Friday, 19 September 2008

Bangkok sewerage works - PART 3

(Return to PART 1, PART 2)

I eventually got a 101 for the proper operation of the Unclemole in English. Hearing the instruction from an Aussie helped me put together the pieces I hadn’t been able to nut out for myself by reading the Japenglish manual. In short, it went something like this.

Dig a hole. Throw in the guide rails and drop a huge thrust wall behind them. Attach hydraulic jacks to the thrust ring and position the machine on the launch rails. Line up a laser to keep it going straight. Push the machine into the earth while rotating the cutting face. Flush the debris away from the face back to a holding tank with low pressure water. At full extension the jacks are retracted. The cables and water pipes are disconnected. A concrete pipe is placed between the machine and thrust ring and all the paraphernalia are reconnected then you push again. Eventually the machine pops out into a retrieval pit a hundred metres or so away and is removed. That section of pipe work is complete and we move on to the next pit.

Sounds easy huh?

In reality, just getting the holes dug was like that movie Mission Impossible. So that you understand the difficulty we faced, here’s some ground structure information. Bangkok is sited on a huge river delta. A lot of city structures are sitting on wooden piles sunk deep into sloppy marine sand. In places, slow moving rivers of sand and mud snake beneath the concrete and asphalt that floats on top of this mess. It can really bugger up a micro-tunneller’s day when he hits one of these rivers. He can only watch helplessly as his machine drifts away, never to be seen again.

The pit walls were under great pressure and would leak large amounts of mud and water if not sealed properly. Dewatering was a constant requirement and a major headache.

The pit, being the lowest point in a given area, would also flood with sewerage. Human and animal waste typically runs down the street to a nearby Klong in the slum areas of the city. There was no way around having to stand knee-deep in shit, needles and condoms to get the pipes in. I put great faith in the many inoculation injections I had before leaving Australia.

Like it? See - (PART 4).

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