On June 16, 2025, students enrolled in the bachelor's program took part in an excursion to the ISTA3-I25 project in Maria Gugging as part of the lecture series on foundation engineering and soil mechanics, accompanied by Prof. Dietmar Adam. The Institute of Science and Technology Austria (ISTA) in Klosterneuburg is a research institute with its own doctoral program. Opened in 2009, the institute is dedicated to basic research in the natural sciences, mathematics, and computer science.
A new institute building is currently under construction, which will be deeply integrated into the hillside. This requires the creation of a 38-meter-deep slope cut with an incline of approximately 75°. Geologically speaking, the construction site is located in the flysch zone, a particularly challenging tectonically influenced sequentially layered sedimentary formation that often has very low shear strength. Slope cuts, as in this case, therefore require geotechnical measures that must be planned and executed with particular care.

Keller Grundbau was commissioned with the implementation planning and construction of the excavation pit safety measures. Andreas Kalcsics and Dr. Peter Nagy, who are responsible for the project on behalf of the company, provided a more detailed insight into the project and guided the excursion participants around the construction site.
An anchored shotcrete wall is being used, with the main load-bearing element consisting of prestressed anchors with a working load of up to 800 kN. A three-layer reinforced shotcrete shell approximately 30 cm thick with projections in the area of the anchor heads serves to distribute the forces to be absorbed by the cut. The strand anchors, which are up to approximately 50 m long, transfer the forces to the subsoil via several meters of staggered grouting sections. Apart from the uppermost rows of anchors, which serve to permanently secure the cut, the remaining anchors are designed as temporary anchors with simple corrosion protection. In addition, bored pile walls are used in the upper area of the cut and on the sides of the existing structure. Some areas are also to be secured with slack nails. To prevent water pressure from slope water in the flysch slope, a row of barrier wells is installed immediately behind the cut. The shotcrete shell is also regularly perforated with holes through which residual water collected in drainage mats behind the shotcrete can be specifically drained from the slope. The lateral boundary to the next future construction site will be sloped, with the slopes covered with foil to protect against erosion and weathering.

Despite comprehensive subsoil investigation measures, the particular challenge initially lies in determining the building ground model and the calculation values for calculating and dimensioning the excavation pit reinforcement. It is essential to continuously adjust the calculations in line with the progress of construction, which is monitored by means of continuous geodetic measurements, anchor force measurements, and inclinometer measurements. The observation method thus complements the calculatory approach to the securing measures. Due to the existing museum directly behind the cut, particular attention must be paid to the deformation of the excavation pit securing.
The excursion concluded with a joint snack and discussion of open questions. We would like to express our sincere thanks to Keller Grundbau for inviting us to this extremely interesting and certainly not everyday project. Special thanks go to Andreas Kalcsics and Dr. Peter Nagy for their professional and clear explanations and for answering the questions of the very interested students. For many, it was their first contact with geotechnical practice during their studies at TU Wien.