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. 26 | Yearbook 2018 | www.waterpowermagazine.com 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 www.waterpowermagazine.com | Yearbook 2018 | 27