Ayres Knowledge Center The Power of Association | Page 2

Projects
Projects
j would have been extremely expensive. Exelon
contracted with Crofton Diving Corporation, and
Ayres provided a turn-key solution in the form of
a sectional hinged floating bulkhead allowing
simultaneous rehabilitation of service gate slots and
the associated spillway gate slots. A second bulkhead
was then fabricated to double the rate at which the
gate-by-gate rehabilitations can be completed.
At another project at a pump storage facility,
a r egulatory agency required the dam owner to
complete a full gate opening test. A full gate opening
without the use of a bulkhead was not desirable
for efficient operation of the pump storage facility.
The owner had a non-floating bulkhead, but the
installation cost and time frame were prohibitive.
Ayres was retained to design a floating bulkhead, with
which the owner was able to install the bulkhead and
complete a full gate opening test in one day.
Tainter gates
The recipe for reliable tainter gate inspections
includes a commitment to safety and experience in
rope access, underwater inspection, and structural
analysis. After the July 1995 failure of a tainter gate
at the Folsom Dam in California, the Federal Energy
Regulatory Commission has required detailed,
close-up inspections of these radial gates, along with
structural analyses of gate arms with consideration
for friction at the trunnion.
Ayres Associates’ tainter gate inspection teams
cover all the bases with their safety regimen and their
training in the use of climbing and diving equipment
and structural frame analysis software.
Safety
From top to bottom:
2D dambreak modelling at
Lake Bronson – depth
2D dambreak modelling at
Lake Bronson – velocity
2D dambreak Modelling at Lake
Bronson – water surface
Below: Map of Ayres-designed
projects
It is important to staff inspections with inspectors
and professional engineers who are experienced
with structure climbing, rope access, and personal
fall arrest systems. One method of training to safely
climb tainter gates is to become certified as a rope
access worker by the Society of Professional Rope
Access Technicians (SPRAT). Ayres Associates
inspectors have become SPRAT-certified and go
above and beyond with in-house training that keeps
all inspection staff up to date on methodology,
equipment, and safety procedures, including rescue
procedures.
Every Ayres inspection begins with the
development of a climbing plan before teams
mobilise to a site and then a safety meeting on site
before work commences. Following tainter gate
inspection projects (as well as other fieldwork), our
teams discuss the effectiveness of the plan and any
improvements that could be made. The completed
plan and post-inspection notes are filed for use on
the next round of inspections for that site and as a
knowledge database for other tainter gate inspection
projects.
is disabled, a team of at least two mobilizes to the site,
preferably with an owner representative present.
Each climber anchors a two-rope climbing system
to the service bridge above the gate. One rope is the
work positioning line that the inspector is suspended
from, and the second is the fall arrest system, which
is the safety line in case the first rope breaks. The
climber rappels down from the top and moves
laterally along the horizontal members to inspect the
entire gate. The inspector is temporarily anchored
in various positions laterally as he or she moves left
and right across the gate. Should the gate be of such
width that moving to one side would induce a swing
hazard into the rope access system, the ropes can be
anchored near one end for work in that area. For the
other half of the gate, the ropes can be repositioned
to inspect the other end. To climb off the gate and
back to the service bridge, the inspector uses the
ropes they rappelled down and used for positioning
and fall arrest.
Knowing what to look for
The inspector gets an up-close look at the skin plate,
cross members, arms, and trunnion pins, checking
for deformation such as bends or kinks, as well as
corrosion and cracks in welds. Inspectors also look
for water that ponds on cross members, which
accelerates corrosion and adds weight to the system
that lifts the gate. Seals are checked for leaks, and the
concrete walls on either side of the gate are sounded
with a hammer to confirm their condition is solid.
As the climber inspects each component, he or she
makes notes on PDF sketches of the gates that are
loaded onto a tablet computer he or she carries during
the inspection. The type, size, and location of each
deficiency is noted.
In the vast majority of cases, the notes lead to
minor maintenance actions such as drilling holes in
a horizontal member to drain ponding water. Or the
notes simply call attention to a spot that needs to be
checked again when the next inspection rolls around
to determine if anything has changed between
inspections. On rare occasions a significant structural
issue is detected, requiring major repairs to maintain
operability. “That ability to operate the gate is what
we are there for,” says Brian Schroeder, supervisor of
structural inspection at Ayres Associates.
Repeated impacts of river debris slamming against
gates can bend gate components and rack the gate
so that it cannot be smoothly raised or lowered.
Schroeder recalls a serious issue detected in one
inspection involved a crack in the weld between
an arm and a gusset plate at the trunnion pin, on
which the gate pivots when raised and lowered. The
problem ultimately was repaired to prevent the crack
from growing, which could have resulted in the gate
failing.
Rope access Dive access for underwater component
inspection
By their nature, tainter gates are surrounded by
dangerous water above and below the dam and are
slippery with moisture and marine growth. Looking
at their components up close requires skilled use
of rope access. After scheduling the tainter gate
inspection for a date when high water is not likely and
making certain that any remote operation of the gate Inspection of underwater portions of the chains or
wire ropes used to hoist a tainter gate open requires a
trained dive team to safely approach this component
from underwater. Contracting with a firm whose
team includes these specialists allows for efficient
completion of both climbing and diving aspects of the
inspection in a single, efficient mobilisation.
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The diver enters the underwater world using
surface-supplied air (SSA) equipment. SSA is a
system in which the air supply resides above water
and is pumped down to the diver via the diver’s
umbilical. The umbilical is constructed of a strength
member (used for retrieving an incapacitated
diver), an air supply hose, a hose for the air of a
pnuemofathometer (a depth gauge that is read at
the surface by the topside crew), and a hardwire
communication line. Via this life line, the diver is
tethered to the boat, allowing for efficient location
of the diver and any deficiencies found. The SSA
equipment provides extended downtime for the diver,
two-way communication between diver and topside,
and underwater video. The equipment is operated
by a three-person crew (diver, tender, and equipment
operator) typically in a 6m john boat, other vessel, or a
location on a hydro facility. The diagram here details
the layout of the SSA system in a boat.
Another critical tool
A tainter gate inspection team also needs structural
engineers who know how to employ structural frame
analysis software to evaluate stresses in the gate
arms, face, and support members, including stresses
resulting from hydrostatic pressure, ice, lifting forces,
and trunnion friction. For example, if section loss has
been documented on cross members due to corrosion
from ponding of water, structural analysis can
determine if that deficiency has reached a level that
could cause bending of those members under load
and consequently potential failure of the gate.
Where a close examination is needed on gates or
other hydro facility components that are not walkable
but also don’t require mobilizing a rope access team,
Ayres Associates also makes inspection by unmanned
aerial systems (UAS), or drones, available.
Ayres’ flight planning and data processing software
is specifically designed for UAS technologies to
provide customized viewing perspectives. We can
capture imagery from multiple viewing perspectives:
● First-person point-of-view (POV) to see the world
from the UAS
● Nadir (top down) and oblique-angle viewing
perspectives
● HD video up to 4k
Successful UAS projects start with safety. Ayres
completes UAS projects in accordance with the
Federal Aviation Administration’s Part 107 guidelines.
Our qualified UAS pilots in command are all properly
certified and complete strict internal training, both
in the lab and in the field. All Ayres projects follow
strict safety protocols, and our personnel invest the
time needed to understand and appreciate the risks
of the work environment before deployment of UAS
equipment.
UAS systems are also capable of supporting
high-accuracy topographic mapping for hydro
facility inspection projects. This technology provides
high-definition surface models for contour generation
and volumetric calculations with rapid deployment
and turnaround time. These systems are especially
effective at mapping sites that require frequent
updates and for accessing potentially hazardous work
environments. Our mapping capabilities include:
● Digital surface models and contour generation
● Volumetric analysis and topographic change
detection
● High-resolution aerial imagery
Above: Surface supplied air
Graphic
Critical knowledge for worst-case
scenario
Dam-break inundation mapping is critical to the third
leg of the dam safety stool. The three legs are:
● Appropriate, well-informed design and construction.
● Vigilance in operating, monitoring, assessing and
maintaining the dam.
● Having emergency action plans ready for instances
when the first two legs fail to prevent a dam breach.
For example, a breach may result when debris in
floodwaters interferes with gate operations or when
a road washout makes it impossible for operators to
access a gate that must be opened manually.
Two-dimensional modelling technology is quickly
changing how we predict and describe dam failure
consequences. The goal is to predict where the water
will go if a dam breaches, at what speed and force,
and at what depth. Flood severity is determined as a
combination of water depth and velocity. Severity can
be quantified by various benchmarks such as flooding
that is sufficient to sweep an adult off their feet or
sufficient to carry away a vehicle.
Traditional one-dimensional hydraulic modelling
– the only option until computers recently became
powerful enough to crunch the much more robust
numbers involved in 2D – can provide average water
depths and velocities at various locations along a river
downstream from a dam break, but severity detail
is lacking. And 1D modeling assumes a linear flow
downstream, while 2D modelling considers much
more nuanced movement of water as it begins to
move out of the channel and onto the floodplain.
2D also allows for high-resolution, colorful, vivid
animations of flooding. The accuracy advantages of
2D modeling are greatest in areas with:
Below: Dewatered gate
● Wide floodplains
● Sinuous channels f
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