I blogged recently on the difficulty estimating the cost of forensic engineering investigation (Ref. 1). The item included a tabulated assessment of the ease or difficulty estimating the cost of a possible 16 or more steps in an investigation.
You could be excused for thinking that the more catastrophic the engineering failure the more difficult estimating the cost to investigate the cause. But, this is not necessarily the case at all.
I thought of this a few days ago when I received a report that is being circulated on the internet about a 13 story residential building collapsing in China in June 2009 (Ref. 2). Take a look below; it’s quite a sight to see a multi-story apartment building lying on its side.
Why would it be fairly easy to estimate the cost to investigate the cause of the catastrophic collapse of a 13 story building? Surely not easy, you say.
Because reading the documents – one of the first steps in a forensic engineering investigation, would identify the type of foundation - piles, supporting the building. A simple site visit and visual examination would then note the blunder made on site. Based on these two simple tasks, it would be easy to hypothesize the cause with considerable reliability.
For certain, a fairly standard investigation of the foundation soil conditions would be carried out to confirm the hypothesis – if, in the unlikely fact, the documents did not contain this soil data.
It is fairly easy to estimate the cost of these particular forensic engineering investigative tasks:
- Document review,
- Site visit, and
- Standard soil tests – if the soil data was not already in the documents..
By way of further comment, an experienced professional engineer would recognize that a basic foundation engineering principle had been violated, that of excavating and undermining the foundation on one side – this alone could cause the problem if the excavation was deep enough. Then, making the situation worst by piling the excavated soil on the opposite side and surcharging the foundation. The rain made the situation worse still by increasing the surcharge weight of the excavated soil on the ground and possibly reducing the strength of the soil beneath the ground surface.
The fact of the piled foundations would tell the engineer that the soils near the surface are weak adding further to the effects of the undermining and surcharging. Piles simply carry or transfer the weight of a structure/building through weak soils to bear on stronger soils at depth.
Violation of this simple principle – undermining one side, surcharging the other, would leap off the note book page containing a sketch of a cross-section through the excavation, building foundations, the normal ground surface on the other side, and surcharge pile on the ground. Never mind a note book - draw the sketch on a cigarette package, the violated principle is that obvious; I don’t smoke but that’s what people use to do.
A similar principle is at work prompting any one of us to be careful walking too close to the high, steep bank along the shore of a lake or river lest we fall in like the Chinese building fell down.
These kinds of catastrophic failures have also occurred in Canada, and estimating the cost of investigating the cause is sometimes easy.
For example, the failure of the nine story high Transcona Grain Elevator in Winnipeg in 1913 – you can find on Google. The elevator failed – and leaned over 27 degrees, while being filled with wheat. The wheat added weight to the foundations such that the bearing capacity of the supporting soils was exceeded. Reading documents, a site visit, and a fairly conventional - and fairly easy to estimate, geotechnical investigation of the foundation soils would confirm a hypothesis of bearing capacity failure.
So, estimating the cost of investigating the cause of a catastrophic failure is not always difficult. And, if you don’t mind, I would like to say that estimating the cost of investigating a simple failure is not always easy.
1. Difficulty estimating the cost of forensic engineering investigation. Posted July 23, 2013
2. Chinese multi-story building failure
YES, IT IS A 13 STORY BUILDING LYING ON THE GROUND.
Anybody who bought a condo here sure has a problem.
Talk about a collapsed market!
(1) An underground garage was being dug on the south side, to a depth of 4.6 meters.
(2) The excavated dirt was being piled up on the north side, to a height of 10 meters.
(3) The building experienced uneven lateral pressure from south and north.
(4) This resulted in a lateral pressure of 3,000 tonnes, which was greater than what the pilings could tolerate.
Thus the building toppled over in the southerly direction.
*First, the apartment building was constructed.*
Then the plan called for an underground garage to be dug out.
The excavated soil was piled up on the other side of the building.
*Heavy rains resulted in water seeping into the ground.*
The building began to tilt
Then it began to shift and the “hollow” concrete pilings were snapped due to the uneven lateral pressures
And thus was born the eighth wonder of the world.
If the buildings were closer together it would have resulted in a domino effect.
They built 13 stories on grade, with no basement, and tied it all down to hollow pilings with no rebar.