I’m going to tell you about defects in a building designed by architects and engineers. Defects that should not have occurred and might have resulted in civil litigation in another time and place.
I don’t know whether to feel delighted or embarrassed on finding defects in an addition to a building constructed while I was at the University of New Brunswick (UNB). I was in the building last fall for a reunion of my engineering class.
I pick delighted because I know that failures occur and finding them reminds us we can’t be too diligent and thorough in our work. Even well educated, trained and experienced planners, architects, engineers and builders. We got to be ever-vigilant that we don’t drop the ball in the face of tight budgets and schedules.
Failure occurs when a component of a building or civil engineering structure doesn’t function as it should, has a defect, or collapses completely.
I noticed the first defect years ago when I was studying at UNB. Construction of an addition undermined the foundations of an existing building causing the foundations to settle and the brick wall in a classroom to crack. (see Appendix) You could see daylight through the 1″ crack (it’s been caulked since).
Cause of 1st defect
The undermining causing the crack was due to the technique used during construction of the foundations to the addition. The technique is well known, including it’s limitations that must be taken into account. (see Appendix) If not, foundations are undermined and cracks appear in brick walls. Or worse. (see pictures of a catastrophic failure in Ref. 1)
I noticed last fall that the floor level of the addition was several inches different from the floor of the older part of the building. Such a difference in floor level contravenes some guidelines and could be construed as unsafe. This is the second defect in this building of which I’m aware.
Cause of 2nd defect
The cause of the mismatched floors is certain to have occurred during planning and design of the room height in the addition – an initial hypothesis. The floor to ceiling height in the existing building was not measured so planning and design could ensure the floor of the addition matched the floor of the existing. Or it was measured but the information not used.
The difference in floor level would not be due to foundation settlement nor to building shrinkage. The difference of several inches is just too great.
Two defects in the planning, design and construction of an addition to a building? Overseered by planners, architects and engineers? I’m certain someone was embarrassed back then.
No excuse for defects
Two defects in a building – one in the planning and design stage and a second in the construction stage – that should not have occurred. These potential problems are too well known to experienced planners, architects, engineers and builders and could have been avoided.
- (Fairly easy) Estimating the investigative cost of a catastrophic failure. August 13, 2013
My first “forensic engineering” investigation.
The following is one in a series of cases I have investigated that illustrate the different types of failures and accidents that occur resulting in civil litigation, and the forensic engineering methods I used to investigate the cause. I investigated this failure when I was studying civil engineering at UNB and hardly knew what a forensic investigation was.
The investigation is reported under the following headings with several sub-heads:
- The case (a description of the failed structure – significant cracks in a building - the “legal”/technical issues, and my “client”
- Forensic engineering investigation of the failure and the methods used
- Cause (of the failure)
- Post mortem (an interesting side story and a lesson learned)
I carried out my first “forensic engineering” investigation during my 5th year studying civil engineering at UNB. As a student I had little or no understanding of forensic engineering and wasn’t even qualified as a professional engineer.
Nevertheless, this was a significant and costly building failure but, fortunately, not a catastropic one. (see pictures of a catastrophic failure in Ref. 1 above)
We took some of our lectures in a room on the second floor of a two story brick-walled building on the campus.
One day a 1″ wide, vertical crack appeared in the front, left corner of a wall of the lecture room. (I measured the caulked crack last fall during our reunion) You could see daylight through the crack. This would be significant damage to an existing building
To me as a student with an interest in geotechnical and foundation engineering, the cause of the crack was interesting. I investigated and reported on the cause to meet the requirements of one of my courses.
My “client” was the professor who was giving the foundation engineering course at UNB.
“Forensic engineering” investigation
My ”forensic engineering” investigation involved the following:
- Visually examine the exterior of the building
- Determine construction of the building’s foundations
- Also construction of the addition to the building
- Research construction techniques
A visual examination of the exterior of the building found that an addition to the building was being constructed adjoining the existing building. Construction involved a deep excavation adjacent the existing building. The sides of the excavation were supported by steel beams and timber planks.
Construction of the building’s foundations
I learned that the existing building was supported on shallow spread footings founded in the natural soils. Excavating near and well below natural foundation soils requires their lateral support to prevent undermining the soils. The soils could cave into the excavation - collapse catastrophically - unless properly supported.
Construction of the addition to the engineering building
I learned during my visual examination that the pile and plank, excavation support system installed by the contractor was a soldier pile shoring system. This system is intended to temporarily support the sides of the excavation and in this way the foundation soils beneath the existing building.
Soldier piles are steel beams installed vertically in the ground at regular intervals of several feet at the side of where an excavation is planned adjacent existing foundations. The piles are set deeper than the planned depth of the excavation. The piles are driven vertically in the ground, or installed in previously bored holes eliminating the ground vibration from pile driving.
As the ground is excavated on one side of the piles, wood planks are placed horizontally bridging between the piles to hold the earth back on the other side – to shore up the side of the excavation from caving in. In this case, the earth at the back is adjacent the earth comprising the foundation soils of the existing building. The planking or lagging “follows” the excavation down. This is a soldier pile shoring system.
A soldier pile shoring system is a good support system if constructed properly and its limitations kept in mind.
Research construction technique
I researched the soldier pile shoring system and found that it “gives” or yields a little – deflects along it’s height - when mobilizing its strength to provide support to the soil it is retaining. The retained soil behind the shoring system gives a little as well - moves sideways and away from the foundation soils to which it is providing lateral support. This undermines the foundation soils a little causing the soils to settle and the building foundations to settle as well.
This deflection is due to the piles bending along their length. The piles will also tilt a little if they are not driven or embedded deep enough during installation.
This lateral movement of the shoring system and settlement of the soils and foundations is normal. It can be negligible – tiny millimetres or less – if the shoring system is properly designed and installed. The movement can be significant - centimetres, inches or more – causing damage to the foundations, if the support system is not well designed and installed.
Installing soldier piles by driving them in place causes the soils in the immediate area to vibrate. Soil settles when it is vibrated. Anything in the soil – like building foundations - settles as well.
I analysed the data that I had collected – construction of the shoring system and the results of my research - and concluded the cause of the failure and submitted my student engineering report.
In this case the soldier pile system deflected too much causing the foundation soils to yield or move sideways and settle in the process. This caused the building walls to settle as well and the corners to crack and open up. The soldier pile deflection was probably due to a combination of the following causes noted above:
- Vibration of the soils during installation of the piles
- Tilting of the soldier piles due to shallow embedment
- Deflection along the length of the piles
I passed my year so I must have got it right. I understand that some of the engineers who inspected the soldier pile system that failed may have been my professors who had formed a consulting engineering company to do this type of engineering design and inspection work. Failures occur in spite of the best efforts of the best people.