If there is one thing that the public love, it is being let in to a secret underground space, to go boldly where no one has gone before… And last weekend, Wellington was allowed to venture into the giant slice through the earth that the NZTA call the Memorial Park underpass. At present it is just a large cut in the ground, but the base slab is under preparation, and soon they will start to work on the walls, and eventually the roof over.

Thousands visited – sadly, no record was kept of how many went through, but you can judge by the photos – packed full, stretching end to end, people were pouring through. NZTA, ever conscious of safety to an almost ridiculous degree, had installed not just temporary fences to stop small children falling in to the works, but in one section, we were even escorted through special temporary elevated walkways across the diggings. Don’t touch the hallowed ground!

Things of note to the technically minded: note the difference between the temporary timber walls, with treated logs slid down between steel UCs pile driven every 2m or so – versus the steel sheet piling used in front of the old Police Station in Buckle St, using hydraulic pressure vibration rather than the more damaging percussion piling of the mighty hammers. Note also the rock anchoring, or soil nailing that has been undertaken on both sides, right along the walls. This is where holes have been drilled into the earth, and steel rods cemented / grouted in place, to help hold the (temporary) wall upright, and hold the ground in place.


What was probably of more amazement to the general populace, was the amount of work going into holding the whole tunnel down, to stop it popping back out of the ground. Although there will be pressure all the time from the ground water that will surround the tunnel when the temp wall is removed, apparently it is the once-in-a-few-thousand-year-earthquake that really needs holding down against. In this scenario, a giant jolt ripples through Wellington, tossing buildings hither and yon, and the whole underground tunnel pops up out of the earth like a beached whale. Or perhaps not quite that dramatic – maybe it just wiggles a bit like a dead snake, but regardless, the Engineers have staked their reputation by staking this giant floor slab flat against the soil for a very long time.

And then there was the drain. There are two drains of note – one, and old one, runs down Tory Street quite some distance underground (just how on earth did it ever get dug so deep, so many years ago?), while the other is a new drain, running from the top (Taranaki Street) right down towards the direction of Mt Victoria. Inevitably, it seems the two will meet, but they haven’t got to that stage yet. And when they do…? But the interesting, and slightly odd thing, was how this new drain was being done. Not just a pipe laid underground, this pipe was set in concrete, within a reinforced concrete wall, within a waterproofed channel, that was itself within yet another reinforced concrete wall. And who knows what was beneath THAT concrete wall – maybe another wall, just for luck?

The answer as to WHY, was simple: they don’t ever want it to break, and they never will get down there again… so they have to have a failsafe solution to their failsafe system. So: now you know.

I’m guessing that with a bit of good management, NZTA might consent to let the public walk through one more time – just before the cars take it over forever. That’s in about a year’s time. See you then!