Geohazard ‘tank models’

Tank models

Over 3000 people attended the BGS Open Day on 8 June 2013 and as part of the day's activities the BGS Landslides Team presented a series of geohazards as ‘tank models’:

  • retaining wall failure
  • quicksand
  • heave
  • sinkhole

The tank models proved very popular at the Open Day so we decided to publish them as time-lapse videos. The photographs were taken every ten seconds for the duration of the processes; some of the videos took up to three hours to film.

Retaining wall failure

This is an example of a retaining wall failure; a familiar hazard in ground engineering.

An engineer designed a wall to hold the dry sandy soil whilst houses have been built above.

Examples of this can be seen where roads or railways or other excavations have been built that cut into the land.

Unfortunately, this wall has not been designed correctly and has started to fail. This slope failure is translational in nature and you can see the slip planes that have formed.

Slope failures in (wet) clays and silts tend to fail at shallower angles and be of a 'rotational' or 'flow' type failure.

Quicksand

Here, our lifeguard is about to experience quicksand conditions.

Water is pumped in from the bottom of the model to simulate a spring, artesian condition or incoming tide that may result in sand grains floating and quicksand to develop locally; the effect can be transient and change location rapidly.

Quicksand develops when the sand grains can no longer remain in their original horizontal layers because the upward flow of water is sufficiently great to make the sand grains float. The sand is behaving as a fluid or quicksand.

Heave

During this video we can see the effect of a clay swelling due to water ingress and the subsequent damage to the house above.

This hazard is known as heave and is associated with the shrinking and swelling properties of clays.

This tends to be a problem in areas of dry climates subject to occasional heavy rain.

As the clay gets wetter, it swells and pushes the ground above it upwards damaging the house.

Shrinkage of clay (the opposite process) tends to be more dominant in wetter climates subject to occasional prolonged dry spells.

Sinkhole

Some rocks such as salt, gypsum, chalk and limestone can be dissolved by groundwater on a local scale, causing the collapse of the overlying ground; this collapse is called a sinkhole.

In this model, the white area labelled soluble rock is salt.

As the water filters down through the rocks above, the salt starts to dissolve and the rocks above drop down to form a sinkhole.

Contact

Contact the Shallow Geohazards and Risk Team for more information.