ex­ca­va­tion en­case­ment with di­aphragm walls down to depths of around 45 m were required for build­ings to be con­structed using open con­struc­tion tech­niques; these ex­ca­va­tion trenches required complex de­wa­ter­ing planning and mod­el­ling in­volv­ing regular con­sul­ta­tion with the com­pe­tent au­thor­i­ties. CDM Smith provided as­sess­ment and con­sul­ta­tion services in all of the deep foun­da­tion en­gi­neer­ing and tun­nelling work during con­struc­tion phase for the southern section of the north-south route of the Cologne Stadt­bahn light-rail service, es­pe­cially as experts in jet grouting and ground freezing. In addition, CDM Smith studied the en­vi­ron­men­tal, ge­ot­ech­ni­cal and hy­dro­log­i­cal effects in prepa­ra­tion for the project using a 3D ground­wa­ter model, and obtained official per­mis­sion for ground­wa­ter ex­trac­tion as based on German water pro­tec­tion law.

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Success depends on shared responsibility and teamwork.

Did you know?

Tunnels were driven with tunnel boring machines (TBM), four stations were partly driven in the mining method shielded by grouting and ground freezing measures; those structures constructed open-cut, required pit linings by up to 45 m deep diaphragm walls and extensive dewatering measures. 

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