They seem mysterious and frightening – Sinkhole!, suddenly appearing in the ground and “swallowing” things at the surface.\u00a0 Like quicksand and all of a sudden there but, in another sense,\u00a0not like quicksand which you maybe can see ahead of time and walk around.\u00a0 Swallowing things like entire cars as shown in the picture on page A4 of the Globe and Mail yesterday.<\/p>\n
The picture was of the rear of a vehicle just showing above the paved surface of\u00a0the\u00a0Highway 174 off-ramp at Jeanne D’Arc\u00a0Boulevard in Ottawa.<\/p>\n
The hole was deep enough that almost\u00a0the entire length of the vehicle was in it, wide enough to take the width of the vehicle, and\u00a0the width of the lane long.\u00a0 A fair size hole to suddenly appear in the highway.<\/p>\n
The traffic lane appears to be one of at least four lanes, two of which are at a lower level.\u00a0 The lower\u00a0lanes appear in the upper, right corner of the picture.\u00a0 The lower lanes glisten with water.<\/p>\n
We don’t expect this to happen in\u00a0our highways, and particularly in the natural environment if the source of the problem lies there.\u00a0 Seemingly natural events like this destroy\u00a0our fundamental assumptions about the safety of the world (Ref. Janoff-Bulman).<\/p>\n
But events like this are not so mysterious and their occurrence can be fairly easily predicted, but, unfortunately, not so easily the timing and location of their occurrence.<\/p>\n
A forensic engineer investigating the\u00a0cause of this sinkhole might consider\u00a0four elements to the problem even before leaving\u00a0his office (I’m pretending I’m the engineer and just got the call and haven’t even seen the site, but know about structures in general):<\/p>\n
As soon as a professional engineer gets to the site and does a visual assessment (see posting, September 4, 2012) he might well refine this listing but I don’t think a lot.\u00a0\u00a0The visual assessment would draw the engineer’s attention to any unusual conditions in the terrain beyond the highway.\u00a0 Conditions like evidence of heavy rain and its effects, flooding, nearby construction works that have impacted the road, etc.\u00a0 The engineer is likely to have checked the recent weather reports for the area.<\/p>\n
Seeing nothing unusual the engineer\u00a0is certain to hyposthesize initially that the problem lies with the infra structure buried in the roadbed, service pipe work of some sort.\u00a0 Like storm drains and\u00a0water\u00a0supply\u00a0distribution pipes.<\/p>\n
He\u00a0might form this hypothesis based on evidence such as the following:<\/p>\n
The forensic engineer might reason that the location of the hole and its shape\u00a0are typical of those that\u00a0might form when a water main bursts.\u00a0 The escaping water seeks the easiest path down and out to the right eroding the roadbed as it flows.<\/p>\n
Of course he would look in the\u00a0hole once at the site.\u00a0 If he sees a burst pipe\u00a0discharging water then he’s\u00a0reasonable in assuming he’s\u00a0solved the problem of what caused the hole to form.<\/p>\n
If he doesn’t see a burst pipe then he will start to think of other possibilities while waiting for documents on the existence and location of buried infra structure\u00a0in the roadbed.\u00a0 It’s possible there is a burst pipe but it’s buried\u00a0deeper and not visible in the bottom of the\u00a0hole.<\/p>\n
One possibility is the types of natural soils and rocks forming the subgrade or foundation of the roadbed.\u00a0 If he has geotechnical engineering experience he would want to know if the area of the road is\u00a0underlain by Karst terrain. This is a type of terrain formed on\u00a0rock like limestone that dissolves in the\u00a0presence of water forming different types of solution cavities – like sinkholes, for example.\u00a0 Or ‘roofed over’ sinkholes that are just about to break through\u00a0like the banana holes in the Bahamas.\u00a0 There is Karst terrain in the Windsor area of Nova\u00a0Scotia.<\/p>\n
Karst terrain has a certain appearance at the surface and the forensic engineer would look for this while waiting for a copy of the geotechnical report for this section of the highway.<\/p>\n
So, the forensic engieer would form different hypotheses during his investigation of the sinkhole – the hypotheses above and possibly others, investigate\u00a0each in turn\u00a0with site work and information from documents until he arrives at the cause of the sinkhole.\u00a0\u00a0The sinkhole\u00a0wouldn’t be a mystery to him.\u00a0 It would be a problem with a solution that he would be confident he could find.<\/p>\n
For certain, professional engineers with the\u00a0Department of Highways in this area are working on the\u00a0problem now.\u00a0 They would follow procedures like I’ve outlined above – consciously or unconsciously forming and revising hypotheses and checking them out.<\/p>\n
The hole formed in the road and the vehicle drove into it on Tuesday.\u00a0 Based on my experience of these things, I’m certain they\u00a0have already solved the problem.\u00a0 It can be that quick in forensic engineering.<\/p>\n
References<\/strong><\/p>\n <\/p>\n","protected":false},"excerpt":{"rendered":" They seem mysterious and frightening – Sinkhole!, suddenly appearing in the ground and “swallowing” things at the surface.\u00a0 Like quicksand and all of a sudden there but, in another sense,\u00a0not like quicksand which you maybe can see ahead of time … Continue reading \n