Buy cheap – buy twice! That’s what an old Irish friend used to tell me. Although the subject of our financial concern would usually be something trivial like a pair of socks, the same adage could easily be applied on a larger scale to many sectors of the tunnelling industry.
The consequences of choosing an inadequate option are well documented regarding some elements of tunnel design and procurement – waterproofing being a prime example.
Water may be something we can’t live without, but it’s certainly something we could do without in the tunnelling environment! Our technical focus this month addresses some of the problems associated with waterproofing tunnels, ranging from the vast and sometimes confusing array of products on the market to the lack of information available and research published on this potential minefield of a discipline.
The problem is, when things go wrong, they can really go wrong, resulting in the contractor blaming the designers, the designers blaming the clients, the clients blaming everyone, and everyone blaming the product manufacturer. Well this blame culture isn’t going to help anybody in the long run, and when it all ends up in court, with costs spiralling out of control and schedules slipping further and further behind, it’s the tunnelling industry in general that starts to look pretty inadequate.
A comprehensive waterproofing solution is far easier to implement effectively before, not after the event. It may cost a little more, but ignoring this initial investment could prove a false economy on a large scale.
Take, for example, probe drilling ahead of the face in any reasonably sized diameter drill and blast tunnel. In the modern age, drilling equipment can produce 4 x 20m long holes in 30mins-60mins. High-pressure water channels, yielding many 10’s of m3/min, can be relatively easily sealed by pre-grouting – if detected early enough by probing.
Even so, this is seldom done, because the client has not specified it from the outset. This is frustrating, in that the cost of probing ahead is marginal if seen as an insurance premium, and more so when you consider the high costs and technical difficulty of post-grouting.
As said, this is just an example, but the same principle could be applied to many tunnelling situations. A small additional investment from the start could pay large dividends in the long run should the unexpected occur. In an industry that prides itself on being challenged regularly by the unexpected, clients should be aware that such investment would be deeply reassuring to all concerned.
Tris Thomas
