Holdfast Training Services Trial Blog

About three weeks ago on a Friday it rained a lot and our site flooded. I’m not exaggerating when I say that most of the basement was under two inches of water. The tower crane bases all flooded and so the power was cut off to avoid electrocuting anyone just before the water reached the junction box.

About a week before we’d seen this coming and so devised a plan to use submersible pumps to cross pump water from the sumps into nearby gullies to get all the water to one place and pump it off site from there. All it needed was five 2″ pumps and one 3.5″ pump.

Despite me personally briefing this plan to the logistics sub-contractor and giving him a copy of the drawing he only had on site four 2″ pumps. It didn’t help that in my original plan I’d not considered two fairly important points:

1. Podium slab penetrations. Incredibly I’d actually thought about this and still messed it up. I got out a drawing of the podium (ground floor) slab and ensured all the podium level service penetrations had been waterproofed. I even considered all the light wells and ensured that where up-stands in the basement were incomplete they were sandbagged to keep the water on the correct side. But I’d done it from a drawing. A drawing that didn’t show the massive holes in the slab that the tower crane pokes through! And stupidly I didn’t get off my ass, wander out onto site and have a look there. Thus the issue with the tower cranes!

2. The ramp. Logistically, and unusually for London, our site is a gift! We’re currently developing about 20% of the old Earls Court exhibition centre car park. Leaving the other 80% for logistical space and offices and the like. We’ve then got a large ramp that leads from the log area to the basement level. What I’d failed to consider is that every drop of rain that landed on that car park made it’s way down the ramp. It was like Niagara Falls (see Brad’s blog for images)! We were simply unprepared for that amount of water flowing onto the slab in that location.

The Monday after “The Wettest day” the construction manager sent out an email detailing what addition measures were to be taken and by who. My job was to ensure the podium drainage penetrations were connected to the basement drainage system with the topside waterproofing removed and that the tower crane penetrations had sandbag bunds around them. I completed my jobs that week. Our services manager was tasked to put a trench across the bottom if the ramp to divert the water somewhere other than straight into the basement. He didn’t bother. I had noticed this by kept my nose out of fear of upsetting anyone. I get enough grief from my project manager as it is – he is very angry and for some reason hates me!

Fast forward to yesterday and on my way to work I read the news on my phone. I saw the headline “month of rain expected in 48 hours”. “Wow, that us not good news!” (Or words to that effect) I said aloud, much to the surprise of the old lady next to me on the tube.

When I got to work I stopped worrying about offending anyone and just set about making it happen. I got a trench cut across the bottom of the ramp. I ordered some teram and 20/40 (aggregate sized between 20 and 40 mm – apparently getting single sized aggregate is pretty difficult these days!) to be delivered the same day. I got a plastic duct left over from installing the tower crane cables and had some holes drilled in the sides. I put the teram in the trench, stuck in the duct, back filled with the shingle and linked the end of the duct into the surface water drainage system that links phase 1 (our bit) to phase 2 (the bit the other side of where the ramp is).

So come the day of the biblical downpour and it hasn’t come.  Sure it rained a bit about lunch time but nothing requiring us to put two of every trade onto a large boat (bar the QS’s who gave me loads of abuse for spending more money doing this than it would’ve cost to actually build an arc).  But the system is working, the basement is dry and definitely has much more capacity than is currently being used.  So I’m taking solace in the fact that it worked.  It may not be pretty, it may not be high tech engineering, it may not have required a Microsoft Project printout on A1 paper, but it worked.

Lessons:

1.  Don’t do anything just off a drawing, get off your ass and have a look – my bad.
2.  You’ll still probably miss something anyway, so just deal with it the best you can when it happens.
3.  French drains work.
4.  Never trust the Met Office.