Geomechanik und Tunnelbau最新文献

This publication presents the data-based technique of Reference Class Forecasting for risk management in complex major projects. Complex projects consist of plannable and dynamic parts, which lead to changes, surprises and unknown events. Not all opportunities and risks can be estimated correctly. Reference Class Forecasting provides a risk uplift which, due to its statistical nature, also adequately considers feedback loop effects, human expertise and problem-solving skills as well as the unknown. Reference classes for new projects are formed using a valid project evaluation and statistics on the risk surcharges required for completed projects. Assignment to a class allows a recommendation to the risk uplift.

Failure scenarios involving tunnel collapse usually occur due to unexpected faults at the face because the support was not designed for this or was underestimated. Failure of the support behind the working face occurs less frequently and can have various causes. Three examples are used to show which stress redistribution mechanisms can lead to failure of the rock support. Using the example of the Arlberg road tunnel, the failure during bench excavation showed that fracture processes exaggerate and due to developing of extended fracture planes trigger a failure of the support. The transfer of high rock stresses to deeper areas prevented the collapse of the cavity in accordance with what Kastner called the protection zone. The example of the Landrückentunnel showed that the excavation of the bench including a heading invert arch with a distance of just 6 m to the ring closure can trigger a total failure of the tunnel. The example of the cavern of the crossover at the Channel Tunnel showed which influences, such as redistribution of the pore water pressure and the longitudinal load-bearing effect of the support, can result in an overloading of the shotcrete structure.

Hard rock conditions in Norway have posed great opportunities and advantages for the design and construction of many tunnel kilometres for many decades, which has normally been accompanied by technological developments. During the latest decades, however, limited research and advancements of practical significance have been implemented in support strategies. This primarily affects the extensive – and unquestioned – use of empirical rock mass classification systems for permanent rock support design in poor rock mass conditions, and the traditional use of uneconomic inner concrete liners to keep sheet waterproofing membranes in place in traffic tunnels affected by water seepages. Based on recently published research work carried out at NTNU Norway and the study of real tunnel construction sites of hard rock tunnels, the authors present in this article some of the main insights about modern and improved support design and waterproofing strategies aiming at economic and optimal support solutions. The presented approaches essentially combine the use of hybrid support design strategies and the implementation of sprayed concrete and pre-excavation grouting as a measure to reduce water leakage, hence increasing concrete durability and support performance. The combined use of such hybrid approach for support design and the substitution of cast concrete lining by high-quality sprayed concrete and rock mass grouting has provided satisfactory and optimised results.

When using Earth Pressure Balance Shields in soft soil, the soil is used to support the tunnel face and the in-situ or excavated soil, which usually does not have sufficient properties to support the tunnel face, is conditioned. For example, suspensions are used in fine-grained soils, tenside foams in mixed-grained soils or tenside foams with polymer additives and fine material suspensions in coarse-grained soils, so that adequate support of the tunnel face with the conditioned soil is possible. Soil conditioning changes various geotechnical properties such as the water permeability and the density of the supporting medium and, if necessary, environmental parameters. The process-specific changes to the geotechnical properties of the supporting medium can have partly a strong influence on the reuse of the excavated soil when used as a construction material or recyclate. This article therefore deals with the challenges to the face stability of Earth Pressure Balance Shields and the influence of the supporting medium on its reuse with regard to the geotechnical properties.

The Uma Oya Multipurpose Development Project (UOMDP) in Sri Lanka provides a comprehensive case study on the interactions between tunnel excavation, groundwater ingress and ground deformations. During the construction of a 15 km headrace tunnel using a double shield tunnel boring machine (DS-TBM), unexpected groundwater inflows exceeding 290 L/s above background triggered extensive aquifer drawdown, surface settlements up to 40 cm and drying of over 340 domestic wells across a 15 km² area. Remote sensing, particularly persistent scatterer InSAR, helped characterise the spatial and temporal evolution of settlements. These phenomena were attributed mainly to the complex geological conditions, characterised by high-grade metamorphic rocks, intensely fractured zones and fault structures that enable rapid water migration. Despite extensive post-excavation grouting, long-term subsidence persisted, underscoring the need for proactive management of hydrogeological conditions. Comparisons with international case studies, such as the Gotthard Base Tunnel, reinforce the necessity of integrated water management and risk mitigation in tunnel projects that traverse fractured rock masses.

Hydrotechnical power waterways in the form of pressurized tunnels and shafts pose geotechnical requirements on the surrounding underground, which vary significantly from those of other infrastructure tunnels, like traffic or mining tunnels. The excavation process and the primary support design requirements of traffic and hydrotechnical tunnels are the same. Nevertheless, the structural design aspects of the final (inner) lining of these two tunnel types are different and misunderstanding of these differences is often the reason for problems occurring in operation. Although the technical issues related to the subject were correctly identified and solved decades ago, it appears that some of the basic technical aspects are not addressed correctly in the design and execution of some hydrotechnical tunnels today. This fact was the main motivation of the authors to summarize current experiences of design and construction in hydropower projects worldwide. The primary focus is placed on the technical requirements for the final hydraulic lining of tunnels and shafts. For unlined and shotcrete lined tunnels, the design is mostly performed by classification systems. The limitations and risks of this approach are explained. For concrete lined and steel lined tunnels and shafts, current experiences and preconditions for the state-of-the-art design approaches are discussed.

Geotechnical engineering is a challenging profession and offers exciting working opportunities. However, in recent years, it struggled to attract young talents. While shifting life and work values are frequently given as contributing factors, empirical evidence to support this claim remains scarce. In view of that, an international online survey was conducted from March to July 2025 to explore generational differences in experiences, beliefs, needs, and goals of members of the applied geo-community. The survey targeted professionals of all ages who study or work in geotechnics or other applied geo-related disciplines. This article focuses on the responses from Austria, Germany, and Switzerland. The results do not suggest that there is a consistent generational gap. While there are certain differences about some topics (e.g., conflicts with younger generations rather revolve around work-life balance and priorities but with older generations more around authority and decision-making), many questions show strong agreement between generations (e.g., finding meaning and fulfilment in the job is more important than income). The results serve as a foundation for increasing the profession's attractiveness, offer valuable insights into intergenerational biases, and lay the groundwork for improved collaboration in the workplace.