Tunnels and Underground Cities: Engineering and Innovation meet Archaeology, Architecture and Art. Volume 6: Innovation in underground engineering, materials and equipment – Part 2 contains the contributions presented in the eponymous Technical Session during the World Tunnel Congress 2019 (Naples, Italy, 3-9 May 2019). The use of underground space is continuing to grow, due to global urbanization, public demand for efficient transportation, and energy saving, production and distribution. The growing need for space at ground level, along with its continuous value increase and the challenges of energy saving and achieving sustainable development objectives, demand greater and better use of the underground space to ensure that it supports sustainable, resilient and more liveable cities.The contributions cover a wide range of topics, from artificial intelligence techniques for geomechanical forecasting, via fiber reinforced concrete segmental lining, to advanced 4-channel scan systems for tunnel inspection. The book is a valuable reference text for tunnelling specialists, owners, engineers, archaeologists, architects, artists and others involved in underground planning, design and building around the world, and for academics who are interested in underground constructions and geotechnics.