Sinkhole in Johannesburg

I heard about this on the radio whilst driving back in from Barberton today:

jozisinkhole.jpg

This collapse appears to be related to tunneling for the Gautrain project. The drillers apparently – and unexpectedly – hit soft, unconsolidated sediment and closed off the road before part of it disappeared, so fortunately nobody was injured. The water in the hole is from a burst main. Has someone not been doing their ground surveys properly, I wonder? And what are they going to do if this unconsolidated stuff goes deeper than the depth of the current tunnel?

Categories: geohazards

Comments (2)

  1. clay says:

    The unconsolidated material under the level of the tunnel will have no effect on the sink-hole as it will just sit there held in place by gravity. The material above the tunnel will rill or self-mine until it it fills the void created by the tunnel. The self-mined unconsolidated material will also take up more volume than it did insitu, as mined or dug-up materials usually have a volume increase of 30% or so.
    Not good news for property values of anyone having a house in the near vicinity.

  2. Erik says:

    Depending on how the tunnel is lined and where that water is going they could get running ground coming in to the tunnel from below to cause some pretty serious settlements at the tunnel alignment.
    This situation is every tunnel engineer’s nightmare. :)