It’s not very glamourous – and it does cost money, but if a structure is not maintained as designed and constructed it won’t perform as intended.  Poor maintenance can actually be the cause of a building or civil engineering structure failing, or an accident occurring.

Examples

For example, I investigated a slip and fall accident on a stair landing at a retail outlet several years ago.  Residual detergent from cleaning the landing was a factor in causing a man to slip and fall and injure himself.  The detergent reduced the skid resistance of the floor material covering the landing from adequate to inadequate.

Another example was the classic failure of a soil-steel bridge – a very large, corrugated steel culvert, carrying a road over a stream.  My forensic investigation found that the water corroded the hunches of the culvert causing it to collapse injuring a car driver.  Corrosion of the hunches – a critical part of a soil-steel bridge, is a classic fact of life for these types of bridges.  Better design, and regular inspection and maintenance would have prevented the failure.

To be fair, I’ve not seen reference to the need for proper maintenance on very many design and construction drawings over the years, if any.

Maintenance part of design and construction

Yet proper inspection and maintenance is part of the design and construction process.  I noted this in a blog a couple of years ago on the failure of the Elliot Lake parking garage (Ref. 1)

So, how’s an owner to know?  It seems, at the very least, that if you observe deterioration in your structure then you know you no longer have what was originally designed and built.  And no longer what users of the structure understand it to be – as serviceable and safe as originally intended.

Coming along every now and then and ‘restoring’ a structure doesn’t count because what you’re restoring is the effects of poor or no maintenance.  Regular maintenance is what counts if a structure is to reach its design life.  This is the length of time a structure is designed to be serviceable.  It is quite an important concept in engineering design.

Mysterious report on parking garage maintenance

I was reminded of the importance of proper maintenance when I read an item on the enquiry of the Elliot Lake parking garage failure in a recent MacLean’s magazine. (Ref. 2)  There was frequent reference to maintenance in the two page item.

I also see an item in today’s Chronicle Herald, Halifax, about the maintenance needs of the 4,300 bridges in Nova Scotia – and the fact the money may not be there for all the maintenance necessary (Ref. 3).  Or some of the money that is available might perhaps be better spent on other projects.  The item noted that maintenance must be done on some bridges just to get them in fair or good condition.  Does that mean some bridges in Nova Scotia are in poor condition?

The MacLean’s article was reporting on the mysterious appearance at the enquiry of a report from the Ontario Ministry of Housing, circa 1988, written by an expert advisory panel on the “Deterioration, repair, and maintenance of parking garages”.

The new-found report wasn’t the first to sound the alarm about “rotting parking garages”.  CMHC (the Canada Mortgage and Housing Cooperation) issued three research reports in the 1980s about the deterioration in parking garages.

The answer

Regular inspection and repair – maintenance when carried out on a regular basis, was the answer running through the reports.

This was also the answer to preventing the failure of the soil-steel bridge.  Simply walking through the culvert at low water, noting any corrosion, and fixing it.  I did this at several intact soil-steel bridges in eastern Canada – simply walked through them, during my investigation of the failure.

The need for cleaning a soapy residue from a stair landing at a retail outlet is not very glamourous maintenance work but simple to do.

References

1. Cause of the roof collapse at Elliot Lake, posted July 10, 2012 http://www.ericjorden.com/blog/2012/07/10/cause-of-the-roof-collapse-at-elliot-lake/
2. Elliot Lake: Warning signs, long forgotten, MacLean’s Magazine, June 9, 2014
3. Chronicle Herald, page A5, June 12, 2014

A reader in the U.K., Len Threadgold, (see profile below) commented on last week’s blog. (Ref. 1)  Len speaks with some authority when he notes that the problems with water can be grouped under the following three headings.  He also notes that separating problems into neat categories is useful but sometimes the categories work in association with each other – see examples below.

This classification is good: A way of understanding natural events and environmental processes.  In a sense, a way of measuring things.  Engineers like that.  It helps us solve problems and explain causes and technical issues to the justice system.  As such, it’s a forensic engineering method:

1. The problems that the presence of water causes

We don’t like flooding or working under water – so this problem concerns water level.

Examples would be your flooded basement, also the water pooling in your back garden that has drained from the land above – sorry to bring these examples up.  And the recent flooding that occurred in Truro, N.S., and in the U.K., and forecast for the Saint John River, New Brunswick.  Water pressure would also be a factor in a wet basement; see #3 below.

2. The problems that the flow of water causes

These problems are about erosion, the removal of soil as a result of water flow, the speed of the water.

For example, coastal erosion such as that occurring around the entire coast line of Prince Edward Island and also at Red Head, on the Bay of Fundy near Saint John, New Brunswick.  The flowing water on the coast is wave action and long shore currents.

I investigated one landslide at Red Head some time ago that destroyed a home at the top of a sea cliff.  I learned two weeks ago that erosion of the bottom of the cliff continues to remove the buttressing effect of the soil there.

Rain triggered the landslide at Red Head that I investigated – after erosion of the toe set the stage.  Rain did this by increasing the pressure in the ground water behind the cliff; see #3 below.

3. The problems that the pressure of water causes

These problems arise because water pressure affects soil strength.  You know this when your boots sink into the mud – clay in engineering – after a rain storm.

The problems are bigger than sinking, muddy boots though.

Water pressure – what we call pore water pressure in engineering – is often a factor in landslides as it was for the landslide at Red Head.  At times water pressure is the principal cause in changing an adequately stable slope to an unstable one.  Its effect is to reduce the frictional strength of the soil.

Water pressure was certain to have been a factor in the recent landslide in Washington State, U.S.  This landslide took more than a dozen lives with others still missing.  I saw early reports that there was a known risk of a landslide at this location.  The assessment leading to that conclusion is certain to have considered pore water pressure and its potential to change.

Len has investigated the potential for landslide problems in Hong Kong.  These would  be slopes that were susceptible to increases in pore water pressure.  Simple drains often fixed the problems but sometimes more in-depth water interception was necessary.

Water pressure is a factor in our wet basements.  And, believe or not, in many slip and fall accidents.  It’s the reason signs in a swimming pool caution us not to run on the pool deck.

In some slip and fall accidents, a person’s weight is momentarily applied to water on the floor surface.  The frictional or skid resistance of water is much lower than the material forming the floor surface – almost negligible by comparison.  So low in fact that the person slips and falls.

Len’s classification is a good one, an aid to those of us investigating problems with water and needing to explain the cause of a problem to the justice system.

Many of the forensic engineering problems I investigate – not just a few, and not just the obvious drainage and flooding problems – can be traced back to water and fall under one or more of the headings Len has identified.

Reference

1. Image credits and why forensic engineers like wet weather, the heavier the rain the better, posted April 9, 2014 http://www.ericjorden.com/blog/2014/04/09/image-credits-and-why-forensic-engineers-like-wet-weather-the-heavier-the-rain-the-better/

Len Threadgold’s Profile

Len is a civil engineer in the U.K. specializing in soil, rock, and ground engineering – geotechnical engineering.  We were colleagues when I practiced there.  Len’s firm, Geotechnics Ltd, provides consulting services to an international clientele including dealing with slope stability problems in Hong Kong and the U.K. – problems that would fall under #3 above.  The U.K. had their share of severe flooding problems this past year, problems with the mere presence of water; #1 above.  Len read a draft of this blog because it’s his classification system and some of the examples and comments are his.

Should experts do forensic engineering investigative work for free?  Would this jeopardize their objectivity or the justice system’s perception of it? (Ref. 1)

I have concluded that, in general, we should not and yes it would.

A possible exception would be a financially strapped client who otherwise might not have access to the justice system.

This question came up recently during lunch with a colleague who had referred an Atlantic Canada legal aid group to me.  One of their clients had a problem the cause of which my colleague recognized was more in my area of expertise to investigate than his.

I was contacted by a student lawyer with the legal aid group and called to a meeting.  I was told by an administrator almost before I could sit down, “We don’t have much money..!!  What’s your fee?”

I told them my hourly fee and also referred them to the Fees page on my website. www.ericjorden.com/fees  My schedule of fees is comparable to other senior professional engineers practicing forensic engineering in eastern Canada and, for that matter, elsewhere in Canada and the U.S.

They briefed me on the problem – an environmental failure, experienced by their client, the plaintiff.  Also that they had a court date about six weeks hence.

One of their biggest problems – aside from the tight court schedule, was that they did not know the precise location of the structure alleged to have caused the failure.  The location was critical to determining if the structure was the cause.

I outlined some of the tasks I would need to carry out in a forensic engineering investigation – including first locating the structure. (Ref. 2)

They said they would get back to me but I haven’t heard from them since.

Should I have said I would do the work pro bono instead of stating my fee?

In discussing this later with my colleague, he noted, “You’re doing the work for free for one party.  How is that different from doing the work for a fee for one party?”  He’s done work pro bono for the clients of this legal aid group feeling, “I should put back into the community”.

But we’re not doing the work for one party, we’re doing the work for the justice system.  The one party is paying an expert to gather technical evidence to be submitted to the court.  Also to explain the technical findings to the judge and jury, and to the counsel for the parties involved.  And to do this objectively, thoroughly, and reliably.  The justice system’s requirements for the expert to be objective are very clear.  There are no qualifications on this objectivity. (Ref. 3)

But the justice system represents the community’s interests.  Shouldn’t we from time to time put back into the community?

We must do this but not in this forum.  The justice system’s understanding of where we are expected to come from as experts affects their perception of our actions.  Lawyers are expected to be subjective and advocate on behalf of the client.  Experts are expected to be objective and advocate on behalf of the truth.

In our society, doing something for free for someone tends to imply a closeness that would not be acceptable for an expert in forensic work, even if the closeness is only slight.  There is the implication that we want to help someone when the clear implication should be that we want to help the court.  The requirement that we ‘stay at arm’s length’ is compromised.  If there’s any uncertainty at all about the objectivity of the relationship between the expert and the client there’s risk of being perceived as biased to the client’s interests.

We pay for goods and services in our society.  We can’t get away from that.  And you get what you pay for.

“Perception is extremely important.”, noted Alan E. Mitchell, a former lawyer in private practice and former Nova Scotia Minister of Justice.  Alan was of this opinion in a recent discussion I had with him about the Senate and Rob Ford scandals.  Perception applies across the board in human affairs.

We as experts must not do pro bono work – as a rule, even if we might want to as community minded citizens.

References

1. Do forensic engineers jeopardize the appearance of their objectivity?  Posted June 28, 2013  http://www.ericjorden.com/blog/2013/06/28/do-forensic-engineers-jeopardize-the-appearance-of-their-objectivity/
2. Steps in the forensic engineering process with an Appendix on costs.  Posted July 15, 2013 http://www.ericjorden.com/blog/2013/07/15/steps-in-the-forensic-engineering-investigative-process-with-an-appendix-on-costs/
3. Rule 55 Nova Scotia Civil Procedure Rules

(You are likely to be concerned, as I am, at the situation described in the following – a situation that wastes our client’s time and money)

The update is of a short item that was the 8th in a series on the role of a professional engineer at the different stages of civil litigation.  All the items in the series are listed below in the Bibliography and can be read on this blog site.

The series was intended to help lawyers and their clients understand how they can use professional engineers in the resolution of disputes with technical issues.

Update

My update expresses concern that civil cases are getting to the Settlement Conference stage before a forensic engineering investigation of the cause of the failure or accident is carried out.

Someone is going to get stung one of these days going forward with a case without a reliable determination of cause.  I haven’t seen this happen yet but it’s due.  And the more unusual the technical problem, the greater the risk.

At a Settlement Conference, you put forward a summary of your arguments to the judge on behalf of your client.  Too often the arguments are based on a cause that seems obvious.  But until the investigation is commissioned and completed and a technical expert has rendered a reliable, objective opinion – as per the requirements of Rule 55, you just can’t be sure.

To some extent, implicit in reliable is thoroughness.  Thorough case preparation on your part can’t be had without a reliable investigation of cause early in the litigation.

Also, cases settle quicker once a forensic investigation is carried out.

Fairly recently, I’ve seen two cases settle within a few weeks to a couple of months after technical opinions were rendered – many years, that’s many years, after a failure in the one case and an accident in the other had occurred and litigation begun.  I suspect another accident that I’m aware of will resolve just as quickly.  Time is money.  I don’t know what the injured parties were thinking letting these cases go on for years.

The six tasks listed below were originally identified for a perfect litigious world – civil litigation unfolding as it should; in the best interests of the parties involved.  I’ve suggested a seventh task after checking the investigations I’ve completed and realizing how imperfect that world is.

Seriously, counsel can take a case forward to a Settlement Conference with greater confidence – much greater than that possible based on the seemingly obvious, if a forensic investigation of cause is carried about the time a statement of claim or defence is filed.  And litigation resolved earlier and money saved.

Original Settlement Conference

If mediation or arbitration is not tried or is unsuccessful then lawyers for the parties meet and confer with a judge to decide if a settlement is possible with his assistance.  By this time the parties will be ready to go to trial.  They will have the documents that they will be relying on, reports from professional engineers and other experts, physical and demonstrative evidence, and testimony from discovery.

The lawyers, in advance of the Settlement Conference, send the judge a brief summary of their arguments and any relevant documents.

At the conference the judge will listen to the lawyers and try to achieve a settlement.  The judge will sometimes give an opinion on how they would decide the case if they heard it at trial.  However, they cannot force a settlement and would not officiate at the trial because of their role in the Settlement Conference.

A professional engineer might assist counsel at this stage of civil litigation by carrying out the following tasks:

1. Review all technical evidence and technical facts identified at discovery, paying particular attention to new evidence
2. Re-assess determination of cause of failure, inadequate performance, or cause of accident
3. Check all technical documents and information that will be relied on in counsel’s arguments during the Settlement Conference
4. Identify technical evidence and facts favourable to the opposing party
5. Re-assess the technical strengths and weaknesses of the claim or the defense and brief counsel
6. Review and comment, as appropriate, on the technical content of counsel’s proposed summary to the judge of their arguments and documents
7. Carry out a forensic engineering investigation if you didn’t do this years ago

Biblio

1. What is forensic engineering?, published, November 20, 2012
2. Writing forensic engineering reports, published, November 6, 2012
3. Steps in the civil litigation process, published, August 28, 2012
4. Steps in the forensic engineering investigative process, published October 26, 2012
5. The role of a professional engineer in counsel’s decision to take a case, published June 26, 2012
6. The role of a professional engineer assisting counsel prepare a Notice of Claim, published July 26, 2012
7. The role of a professional engineer assisting counsel prepare a Statement of Claim, published September 11, 2012
8. The role of a professional engineer assisting counsel prepare a Statement of Defence, published September 26, 2012
9. The role of a professional engineer assisting counsel prepare an Affidavit of Documents, published October 4, 2012
10. The role of a professional engineer assisting counsel during Discovery, published October 16, 2012
11. The role of a professional engineer assisting counsel during Alternate Dispute Resolutionn (ADR), published November 16, 2012
12. The role of a professional engineer assisting counsel prepare for a Settlement Conference, published November 29, 2012
13. The role of a professional engineer assisting counsel prepare for a Trial Date Assignment Conference, published December 12, 2012
14. The role of a professional engineer assisting counsel prepare for Trial, published, December 19, 2012
15. Built Expressions, Vol. 1, Issue 12, December 2012, Argus Media PVT Ltd., Bangalore, E: info@builtexpressions.com, info@argusmediaindia.com

(This is not an East Coast ghost story)

(The following is one in a series of cases I have investigated that illustrate the different forensic engineering methods I use to investigate the cause of failures and accidents that result in civil litigation.  Knowledge of simple frost heave was important in this case)

The investigation of the vibrating building is reported under the following main headings with several sub-headings:

• The case (A description of: 1. The building and the problem experienced by the owner; 2. The building’s foundations, and the problems with the building, 3. The legal/technical issues, and, 4. My client)
• Forensic engineering investigation of the problem and the methods used
• Findings of the investigation (conclusions with respect to the technical issues)
• Resolution
• Lessons learned

The case

Description of the building and the problem 

The building was a large, well appointed mobile home in the Halifax area that vibrated quite noticeably during the winter months.  The vibration occurred when the owner and his family walked the length of their home from one room to another.

The owner also wanted to know why the interior partitions at some locations were separating from the ceiling.

Legal/Technical Issues

The main issues were the cause of the vibration and the cause of the gaps at the tops of the partitions.

Client

I was retained to investigate the problem by the company who placed the mobile home on the site.

Forensic engineering investigation

My forensic engineering investigation involved the following methods:

1. Take a briefing on the problem from the owner.
2. Visually examine the building and the site it was on.
3. Examine and determine how the building was supported and the foundations constructed.
4. Sample and determine the type of foundation soils underlying the building site and their physical properties.
5. Analyse the data collected during these examinations.

Investigations and Findings

Briefing  The owner was quite clear in describing how the building vibrated in winter in walking from one end of his home to the other.  He also described the gaps at the top of the partitions.  The building did not vibrate during the summer.

I wasn’t on site during the winter but saw and measured gaps of about 1/4 to 1/2 inches during my visit.

Visual examination:  The home was on a sloping site with the length of the building aligned up the slope.

Examine foundations:  I crawled under the building and established that the mobile home was supported on two continuous steel beams running the length of the mobile home.  The beams were in turn supported by concrete block piers at regular intervals.  The piers were supported on the sloping ground a few inches below the surface.

Because of the sloping ground, the height of the piers and the home above the ground gradually increased from 1.5 feet at the upslope end to 3.5 feet at the downslope end.

Test foundation soils:  I took samples of the soils supporting the piers and had the samples tested in a laboratory.  I also researched the soil geology of the area – the surficial geology.

The tests and research established that the foundation soils comprised a dense, silty glacial till typical of the many drumlins in the area.

Drumlins are teardrop shaped glacial soil deposits.  The Citadel in Halifax is on a drumlin.

Analyse data: The fact that the mobile home vibrated in winter but not in summer was interesting, and took some reflection on my part.

The shallow depth of the pier foundations supporting the mobile home – a few inches, was not typical for foundations in this area.

We dig our foundations down typically about 3.5 to 4.0 feet in the Halifax area to get below the depth of frost penetration and the effects of frost heave.

A characteristic of the fine grained soils found beneath the piers is that they are very frost susceptible – water collects in the soils easily and freezes in winter.  The mixture of water and soil expands on freezing – frost heave to everyone.  The more soil freezes – the greater the depth of freezing, the greater the frost heave.

The pier foundations would have heaved in winter for certain considering they were only a few inches below the ground surface, not 3.5 to 4.0  feet..

The depth to which the soil freezes depends on the severity of the winter.  Deeper in cold winters, shallower in warmer winters.

A source of heat from an external source other than the weather can also affect the depth of frost penetration in the ground and the amount of frost heave.

Regardless of how well we typically insulate our homes, heat is lost in winter to the surrounding air.  The air is warmed in the process and in turn warms other surfaces in contact where it is protected from the wind.

That was the case at the upslope end of the mobile home where the building was closer to the ground – 1.5 feet.  The depth of frost penetration and heave could be expected to be less at this end of the building than at the downslope end where the home was 3.5 feet above the ground.  It was also exposed to the wind at this downslope location.

Frost was penetrating the ground to an increasing depth from the 1.5 foot end of the mobile home to the 3.5 foot end.

All the piers along the length of the home would heave due to frost action but not necessarily a proportionate amount.  This is because conditions at each pier could be expected to vary a little: Foundation soil conditions could vary, also heat loss from the mobile home, protection from the wind, etc.

The steel beams could be expected to be lifted off the piers completely at some locations – and “suspended” between adjacent piers, because of the disproportionate amount of heave at the adjacent piers.

Steel beams deflect between piers.  The greater the suspended distance between piers providing support to a mobile home the greater deflection.  Walking along a floor supported on such beams causes the floor and the beam to deflect and vibrate.  I think a good many of us have walked along wooden planks supported at each end and felt the deflection and vibration.

Conclusion

I concluded that the mobile home was vibrating as much as it was because it was not properly supported by the piers in the winter time.  Because of the magnitude of the vibration, I believed that the mobile home was only supported by the piers at the ends of the two beams.

The gaps formed at the top of the partitions because the joints between the tops of partitions and the ceiling are relatively weak and would separate when the supporting beams deflected.  I suspect that small gaps would have formed at the bottom of the partitions as well but went unnoticed.

Resolution

I recommended digging and founding the piers deeper and below the depth of frost penetration and heave.

Lessons learned

1. Always look at the weather conditions along different parts of a foundation when unusual problems are occurring in the structure above.

(The following is one in a series of cases I have investigated that illustrate the different forensic engineering methods I use to investigate the cause of failures and accidents that result in civil litigation.  The methods are listed in this blog and described in some detail in a future posting)

The investigation of the fatal motor vehicle accident (MVA) is reported under the following main headings with several sub-headings:

• The case (a description of the fatal MVA, the legal/technical issues, and my client)
• Forensic engineering investigation of the failure and the methods used
• Preliminary findings of the investigation
• Post mortem (resolution and lessons learned)

The case

Description of fatal motor vehicle accident (MVA)

The accident occurred a few years ago on a remote, snow-covered highway along the top of a seaside cliff in eastern Canada.  A jeep-like vehicle travelling along the highway at dawn struck a pile of soil-like material left in the travel lane.  The driver lost control of the vehicle and drove over the cliff and into the sea.  The driver died in the accident.  Passengers in the vehicle survived.

Legal/Technical issues

At issue, for purposes of the forensic engineering investigation, was the following:

• Whether or not the pile of material on the highway was a hazard
• If it was, determine the degree or severity of the hazard
• Also, whether or not the pile of material caused the accident

Client

I was retained by the RCMP to investigate the accident and resolve the technical issues.

Forensic engineering investigation

There were no guidelines or well developed methods in the engineering literature on how to investigate this type of accident and resolve the technical issues.  The investigation was unique in this respect.

Fortunately, in researching the literature, I did find some very relevant scientific research that I was able to adapt to my problem with excellent results.

My forensic engineering investigation relied on the following methods.  The methods will be described in some detail in a future posting.  I believe the following listing of methods is quite informative by itself:

1. Take briefing on the accident from RCMP
2. Review documents on the accident provided by the RCMP including police reports and survivor’s statements
3. Travel to the area and visually examine the scene of the accident
4. Generate a picture of the accident scene using Photoshop as it might have been seen by the driver moments before the accident
5. Research engineering literature for methods on the investigation of obstructions on a highway
6. Research scientific literature on speed bump research and design
7. Research transportation authorities in North America and Europe
8. Design a full scale preliminary re-enactment of the accident on bare roads
9. Plan a full scale re-enactment of the accident on a snow covered test site implementing refinements to the re-enactment including safety measures derived from the preliminary testing
10. Design a videotaping and measuring of the re-enactment
11. Construct a re-enactment site on an airport taxiway
12. Re-enact and videotape the accident on the test site
13. Analyse the videotape for evidence respecting the technical issues
14. Edit the videotape to portray the re-enactment in a report
15. Report on the preliminary findings including safety issues

Description of methods of forensic engineering investigation

(The methods will be described in some detail in a future blog posting)

Cause

(The findings of the investigation will be reported in a future posting)

Post mortem

The matter was settled out of court.

(Lessons learned from the investigation will be shared in the future blog posting)

References

1. “Technical” visual site assessments: Valuable, low cost, forensic engineering method.  My blog posted on this site, September 4, 2012

(The following is one in a series of cases I have investigated that illustrate the different forensic engineering methods I use to investigate the cause of failures and accidents that result in civil litigation.  The methods are described in some detail)

The investigation of the wall collapse is reported under the following main headings with several sub-headings:

• The case (a description of the collapsed gabion wall, the legal/technical issues, and my client)
• Forensic engineering investigation of the failure and the methods used
• Cause (of the collapse)
• Post mortem (an engineering “rule of thumb” might have prevented the collapse)

The case

Description of collapse

The gabion wall was on the shore of a harbour in eastern Canada.  The wall was 10 feet high and more than 100 feet long.  There were short wing walls to the main wall aligned shoreward.  A “gabion” is a wire basket about 3 feet by 3 feet in section and 10 feet long filled with course stone several inches in size.

The wall was being constructed to reclaim land on the seaward side of a quite large townhouse property.  The wall fell over just before construction was complete.  It was rebuilt before I was retained.

Legal/Technical issue

At issue was the cause of the wall’s failure.  This was in connection with a claim of damages against the designer and his insurance company.

Client

I was asked by the plaintiff, a property manager who was acting on behalf of a contractor, to determine the cause of the collapse.

Forensic engineering investigation

My forensic engineering investigation relied on the following methods.  The methods are described in more detail below:

1. Examining the site of the rebuilt wall
2. Studying photographs taken of the collapsed wall
3. Studying a design sketch of the wall
4. Interviewing two workers who were on the wall at the time it failed, including one who slid down with the wall on a piece of construction equipment as it fell over
5. Interviewing the design engineer
6. Reviewing design principles for coastal and marine structures
7. Reviewing weather and sea conditions at the time of the failure

Description of methods of forensic engineering investigation

1. Examining the site of the rebuilt wall

This initial site visit and visual assessment is standard in an engineering investigation and an important initial task by a forensic engineer (Ref. 1).  Drawings and photographs are fine but picking up a concrete impression is important.  It’s well recognized that, “A picture is worth a 1,000 words”.  However, a visual assessment is invaluable.  This is so even if the collapsed structure has been rebuilt as was the case with the gabion wall.

I was able to see how the toe of the gabion wall was constructed where it was exposed to the scour and erosive forces of wave action in the harbour.

I also saw the location of the townhouse with respect to the wall.  The contractor had expressed concern that construction of the wall as designed would undermine the townhouse.  A simple rule of thumb ruled this out.

2. Studying photographs taken of the collapsed wall

Photographs are important, and sometimes all we have.  They are particularly important when detailed photographs are taken during construction.  They are also important when taken of the failed structure that is subsequently removed before the forensic engineer gets there.  The latter was the case in this instance.

The photographs showed the actual wall construction and that it failed in a quite classic manner – it just tipped, tilted, leaned over along most of its length.  The exception was where the wall was tied in and anchored to the wing wall at one end.  It remained upright there.

3. Studying a design sketch of the wall

It goes without saying that a professional engineer investigating a failure would want to know how the failed structure was designed and intended to be built.  This is a standard task in a forensic investigaion.

The sketch showed how the design engineer originally wanted the base of the wall constructed and the toe of the wall protected against scour and erosion.  Simple rules of thumb suggested the base design was adequate.  The toe protection was less so.

4. Interviewing workers

Interviewing workers is a standard task in a forensic investigation.  The interviews sometimes provide quite valuable information on conditions at the moment of failure.

I interviewed two workers who were on the wall at the time it failed, including one, an equipment operator, who slid down with the wall on a piece of construction equipment as the wall collapsed.

In engineering analysis we speak at times about a “trigger” in a failure.  All conditions are present – or nearly so, for a structure, a wall, an earth slope, etc., to collapse.  The trigger pushes the structure over the edge in a sense.  Sometimes there is heavy rain – the trigger, just before a landslide.

The construction equipment just back of the gabion wall at the time was the trigger in this case, an extra surcharge/weight on the wall.

5. Interviewing the design engineer

We always want to talk with the design engineer when investigating a failure but often don’t have the opportunity during the investigative stage.  This lack of opportunity is particularly the case when the design engineer is the defendant in a civil action.

In this case, however, the design engineer was quite professional in agreeing to talk with me.  His design was okay in the short term.  It turned out that a change he approved during construction caused the problem.

The change involved reducing the width of the base from about six feet – 2/3 the height of the wall, to three feet – 1/3 the height of the wall.  The change was made because the contractor said he couldn’t build a six foot base.  He also expressed concern that the townhouse would be undermined.  Consideration of a simple rule of thumb would have raised an alarm that the wall would not be stable with a three foot base.  Another rule would have demonstrated that the townhouse was not endangered.

6. Reviewing design principles for coastal and marine structures

Reviewing the design prinicples applicable to a situation is standard fare in a forensic engineeing investigaion and I did this.  I was particularly interested in the requirements for protecting the toe of the wall against scour and erosion due to sea conditions.

7. Reviewing weather and sea conditions at the time of the failure

This is also standard fare during a forensic investigation and in this case it tied in with reviewing the design principles mentioned above.  Sea and weather conditions were calm at the time of the wall collapse.

Cause

I concluded, based on the evidence, that the wall failed because of a change in the design of the wall during construction.  The principle defect was that the base of the 10 foot wall was not wide enough at three feet.  I also found that the toe of the wall was not well protected against wave action in the harbour.

Post mortem

There is a rule of thumb in the design of conventional gabion retaining walls that the width of the base of the wall must be about 2/3 the height of the wall – about 6.5 feet in this case, not 3.0 feet as agreed during construction.  A design engineer starts off with this conventional wall geometry and then checks that the rule of thumb holds in the particular case.

There are lots of rules of thumbs in engineering,  They expedite matters but must always be checked.  And they should always be referenced when the pressure is on to change things during construction.

The matter was settled out of court.

References

1. “Technical” visual site assessments: Valuable, low cost, forensic engineering method.  My blog posted on this site, September 4, 2012

(The following is one in a series of cases I have investigated that illustrate the different types of structural failures and accidents that occur resulting in civil litigation, and the forensic engineering methods I used to investigate the cause.  The series is designed to assist counsel gain an appreciation of the engineering investigative methods used by forensic engineers.

The methods are most important for purposes of this illustrative series.  As such, I do not report on the analysis of the evidence uncovered during the investigation)

The investigation is reported under the following main headings with several sub-headings:

• The case (A description of the accident and the scene, also, the client and the legal/technical issues)
• Forensic engineering investigation (Building construction/snow and ice formation)
• Cause (Addresses the legal/technical issues)
• Resolution
• Litigation
• Post mortem (Binoculars were an important investigative tool)

The case

A man was walking along a sidewalk in a city in eastern Canada several years ago when a piece of ice fell from a building hitting him on the head and knocking him out.  The man regained consciousness some time later in an ambulance on his way to the hospital.  A doctor diagnosed severe head trauma.  The man took time off work and was treated for his injuries.

The three storey building had a mansard roof – a roof with two slopes, covering the upper level.  The roof had several dormer windows.  The building was several decades old.  The accident occurred on the sidewalk on the south side of the building below one of the dormers.

The man retained counsel to assist him claim damages associated with his injuries.

Client

I was retained by the counsel in connection with the claim for damages and asked to investigate the accident.

Legal/Technical issues

Counsel identified the following issues relevant to a resolution of the dispute by the court:

1. The design and construction of a building and its roof in relation to safety issues concerning the accumulation of ice and snow.
2. Alterations that could be made to a roof or safety precautions that could be taken to prevent accidents.

Forensic engineering investigation

Following is a list of some of the methods I relied on during my investigation of the accident.  The methods and tasks are separated according to the issues identified by counsel:

Building construction/Snow and ice formation

1. Review documents in general as provided by counsel
2. Study photographs of the building and the scene taken at the time of the accident, particularly those marking the location of the accident and the construction of the roof
3. Visually examine the scene and the exterior of the building.  Note the formation and location of icicles on the roof
4. Examine with binoculars details and features of the roof construction, and the general repair and condition of the roof
5. Visually examine the formation and build-up of ice and snow on different buildings in other locations I travelled during the forensic investigation.  Reflect on the build-up of ice and snow on the roof of my home in the past
6. Research the formation of ice and snow build-up on roofs
7. Study victim’s statement of accident noting, in particular, what the victim heard at the time of the accident and the extent of the victim’s injuries
8. Study a floor plan of the building
9. Read the pleadings

Roof alteration

1. Research methods of altering the roof at the scene of the accident to prevent the formation of ice and snow on the roof
2. Examine products available in building supply stores for altering the roof
3. Research safety precautions that could be taken to prevent accidents from falling ice

Cause

Building and roof construction, including collecting runoff from the roof, were typical for the city.  As such, as an older building, the conditions were present in our climate for ice and snow to form and collect on the south side of the building.  Inspection and maintenance of the roof drainage system would be necessary to prevent ice and snow falling on people below.

The roof could be altered by various methods, and the methods maintained, to prevent ice forming and snow accumulating.  These methods are sold in building suppy stores.  One method would involve lining the roof above the eaves with metal sheeting to prevent ice and snow accumulating.

The area of the sidewalk below could be roped off and signs posted cautioning people of the danger of falling ice.

Resolution

The claim was resolved by alternate dispute resolution (ADR).

Litigation

The case did not go to trial.

Post mortem

The extent of the man’s injuries was evidence in giving some indication of the size of the piece of the ice that struck him.  I now want to know the extent of a victim’s injuries in all accidents I investigate.

Also, the sound the man heard, suggestive of ice hitting the roof of the addition, corroborated the location of the accident and the area of the roof from which the piece of ice fell.  It was easy to explain the formation of ice at this area of the roof.

Examining the roof with binoculars was the only way to assess maintenance of the roof drainage system.  Less than adequate maintenance was a factor in my analysis.  I wasn’t privy to its importance in resolving the case.