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The current first generation of Eurocodes is a suite of ten European standards for the design of buildings and civil engineering works, whose implementation started in 2010. EN 1990 sets the basis of structural design, with the other Eurocodes dealing with different materials and specific aspects of design. Geotechnical aspects of design are covered by EN 1997 "Geotechnical design", usually called Eurocode 7. The evolution of the Eurocodes started in 2012 and the main objectives of their revision were to incorporate improvements that reflect the state‐of‐the‐art in engineering design and the needs of the civil engineering market, to improve the ease‐of‐use and to harmonize practice between countries. While the original version was developed largely based on soil mechanics, the aim was that the revised version treats soil and rock on an equal basis. The second generation of the Eurocodes is now nearly finished, and the revised EN 1997 is expected to be formally approved in 2024. This paper is the first of a set of six informative papers on the revised Eurocodes and rock engineering, prepared by members of the Rock Engineering Platform of CEN/TC250/SC7, a group of rock engineering experts that has been assisting in drafting EN 1997 from a rock‐engineering perspective. The paper presents the main changes to EN 1990 and EN 1997 as far as they affect geotechnical and rock engineering design. [ABSTRACT FROM AUTHOR]

The wear of cutting tools in mechanised tunnelling is closely linked to the abrasiveness of the present subsoil. Therefore, most of the models used for wear prediction take an abrasiveness index into account. The most common index used for hard rock is the Cerchar Abrasiveness Index (CAI); whereas such a standard does not yet exist for soil. Both the literature research and the results of calculation examples presented in the article show that significantly more practical models are currently available for wear prediction in hard rock. One reason for this is that far more wear‐relevant influencing factors have to be quantified for soft ground. Another reason is that the scientific studies concerning this topic only started in the course of mechanised tunnelling. Since especially the calculations carried out for low‐abrasive rocks differ widely among the different models for tool life, further research is needed also for wear prediction in hard rock [ABSTRACT FROM AUTHOR]

This paper presents an overview of the contents of 2nd Generation Eurocode 7 Part 2, highlighting two of the major changes introduced, being the Ground Model and the Rock Engineering implementation. The document is organized from a ground property perspective so that the role of Part 2 and the links with the geotechnical design are much clearer than in the previous edition. Its new title is a clear indication of this idea: "Ground properties" including both soil and rock properties. The need to have representative values for the ground properties is the objective of this new Part 2, which is intended to guide designers on the path to obtain those values by means of the Desk Study, Site Inspection, Field Investigation and Laboratory Testing. Given this framework, the paper explains the concepts behind the Ground Model, the main output of the Ground Investigation, which includes the ground profile, the geometric properties of the ground and its layers, groundwater, and the derived values of the ground properties, paying attention of the role of discontinuities in such ground profile. The tasks that form the Ground Investigation and the minimum number of activities to be performed are described. This new version of EN 1997 will include a Rock Engineering perspective for all above items. And finally, the ground properties of the rock material and the rock mass are listed and discussed. [ABSTRACT FROM AUTHOR]

The current Eurocode revision process is sought to improve Eurocode 7 for application to rock engineering, while including only techniques and procedures that are in widespread customary use. The revision process has exposed much about the application of the Eurocodes to rock engineering, thereby offering hints as to what material should be included in the next revision – tentatively suggested for publication in 2035. Crucially, ideas have developed about how rock engineering practice may need to develop to embrace the principles on which the Eurocodes are based. In particular, aspects of determining the properties of rock masses, and design verification by observational methods, partial factors, numerical modelling, and prescriptive rules are all thought to require significant improvement or dramatic modification. This paper highlights challenges identified regarding the application of the Eurocodes to rock engineering, and which will need to be addressed in the future. Ideas are presented about how these challenges may be overcome, but these are given in the spirit of stimulating ongoing conversation within the rock mechanics and rock engineering community rather than presenting definite proposals. [ABSTRACT FROM AUTHOR]

In 2025 the new generation of the Eurocode 7 will be introduced and set a framework for geotechnical design for the next 20 years. As Eurocode 7 is an essential design code, the changes will affect numerous practising geotechnical Engineers. The paper provides an overview of significant changes in rock engineering design introduced in the new EN 1997 part 3, considering limit state design, durability, reliability, testing and other crucial design aspects. It focuses on the anchor clause revision and first introduced design rules for rock bolts and soil‐nailed structures. The improvements described include distinguishing between different tension supporting elements that have often been confused. Furthermore, the provisions for groundwater control measures influencing the working condition and limit states for all other geotechnical systems that have not yet been comprehensively addressed in the current Eurocode 7 are also clarified. Finally, the design of the described geotechnical structure will also be strongly affected by changes in the overall philosophy of the Eurocodes, which is also explained. [ABSTRACT FROM AUTHOR]

The second generation of Eurocode 7 includes both soil and rock. In addition to the current practice of ground engineering, this document aims at incorporating rock engineering, improving the ease of use, the harmonization of regulations and covering new developments. This paper provides an overview of some of the significant changes to Eurocode 7 in rock engineering design, taking into consideration limit state design, robustness, durability, and reliability. It focuses on the design of slopes, spread foundations, and retaining structures. The clauses focus on soil mechanics, but also include special rock mechanical issues such as the influence of discontinuities and strength anisotropy on the limit states. Many matters associated to verification of rock mechanical design are linked to the use of prescriptive rules and shall be given in National Annexes. For geotechnical structures in rock, it is mentioned that geotechnical mapping and documentation is important to verify the limit states. However, the basic issues with partial factor methods for verification of the ground‐structure interaction of reinforced slopes and retaining structures are not fully resolved. This has caused some difficulties in setting up partial factors and obtaining a sufficient overview of the application of partial factor method, especially in rock engineering. The design of slopes, spread foundations and retaining structures must likewise consider other clauses in the Eurocode. Rock support for slopes and retaining structures is described in Clause 13 "Rock Bolts and Surface Support". Groundwater‐related issues are described in clause 12 "Ground water control" which influence the design and limit states for the actual geotechnical structure. Dams and levees are featured in Clause 4 "Slopes, Cuttings and Embankments". [ABSTRACT FROM AUTHOR]

The second generation of Eurocode 7 aims at covering ground, including both soil and rock. Current practice of ground engineering forms the basis, and the aim is to include rock engineering, improving ease of use, harmonization of regulations, and covering new developments. This paper deals with EN 1997 part 1 addressing the general rules of geotechnical design, connected to EN 1990, the basis of structural and geotechnical design, and parts 2 and 3 of EN 1997. The design process from ground investigation to the verification of limit states is illustrated with a focus on rock engineering. The following topics are dealt with in more detail: Geotechnical Categories: They are now based on Consequence Classes and newly introduced Geotechnical Complexity Classes. A limit state design to be sufficient has to be combined with other checks depending on these classes.Replacement of the Design Approaches of the current Eurocode 7: Ultimate limit states will be verified by a combination of Verification Cases with partial factors on actions and action effects, and sets of partial factors on ground properties and resistances, respectively.Application of numerical methods, where a ULS‐verification with two sets of partial factors is defined.Use of probabilistic methods in design by calculation, especially appropriate in cases where properties of discontinuities govern the design.Practice of the Observational Method, including design variants and regulations about their choice. [ABSTRACT FROM AUTHOR]

In any underground excavation project, choosing the best excavation technique and careful preliminary assessments of wear costs and production rates are crucial aspects to consider. The production rate and costs of tools, as well as the frequency of tool replacement, deeply affect the duration and cost‐effectiveness of the whole project. Among the rock‐specific characteristics affecting tool wear, Cerchar abrasivity index (CAI) and uniaxial compressive strength (UCS) play an important role. In this article, the relationship between these two parameters was examined by regression analyses for 237 different rocks with the aim to define a preliminary and expected wear potential of three groups of rocks: sedimentary, metamorphic and igneous rocks. The analysis of the results showed that 86 % of the igneous rocks analysed have a CAI > 2, which is a medium or high level of abrasiveness. In sedimentary rocks, over 70 % of the samples are characterised by low abrasiveness behaviour (CAI < 2). Results obtained for these rocks can represent an instrument for predicting the abrasiveness potential of a rock when the UCS is known associating it with an expected range value of CAI. Metamorphic rocks, on the other hand, cannot be classified in specific ranges of UCS and CAI. For this rock group, therefore, a univocal tool for forecasting could not have been obtained, but analyses of rock type and quartz content show that the mineralogical content cannot be considered the only parameter for a wear analysis. [ABSTRACT FROM AUTHOR]

Developing large‐scale tunnelling projects in orogenic regions implies enormous technical challenges. Las Leñas International Tunnel Project through the Andes Main Cordillera of Chile and Argentina has been a long‐awaited infrastructure project, whose geological and topographic settings suggest several complex singularities to be considered, analyzed, and assessed during its development. Throughout the course of this feasibility study, the complex geological subsurface interpretation offers a broad spectrum of technical demands to be fulfilled. The overburden conditions, the presence of certain lithologies such as expansive clays or soluble evaporitic sequences, along with regional stress assessment, are major technical challenges. Through extensive geological, geotechnical, and hydrogeological mapping, subsurface 3D modelling interpretation, along with numerical analysis and its relationship with similar projects in the region, brittle, and plastic behaviour are analyzed. A wide range of modern techniques are used to assess those mentioned tasks, which enable an extensive comprehension of the geological and geotechnical conditions of the area. The purpose of this contribution is to enrich the knowledge on geological and geomechanical challenges faced in large tunnelling infrastructure projects in high‐mountain environments and what specific lessons may arise from them for similar future projects. [ABSTRACT FROM AUTHOR]

Since ancient times, rocks and their geomechanical and mineralogical properties have played a fundamental role for realising construction and infrastructure projects. Workability and excavability of the material itself are still decisive factors controlling tool wear and advancement rates. In engineering geology, standardised tests and analyses related to the strength, hardness, abrasivity and mineralogical composition are commonly conducted in this context. The uniaxial compressive strength (UCS), CERCHAR Abrasivity Index (CAI) and equivalent quartz content are widely used parameters for such an assessment, in order to estimate and predict drillability and associated wear of drill bits, cutting discs or chisels. In this article, the correlations between strength, abrasivity and mineral content of various rock types are investigated. The concept of hardness in geotechnics and engineering geology is elaborated in greater detail, shedding light on hardness definitions, testing methods and how hardness parameters are interrelated. Under the aspect that the CAI shows a good correlation with the Mohs hardness commonly used in mineralogy, a novel approach for estimating the CAI is presented. It is suggested that the CAI of a rock can be estimated within 50 % of the actual value, if its UCS exceeds »60 MPa. On the data basis of various rock types analysed from national and international construction projects, the potential and limitations of this method are discussed. [ABSTRACT FROM AUTHOR]

One of the main hazards during tunnel boring machine (TBM) excavation in hard rock is related to the occurrence of unforeseen adverse conditions, leading to unfavourable rock mass behaviour during tunnel boring. In this respect, the continuous analyses of TBM excavation parameters may represent an interesting tool for a continuous monitoring of geotechnical conditions at the tunnel face and for early detection of changing ground conditions in the rock mass. This work provides a back‐analysis of TBM data recorded during the excavation of the Frejus Safety Tunnel, bored across the French‐Italian border in the Western Alps. It is a 13 km‐long tunnel excavated by a 9.4 m diameter, single‐shield TBM through strongly anisotropic calcareous schist, with cover up to 1800 m. Main problems faced during TBM excavation were related to the local occurrence of buckling‐related convergence and consequent asymmetrical loading on the precast segment rings. Correlating TBM performance parameters to the encountered geological and geomechanical conditions provides the possibility to identify which parameters are most affected by geomechanical properties of the rock mass at the tunnel face and by rock mass behaviour. Conversely, the analysis indicates which parameters can be adopted as monitoring tool of ground conditions during TBM advance. In addition, this work highlights how buckling phenomena can be distinguished, in terms of TBM operation and performance, from other adverse conditions as, e.g., blocky ground or squeezing. [ABSTRACT FROM AUTHOR]

In 2013, the Austrian Society for Geomechanics published the Guideline for the Geotechnical Design of Underground Structures with TBM Excavation. The Guideline contains general procedures for the geotechnical design and construction. In the design phase, the first steps are evaluating different ground conditions by classifying different ground types, different ground behaviours, their categorization into ground behaviour types, and the determination of construction measures derived from the ground behaviour. On this basis the expected system behaviour in each system sector of the tunnel boring machine (TBM) is predicted and described in detail to enable comparison in the construction phase. In the construction phase, geotechnical relevant ground parameters as well as observations regarding the actual system behaviour are recorded and compared with the assumptions of the design. The geotechnical design is updated continuously based on the encountered ground conditions and geotechnical observations. The improved quality of the geotechnical model allows an optimization of the construction while meeting all safety and environmental requirements. In the first part of the article, the general procedures of the guideline are described and parameters to describe the system behaviour in each system sector adequately are listed. In the second part of the article, the implementation of the guideline during design and construction at the Semmering Basetunnel in Austria is described. [ABSTRACT FROM AUTHOR]

The Rudolf‐Fettweis hydropower plant, owned and operated by EnBW Energie Baden‐Württemberg AG, is situated in the Murg valley in the Northern Black Forest. The construction of a new underground Lower Basin is planned to upgrade the existing hydropower station. The in‐situ rock mass consists of Forbach Granite with local weakness zones, as encountered in the boreholes. Considering the extent of the project area, a 3D geological prediction model was used to allow a better interpretation of the spatial relationships of weakness zones in the rock mass and to optimize the orientation of the underground caverns. Adverse effects for the public were counteracted at a very early stage, so that the project received a high level of public acceptance. The present paper describes the current state of the project. [ABSTRACT FROM AUTHOR]

Research has demonstrated that machine learning algorithms (MLAs) are a powerful addition to the rock engineering toolbox, and yet they remain a largely untapped resource in engineering practice. The reluctance to adopt MLAs as part of standard practice is often attributed to the 'opaque' nature of the algorithms, the complexity in developing them, and the difficulty in determining how the algorithms use the datasets. This article presents tools and processes for developing MLAs, input selection, and data balancing for practical underground rock engineering. MLAs for classification and regression – two main machine learning applications – are presented in terms of developing MLA to extract information from the dataset to obtain the desired output. Engineering verification metrics are selected based on their suitability for specific output. Methods for input selection and data balancing are discussed with a focus on selecting appropriate input data for the problem without introducing bias or excess complexity. Each tool and process for algorithm development, data preparation, and input selection is illustrated with a case study. This article demonstrates that geotechnical practitioners can extract additional value by applying MLAs to rock engineering problems. Once an understanding of the functions of MLAs is reached, the building blocks and open‐source code are available to be adapted to suit the rock mass behaviour of interest. [ABSTRACT FROM AUTHOR]

In tunnel boring machine (TBM) excavation, cutter maintenance is necessary, but the time for it has to be minimized for efficiency. Although there is extensive literature on TBM cutter wear and predictive maintenance for different industrial applications, there is no optimized policy for cutter changes in TBM tunnelling today. This study aims to investigate the application of reinforcement learning (RL) – a branch of machine learning – for finding optimized policies for cutter changing that maximize the number of working cutters and minimize the maintenance effort. A simulation of a TBM excavation process is developed that focuses on the cutter wear and an agent that controls when cutters must be changed. The simulation uses generated parameters that indicate the cutter life, but the results could be transferred to real sensor data in future excavations once that level of development is reached. The article presents the first results from this RL scenario which can give valuable insights into TBM excavation logistics and presents a challenging multiaction‐selection RL problem. [ABSTRACT FROM AUTHOR]

Machine Learning (ML) and Building Information Modelling (BIM) are two topics that are part of a revolutionizing transformation in the construction industry – commonly referred to as digitalization. Being part of the research for artificial intelligence (AI), most of today's ML applications deal with computational processes that try to make sense of data. Automatic rockmass behaviour classification based on tunnel boring machine (TBM) data or tunnel construction site surveillance via closed‐circuit television (CCTV) analysis is an example for applications of ML in tunnelling. BIM describes a new type of planning, including model‐based collaboration and information exchange, which requires well‐organized storage and handling of data – a precondition and valuable source for any automated analysis method like ML. While other sectors of the construction industry have implemented BIM systems successfully, the development in underground engineering is currently at its beginning with multiple actors working towards common standards for semantics, data exchange formats, etc. This article seeks to combine the two fields by giving an overview of the two topics and then points out four potential fields of applications: semantic enrichment and labelling, automation of technical processes, knowledge derivation and online data analysis. [ABSTRACT FROM AUTHOR]

To increase the use of geothermal energy in Bavaria, the subsurface, which serves as a reservoir, must be explored as precisely as possible. In the projects of the Geothermal‐Alliance Bavaria, the most promising areas for geothermal exploration in Bavaria were characterised based on an extensive geomechanical laboratory testing program which was carried out on both drill cores and analogue samples from quarries. In the North Alpine Foreland Basin (SE Germany), the geomechanical test results on Upper Jurassic carbonate rocks show a high heterogeneity. On the contrary, in the Franconian Basin (NE Bavaria) the geomechanical properties of granite analogues are rather homogenous. For the numerical simulation of the borehole stability, the determined parameters from ultrasonic‐ and compression tests serve as input parameters for different scenarios. For both locations, the determination of the failure depth around the borehole and the stress distribution in the near‐field of the borehole were accomplished. In the North Alpine Foreland Basin, the borehole stability decreases with increasing depth. For all scenarios in NE Bavaria, the borehole stability is very low. In the future, the determined parameter ranges will allow to validate already existing models and to develop new ones. This will enable a better knowledge of the sedimentary and crystalline reservoirs and a more effective use of geothermal energy in Bavaria. [ABSTRACT FROM AUTHOR]

In Southern Germany, geothermal wells target Upper Jurassic carbonates, formerly referred to as Malm, below the Northern Alpine Foreland Basin (NAFB). In the northern, shallower carbonates (3000 m depth), e.g., in the Munich area, hydrothermal systems prevail, and wells yield proper flow rates. Deeper carbonates (< 4000 m) towards the south indicate a petrothermal system due to a decline in porosity and permeability. Inexplicably, fractures only contribute poorly to larger flow rates. This sets the goal for the project Dolomitkluft to analyse the rock mass for options countering low flow rates in two geothermal wells at Geretsried, Bavaria. Therefore, 20 m drill cores from 4600 to 4715 m total vertical depth (TVD) depict the initial structure of the rock mass: the rock parameters, the discontinuity network, and the in situ stresses. Alternating homogeneous, micritic, strong, to inhomogeneous, porous, weak limestones and massive, crystalline dolostones define the stratigraphy. Five joint sets from the cores can be distinguished into the bedding, two paleo anti‐ and synthetic normal faults and two recent strike‐slip faults. The latter, in combination with core disking, allows exclusively a strike‐slip (SS) stress regime and delimits the ratio to at least SH : Sv : Sh = 1.7 : 1.0 : 0.7. According to the results, including dilatation‐ and slip‐tendencies, drill trajectories of prosperous geothermal wells should head ESE/WNW, perpendicular to SS‐faults, and avoid the presence of normal faults. [ABSTRACT FROM AUTHOR]

As a source of sustainable, renewable, and clean energy, deep geothermal systems increasingly gain importance for the energy transition. In Germany, the North Alpine Foreland Basin is the success story for hydrothermal systems. Besides successful projects in the Munich area, recent attempts to establish successfully operating geothermal wells southwards, e.g., in Geretsried, failed due to a lack of permeability of the rock mass. Subsequent research in Geretsried found that all existing discontinuities are low to non‐productive. The current project ZoKrateS, rethinking the Geretsried reservoir being a petrothermal play, bypasses these limitations by stimulating the existing fractures, and trying to keep them conductive by embedding proppants that prevent full closure. Four detached sections of the well GEN‐1ST‐A1 were subject to individual stages of stimulation. These four sections have been stimulated by placing proppants at injection pressures below the in‐situ least principal stress at no microseismic activity. After injection the communication between well and formation appeared to be increased. Although data processing is still ongoing, linear correlations between cumulative injected volume and quasi‐static pressure may be interpreted as channel flow within highly disturbed rock masses at intersections of faults. The high elasticity of these sections enables even low pressure to cause discontinuity opening below the least principal stress. [ABSTRACT FROM AUTHOR]

For the transition to sustainable heat sources, storage infrastructure is required to provide heat evenly throughout the year. Solar heat is typically produced in the summer and can be stored in underground heat reservoirs for the winter. Flooded coal mines, e.g., are potential heat reservoirs. To assess whether the geomechanical integrity of a colliery and the surrounding rock mass are affected by seasonally stored heat, a numerical case study was performed at "Zeche Dannenbaum" in the Ruhr valley, Germany. During summer, hot water was injected into level 8 of the colliery while cold water was produced from level 4. This process was reversed in winter. Detailed subsurface models of the colliery, rock mass and tectonic faults were used to numerically simulate the cyclical changes in pore pressure and temperature and the resulting stress changes. The displacement of the land surface, and geomechanically critical regions in the rock mass were derived. Moreover, the reactivation potential of the fault zones and the risk of induced seismicity were evaluated. The high injection temperatures induce strong thermoelastic effects, which could potentially lead to fault reactivation and induced seismicity. Surface displacements, however, are negligeable. [ABSTRACT FROM AUTHOR]

The urgent need to speed up the process of reducing CO2 emissions, as well as to stimulate the production and use of renewable energy demands sophisticated technologies to reach these goals. By developing an advanced drilling technology, the EU H2020 project ThermoDrill set itself the target to make the utilization of geothermal energy more economical. The new drilling technology is based on the combination of rotary drilling and high‐pressure fluid jetting. Rock mechanics largely contributes to the achievement of the common purpose of the project. Especially the investigation of the rock destruction process due to the combined hydraulic and mechanical impact plays a major role. The results are based on extensive experimental research concerning rock fracture under varying conditions. Additionally, various methods of crack detection are applied to identify the underlying mechanisms of the drilling technology. As a result, the specifications of the developed prototypes are to a considerable amount based on the rock mechanical findings. The huge potential of the advanced drilling technology is supported by the results of laboratory tests and field tests. [ABSTRACT FROM AUTHOR]

Based on multi‐scale and multi‐disciplinary measured data, gathered at the Geretsried geothermal site, a 3D reservoir model of the deep and fracture‐controlled Upper Jurassic carbonates in the North Alpine Foreland Basin is generated in this work. An efficient methodology is developed to numerically simulate the coupled reservoir processes of fluid flow, heat transport and thermoporoelastic stresses resulting from possible geothermal doublet operating schemes with cold fluid injection and production profiles in an enhanced naturally fractured reservoir. A variety of numerical experiments is conducted to study the reactivation potential and dilation tendency of the fracture and fault system. Simulation results show the spatiotemporal evolution of the thermoporoelastic stresses and the zone affected after 50 years of geothermal doublet operation. From these simulations, the thermoelastic response of a geothermal doublet operating with 60 °C fluid injection temperature and 20 l/s flow rate translates into a maximum induced thermal stress of around 49.4 MPa near the injection well. In terms of a long‐term reservoir performance and fault and fracture reactivation potential, the findings reveal a negligible risk to a sustainable geothermal doublet operation. [ABSTRACT FROM AUTHOR]

High‐pressure water jet drilling technologies are widely used in the drilling industry. Especially in geothermal and hard rock applications, jet drilling is, however, confronted with several limitations like lateral length, hole size, steerability and jetability of the reservoir rock. The application of jet drilling technologies in the field can only be estimated based on the experience of the operator and surface experiments imitating downhole conditions. To predict a successful jetting operation in the field, a modelling framework has been developed, which considers operational and technical parameters as well as reservoir rock specifications. The framework consists of calibrated models describing downhole hydraulics and mechanics during the jetting operation and estimates the required technical equipment to successfully penetrate the reservoir rock and the maximum achievable lateral length for various hole configurations. The modelling framework is applied on a theoretical case study. [ABSTRACT FROM AUTHOR]

Applications of seismic measurements for the prediction of hazard zones are applied practice in many tunnel drives in rock mass today. Next to a large exploration range and accurate localisation of discontinuities, seismic data provide attributes for a comprehensive characterisation of the ground conditions. A good synchronisation of all technical components is required to obtain optimum data quality and quantity while the tunnel excavation is not obstructed thereby. Firstly, the signal source must feed as much energy as possible into the rock in a very short time. Secondly, continuity of the signal generation with constant quality and its precise timing by means of wireless data transmission also ensure a reliable measurement process. Artificial intelligence is used to determine the quality of the recorded data already in the tunnel and feedback is given to the user keeping the data quality high. From the tunnel site, recorded raw data can be transferred to a cloud, from where an authorised processor collects them, wherever in the world. An immediately started data processing delivers a result within an hour that includes a geological forecast of up to 150 m of heading, depending on the rock mass condition. In addition to data quality, the quality of the results is crucial. Therefore, techniques are currently under development using machine learning to correlate and analyse seismic attributes with geological properties. This should lead to a more objective evaluation of the geological forecast in the future. [ABSTRACT FROM AUTHOR]

Geotechnical monitoring and instrumentation are indispensable parts of the Observational Approach. in tunnel design and construction. They are an essential requirement for a proper risk management. Since 2013 several standards, valid both in Europe under CEN and international under ISO, were developed dealing with geotechnical monitoring. Five standards have been published by 2020, covering general rules, extensometer, inclinometer, piezometer and pressure cells. Further standards on settlement measurements, strain monitoring and load cells are in progress and will be published in the next few years. [ABSTRACT FROM AUTHOR]

An empirical and a numerical calculation model were developed to predict the surface settlements due to EPB tunnelling in hard rock with heterogeneous face conditions. For this purpose, surface settlement and TBM driving data from Boßler Tunnel were considered. The TBM launching area characterised by a low overburden (z/D < 2) and a nature conservation area at surface was examined. The developed models were calibrated against the measured surface settlements of the first eastbound tube and were used to predict the surface settlements of the subsequent westbound tube. The prediction was then compared to the actual measured settlements during the excavation of the westbound tube. From this, findings for future settlement predictions in similar ground conditions were derived. It could be shown that both models are suitable for the application in the investigated subsoil conditions and can be used successfully in practice in different phases of the project development. [ABSTRACT FROM AUTHOR]

Over the last few decades, pronounced changes of mountain environments during exceptionally warm summers have raised strong awareness towards changing cryospheric conditions in high mountain areas. Alpine regions are considered particularly sensitive to climate change, observations as well as projections report a significantly higher temperature rise in comparison to lowland areas. Rising sub‐zero temperatures were demonstrated to alter rock‐ and ice‐mechanical strength, namely compressive and tensile intact rock strength, friction, ice creep and fracturing of rock‐ice interfaces as well as elastic moduli. So far benchmark studies have only investigated the impact on rock masses irrespective of the interaction with high‐alpine infrastructure. This study investigates the interconnection between a high‐alpine cable car station and its permafrost‐affected surroundings. For engineering applications, the understanding of the state of natural systems is combined with numerical modelling of interactions between constructions and their frozen subsoil. This enables an improved design of high‐alpine infrastructures in the long run. [ABSTRACT FROM AUTHOR]

The construction of underground structures in metro rail projects is always challenging as the project works normally affect a large number of adjacent surface structures with stringent settlement criteria and protection requirements. Project implementation becomes even more complex when the overburden is shallow and the area of the cross‐section is comparatively large. In the case of design and build metro rail projects, the Client provides a tender stage design to the Contractor's designer; this initial design is often based on limited data and does not consider the construction phase in detail. This is a significant challenge for the Contractor's designer as the new design has to consider all relevant parties and boundary conditions with respect to the compatibility of other parts of the project. This paper describes such a challenge at Mumbai metro line 3, where a crossover structure had to be implemented during the detailed design as a change of scope. The initially proposed crossover cavern was re‐arranged during the detailed design. The main emphasis of this paper is to explain the revised crossover arrangement, for optimized construction feasibility, construction staging and geotechnical stability of the excavation. After the options presented by the Contractor's designer met the original objectives, the detailed design of the primary support and modified construction sequence was carried out in accordance with the principles of NATM design. [ABSTRACT FROM AUTHOR]

Tunnels and underground works in sulphate bearing rocks are very challenging. For more than a century experience has accumulated in Switzerland and southern Germany with difficult conditions during construction and operation, which show the difficult conditions with extreme, long lasting heave of the invert and extreme swelling pressures. The analyses of published experience over more than a century and recent personal experience led to the compilation of many pieces of a puzzle and to a better understanding of complex processes. The swelling processes in sulphate bearing rocks are triggered by the formation of flow path for water, the dissolution, concentration and precipitation of minerals. In particular Anhydrite is dissolved and the solution becomes saturated, until precipitation and crystallization of Gypsum starts. The applied construction methods play an important influence on the rock mechanics and geochemical processes and finally the magnitude of in‐situ swelling pressures. The in‐situ swelling pressure are still large, but substantially less than the swelling pressures from laboratory tests. Estimated swelling pressures will be indicated. [ABSTRACT FROM AUTHOR]

The resistance of aggregates to abrasion estimated by the Micro‐Deval test is an important mechanical parameter for aggregates used as railway ballast. At present, testing intervals are sparse due to the cost of the tests. Cost‐efficient testing methods would be greatly appreciated. A detailed study of the applicability of alternative testing methods, as commonly used to estimate the potential of a rock or soil to cause wear to a tool (LCPC Abroy test and Cerchar test), demonstrates the advantage of implementing these testing methods in addition to the recommended tests. [ABSTRACT FROM AUTHOR]

Digital data acquisition and processing in geology and geotechnics are essential in all phases of a tunnelling project. This article describes typical work flows of engineering geology and the digital tools used, and discusses the requirements, chances and risks associated with the integration of ground models into BIM projects. The handling of factual data is depicted, but the main topic is the development and application of interpreted geological models for tunnelling. Aspects like the transferred information and its localisation, uncertainty of a prediction and requirements for formats, data structures and software environment are discussed. Efficient exchange and long‐term usability of information demands clear definitions for the specialist models and use cases to be covered. [ABSTRACT FROM AUTHOR]

Runout processes originating from rock slopes can be classified according to their process behaviour into rockfall, rock mass fall and rock avalanche. Their process behaviour is primarily determined by the volume of the detached rock mass, the degree of fragmentation of the moving mass and the morphology and nature of the runout path. The initial conditions of these processes depend on the initial failure mechanism. It is difficult to predict the runout and magnitudes of these types of rapid landslides since the complexity of the processes requires major simplifications in the calculation approaches. A good understanding of the process and clear mechanical model conceptions are therefore crucial in the development and choice of prediction models. The paper presents a classification of the runout processes originating from rock slopes on the basis of clearly defined mechanical models and provides an overview of the currently available models for prediction. [ABSTRACT FROM AUTHOR]

Geotechnical assessment of the refilling of the Lüschersee A mass movement of several m/year towards the Nolla stream was detected at the southern Heinzenberg (Grisons, Switzerland) in the 19th century. Debris flows originating from the upper stream valley reached the Hinterrhein valley at irregular intervals, creating temporary dams, which raised the river > 10 m above normal levels. Since 1870, comprehensive mitigation strategies, including torrent control and drainage of the 3‐ha Lüschersee lake situated in the landslide area, have reduced the deformation velocity to approx. 4.3 cm/year and prevented further debris flows. Whether draining of the Lüschersee has influenced the slope deformation was debated back then and has not been conclusively resolved till this day. A potential use of the lake to store water for the local ski area makes the topic current. The integration of geological data with the results of numerical simulations shows that both the mechanical effect of the artificially raised riverbed and the subsequently reduced erosion have a positive influence on the slope, although the effects of changing the hydrogeological situation by refilling the Lüschersee remain uncertain. Therefore, the decision on refilling is dependent on a successful test filling accompanied by permanent GPS measurements. [ABSTRACT FROM AUTHOR]

The influence of a tunnel drive on an existing tunnel is primarily the result of the tunnel geometries, the relative location of the two tunnels, the geological‐geomechanical conditions and the associated primary stress state. During construction of the Brenner Base Tunnel, there are constructionally relevant interactions in some places between the running tunnels and the exploratory tunnel (EKS) running centrally and 12 m deeper. The rock mass stress as a result of driving the running tunnels here leads to deformations of the previously driven exploratory tunnel. Due to the high loading on the outer linings of deep tunnels and the high stiffness of the already hardened shotcrete support, slight deformation can cause local cracking in the support layer. This article compares the observed deformations in a fault zone intersecting at a flat angle with numerical simulations, which enables investigation of the geomechanical problems. Comparison of the calculation results with the real deformation behaviour permits the validation of the numerical simulations and the reliability and limits of such analyses. [ABSTRACT FROM AUTHOR]

This report deals with tunnelling over and under existing tunnels with unreinforced concrete linings and tunnelling under an existing tunnel only supported with shotcrete. The uppermost task was to avoid damage to the existing tunnel and this could be fulfilled through carefully staged advance steps, technically correct construction by the contractor and a dense observation network. The experience tunnelling over an existing tunnel supported only with shotcrete shows that despite slight deformation, cracks and spalling occurred to the shotcrete support layer of the tunnel beneath. This damage did impair the serviceability of the support layer although the structural safety of the tunnel was never in danger. The impairment of the serviceability was temporary and could be remedied by installing overhead protection. In the long term, repair measures were necessary to the support layer in zones with poor geological conditions. [ABSTRACT FROM AUTHOR]

The engineering geological investigation for the environmental impact assessment of the more than 20 km long route section Schaftenau–Radfeld in the Lower Inn Valley (Tyrol) was conducted in 2017/18. As a central structure, a nearly 3 km long tunnel will be built through the Unterangerberg. The bedrock of the Unterangerberg consists of turbiditic, marine deposits of the Inneralpine Molasse with interbedded layers of marl, claystone and sandstone. The proximity to the Inntal shearzone and exogeneous effects like several glaciations have softened the surface of the inherently weak bedrock and led to heterogeneous mechanical properties. The monotonous lithology is therefore accompanied by an inhomogeneous rock mass characterization. This paper describes experiences of the geotechnical investigation of this weak rock. It was observed that only a quick transport of samples from the drilling site to the laboratory can guarantee for test results in accordance with the standards. The results, lying in the transitional zone between soft rock and hard soil, are in good accordance with data from other studies. [ABSTRACT FROM AUTHOR]

The Semmering Base Tunnel with a total length of 27.3 km is being excavated from the Gloggnitz portal as well as from three intermediate faces at Göstritz, Fröschnitzgraben and Grautschenhof. The geological conditions of the project are characterized by tectonically extremely complex rock formations with difficult geotechnical conditions. The excavation passes through numerous fault zones with deep overburden. During the excavation works, some large‐volume collapses occurred. In this article, the collapse events are reconstructed from the available geological and geotechnical information. The reconstruction of the observed system behaviour is based on analytical and numerical calculations. The aim is to identify the respective failure mechanisms. [ABSTRACT FROM AUTHOR]

Forecasts made during tunnelling of the daily advance, to control the machine, specify the lining and verify system behaviour are of great importance for safety and for the success of the whole project. In practice, such forecasts are obtained in deep tunnels by probe drilling, leading to downtime periods and by analog/digital face documentation with shorter downtime periods. Measurement and evaluation of rock mass cutting at the cutterhead of the TBM enables continuous monitoring without downtime. From the spatial distribution of the disc forces, basic geological/geotechnical information about the tunnel face can be derived. In addition, this data is valuable for load monitoring and monitoring the condition of the discs to determine the optimal changing time. This contribution deals with a geological‐geotechnical interpretation of the disc forces of the open TBM on contract H33 Tulfes‐Pfons of the Brenner Base Tunnel. The spatially distributed disc forces are evaluated and compared with the geological documentation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The proposed method can be seen as an adaption of the "Seeber" concept considering developments in geomechanics, calculation methods and steel technology over the last decades. When exposed to inner pressure, the cracking condition is transgressed and steel linings will not protect the rock mass against cracking. Accordingly, the post‐failure behaviour of the rock mass is an essential basis for structural design. The effects of crack water pressure on radial displacements and the width of gaps are considered. The resistant behaviour of the rock mass is determined by its minor primary principal stress. Under mountain ridges and slopes, there is no correlation between the minor stresses and the height of overburden. Obviously damage cases in concrete lined tunnels are the result of inappropriate assessment of principal stresses. A better approach is proposed based on fundamental considerations and FE calculations. Crack water pressure close to the level of the minimal principal stress will induce progressive hydraulic fracturing in the rock mass, which requires safe waterproofing sealing of the shaft. Grouting the coaxial gap in rock mass is a firm part of any design concept. In shafts sealed by membranes, the capability to bridge fissures must be proved by tests. In steel lined shafts, the usable passive resistance of rock mass is determined by the acceptable radial displacement. [ABSTRACT FROM AUTHOR]

Grouting into an open borehole is a process that has been well described academically. Numerous grouting techniques and grouting criteria are available for various applications and combinations of rock mass/ground. Tube á manchette (TAM) or sleeve port grouting systems have until now mostly been used in specialized civil engineering work in soft ground. In order to be able to carry out grouting successfully in faulted rocks, cased drilling is necessary in order to maintain the stability of the borehole for the insertion of the sleeve pipe. Under these premises, fundamental considerations for successful TAM grouting in faulted rocks are presented. The rheological properties of the grout used, the form and size of the injection opening and the strength and thickness of the sheathing compound significantly influence the penetration into the surrounding rock mass. Increased effective pressure is necessary in order to break through the sheathing compound and also to overcome friction losses during the grouting process. The necessity of high effective pressure and the emergence of the grout at the sleeve ports can, in contrast to an open borehole, increase the risk of jacking the ground in the course of grouting and this has to be carefully taken into account and investigated in advance. The interaction of effective grouting pressures and friction losses of the grouting system and their effect on the grouting process in faulted rock are described through the formulation of a general grouting criteria for TAM grouting. [ABSTRACT FROM AUTHOR]

Optimization of rock grouting procedures during construction is necessitated when sparse data sets and incomplete geologic understanding form the basis of initial design. Relying on geologic investigation findings that often have limited budgets, initial designs typically consider data from only a small volume of the entire rock mass to be grouted. During construction, thousands of production boreholes may be drilled and grouted, and each of these boreholes has the potential to provide valuable information for modifying the injection materials and construction means/methods. Implementation of procedural changes is greatly facilitated by the ability to efficiently assemble, query, visualize and interpret vast amounts of 3D data in near real‐time. This contribution summarizes the main targets of rock mass characterization in the context of grouting works, along with investigative tools that provide valuable information: (1) regarding the distribution and properties of in situ permeability features; (2) for modifying and optimizing grouting procedures; and (3) for verifying grouting results in situ. Three dimensional modeling approaches that are amenable to data visualization are reviewed, including the workflow for near real‐time model updating as construction proceeds. [ABSTRACT FROM AUTHOR]

The document titled "Diary of Events: Geomechanics and Tunnelling 6/2023" provides a list of upcoming conferences and events related to geomechanics and tunneling. The events are scheduled to take place in various locations such as Austria, Germany, China, Spain, and Norway. The topics covered in these events include projects in different cities, sustainability, new developments in foundations, measurement techniques, numerical analysis, tunnel construction, rock mechanics, and geotechnical engineering. The document also provides contact information and websites for further information on each event. [Extracted from the article]

This article reports on the development of tunnel boring machines (TBMs) in the past decades and the current state of the art. The development is presented with a look back and a look forward into the near future. Starting with the questions on the development of diameter and operating pressure of closed tunnelling machines, the perspective is expanded to general developments and current trends in machine technology for soft ground and hard rock. Finally, the possibilities and potentials arising from environmental requirements, further increases in performance and digitalization in mechanized tunnelling are shown. [ABSTRACT FROM AUTHOR]

Knowledge about the joint network is important in rock engineering. It controls the stability and strength of blocky rock masses. Thus, the joint network is mapped in more or less detail, regarding the specifications. To do so, different methods have evolved over the years. One of these methods is digital mapping, based on the visual and spatial appearance of the distinct joints. This mapping usually is done by an experienced geologist. However, the trend in digital mapping is towards a supervised but mainly autonomous identification of discontinuities. One aspect of this automated process is the recognition of joints in digital outcrop images by their optical attributes. This contribution presents a density based joint plane detection. By the combination of a vector based joint plane detection and a pixel based joint trace detection, not only joints, but also the foliation in the investigated tunnel face could be extracted very accurately. The approach represents the current state of research and further improvements are to be expected. [ABSTRACT FROM AUTHOR]

Abstract: After a landslide in 2007, a quarry face is to be restored. Consequently, models had to be formed of the geological conditions, of the material behaviour and of the failure mechanism, as well as a calculation model to simulate this mechanism. The geological structure and observations during and after the landslide suggested that the failure was a result of the toppling of slab‐shaped rock blocks. The landslide facilitated a back analysis of strength parameters from this large‐scale in‐situ test, thus making laboratory tests, derived from classification systems and estimations of these parameters, unnecessary. A limit equilibrium method and a numerical model available for the simulation of toppling correspondingly showed that flattening of the face up to the mining boundary results in a sufficient factor of safety. However, the transition from weathered material to rock could not yet be considered. Only the first step of the face restoration, and excavation of the weathered cover, managed to shed light on its thickness, which facilitated precision of the calculation model. Only the excavation of the rock mass displaced by the landslide will show whether the quarry face geometry necessary for a sufficient factor of safety is feasible with respect to the actual loosening of the rock mass and to the actual depth of the landslide. [ABSTRACT FROM AUTHOR]

Abstract: It is state of the art to drive long tunnels in Alpine areas using hard rock TBMs. Mechanised tunnelling has much less flexibility than conventional excavation, so a deeper analysis of the available geological and geotechnical fundamentals is needed. In the course of planning the mechanised drives of the main tunnels on the Austrian side of the Brenner Base Tunnel, a detailed tunnelling concept was created, which deals with the project‐specific features and boundary conditions. The exploratory tunnel, which is used for geological and geotechnical exploration for the construction of the main tunnels, is currently being excavated. Through additional analyses, the geotechnical model could be verified and a reliable update of the rock parameters and the associated critical decisions has been achieved. All further specifications regarding TBM requirements, additional and auxiliary measures, support concept, bill of quantities and construction time model were based on the prognosis of system behaviour. [ABSTRACT FROM AUTHOR]

Abstract: The article describes the fundamental geotechnical model assumptions in the design phase of the Semmering Base Tunnel. Two selected case studies show the verification of the geotechnical model during tunnel construction. The verification process is essentially based on geotechnical monitoring in combination with specific back analyses. It is shown that particularly in complex geotechnical conditions, such as deep tunnels in weak rock mass, the designer can only assess a range of expected behaviour. Most information about system behaviour and thus about the geotechnical model conceptions can only be gained during construction. An improved understanding of the geotechnical model provides the potential to identify and minimize geotechnical risks earlier and to adapt excavation and support measures to the actual conditions. [ABSTRACT FROM AUTHOR]

Abstract: Like every civil engineered structure tunnels are subject to an ageing process. The reasons for the degrading of the condition are manifold: not fully completed stress redistribution, deterioration in the rock mass quality through long‐term exposure (creeping), weathering or dynamic loads and stresses, to name but a few. All this processes lead to a deformation of the surrounding bedrock and the lining. For a continuous monitoring of a tunnel condition the measurement of the deformation is necessary. Conventional methods are elaborate and time‐consuming and require almost always a shutdown of the tunnel for traffic. Therefore, an inspection is done selectively with large time gaps. A continuous condition assessment becomes hardly possible. Currently no robust method for permanent monitoring of tunnels exists. With a fibre optic measuring method many of these restrictions can be overcome. In the course of this research project, a novel and innovative measuring methodology has been developed to continuously and extensively measure rock deformations. The measurement results were evaluated performing laboratory tests. Subsequently, they were installed in the course of a field test at the Semmering Base Tunnel. With complementary technologies such as laser scanning, the measurement methodology could be verified for its applicability. [ABSTRACT FROM AUTHOR]

Abstract: The Institute of Rock Mechanics and Tunnelling at the Graz University of Technology was founded in 1992. From the beginning, the primary focus of research and development was on Alpine tunnelling and slope stability issues, considering geological conditions and their impact on construction. The aim was to improve the current practice, as well as to reduce uncertainties. The research areas can be roughly grouped into rock mass characterization, improvement of monitoring data interpretation, ground behaviour assessment, as well as development and improvement of support elements. The research is documented in about 110 master theses and 30 doctoral theses, and approximately 350 papers. [ABSTRACT FROM AUTHOR]