Parking cavern "Hinterer Zwinger", Leonberg

The up to 10 m thick covering layers largely comprise artificial fill (mostly cohesive soil) and to a lesser extent detritus (clay silt soils, in some cases, silt and clay). This is followed by an up to 5 m thick layer of gypsum keuper weathered to silt. Below the gypsum keuper, there are layers of Letten keuper ( interchanging beds of partly extremely weathered clay marl stone, clay stone, dolomite, sandstone, the original state of which was bedrock). Layers of shell lime are to be found at a depth of 19 to 20 m below ground level. A continuous groundwater table is located far beneath the cavern (47 to 50 m below ground surface) within the shell lime zone. In the quaternary and Letten keuper layers, there is extremely weak encroaching water. The cavern had to be driven for a special geometry given relatively slight overburden. On account of its interurban position, a construction method involving minimal settlements was called for, during which the effects of vibrations on the buildings in the vicinity had to be restricted to the permissible immission values. The cavern, a helical structure as well as the access and exit tunnels were driven by mining means with the shotcreting method. The second helical structure was created by cut-and-cover. The cavern was developed storey-by-storey, with the park decks supported by the side walls and also by concrete pillars. The cavern has 4 parking levels. The upper one below the crown vault is not supported. Construction data: Construction pit excavation: approx. 20,400 m³ Tunnel and cavern excavation: approx. 47,000 m³ Shotcrete: approx. 2,750 m³

Country: Germany
Region: Baden-Württemberg
Tunnel utilization: Cavern
Type of utilization: Car parking
Client: Stadt Leonberg
Main construction method: Trenchless
Type of excavation: Drill-and-blast
Lining: Shotcrete
No. of tubes: 1
Tunnel total length: First section 29 600 m³, 2nd section 19 900 m³
Cross-section: 19 to 200 m²
Contract Volume: First section 14.7 mill. DM, 2nd section 12,7 mill. DM
Construction start/end: First section 24 months, 2nd section 32 months
Opening: ~ August 1995