The main objective of this guideline is to give infrastructure owners and their advisors the confidence to incorporate permanent sprayed concrete linings (PSCL) into their underground space design. In line with the objectives of the ITA Statutes this document aims to encourage the use of tunnels and underground space for the benefit of the public, the environment and sustainable development and to promote advances in tunnelling through the provision of information.
This guideline will share state-of-the-art expertise on PSCL to encourage wider acceptance of this tried-and-tested solution. PSCL can be used for primary linings, secondary linings or both. Using PSCLs can lead to lower capital costs, operational costs and carbon footprints when compared to traditional lining solutions. Wider adoption of PSCLs will have a positive impact on the sustainability of underground spaces and increase their viability and potential uses.
PSCL has already been used in underground works throughout the world in a wide variety of ground conditions (see case studies in chapter 15 (Appendix). By 2017, over 1500 km of PSCL had been built in hundreds of projects. Its use is well established in many northern European countries and Australia. In other parts of the world, its acceptance amongst clients and their advisors has been more limited for a number of reasons, despite comparable ground conditions. This can either be because there are no relevant national standards or because local design practice does not favour PSCL, even when standards exist. 
This document is not intended to be a comprehensive design guide or construction specification. Instead it aims to inspire and inform so that more projects can take advantage of this technology. It focuses on wet sprayed concrete and machine application since PSCL is almost always applied in this way.
This document is specific to PSCL and does not discuss routine construction practices. It does not replace the need for expert advice during planning, design or construction, but should give project teams a resource for understanding the key risks and issues and how to manage them. The approaches proposed here can be adapted to a specific project to suit the parties involved and the details of each scheme.