There are many trenchless renovation methods that have been developed in the past several decades. Some can be generally applied in a wide range of existing pipes and underground structures, others have a much narrower range of application. All allow new linings or coatings to be installed within existing pipes or tunnels with minimal surface disturbance and often using only the existing manholes or other access points to the utility system. The term “renovation” as used here also implies that the main fabric of the existing pipe is incorporated into the upgraded system and is in some measure enhanced by providing a structural lining to renew the structural capacity or a protective layer to prevent future corrosion.
Linings termed "fully structural" are those that are designed to completely replace the structural function of the original pipe – including resistance to external ground pressures and groundwater pressures and the ability to withstand internal fluid pressures. "Non-structural" linings or "coatings" are not intended to provide any significant structural enhancement to the existing pipe. They are used principally to provide a thin coating to the existing interior surface of the pipe to improve the functioning of the pipe and to extend the longevity of the pipe. This distinction in terms of structural function is not used here to sub-divide renovation methods because many lining and coating systems can be designed or modified to provide the level of structural function required for a particular application.
When lining systems are designed to be fully independent of the host pipe (i.e. designed to carry all external internal loadings without consideration of the existence of the host pipe (including any enhancement to the buckling resistance of the liner), they can be considered as a replacement technique.