A structural integrity assessment scheme for lined tunnels

This paper discusses an assessment scheme developed by Dames and Moore to evaluate the structural integrity of existing tunnel linings. The scheme involves selecting ratings for several key parameters which represent particular visible defects that contribute to the overall integrity of the tunnel lining. These parameters include: lining condition; condition of concrete, mortar and joints, ribs and other supports; water seepage; encrustations and staining; deformation and cracking. Individual parameter ratings are summed to provide an overall rating for different tunnel sections to produce an Overall Condition Rating (OCR). The tunnel evaluation involves gathering the above information on site into pro-formas designed to receive the data. After survey of a section of tunnel, the individual ratings are assessed to produce the OCR, which in turn can be numerically related to the condition of the section of tunnel based on a given formula to produce a Numerical Average Rating of NAR. The four different overall conditions adopted include good, fair, poor and very poor based on a classification system defined for the tunnels.