(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.