12 June 2009

The latest update on the Chongqing landslide rescue

Posted by Dave Petley

Xinhua and CCTV have published updates on the Chongqing landslide rescue. The picture is looking increasingly grim given that the estimated survival time of the miners was five to seven days, and it is now a week since the landslide. Highlights of the reports are as follows:

  • Drilling continues but to date no signs of life have been detected. Drilling (or is this tunnel construction – see below) is only progressing at 5 m per day as they are creating an inclined hole to try to prevent secondary failures;
  • Unfortunately the mine plans were buried in the landslide, so the exact location of the mine entrances is unknown. The chances of being able to build a tunnel that will intersect the mine entrance is considered to be less than 20%;
  • A small landslide that a the drilling platform interrupted rescue operations today. No-one was injured. However, it is now believed that over a million cubic metres of the slope above the site is unstable, and the possibility of more landslides is considered to be “very high”.
  • The heavy lift helicopter is transporting heavy equipment onto the site (see image above). This is expected to increase the rate at which excavation can occur;
  • The barrier lake now contains 40,000 cubic meters of water (this is a big increase in estimated volume compared with yesterday – but is still not a huge amount of water as these things go); The lake level rose by 0.5 m in the last 24 hours.
  • The team continues to build an embankment to keep the water away from the rescue site. The water level is now 1 m below the embankment
  • However, the drainage pipe is now in place and will start pumping today. With a capacity of 15,000 cubic metres per day this should keep the level below the maximum under current conditions;
  • In due course a proper drainage channel will be needed, but at the moment the focus is on the rescue.

Three observations:
1. The news that the authorities do not know the actual location of the mine entrances is new – and very candid. One should not be critical of them for this – a characteristic of the Guinsaugon (Leyte) landslide was the huge difficulties that the rescuers, including the US Marine Corps, had in determining the former location of buildings and infrastructure;
2. It seems to me that there are two operations occurring simultaneously here – one to drill bore holes to allow detection equipment to be located and, I suspect, to try to find the mine entrances. This explains why 40 rigs are being used.
3. There is a double race occurring here – one associated with the limited survival time of the miners and the other to beat the seasonal rains. Unfortunately the slope could collapse even without further rain (i.e. through a progressive failure), so the danger to the rescuers is real and very immediate.