Under the conditions underground how can it be possible for any contractor to honestly police his own work and honestly self-certificate? And once the work gets behind schedule for the contractor to be unexpectedly called on, for example, to 'open a couple of new faces', means that all the available time will have to be devoted solely to that end.
It has always appeared to me that for a client to enter into a tunnelling contract without 'the Engineer' to provide, among his other traditional duties, continuity of design and independent continuous inspection of the works, would be nothing less than sheer folly.
I spent the last 20 years of my life working for 'the client' and in all those years we never considered entering a contract for underground works without the Engineer function.
There may be clients who may be ill advised or naive, or who have the odd £100M to spare, but if they think that the contractor can or will truly police the quality of his own work (unless and where it suits him) and honestly 'self-certificate' tunnelling works then they are living in cloud cukooland.
P G Whyatt (F), 2 Wayside Drive, Clevedon, North Somerset BS21 7DU