Segmental lining defect types, and how each is recorded

What is a segmental lining defect?

A bored tunnel is lined ring by ring with precast concrete segments, and a segmental lining defect is anything in that lining, or in the invert or cross passages built with it, that has to be recorded and dealt with before the work can be handed over. Most fall into two families. Leaks, wet cracks and gaps are sealed by injecting resin or grout through packers, and are worked by injection crews. Surface items, such as spalls, honeycombing, dry cracks, holes and cleaning, are made good by labour crews. A few need investigation before anyone can say what the repair is. Each defect is located by tunnel drive, ring number and clock position, so a type on its own is never the whole description: it is the type plus the place that tells a crew exactly what to do and where.

Which defects are leaks treated by injection?

In DEFECTED's taxonomy, the injection stream holds the defects where water is getting through the lining or a gap needs filling. The most common are joint leaks, where water comes through a joint between segments, and segment leaks, through the body of a segment. Wet cracks are cracks that are letting water through. Gaps are recorded as segment gaps or joint gaps, with separate types for a segment gap wider than 10 mm and a joint gap wider than 5 mm, so the wider gaps can be counted and filtered on their own. Leaks at fittings have their own types too: grout socket leaks and spear bolt leaks. Every injection defect carries packer counts and product drawn from a kit, which is why the stream matters: it decides which fields the crew fills in and which crew sees the defect at all.

How are invert and cross passage defects recorded?

As their own types, so they can be filtered and reported apart from the main lining. Types that begin with XP belong to a cross passage, the connecting passage between twin tunnels: cross passage joint leaks, wet cracks, grout boxes, grout port leaks and canisters on the injection side, and cross passage spalls and cleaning on the labour side. Cross passage defects are located by the cross passage rather than forced onto a ring number. Invert defects, in the floor of the tunnel, have their own leak and crack types. Invert Crack is the one type that sits in both streams on purpose: the same name is an injection defect when the crack is wet and a labour defect when it is dry, and the category recorded with it tells the two apart. On Sydney Metro West the invert defects are also exported to ACC under their own category, separately from the segment defects.

Which defects are labour, or rectification, work?

The labour stream holds defects that are made good by hand rather than by injection. The surface defects are spalls, where concrete has broken away; honeycombing, where voids show in the surface; potholes; and dry cracks, with a separate type for dry cracks wider than 0.2 mm. Embedded foreign material covers anything set into the concrete that should not be there, and cleaning is its own type. Several labour types are named for the item they concern, such as crack inducers, drill holes, packers, packer removal, backing rod and spear bolts, and the engineer's instruction on the defect says what is to be done with it. Investigated Dry records a location that was checked and found dry, and Other catches anything the list does not name. Labour defects carry no packer counts; their evidence is the before and after photos and the history.

Investigation

Damaged Ferrule (DF) is the one type in the investigation stream: it is looked at before a repair is decided. A defect whose stream is not yet known stays pending assignment, and a defect that needs no work can be marked no action.

How is each defect type recorded and evidenced?

The same way for every type, with extra fields for injection. A crew picks injection or labour, the ring, the defect type and the clock position on a clock face, on the phone, with or without signal. Imported defects arrive with these already set from the issued list. For injection defects the crew records packers installed, injected and patched, and draws the product from a kit, which puts the litres, the product and its batch on the record. Every defect gets a before and an after photo, with the capture time burned into the image, and it cannot be marked done until the after photo is attached. Done means awaiting validation: an engineer validates the defect, which closes it, or sends it back with a comment. Each step goes into the defect's history, written by the database.

More on the injection fields is in what a defensible injection record contains.

Why does a fixed list of defect types matter?

Because the register is only as good as its counts, and counts break when one defect type is spelled five ways. Engineers' source files use their own names: one list says Joint Leaks, another says Injection - Joint Leak. DEFECTED matches every incoming name against its reference list, ignoring case and extra spaces, and maps known alternative names onto the type already in use instead of creating a parallel duplicate. A name that matches nothing is flagged for a person to review, not added silently. Each type also has a short code, such as JL for a joint leak or SG+ for a segment gap over 10 mm, used on badges and in compact views. The result is that a filter for joint leaks finds every joint leak, whichever file or phone it came from, and the weekly figures add up.

See the types at work in the tunnel defect register, or in the Sydney Metro West Portion 1 case study, where segment and invert defects run across twin tunnels. To try the taxonomy on your own list, start a 14-day pilot.