The application of 3D laser scanning technology in tunnelling has gained increasing significance in recent years. Laser scanning is an innovative holistic approach for data acquisition in tunnelling regarding the geometrical parameters. It is a distance‐based imaging technique for three‐dimensional and high‐resolution illustration (3D point cloud) of the surrounding rock that can be applied at various times to provide a variety of visualization and analysis possibilities. A new approach deals with excavation forecasting by linking the acquisition of the 3D geometry of previously excavated rounds with the geological documentation of the tunnel face. This approach enables the gathering of information about the expected overbreak or underprofile of subsequent excavation in similar rock conditions. Using this information, an optimization of the borehole positions (especially of the peripheral boreholes) can achieve the best possible excavation profile. This approach offers an improvement of excavation performance and saving potential with regard to excavation quantity and shotcrete consumption. The uniform excavation shape and consistent shotcrete thickness improve tunnel stability and finally increases the service life the tunnel structure.
Abstract:A new experimental program, focusing on the evolution of the Young's modulus, uniaxial compressive strength, shrinkage and creep of shotcrete is presented. The laboratory tests are, starting at very young ages of the material, conducted on two different types of specimens sampled at the site of the Brenner Basetunnel. The experimental results are evaluated and compared to other experiments from the literature. In addition, three advanced constitutive models for shotcrete, i.e., the model by Meschke, the model by Schädlich and Schweiger, and the model by Neuner et al., are validated on the basis of the test data, and the capabilities of the models to represent the observed shotcrete behavior are assessed. Hence, the gap between the the outdated experimental data on shotcrete available in the literature on the one hand and the nowadays available advanced shotcrete models, on the other hand, is closed.
In the construction of major tunnel structures, large quantities of rock material are generated by the excavation of, for example, tunnels or caverns out of the in situ rock mass. Excavated rock material was often considered as undesired by‐product and from a legal point of view as waste in the past. Nevertheless, there is the need for construction material at the tunnel construction site directly where the rock material is generated. Broad scientific research is conducted concerning the utilization possibilities and optimization of recycling implementation. This article deals with the recycling of tunnel excavation material substituting conventional aggregate for concrete by the example of the Brenner Base Tunnel in Austria. Concrete design, material processing, and concrete production were affected by challenging geological bedrock conditions. This article presents the scientific approach, experimental setup, verification, and the realization on the construction site. The way from preliminary mixing designs to the final product is illustrated for two main rock types: calcareous schists, which successfully were recycled and processed as aggregate for shotcrete, structural and inner lining concrete; and quartz phyllite with unsuitable rock properties for concrete production due to intense foliation and mica‐rich mineral composition. The results are demonstrating the need for detailed examination of rock and concrete properties regarding the usability of tunnel excavation material.
For the construction of the Brenner Base Tunnel with a total length of the whole tunnel system of 230 km, the geotechnical characterisation of the rock and the rock mass based on the geological mapping, the exploration and the geological models is of essential importance. The reliability of the ground prediction and consequently the effectiveness of the construction and support measures are mainly influenced by the methodology for the evaluation of the characteristic material parameters of the ground. This mainly influences the project process and the construction as well as the maintenance costs of a tunnelling project. In this paper, the applied methodology with its approaches of resolution for the improvement of the reliability of the ground prediction at the Brenner Base Tunnel project are explained in detail. Furthermore the improvements to this methodology during different project stages are shown. The paper concentrates on the implementation of the results gained from the exploratory tunnel and the influence of these results on the methodology for the improvement of ground prediction and the reduction of ground risks. In addition problems and approaches for solving these problems are explained in detail. For instance the avoidance of the double consideration of the influence of schistosity by using a rock mass classification system for rock mass parameter identification.
Longitudinal displacement profiles describe the displacement history during tunnel excavation, including that occurring ahead of the tunnel face. These deformations have an influence on the structural design of tunnel support. Theoretical approaches are used to estimate these deformations. However, as the approaches are based on assumptions, they should be applied with caution, particularly in case of deep tunnels. Therefore, experimentally determined longitudinal displacement profiles provide a valuable data basis for validation of the approaches. This study compares 40 m long horizontal chain inclinometer measurements in two lithologies in the exploration tunnel of the Brenner Base Tunnel with theoretically calculated profiles. The chain inclinometers were installed above the tunnel before the start of tunnelling. A measured radial displacement profile was created for each round, the statistical mean value curve was calculated and finally compared with the theoretical approaches. The measurement results show good qualitative agreement ahead of the tunnel face.
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