Where does an expert’s initial hypothesis come from?

When you rely on an expert’s initial hypothesis during the merit assessment stage you rely on a well-founded hypothesis.  In fact, it’s more than a hypothesis – a guess – it’s an initial oral report based on the evidence. (Refs 1 and 2)

The evidence is

  • Your briefing on the claim, accident, failure, dispute
  • The expert’s experience
  • Published data on the causes of failures and accidents in the built and natural environments

You telephoning and briefing an expert on a situation triggers his thoughts of past experiences and also modes of failure as published in the literature for different structures.  He’ll tell you, orally, what he thinks about cause, and it’ll be more than just a guess.

Tell me the issue is foundation subsidence on filled ground and I’ll tell you it’s likely inadequate materials testing and inspection during construction (experience) or inadequate geotechnical investigation (experience plus published research).

Brief me about a slip and fall accident on a wet floor in a dry sauna and I’ll tell you where the water came from (experience).

Tell me a site is still contaminated after an environmental assessment and remediation and I’ll identify three possible causes, one more likely than the other two (experience) .

Other experts in different branches of engineering and applied science can do the same.

There’s some interesting and helpful information in the following on where initial oral reports come from.

1. Your briefing You’ll describe the situation to the expert and report what you know about the claim, dispute, failure or personal injury.  This based on what you have learned from the parties involved, or your understanding if you are one of the parties or represent one.  Your briefing would include the technical issues as you might understand and perceive them.  Also what you believe must be investigated.

The expert will ask questions based on what he’s hearing.  He’ll ensure the Who? What? Where? When? Why? and How? of the situation are answered.  He’ll note technical issues that he might see at this early stage and comment on yours. The expert will sift through your briefing for hard and soft evidence.

Hard evidence might be the size and character of cracks in a damaged wall, the reported findings of an environment assessment of a contaminated site, the rainfall recorded the day of the flood, video of a property taken from a drone or the floor covering in the room where the slip and fall occurred.

Soft evidence might be what the real estate agent told you before you bought the property about how the high, steep slope down to the sea was really stable – only to have a landslide undermine your house later.

In a sense, I took a briefing from news reports a few days ago – quite soft evidence – on the appearance of sink holes in ground near Vancouver and the need to evacuate 14 homes from a subdivision.  Out of interest, based on my experience as an engineering expert, I hypothesized on what was wrong at the subdivision.

One conclusion: The ground should not have been built on in the first place.  Another conclusion: It was built on but something went wrong during the geotechnical investigation and/or the acceptance and implementation of the investigation’s findings.(Ref. 3)

2. The expert’s experience Our experience is grounded in our professional discipline and will include our successes and failures. (Ref. 4).

For example, disciplines like civil, mechanical, electrical and industrial engineering.  Civil engineering has in turn branched off to structural, foundation, geotechnical and environmental engineering.

My discipline and consulting practice has evolved to focus on civil engineering and the civil engineering branches except structural.  I have also practised as a generalist engineer overseeing an investigation and retaining specialists like structural, mechanical and electrical engineers. (Ref. 5)

For example, I investigated the cause of a power tool accident knowing full well at the start that I would likely retain experts in the design and manufacture of the tool.  As it turned out, a video taken of the re-enactment of the accident indicated the likely cause of the accident.

In another problem, I called on a structural engineer to guide my investigation of the stability of a concrete block wall and also the floor beams in the building.  These were elements in the environmental assessment and remediation of a contaminated site, one of my areas of practice.

Experiences like these guide me in advising you during the merit assessment stage. Ask me about problems like these and I should be able to help you.

Tell me it was a concrete block wall that collapsed and I’m sure I can tell you why.  Tell me the size of the cracks in a wall and the component material and I’ll tell you the likely cause of the cracks.  If a structure subsided I’ll tell you the likely cause with great certainty.

If you come to me during the merit assessment stage about the cause of a traffic accident I’m not going to say anything.  I’m going to refer you to one of three specialists in this work depending on the location of the accident.

In the last four or five years right up to the last three or four months I’ve got very suspicious of the quality of Phase II ESAs (Environmental Site Assessments) in the Atlantic provinces.  My suspicions are based on peer reviews I’ve done and experience with a drilling company and comments by the owner.  If your merit assessment involves a problem in the environment my initial oral report will draw attention to the Phase II ESA if one was carried out.

If your problem has anything to do with earthworks, foundations, the subsoils, surface and ground water, flooding, the terrain in general, I’ve got a wealth of experience to call on including education and practice as a land surveyor.  My experience was gained in Atlantic Canada, offshore NS, out west, up north and overseas.

It’s the same with experts in disciplines like mechanical, electrical and industrial engineering.  After a few years the experience is in our gut.  It just comes out during your briefing.  It’s hard to suppress it.

It comes out with considerable confidence too because we know there is a lot of published information that can be reviewed during a merit assessment..

3. Published data The principal modes of failure of buildings and civil, mechanical, electrical and environmental engineering structures and their components have been studied at length and published. (Refs 6, 7 and 8)  Some of the published material is fairly general and leads us in the right direction but doesn’t tell us what’s at the end of the trip. (Ref. 9)  Some other is quite specific and gives us a good idea where to look for the cause of the problem.

Fairly General  Researchers in the US and Europe reviewed the causes of hundreds of structural failures – that’s 100s, plural – and categorized the primary causes as follows:

  • Human failure
  • Design failure
  • Material failure
  • Extreme or unforeseen conditions or environments
  • Combinations of the above

When professional engineers were at fault (human failure) the causes of failure could be classified as follows:

  • 36%…Insufficient knowledge on the part of the engineer
  • 16%…Under estimation of influence
  • 14%…Ignorance, carelessness, negligence
  • 13%…Forgetfulness, error
  •   9%…Relying on others without sufficient control
  •   7%…Objectively unknown situation
  •   1%…Imprecise definition of responsibilities
  •   1%…Choice of bad quality
  •   3%…Other

When the percentage distribution of the failures were summarized the US and European research found that almost half were due to errors in the planning and design of a structure and a third occurred during construction:

  • 43%…Planning and design
  • 36%…Construction
  • 16%…Use and maintenance
  •   7%…Others and multiple factors

For example, I reviewed research a few years ago that found many, possibly most, foundation failures were due to inadequate geotechnical investigation of the ground and foundation soils.  In the above classification, that would be human error – the professional engineer – and the 36% with insufficient knowledge category.

Another example; if you’re got an earthworks failure, like on a highway or in an industrial park, I would look through the 11 different stages of the life cycle of a structure.  Based on my experience I would quickly focus on the materials testing and inspection during the construction stage.  In the above, that would be material failure and the 14% ignorance, carelessness, negligence category.

In a sense, yet another example; it doesn’t help when you’re hypothesizing on cause to know the following but important fact: The National Research Council (NRC) have found that the most complex structure in the built environment is a basement and it’s foundations – not the most glamourous structure just the most complex and rife with potential problems. (Ref. 10)

I can imagine dozens of possible problems down in the basement.  Where do you start looking for a cause?  If no go-to-answer, based on your briefing and experience, it’s important to get this out at the merit assessment stage – in spite of the aggravation.

Quite Specific The American Society of Civil Engineers (ASCE) published a book that categorizes 209 causes of component failure in buildings. (Ref.7)  It’s interesting that the basement was not looked at in detail by the researcher and editor, David H. Nicastro.  I can imagine he didn’t know where to start considering that there are 100s of ways a basement can fail..

The ASCE categorization is a detailed source of information for an expert hypothesizing cause.  To get an idea of this resource, take a look at the blog I posted July 10, 2014 entitled “How many ways can a building fail and possibly result in civil litigation or an insurance claim”. (Ref. 6)  If you’re up for it, take a look at the ASCE publication itself (Ref. 7)

Following are two examples from my blog on how an expert might use the book:  The examples are 2 of 209 ways a building can fail:

The item in red is one of the 209 ways selected from the alphabetical list down the pages of the book.  The items in blue are column headings across the pages.    They note the distress in the building when the failure occurs, the materials affected, and one or more typical case histories.

Example #1, A client’s structure experiences:

  • Differential foundation settlement - the way in which his structure failed, the technical cause.
  • The distress to the structure is manifested as unwanted movement and distortion.
  • The materials and systems affected by this movement are the structural systems and foundations.
  • case history in Nicastro’s book is the differential settlement of the temporary foundation support of a bridge deck during construction.

Example #2, A client’s structure experiences:

  • Corrosion - the way in which a component failed, the technical cause.
  • The corrosive distress to the structure manifests itself as an unsightly appearance
  • Affecting the component’s materials, the metals.
  • Case histories in the book include a steel masonry shelf, and reinforcing steel in a concrete wall façade.  Both corroded with the infiltration of rain water.

Brief Summary

This is the kind of published data - 

  • exhaustive categorizing of failures, like 209 for a building 
  • good evidence on the primary causes of failure
  • the percentage distribution during the life cycle of a structure, and
  • the percentage distribution of errors professional engineers make -

that allows an expert,

  • based on your briefing and his experience,

to orally report during the merit assessment stage on the cause of a failure or accident or the basis of a claim.  It’s a preliminary oral report, that’s for sure, but more than a hypothesis, a guess.  The expert’s initial oral report comes from good evidence.- your briefing, his experience and published data.

References

  1. Merriam-Webster dictionary, on-line, February 2019
  2. Cost management of expert services. Posted January 31, 2019
  3. What’s wrong with this (sink hole) picture near Vancouver? Posted February 20, 2019
  4. Petroski, Henry, To Engineer is Human; The Role of Failure in Successful Design, Random House, New York, April 1992
  5. American Society of Civil Engineers (ASCE) Guidelines on Forensic Engineering Practice
  6. How many ways can a building fail, and possibly result in civil litigation or an insurance claim? Posted July 10, 2014
  7. Nicastro, David H., ed., Failure Mechanisms in Building Construction, ASCE Press, American Society of Civil Engineers, Reston, Virginia 1997 (Readily available by interlibrary loan from Memorial University, Newfoundland)
  8. Janney, Jack R., ed., Guide to Investigation of Structural Failures, American Society of Civil Engineers (ASCE) 1979 and 1986
  9. Built Expressions, Vol. 1, Issue 12, December 2012, Argus Media PVT Ltd., Bangalore, E: info@builtexpressions.cominfo@argusmediaindia.com
  10. Swinton, Michael C. and Kesik, Ted, Performace Guidelines for Basement Envelope Systems and Materials, National Research Council of Canada Research Report 199, pp 185 October 2005

 

What’s wrong with this (sinkhole) picture near Vancouver?

I was surprised at the news last week about the evacuation of 14 homes in Sechelt, on the Sunshine Coast near Vancouver because of sink holes and unstable ground.

What’s wrong with the picture is why such unstable ground was developed and built on in the first place if the risk was known.  Sink holes as large as an estimated 15 feet across and 3 to 4 feet deep in one news picture if typical are an obvious sign of unstable ground.

A geotechnical investigation – a well developed applied science – had been carried out and the risk identified according to news reports.

Sink holes not unusual and easy to investigate

Sink-hole-prone ground is not unusual in nature.  We got unstable ground like this in the Atlantic provinces.  There’s lots of sinkholes in the Bahamas where they’re called banana holes because banana plants grow in them.

A neighbourhood of 14 homes is about the size of my neighbourhood, and compact and the ground easy to investigation.

Geotechnical investigation identifies ground that is susceptible to sink holes like this.  The ground can be natural or due to the works of man.  It also identifies the different layers of soil and rock beneath the ground – the stratigraphy in geology – and the areal extent of the different layers.  It determines the physical properties of the materials forming the layers and their susceptibility to conditions of interest – sink hole development in this case.  Finally, it checks out the depth to the ground water and where it’s flowing.

Was the risk of building a house high or low?

Did the geotechnical work really conclude that the risk was 10% – possibly a low number to some?  Or did the work miss something which seems likely as evident by the evacuation?  How was the 10% calculated?  A probability analysis was not mentioned in the news.

It occurs to me that I wouldn’t build a house in an area where there was a 1 in 10 chance of my house being undermined by a sink hole.

Easy to investigate and improve the ground

Ground terrain like this can be improved.  It’s called ground improvement in engineering and is a well developed technique.  But it can be expensive involving lots of geotechnical work and construction work.

These kinds of investigative and improvement techniques are so well developed and understood in engineering that it’s motherhood.  The ground may be complex but finding this out and doing something about it is fairly straightforward.  Not building on the ground is one solution.

Simple, preliminary investigation

There’s a list of geotechnical techniques in the Appendix.  They are roughly in the order they might be carried out.  You can repeat some depending on what you’re finding.

One of the least expensive at the beginning of an investigation is a good walk-over survey of the ground.  This would be accompanied by a study – before, during or after the walk-over, or all three – of published topographic and geologic maps of the area and published aerial photographs.  New and old sink holes like those reported would be seen in a good walk-over.  An engineer experienced in terrain analysis could also pick out big sink holes on aerial photographs even those taken from 1,000s of feet high.

Such a walk-over and study are standard procedures in geotechnical investigation.  They’re cast in stone.

Video and stills taken from drones 10s and 100s of feet high have been available for a few years now.  They have been invaluable in my work.  Sink holes and unusual features on the ground show up well in aerial video.

Before drone photography I hired a small plane and had the pilot fly low over a site as I took photographs of the ground.

These preliminary techniques would be standard at the beginning of a geotechnical investigation of a site like the one evacuated near Vancouver.  The results would indicate if more expensive investigative work was justified like that mentioned above and listed in the Appendix and how to plan and do it.

Investigation and/or use of findings questioned

Of course, good and thorough geotechnical investigation must be followed up with good use and implementation of the findings.  The evacuation would seem to call into question the investigation and/or the use of the findings.  What’s wrong here is that something went wrong and shouldn’t have.

Appendix 

There are many techniques that could be employed during a geotechnical investigation.  I’ve used all of them in my consulting engineering practice at different times over the years:

  1. Terrain analysis using published aerial photographs from high flying aircraft – 1,000s of feet high
  2. Walk-over surveys and examination of the terrain on foot
  3. Studying published topographic, superficial (soil) geology and bedrock geology maps of the area
  4. Terrain analysis using published Lidar mapping of the area
  5. Terrain analysis using video and stills taken for the purpose from low flying drones 10s and 100s of feet high
  6. Studying contour and topographic maps prepared for the area
  7. Carrying out and studying a geophysical survey of the area
  8. Carrying out and studying ground penetrating radar (GPR) surveys of the area
  9. Drilling boreholes, measuring the thickness of the different layers of soil and rock, testing the physical properties of the soil in-situ and sampling the soil and rock for laboratory testing
  10. Testing the physical properties of the soil and rock in a laboratory
  11. Analyzing the stability of the ground using the data on the different layers of soil and rock obtained during the geotechnical investigation