We recently learned about the potential for failures and accidents in the built environment. (Ref. 1) There are 1,000s of different ways these can happen based on the great number of structures that are out there – at least 124. (Ref. 1) But where are the failures? Where’s the evidence this might be happening?
It would seem to be all around you as you drive and walk in your neighbourhood, your community, your town and your city. And you can’t escape the evidence by taking a break in the country. It’s there too. (I saw a barn on its way to collapsing during a drive in the country in New Brunswick on September 26, 2020)
By way of bringing you up to speed, I describe a few failures and accidents below, in some cases with a typical cause noted. I’ve classified them according to whether they were:
- Small
- Medium
- Large and Catastrophic
- Personal or,
- Stupid
- The Reality
A. Small Failures
1. Manholes and catch basins in the street are sometimes higher or lower than the road surface by a few inches. They are design or construction failures.
Car drivers in trying to avoid the bump sometimes have accidents.
2. A narrow depression a few inches deep across a road – sort of like a hollow, upside down speed bump – is a failure. You know them from the bump-bump as you drive across. They are located above trenches where storm and sanitary sewers and water pipes have been installed.
The depressions result from poor compaction of the soil placed in the trench to fill it after the sewers and water pipes are installed – a construction failure.
They can also cause motor vehicle accidents.
3. Pot holes in roads are a design or construction failure.
They’re due to a weak pavement and subgrade or a poorly drained subgrade.
It’s interesting, pot holes can “grow” larger after water collects in them. The water helps soil stick to the wheel of a vehicle as it drives in and out of the pot hole.
4. Broken pavement in public parking lots and private driveways are failures.
In the case of parking lots, the failure is due either to inadequate design or construction. In the case of driveways, it’s due to inadequate construction.
Like pot holes, the pavement and subgrade are weak or the subgrade is poorly drained or both.
5. Sloping floors in houses or apartments are failures.
They’re due to inadequate construction – an 11″ slope from one end to the other in one house that I examined. The mistake was found in time but not corrected.
6. Wet basements and leaking roofs are failures, of course.
B. Medium Failures
1. The floors of a multistory building, a high-rise, slope and sag at least an estimated 2 and 3 inches – a failure.
I know how high-rises are constructed, and in this case I also learned about the tight schedule the contractor was under to get it up. This was probably a construction failure that unfolded as the floors went up.
There’s an increased risk of slip and fall accidents on sloping floors, particularly if they’re wet.
2. The concrete block and brick walls of buildings sometimes crack – a failure in some cases
The large size and configuration of some cracks point to inadequate design or construction. Tiny cracks are usually normal.
3. The foundations of all manner of structures sometimes fail. The failures are marked by excessive foundation settlement or total, catastrophic collapse.
A little settlement is normal. Excessive settlement damages the structure above. Collapse destroys the structure.
These types of failures are often due to inadequate geo-investigation of the foundation soils but sometimes due to inadequate foundation design or construction.
4. Uneven sidewalks are due to inadequate design or construction of the subgrade support or to poor drainage.
The unevenness is quite noticeable when the sidewalk is constructed of concrete slabs and one slab is a little higher or lower than the next at a joint – and easy to trip over.
I’ve classified these as medium failures because of the increased risk of trip and fall accidents.
5. The three Edmonton bridge girders that bent sideways during construction on March 15, 2015 was a failure. No one was injured because the construction workers went home due to a wind storm. A crane was left standing with it’s cable and strap connected to the outside girder of the three.
Although I was not involved in the investigation of this failure, I did study photographs on line and in newspapers and conferred with structural engineers and bridge designers. I also examined the bridge from a security fence while visiting my daughter in Edmonton.
I concluded – an initial hypothesis – the wind caused the crane’s boom to vibrate and the strap to repeatedly tug on the girder and in time bend it sideways. The outer girder was connected to the other girders causing them to bend too. This was a construction failure.
6. The St. John river in New Brunswick sometimes floods in the spring and causes damage downstream. Some people wondered during the flood of 2019 if it could be due to operation of the Mactaquac dam and reservoir upstream of Fredericton.
The dam was constructed to generate electricity when water pressure on the dam’s turbines cause them to turn. The greater the pressure the faster they turn the more electricity generated. The greater the depth of water in the reservoir behind the dam the greater the water pressure.
There would be interest in the operation of the dam in maintaining as great a depth of water as possible. But, too great a depth would threaten over-topping of the dam and collapse – a failure. Not good.
Water is released from the reservoir to prevent this. But some years melting snow and rain in the watershed would cause the depth of water in the reservoir to rise more quickly. The need to release water would get quite pressing. The reluctance to do this would still be there because water depth/pressure is hydro power.
I can’t help but think these conflicting interests would have something to do with flooding of the St. John river.
7. Rain water flooded the electrical service rooms of a medical practice. My investigation included uncovering the PVC pipe carrying the power lines into the rooms. This revealed water seeping in around the outside of the pipe where it passed through the exterior wall. Further investigation found evidence of rain water inside the pipe.
Water wasn’t supposed to be there because the top of the pipe on the outside wall where the power lines entered from the street was covered by a canopy. Falling rain was shed by the canopy.
This was fine except a driving rain storm out of the southeast has rain soaked up-gusts. These gusts of wind carry water up under the canopy and into the top of the PVC pipe and down the pipe and into the electrical rooms – a canopy design failure.
It’s interesting that the inadequate design was recognized during construction. Steps were taken to accommodate the defect and it was a good solution. Except, another problem developed involving the electric lines that breached the good solution after it was implemented.
At the end of the day, definitely a canopy design failure aided and abetted by construction failure of what seemed like a good idea. Explaining all these issues would make your eyes glaze over so I’ll stop here.
8. The slump of soil on a cut slope along a highway – a mini landslide – is a design failure.
You sometimes see these along our highways. They are often due to excavating the slope too steeply for the natural angle of repose of the soil, or poor drainage of the slope. These types of failures can be up there with a catastrophic failure.
C. Large and Catastrophic Failures
1. The debris flood that happened in British Columbia early Saturday morning July 4th was a failure. A waist high mix of mud, gravel and cobbles slid off the mountain and covered a residential property. Another slide also occurred in the area. The Ministry of Transport reported the likelihood of additional slides.
The slide could be attributed to poor planning years ago in allowing houses to be built in a slide-prone area in the first place or poor maintenance in not monitoring conditions like rainfall that precipitate landslides.
2. The bridge linking Canso to Durell’s Island in Nova Scotia that collapsed Tuesday July 7th was a failure. The bridge fell down as a truck drove over it hauling a flatbed trailer loaded with a crane.
The failure was likely due to either the live load of the truck, flatbed and crane exceeding the design live load of the bridge or maintenance of the bridge or a combination.
(A live load is the weight to which a structure is subjected periodically in addition to its own dead load/weight which is always there)
3. I investigated the cause of a bridge collapse in a residential area. A woman was injured when she drove onto the bridge debris in the stream below.
The failure was due to corrosion of the steel in the bridge that was missed during inspection and maintenance.
4. The crane that collapsed onto a multistory building in Halifax in 2019 was a failure. It came to rest draped over the front of the building, over the top and down the other side. The crane broke/bent at several locations along it’s length during the failure.
I am not involved in the investigation of this failure but from a distance outside the security fence it was easy to imagine – an initial hypothesis – that the wind that night, a live load, was too great for the crane. It looked like an older crane and steel corrosion might be suspect too.
5. High retaining walls that collapse and fall down are usually design failures. The base of one that collapsed on the coast of Nova Scotia a few years ago was too narrow.
Low retaining walls typical of residential landscaping that lean too much are construction failures and often due to inadequate drainage.
6. A man climbed a step ladder to do some work above a hung ceiling in a building. He fell, hit his head on the concrete floor and died instantly. One of the ladder’s legs was bent.
I was retained to investigate the cause of the accident. There were no witnesses to report on whether or not the workman leaned one way or the other while on the ladder nor how far he had climbed up the ladder.
The bent leg and a leaning workman near the top of the ladder were of course initially suspect. I planned a re-enactment of the accident with a professional stuntman however my client resolved a dispute arising from the accident in another way.
7. Ice falling off a roof and hitting and severely injuring a person is a maintenance failure.
8. A landslide that takes a house down with it is a catastrophic failure.
I investigated the cause of one like this on the coast of New Brunswick. It was due to erosion of the toe of the natural slope by the Bay of Fundy.
The landslide was not an act of God because it could have been foreseen and prevented, or avoided by building elsewhere.
9. I saw a catastrophic failure waiting to happen in a drive through the New Brunswick countryside on September 26, 2020 (Example added in a blog update September 29). A barn with a sagging roof – maybe 10 feet in the middle; a lot. I’m sure no longer in use considering the sag. It was the magnitude of the sag that caught my eye.
You see lots of large and small buildings in the country with roofs that are sagging a little or a lot. Many are abandoned, but not all.
You can see buildings in town, houses, with a little sag to the roof, a tiny, few inches, just enough to catch your eye from the street.
The large sags are design failures. Many of the tiny sags are design failures too but some are due to lumber shrinking as it drys after construction is done.
D. Personal Accidents
1. I was cleaning snow off the back of my neighbour’s car in his sloping driveway two winters ago. He gets up a bit late. I was out doing some shoveling so I thought I might as well.
I started to slide sideways down the slope towards the street. As it turns out on some black ice. I did good until I got to the windrow of snow left by the snow plow, fetched up and fell hard.
I like to think to this day that if I had been on skis I would not have fallen considering that East Coast ski hills have some icy runs.
My accident alerted me to the accidents waiting to happen on sloping, paved driveways – surfaces, in general, used by people – due to black ice, due to questionable design and construction.
I see in recent years steel plates with roughed surfaces being installed on sloping sidewalks at intersections. Smart.
E. Stupid Accidents
1. Three months after investigating the step ladder fatality I was up a step ladder putting the finishing touches on construction of a storage shed on my property. I was nailing the fascia board in place and leaned sideways on the ladder to drive that last nail at the end when down I went.
I was lucky and didn’t hit any of the cobbles exposed at the ground surface but I did hit the ground hard and lay there for a while. My ladder was not defective – no component failure, no bent legs – just my use of the ladder.
***
The Reality
There’s a lot of things broken and not working as they should. It’s important to know this and that it’s all around us, even out in the country. Also, that it’s our fault, we designers, builders and operators. But know too, that the great bulk of the built environment works just fine, thank you very much, and that’s due to us too, we folk who live in the built environment. There is the potential for 1,000s of failures but they don’t happen because we get it right almost all the time. (Ref. 2)
References
- What’s in “…the built environment” and how many ways can it fail? Posted July 8, 2020
- Petroski, Henry, To Engineer is Human, The Role of Failure in Successful Design, Vintage Books, Random House, Inc., New York 1992
(Updated September 29, 2020 by Eric E. Jorden, M.Sc., P.Eng., consulting professional engineer, forensic engineer, Geotechnology Ltd., Halifax, NS, Canada E: ejorden@eastlink.ca)