24 April 2012

Landslide Mitigation Housing

Posted by Dave Petley

Last week Archinect website carried a slightly intriguing design concept for “Landslide Mitigation Housing” by Jared Winchester and Viktor Ramos, which are residential units to be intentionally constructed on a landslide site.  The inspiration is a location in California at Rancho de Palos Verdes , near to Los Angeles, where there is a site that is currently impossible to inhabit because of an active earthflow.  This is the site, as per a Google Earth perspective view:

The proposal, which is very conceptual at this stage, is to locate housing units onto the landslide in order to (in the words of the architects):

…mitigate future catastrophic events, salvage currently unbuildable landscape, and to evolve an architectural vernacular of dwelling within tight topographic settings

The idea is to tether a network of houses onto the landslide.  The design appears to tie the houses onto the slope using a network of cables linked to ground anchors.  The houses themselves are designed to be able to change form as the landslide moves beneath them:

The idea seems to be to slow down the movement of the landslide by using these housing units to provide a drag force.  Presumably therefore the cables are tied in below the shear surface and the movement of the landslide then pushes against, and is impeded by, the houses.  Thus, the landslide is partially mitigated and the slope is inhabited, but the natural system continues to function.

There is much to be commended in this design, which is both innovative and interesting.  I like the way that the structures respond to the landslide and provide an indication as to its behaviour.  There are of course several aspects that the designers might need to think rather carefully about though:

  • The key is that the anchors at the end of the cables need to be fixed into bedrock.  As the landslide moves these anchors (and the cables) will be buried, which means that a protective structure would be needed;
  • Generally, we do not use cables in tension to provide support to landslides.  Rock anchors are in tension, but they are designed to induce compressive forces in the ground to mobilise frictional forces rather than to resist movement through their tensile strength.  Landslide forces are very large, such that the strength of the cables would need to be high.  The possibility of a cable under tension snapping is potentially serious for both the landslide and any people in the vicinity;
  • A poorly-understood aspect of house viability is the need for the structure (especially the floors) to be level.  One reason that houses on landslides quickly become unoccupiable is that levels are lost, which is deeply uncomfortable for the occupants.  Keeping these structures level as the landslide moves would be a serious challenge;
  • Provision of services would also be interesting – providing in particular water and sewerage across an active landslide is difficult, and needless to say leakage of the pipes on a landslide cannot be tolerated.  Presumably they could be designed to minimise the need for electricity, and could generate power locally using wind and solar sources;
  • I wonder how an insurance company would view these structures?  In most countries landslides are not an insured risk.

I think that all of these problems are solvable with thought, and really welcome the innovation that is being shown here.