I built adjacent to a sewerline and we had to have the peirs down further in the ground to remove it from the zone of influence.

What your looking at sounds like an alarm bell as if you’ve built over the top and its not encased in concrete then you take the risk if the pipe get damaged.

Was the garage added after the townhouse was built? I know for my situation we could not get approval from Sydney water to build unless we had engineering plans that showed the depth of the peirs