Counsel benefits when they have some knowledge of the forensic engineering investigative process that is followed by an expert. The process determines why a structure failed or an accident happened. The process results in a thorough investigation leading to an objective opinion rendered with considerable certainty.
This item identifies and describes the steps in the process. The process is followed regardless as to whether the professional engineer is retained as a consulting expert or a testifying expert.
A structure is anything in the built environment, including alterations of the natural environment like highway embankments and earth and rock slopes. A failure can involve total collapse of a structure or its inadequate performance.
There are three fundamental components to the forensic engineering investigative process:
- Acquisition of data
- Analysis of data
- Presentation of conclusions and opinions
Rigid formulae for investigating failures and accidents do not exist. But all forensic engineering investigations contain the following steps to a greater or lesser degree.
- Document Review
- Visual Assessment
- Field Investigations
- Laboratory Investigations
- Research
- Follow-up Investigations
- Data Analysis and Formulation of Opinion
- Report
Field investigations can be broken down further:
- Describe the Failure or Accident
- Survey and Document the Damage to the Structure
- Determine how the Structure is Built
- Determine the Site Conditions
Most of the investigation involves gathering data and most of the report – more than 3/4, involves presenting and analysing the data. This points to the importance of the data gathering. The degree of certainty in the final opinion of the cause of the failure is often a function of the amount of data gathered and the budget for this.
Following is a brief description of each step in the investigative process:
1. Document Review
Documents provided by counsel during the initial briefing are important in a forensic engineering investigation. They sometimes provide the only data available to an engineer investigating a failure. Documents include items like the following:
- Client narrative
- Discovery transcripts
- Text
- Drawings and maps
- Photographs
- Maintenace records
Additional published documents almost always researched by a professional engineer include:
- Legal surveys and descriptions
- Land development and drainage plans
- Aerial photography of the area of the site
- Topographic and contour maps
- Surficial and bedrock geology maps
- Agricultural soil maps
- Hydrological maps and studies
- Hydrogeological maps and studies
- Flood plain mapping
- Mining activity mapping
- Environmental reports
Documents like these are often studied a number of times during the different stages of an investigation.
Information from the documents along with an initial site visit and visual assessment enables the engineer to plan the different investigations based on what he thinks caused the failure or accident – his initial hypothesis. Investigations are designed to confirm, revise, or refute the initial hypothesis.
In checking the hypothesis, engineering investigations determine:
- What took place during the failure or the accident,
- The nature and extent of the damage or inadequate performance,
- How the structure was built, and its conformance to the design and construction plans, and,
- The nature of the area the structure is in and the ground beneath the structure
2. Visual Assessment
This step involves visiting the site as soon as possible after the failure or accident, walking and poking around the site to get a feel for where things are and the nature and extent of the damage, and examining exposed surfaces. It’s a very simple task – not very technical at all, but invaluable in getting a feel for the scene and bringing the documents to life.
Measuring in a number of different ways characterizes the investigation carried out by professional engineers.
3. Field Investigations
Describe the Failure or Accident
This step involves learning what happened – getting a description of the failure or accident by interviewing witnesses. This discription may be gleamed from the documents but talking with people who were there and saw or experienced the failure – particularly if it was a sudden collapse of a structure, or an accident, is much better.
Survey and Document the Damage to the Structure
This step involves recording the damaged condition of the structure that has collapsed or does not perform properly. The condition is recorded by means of tasks such as the following:
- A visual examination and description of the structure’s condition,
- Measuring the extent and location of the damage, and
- Photographing and videotaping the damage.
This should be done as soon as possible after the failure before data and evidence are altered or lost. The information enables a before-after comparision to be made after the next step is completed. This type of comparison is often helpful.
Determine how the Structure is Built
How the structure is built, whether or not it comforms to the design, and the adequacy of the design is determined in this step. Also, whether or not the design reflects the standards of the day. This information is obtained from various plans and research of standards and checking these against the structure on site. Tasks involved in this step include the following:
- Obtaining copies of the design and construction drawings – often quite similar
- Checking the design that it conforms to good engineering practice
- Checking that the construction drawings conform to the design
- Obtaining a copy of the as-built drawings – drawings that record changes made during construction due to various reasons
- Checking that the existing structure conforms to the as-built drawings. This involves examining and measuring the different components of the structure. It often involves taking things apart or using remote sensing techniques to detect what is below the surface. To facilitate this examination, drawings of the damage might be superimposed on the as-built drawings. This superimposing would eventually be done during the data analysis (see below)
- In the absence of drawings – often the case for older structures, measure the structure and prepare drawings, and then supepimpose sketches of the damage
How many of these tasks are carried out and in what detail depends on the situation, the structure, and the failure. Sometimes very little of the above is done. Sometimes it’s enough just to measure and prepare sketches of the damage and view and study the structure with these sketches in hand.
Determine the Site Conditions
The site is the area the structure is on and the terrain beyond the site including other structures.
The site conditions of interest at this stage of the investigation include:
- The lay of the land; the topography
- Surface features like bedrock exposures, sinkholes, and wet land
- Drainage features like ponds, lakes, and water courses (hydrology)
- Subsurface and foundation soil and rock conditions
- Groundwater conditions (hydrogeology)
Investigation of site conditions includes:
- Photographing and videotaping the site
- Aerial photography and map making
- Topographic and elevation/contour surveys
- Drainage studies
- Geotechnical and foundation soil and rock investigations
- Full scale field tests like plate load tests and pile load tests
- Accident reconstruction
Detailed topographic and elevation surveys are usually made when the failure of a building or a civil engineering structure, or the cause of an accident, is thought to involve the terrain in which the site is located.
Drainage studies (hydrology) are made when surface or groundwater may have been a factor in a failure or an accident.
Geotechnical and foundation investigations may be necessary if the cause of the failure of a structure appears to be in the foundations or the subsurface soils.
Full scale field tests and accident reconstruction may be carried out. This is done when these methods are assessed as the most reliable means of gathering data on the effects of the terrain and features in it on the failure or the accident.
4. Laboratory Investigations
It is often necessary to carry out laboratory tests to determine the chemical, physical, mechanical, strength, and/or drainage properties of materials used in construction at the site of a failure or an accident. It might be necessary to measure the toxic fumes emitted by a compound or product used in construction.
Typical materials used in construction are soil, rock, steel, concrete, wood, plastic, adhesives, asphalt, and masonry products.
Composite materials like asphalt or reinforced concrete can be taken apart in a laboratory to determine how the material was formed. For example, the location, type, and size of reinforcing steel in a reinforced concrete slab that failed.
5. Research
To some extent, research studies and investigations – desk studies in some disciplines, are on-going like document review during a forensic engineering investigation.
The work often involves literature searches, telephone and internet work, and leg work to sources outside the office like libraries and the offices of persons to interview and consult with.
It also involves research and study of aspects of the engineering investigation that have assumed some relevance. For example, past mining activity in an area, the standard of care at the time the structure was designed and constructed, the shrinkage properties of a fill material, and the different modes of failure of a soil-steel bridge.
Research also identifies and gathers together all information in appropriate categories relevant to the investigation of the failure (see Document Review above). This would be information usually not contained in the documents provided by counsel during the initial briefing. Information like original construction and as-built drawings, geotechnical and environmental reports, and published mapping of the area
6. Follow-up Investigations
This task of carrying out one or more follow-up investigations results from the need to “follow the evidence”. This concept hardly needs explaining to counsel. It is equally important in a forensic investigation. Data will be gathered and evidence uncovered during a previous investigation that suggests another line of enquiry should be followed up or another area investigated. This is like cross-examination during discovery uncovering evidence that suggests a new line of questioning.
Implicit in the fact that there might be evidence that should be followed up is the possibility that the initial hypothesis on the cause might need to be revised or rejected completely.
The possibility of the need for follow-up investigations is a fact of life during forensic engineering investigations.
7. Data Analysis and Formulation of Opinion
In analysing and reasoning to a conclusion, the data from any one stage of the investigation is looked at critically – taken apart, in a sense, and each part looked at carefully, and how they are related and their interaction examined.
The data is also looked at closely to see if it is characteristic of or associated with a mode of failure or a cause based on past experience and/or mathematical calculation. Professional engineers have identified and published typical modes of failure for the various structures in the built environment. These are available for review and guidance to the forensic engineer during a forensic investigation.
The data from other stages of the forensic investigation are similarly looked at, and also studied to see if there is corroboration of conclusions between stages. Pattern is looked for within individual data and amongst different sets of data. And if there is a pattern, considering if it is typical of a known cause of failure.
At some point, when engineering judgment dictates, conclusions are drawn from the analysis and the hypothesis confirmed, revised, or refuted. If revised or refuted then a new hypothsis is formed and this investigated with follow-up forensic investigaions.
If the initial hypothesis is confirmed then the cause of a failure has been identified and an opinion can stated.
Sometimes the data analysis and development of an opinion is quite easy. For example, when field work uncovers a concrete floor slab that is supported by irregularly spaced columns and the type of slab that should be beneath the structure is required to be uniformly supported. Then it’s easy to hold the opinion that the floor slab is inadequately supported.
At other times it’s complex. For example, when there are more than 20 possible modes of failure for the collapse of a soil-steel bridge. When the collapsed bridge is not available to examine, then the data must be analysed for each mode and the cause identified by a process of elimination.
Sometimes it’s mysterious. Why is there a toxic odour in the concrete enclosed lower level of a structure and the lighter-than-air fumes are not detected in the timber framed upper levels? A chance remark about timber structures “breathing” – are more pervious, in a sense, in engineering terms, solves the mystery as to cause. The fumes in the upper levels diffuse through the exterior timber walls to the outside of the structure.
8. Report
The report, in particular, the written report, is an important step in a professional engineer’s investigation of a failure or an accident. It is an objective documentation for the judicial system of the methods used during the investigation, the data gathered, the analysis of the data, and the reasoning to an opinion on cause. It’s importance is highlighted by the fact that civil litigation rule changes in some provinces are resulting in the report often replacing the discovery stage.
The results of an engineer’s investigation of a failure or an accident are presented in:
- Oral reports,
- A written report, and,
- Occasionally, one or more supplementary reports
If possible, an oral report is given to counsel as soon after the documents are read, an initial site visit and visual assessment completed, and an initial hypothesis formed as to cause. The report will indicate the direction the investigation appears to be leading. This will give counsel an early indication as to whether the professional engineer will serve as a consulting expert or as a testifying expert.
A written report is provided at completion of the investigation. It is prepared on instruction of counsel for the court and judge and submitted to counsel.
The need for supplementary reports might depend on whether or not new evidence is found during discovery, in follow-up investigations, or presented in rebuttal reports.
The outline of a report will vary depending on the nature of the failure or accident and the extent of the investigation. Many will be in chronological order, generally the order of the steps in the forensic engineering investigative process. The process is a series of investigations and follow-up investigations. My reports generally:
- Describe the individual investigations,
- State the purpose or reason for carrying out each investigation,
- Identify the data obtained, and,
- If possible, do a little preliminary analysis and reasoning and comment on the validity of the initial hypothesis.
References
The foregoing is based on several sources. The citations are not complete:
- ASCE, Guidelines for failure investigation, 1989
- ASCE, Guidelines for forensic engineering practice, ed., Gary L. Lewis, 2003
- ASCE, Guide to investigation of structural failure, Jack R. Janney, 1986
- Mr. Jack Osmond, NSPL, Affinity Contracting, Halifax
- Expert Witnessing; Explaining and Understanding Science, ed., Carl Meyer, 1999
- Steps in the civil litigation process
Copyright 2012, Eric E. Jorden. All rights reserved