The objective of HYBRIT RP1 is to explore and assess pathways to fossil-free energy-mining-iron-steel value chains and thereby provide a basis for industrial development activities and the necessary future transformative change in this field. A large-scale storage capacity for hydrogen gas is an important component of the proposed HYBRIT concept. Underground storage in lined rock caverns provides a reasonable option: a large-scale demonstration plant for storage of natural gas was constructed in Sweden in 2002 and has operated safely since then. Considering that this lined rock cavern facility was constructed for natural gas, the present report investigates the current research needs to allow for underground storage of hydrogen gas in such a facility. This will serve as a basis for the research in Work Package 2.3 of HYBRIT RP1.

Studying the experiences from decades of Swedish and international research and practice on the construction of underground gas storage facilities, the conclusion is that the lined rock cavern concept seems a reasonable way forward. In terms of rock engineering research, there are currently no critical research issues; however, a development of a previously proposed risk-based design framework for lined rock caverns may further strengthen the ability to manage risks related to underground gas storage facilities. The report identifies several potential research questions on this topic to be further studied: development of a risk-based design approach using subset simulation, the optimization potential of the concrete thickness in the lining, and the effect of spatial variation of rock mass properties on a location’s suitability for the storage facility.

Additionally, the report identifies the potential effect of hydrogen embrittlement on the steel lining as a critical research issue to ensure safe storage of hydrogen gas in lined rock caverns. However, as this issue is not related to rock engineering, but a material issue, it will not be covered further in Work Package 2.3.

Syftet med HYBRIT RP1 är att undersöka och utvärdera möjliga vägar till att göra värdekedjorna för energi-gruva-järn-stål fossilfria och därigenom ge en grund för industriella utvecklingsarbeten och den framtida omställningen. En viktig del i HYBRIT-konceptet utgörs av behovet av lagring av stora volymer vätgas. Lagring i inklädda bergrum är ett möjligt alternativ: en storskalig demonstrationsanläggning för lagring av naturgas byggdes 2002 i södra Sverige och har använts sedan dess. Eftersom denna anläggning konstruerades för naturgas, är syftet med denna rapport att undersöka det nuvarande forskningsbehovet för att kunna lagra vätgas i en sådan typ av anläggning. Detta kommer att utgöra basen för det fortsatta arbetet inom delprojekt 2.3 i HYBRIT RP1.

Efter att ha studerat resultaten från svensk och internationell forskning, samt erfarenheterna från byggnation av inklädda bergrum för gaslagring, är slutsatsen att inklädda bergrum utgör ett rimligt alternativ för lagring av vätgas. Avseende bergmekanik finns det för närvarande inga kritiska frågeställningar. Däremot finns möjlighet att vidareutveckla riskbaserade dimensioneringsmetoder för inklädda bergrum, vilket kan stärka förmågan till god riskhantering vid byggnation av sådana anläggningar. Rapporten identifierar flera forskningsuppslag inom detta område att arbeta med inom delprojekt 2.3: utveckling av en riskbaserad dimensioneringsmetod med hjälp av subset-simulering, studie av optimeringspotentialen för betongliningens tjocklek, samt hur bergmassans rumsliga variation påverkar en plats lämplighet för anläggandet av ett inklätt bergrum.

Avseende materialfrågor finns dock en kritisk frågeställning för underjordisk vätgaslagring: vätgasförsprödning av stålliningen ses som ett möjligt problem och bör studeras vidare. Men eftersom detta inte är relaterat till bergmekanik kommer det inte att studeras vidare inom delprojekt 2.3.

The European design code for geotechnical engineering, EN-1997 Eurocode 7, is currently under revision. As design of underground openings in rock fundamentally differs from design of most other types of structures, the revised Eurocode 7 must be carefully formulated to be applicable to underground openings. This paper presents the authors' view of how a design code for underground openings in rock needs to be organized to ensure that new structures are both sufficiently safe and constructed cost-effectively. The authors find that the revised version of Eurocode 7 carefully must acknowledge the fundamental decision-theoretical connection between design and risk management that should permeate all geotechnical design work. Otherwise, if the revised code is not given a risk-based framework, the authors fear that, as a consequence, the observational method will not be favorable to use in excavations of underground openings in rock. Then, cost-effective construction will be very difficult to achieve.

The aim of the paper is to show how Eurocode 7: Geotechnical Design Part 1: General Rules (EC7) could be developed in order to be in accordance with practise in rock engineering and construction. A main feature is the geological uncertianties, which imply that a risk based approch should be used. The use of Geotechnical Category (GC) has therefore to be improved by (1) combining the consequences of a failure to the geological uncertainties before excavation, and (2) combining the consequences to the ground quality found after excavation. Three GC classes are needed to properly use the GC in rock construction. The paper further describes how GC influences the design, which design method to be applied. It also outlines the types of control, inspection and supervision to be applied in the various GC classes during various stages of a project. An example is presented showing how GC can be determined at various stages of a rock construction.

The Swedish Geotechnical Society has adopted a general methodology for risk management in geotechnical engineering projects to reduce the costs related to negative outcomes of geotechnical risks. This technical note highlights the main features of the methodology and strives to inspire the international geotechnical community to apply sensible risk management methods. In the authors' opinion, a successful geotechnical risk management needs to be structured, be tailored to the project, and permeate the engineers' everyday work. Then, sufficient quality can be achieved in the project with larger probability.

In 2010, the Eurocode for Geotechnical Design, EN-1997-1:2004 (CEN, 2004), informally known as Eurocode 7 or EC7, became the Reference Design Code (RDC) for geotechnical design - including rock engineering design - within the European Union (EU). EC7 is one standard within the comprehensive Structural Eurocode suite, which as a whole has been also adopted by a number of other countries beyond the EU. EC7 is thus becoming a key design standard for geotechnical engineering worldwide. As part of the Structural Eurocode suite, EC7 requires designs to adhere to the principles of Limit State Design. However, it is not clear that current rock engineering design practice can satisfy this requirement. In addition, evidence is accumulating that EC7 is currently difficult to apply to, and may even be inappropriate for, rock engineering design. These issues may be due to the fact that the development of EC7 to date took place without any formal input from the international rock mechanics and rock engineering community. In early 2011 under the auspices of CEN (Comité Européen de Normalisation / European Committee for Standardisation), EC7 entered a formal period of maintenance which was aimed at improving the applicability and ease-of-use of the Code. This maintenance cycle will conclude in 2020 with the publication of a revised version of EC7. This paper describes a number of critical aspects for rock engineering in the context of EC7, in particular the following: - the history of the Structural Eurocodes and the concepts they embody; - the nature of Limit State Design and the challenges and opportunities it poses for rock engineering design; - the formal means by which the Structural Eurocode maintenance cycle proceeds; - the plans currently being developed for improving EC7 with regard to rock engineering design and construction; - the unique and vital opportunity for the entire international rock mechanics and rock engineering community to comment on the Code and make suggestions for its improvement.

Two extra-long tunnels, with two tubes each, were excavated in a corridor of about 200 m in Qinling Mountain in the central part of China, for railway and road lines from Xi'an to Ankang, respectively. During tunnel excavations, severe rockbursts have occurred in several gneiss sections. The rockburst features indicate the pronounced effect of the fabric of the schistous structure of gneiss on the strength and deformation characteristics of intact rocks. The analysis on the geological conditions in terms of initial geostatic stress, rock strength and the occurrence of the gneiss foliation planes indicates that the schistous structure of gneiss is in favor to the severe rockburst in the section of magmatic gneiss with large overburden. The influence of anisotropic feature of the gneiss on the rockburst becomes significant on the condition that a large initial principal stress is nearly parallel to the foliation planes and the foliation structure composed mainly of biotite and quartz provides a weak plane to brittle failure.