6 August 2011

Landslides from the Christchurch earthquakes part 5: landslides that involve sliding

Posted by Dave Petley

The other posts in this series are as follows:

Part one: boulder damage to a house

Part two: evil dancing rocks

Part three: topographic amplification at the cliff tops

Part four: large-scale cliff collapses

There were a small number of landslides with sliding associated with the earthquake, mostly in the hills to the south and east of Christchurch.  This post includes images from two of these slides.  Both are poorly understood at the moment but have caused substantial levels of damage.  In both cases, substantial tension cracks have opened up at the rear of the slide, with very serious implications for the buildings in that area.  From a structural perspective, this is probably the most heart-breaking site that we visited.  This beautiful, old clifftop home has the tension crack from a translational slide running straight through the front of the house:

Look carefully at the structure and the roofline and you can see the damage that is being caused by the landslide.  The tension crack is now up to about a metre wide.  There seems little hope to me that the structure can be saved:

The tension crack exits on the other side of the house, undermining the foundation:

Elsewhere, brick structures also showed the effects of the development of tension cracks:

In some cases, desperate measures have been employed to try to prevent buildings from being pulled apart:

The landsliding is also having a major impact on the roads in the affected areas.  This is an area of extensional cracking close to the house shown in the first image:

In one of the landslides, the movement is also toeing out in an area of houses.  In this case, the buildings are affected by compression.  This fence line has been buckled by these compressive forces:

It is really important to remember the human cost of these landslides, which is very high.  In some cases, despite their losses, home owners have been very thoughtful about the risks to others:

In other cases, there are some very sad appeals to the authorities:

The other posts in this series are as follows:

Part one: boulder damage to a house

Part two: evil dancing rocks

Part three: topographic amplification at the cliff tops

Part four: large-scale cliff collapses