Chongqing landslide - NASA satellite image

NASA have provided the first decent overview of the Chongqing landslide via a high resolution satellite image. This can be found here.


The morphology of this is decidedly odd - I will spend some time trying understand it better. According to the NASA page the source is to the north and the landslide has moved southwards and then spread out to the southwest.

Meanwhile, the search for victims continues according to Xinhua.

Cayton Bay / Knipe Point landslide - report on options

A year or so ago I posted on an ongoing landslide at Cayton Bay in North Yorkshire, just an hour or so down the road from my base Durham. This landslide, which is no commonly called the Knipe Point landslide, was threatening 50 or so houses (see image below) - in the end three were demolished, although the rest are still under threat from the slide. Since my post the BGS have created a nice summary website here, from which this picture is taken:

The local council, Scarborough Borough, managed to find from a range of sources about £300,000 to pay for an investigation of the site, which was undertaken by Halcrow. This investigation was completed this week and will be discussed by the Council in a few days time. The Council has put out a press release here, although the report is not available online. The key findings are as follows:

a. The landslide is a deep seated, ancient landslide system. consisting of:
1. A main deep seated failure for which ground movement is controlled by the residual strength of the clay and a deep confined natural groundwater table;
2. Shallow mudslides in the overlying glacial tills for which the ground movement is controlled by an upper natural groundwater table. This slide is highly sensitive to small changes in the groundwater conditions.

I find the above quite surprising as the failures affecting the houses do not move that often - so this apparent high level of sensitivity is a little odd. I will need to read the report (I will try to get a copy).

The press release then discusses stabilisation issues - which is I am sure what the householders are worried about. It briefly mentions the constraints (minimal impact on the environment as the landslide contains a Site of Special Scientific Interest (SSSI), but a 50 year design life).

Three key actions are recommended:

1. "Maintain and continue monitoring of the surface and subsurface ground movement, groundwater and weather station network."
2. "Liase with stakeholders to review the findings of the report and discuss the way forward for managing the cliff instability risk at the site in the short and long term."
3. "Review funding options for promotion of the preferred engineering stabilisation options, and prepare an application for funding under the relevant and most appropriate legislation."

The preferred stabilisation option is unfortunately large and complex:

• Installation of deep drainage to reduce and control groundwater levels in the deeper water table.
• Construction of bored piles at Knipe Point to isolate the lower Cayton Cliff landslide system from the land above the cliff top.

The press suggest that this would cost £12 million (some reports suggest £20 million!). I would think that finding this sum of money is going to be tricky given the limited number of houses involved, although maybe the threat to the main road will help here.

The Chongqing landslide - update 16th June

The latest update on the Chongqing landslide rescue is provided by Xinhua. Key points:

• Rescue operations continue, with 3,000 people working on site;
  
• Ten small-scale landslides have occurred at the landslide site since Friday;
• southwest China's Chongqing Municipality from Friday, and rescuers continued to search for 64 missing for the 10th day on Tuesday.
• The water level in the barrier lake has dropped to 10 m below the top of the temporary embankment;
• The rescuers have not yet found the mine entrance.

Chongqing landslide update - 15th June 2009

An update on the Chongqing landslide rescue is provided by a CCTV report. Latest news:

• Contrary to the reports yesterday, rescue operations are continuing;
• The pumps to lower the barrier lake are now in operation and are succeeding. It will take about a week to empty the lake, whereupon construction of the channel will start.

The Chongqing landslide - the rescue is probably about to be abandoned

Xinhua is reporting that the rescue at the Chongqing landslide is likely to be abandoned shortly. Given the length of time that has elapsed since the failure the chances of rescuing the miners alive are now very small. More worryingly, there is an increasing risk of further failures at the site:

"According to a geologist with the rescue headquarters who declined to be identified, cracks with the span of eight to ten meters wide and up to 30 meters deep have appeared on the landslide-induced hills. "If the 1.75 million cubic meters of soil and rocks fell down from 80 to 100 meters high, another massive landslide shall occur," he said. Four remaining big stones that stood on the edge of the mountains are also likely to slip off when it rains, he said. Two landslides of smaller scale forced suspension of rescue work twice early Friday morning. The landslide site has entered the flood season, and landslide-induced lakes are likely to trigger mud-rock flows, said Zhu Xiansheng, head of the water conservancy bureau of Chongqing."

Such rescues are always a balance between the benefits of successfully rescuing the victims and the risks to the search teams. Given the time that has elapsed, the difficulties involved in the operation and the lack of indications that the miners are alive, the increasing risks to the rescue teams do suggest that stopping the operation is probably prudent, even though it is a very difficult decision to make. Thirty metre deep cracks that are widening are a strong indication that all is not well on the hillside, although failure is certainly not inevitable.

The latest update on the Chongqing landslide rescue

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.

Latest update on the Chongqing landslide

The desperate rescue attempts continue at the site of the Chongqing landslide, but time is now clearly running out for the miners. The heavy lift helicopter, the same one that assisted at Tangjiashan, is now in full operation, and the drilling continues using 20 machines according to this report. The drilling operations have now reached 100 m below the surface and thus have reached the position of the portal. Unfortunately this appears to have collapsed (unsurprisingly). Additionally, the rescue teams have had to abandon their use of explosives due to the instability of the landslide mass.

There can be little hope for the trapped miners now, although it is still worth trying to get to them.

Meanwhile, according to this report the barrier lake volume has now reached 10,000 cubic metres (this is not a huge volume). Operations to lay a drainage pipe are ongoing.