F-3: Sliding Retaining Wall

 Statement of the Case: Engineer A had several years’ experience in the design of water and
sewer systems and municipal streets, but had no experience in the design of retaining walls. A
client, who was building a large lake-view house on the lower slopes of a hill, asked Engineer A
to design a retaining wall 3 m high and 50 m long to provide a flat lawn area in front of the
house. Engineer A accepted the assignment, even though he had never designed a retaining wall
before. His university education, some 20 years earlier, had touched briefly on the topic of
retaining wall design, so Engineer A consulted the concrete design textbook used in that course
and took dimensions, bar size, and spacing from a diagram in the textbook. He then produced

drawings and specifications for the client, who hired a contractor to build the wall.

Question: Was this effort adequate for a professional engineer?

Outcome: Soon after construction, the wall’s foundation failed by sliding. In the investigation
that followed, it was revealed that Engineer A had performed no foundation investigation. At the
very least, he should have drilled a few hand-auger holes and performed soil classification to
estimate bearing resistance, compressibility, and so on. He made no checks for sliding and made
no provision in the design to resist sliding. He did not consult any current codes, but simply
copied the old textbook design. Moreover, the textbook diagram illustrated structural aspects
only, not foundation details, and the textbook stated this fact. The client launched a successful
lawsuit. Engineer A was also disciplined under the provincial professional engineering Act.

Authors’ Comments: Competence is the result of education and experience. Although Engineer A was competent in his established field, he was not competent in the area for which his client

was paying, and while he made a minimal attempt to learn about the topic, his knowledge was

superficial. An engineer or geoscientist need not be an expert in every phase of a proposed

project before accepting it; however, a professional must be sufficiently familiar with the subject

to know that he or she can become competent through study or research in a reasonable period of

time, or that a colleague or consultant can be hired, without delaying the project, at reasonable

expense. The key point is that the professional’s lack of competence must not put the client’s

project at risk.