In this category, a flexible liner is used that typically is made from a plastic sheet that is smooth on one side and with raised studs on the other side. The liner sheet is welded longitudinally to form a tube, then folded into a U-shape and pulled into the pipe to be renovated. When in position within the host pipe, the liner is expanded into contact with the host pipe. The smooth side of the liner faces inwards and the T-shaped studs face towards the host pipe. A structural grout is then inserted into the annular space with the studs anchoring the liner sheet into a composite structure with the grout. For applications where leakage detection is critical, e.g. chemical pipelines, it is possible to include a second liner as part of the system and for which the annular space is not grouted. Should the primary liner experience leakage, any leakage flow can be monitored via the created annular space before the leakage can cause external contamination.