As part of the course Foundation Engineering and Soil Mechanics, a site excursion to the inner-city Kriehubergasse Sports Centre construction project took place on 29 June 2026. On the premises of the Rainergymnasium secondary school in Vienna's 5th district, a fully underground sports centre is being constructed on behalf of the Austrian Federal Real Estate Company (BIG). The facility will comprise four gymnasiums, a bouldering area, and ancillary rooms. The new building is located beneath an excavation area of approximately 60 m × 40 m, allowing the existing open spaces to remain available. In addition, the courtyard is being refurbished, while the existing trees are preserved through dedicated tree protection measures and reinforced earth structures. Continuous skylights will provide natural daylight to the underground sports halls.
The geotechnical site investigation already revealed significant challenges. Historical maps dating back to 1865, together with the name of the nearby Ziegelofengasse ("Brick Kiln Lane"), indicated the presence of a former clay pit within the construction site. As a result, several metres of heterogeneous man-made fill with highly variable soil properties had to be expected. In addition, an unexploded ordnance (UXO) investigation was required. Since the entire structure will remain permanently below the groundwater table, groundwater control is achieved by means of dewatering wells providing continuous groundwater drawdown, complemented by groundwater monitoring wells. Owing to the comparatively low inflow rates, the pumps are operated intermittently, providing sufficient response time in the event of operational disturbances.
The stabilization of the approximately 9.5 m deep excavation as well as the underpinning of the more than 100-year-old school building require several specialized geotechnical construction methods. Three sides of the excavation are supported by watertight diaphragm walls constructed using the trench cutter (slurry trench) method with bentonite support. In particularly sensitive areas, temporary steel struts minimize wall deformations. Along the existing building, a jet grouting cut-off wall provides groundwater sealing, while the existing foundations were successively underpinned and strengthened using approximately 2,000 m³ of jet grout columns constructed in a staggered sequence. In selected sections, additional prestressed ground anchors were installed to ensure structural stability.
Due to the confined site conditions, the top-down construction method was selected. A reinforced concrete roof slab, temporarily supported by auxiliary piles, serves as a working platform, transport route, and storage area throughout construction. Excavation is carried out through dedicated logistics openings left within the slab. After completion of the base slab, internal walls, and intermediate floor slabs, the structural loads are gradually transferred to the permanent load-bearing system using hydraulic jacks, after which the temporary piles are removed. Groundwater ingress and uplift are resisted by tension piles together with a waterproofing concept combining white and yellow tanking systems in the new structure and green and black tanking systems in the existing building.
A comprehensive geotechnical safety management plan, including predefined warning and limit values as well as an alarm escalation procedure, accompanies the entire construction process. Despite requiring approximately 7,600 m³ of concrete and more than 800 tonnes of reinforcing steel, the project is being delivered in accordance with the klimaaktiv Silver sustainability standard.
Our sincere thanks go to Prof. Dietmar Adam and all experts involved on site, especially Mr. Michael Schmidle (Project Manager, BIG) and Mr. Patrick Hollensteiner, Dipl.-Ing. (Resident Site Supervision), for the informative guided tour and the valuable insights into geotechnical engineering practice.