Guest Post by James L. Gordon, P.Eng. (Retired)
There have been two recent incidents at Muskrat which indicate that there is an inadequate
quality control process at the construction site.
The first was the announcement by Andritz, the spillway gate contractor, that they were suing NALCOR and Astaldi. The contractor cited changes in the schedule by NALCOR and errors by Astaldi in their work on the spillway concrete, as stated on the CBC news on May 25. The second, and far more serious incident, was the collapse of a concrete form in the powerhouse on May 30.
The first was the announcement by Andritz, the spillway gate contractor, that they were suing NALCOR and Astaldi. The contractor cited changes in the schedule by NALCOR and errors by Astaldi in their work on the spillway concrete, as stated on the CBC news on May 25. The second, and far more serious incident, was the collapse of a concrete form in the powerhouse on May 30.
To comment on
the Andritz situation first: Andritz base their claim on two factors, the delay
in the schedule, and defective work by Astaldi. Their claim states “However, by
the first half of 2014 it was obvious to Muskrat and Andritz that the civil
works performed by Astaldi were delayed,". The construction delays are
well known, but their impact on Andritz required “(an) aggressive and in
Andritz's view, likely unattainable on Muskrat's stated budget."
Work on the
spillway concrete was completed in November last year. This work included the
placement of the gate primary spillway gate anchors within the concrete, to
protrude through the formwork. The primary anchors are then used for
installation of the secondary anchors required to align the spillway gate
guides to within a few thou (a thou is equal to 0.0254 millimetre) by Andritz. The late completion of the concrete
work required changes in the gate installation schedule, forcing Andritz to
work during cold winter weather instead of in the summer, resulting in extra
cost for heating the work site.
The lawsuit also indicates a lack of
understanding by NALCOR management on how to work with contractors. NALCOR
issued a “Notice of Default” and threatened to call in a $20.5M letter of
credit Andritz had provided when awarded the contract. This just poured
gasoline on the fire (dispute) instead of trying to work with Andritz to
resolve the issues. All contractor claims, and there will be many, should be
resolved on site within a week of the claim being submitted, otherwise they
eventually escalate into an expensive lawsuit.
The other far more serious incident was
the collapse of a concrete form during a concrete pour in the lower part of the
powerhouse. Again, as reported by the CBC on May 30, “Concrete was being poured
to construct the lower draft tube, essentially a large pipe that
will return water to the Churchill River”.
Concrete forms do not collapse. During my
64 year career in the hydro industry, I have never encountered such an
incident. Their collapse is so serious, that formwork design is rigorously
verified, since a collapse will endanger worker safety, and if a worker is
drowned in the heavy wet concrete, retrieval is impossible. NALCOR was very fortunate
that no lives were lost, and only seven workers were injured.
The draft tube is located below the
hydraulic turbine and returns the water to the river through a right angled
bend. The bend is an extremely complicated shape, changing from vertical and circular
at the beginning below the turbine, to almost rectangular around the bend and
almost horizontal to the exit at the river.
 |
| Author inside large draft tube bend |
The photograph (above) places the author inside a large draft tube bend. Streaks are from
water leaking out of the concrete form during repairs at the top of the draft
tube.
The formwork for the bend used to be made
out of wood, with a shipwright in charge of the carpenters – a time-consuming
task. Current practice calls for the form to be fabricated off-site in steel,
designed for permanent placement within the concrete, one form per unit.
Alternatively, the form can be designed to be dis-assembled from the interior
and re-used on the other turbines.
NALCOR states that “the piece of failed of
equipment was manufactured in the United States, but assembled on site by
the project's main contractor, Astaldi”. The failure could then be due to
inadequate design, incorrect installation by Astaldi, or even a fault in the
manufacture.
The question is: who was responsible
for the work? It could be either Astaldi or the manufacturer. Nevertheless, the
work has to be verified, and since the component is so critical to the progress
and safety of the work, the design, manufacture and installation should have
been verified by NALCOR engineers, again indicating a lack of quality control.
These incidents
clearly indicate that the quality control measures currently used by NALCOR,
need to be revised to place more control within the jurisdiction of the NALCOR
design team.
What is not mentioned is that the wet concrete from the formwork collapse should have been immediately removed before it had time to set. Now, the failure investigation will be compromised by the inability to verify that the formwork was manufactured correctly, since part of the formwork will be embedded in solid concrete, and can only be inspected after it has been carefully chipped out of the concrete – an almost impossible task. This indicates a complete lack of foresight by those involved.
Jim Gordon, P.Eng. (Retired)
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Editor's Note:
Jim Gordon has authored or co-authored 90 papers and 44 articles on a large variety of subjects ranging from submergence at intakes to powerhouse concrete volume, cavitation in turbines, generator inertia and costing of hydropower projects. He has worked on 113 hydro projects, six of which received awards "for excellence in design" by the Association of Consulting Engineers of Canada. He was also awarded the Rickey Gold Medal (1989) by the American Society of Civil Engineers "for outstanding contributions to the advancement of hydroelectric engineering...". As an independent consultant, his work assignments have ranged from investigating turbine foundation micro-movements to acting on review boards for major Canadian utilities. He has also developed software for RETScreen and HydroHelp.
Editor's Note:
Jim Gordon has authored or co-authored 90 papers and 44 articles on a large variety of subjects ranging from submergence at intakes to powerhouse concrete volume, cavitation in turbines, generator inertia and costing of hydropower projects. He has worked on 113 hydro projects, six of which received awards "for excellence in design" by the Association of Consulting Engineers of Canada. He was also awarded the Rickey Gold Medal (1989) by the American Society of Civil Engineers "for outstanding contributions to the advancement of hydroelectric engineering...". As an independent consultant, his work assignments have ranged from investigating turbine foundation micro-movements to acting on review boards for major Canadian utilities. He has also developed software for RETScreen and HydroHelp.
