USACE Vicksburg District Engineers Innovative Solution for Hydropower Safety
By MAJ Christopher Ross
USACE, Vicksburg District
February 16, 2023
An adage and proverbial saying, “if it ain’t broke, don’t fix it”, is often a good rule of thumb... However, engineers routinely defy status quo and seize opportunities to improve processes, promote safer environments, enhance ergonomics, and accelerate procedures. The U.S. Army Corps of Engineers (USACE) Vicksburg District prides itself with diverse talent, expertise, and continuity that executes engineering solutions serving communities along the lower Mississippi River.
The Vicksburg District’s (MVK) area of responsibility is confined within northern Louisiana, western Mississippi, and southern Arkansas. MVK’s mission is to deliver world-class projects and engineering solutions with our partners, for our communities and our Nation. MVK’s employees do just that, every day, every mission, every emergency, and everywhere! Hydropower is one of MVK’s esteemed domains. MVK trains experts and provide services for communities along the rolling hill communities of Southwestern Arkansas.
Upstream leak of expansion joint prior to repair.
Blakey Mountain Dam is surrounded by the Ouachita National Forest residing in the hunting, camping, and recreational city of Mountain Pine, Arkansas. The dam’s power generation jurisdiction falls under Southwestern Power Authority (SWPA)1. The dam officially came on-line in July of 1956. An earth dam, with a volume of 4 million CuYds of earth, it has a base width of 1400 ft. The dam houses two generators with a maximum
output capacity of 75,000 KWs. Above the dam is the Lake Ouachita flood control reservoir with a designed maximum power pool area of 40,100 acres and a spillway flood control pool area of 48,300 acres. Total storage capacity is 2.768 million acre-feet (1 acre-ft equals 1 acre of water at 1 ft deep).
1990/2006 historical photos of crew’s positions on top and side of expansion joint using multiple chain come alongs to peel back the compression ring and expose existing packing material in need of replacement.
Critical thinkers of USACE continuously overcome obstacles and engineer solutions for processes that increase efficiencies and promote safety. Consequently, reductions in operating costs, man-hours, mitigation of injuries, and improve production are outputs. For an example, MVK’s Hydropower section reverse engineered a method of repacking an expansion joint to reduce man-hours and cost for the Blakely Hydropower Dam, Arkansas.
Blakely Mountain Power Plant is maintained by a small staff of electronic mechanics, electricians, and mechanics to include Ronald Packer (Senior Power Plant Mechanic). Mr. Ronald Packer accumulated over 30 years of mechanical experience with a 13-year tenure with USACE. Ron has supported MVK’s hydropower section at Blakely, Narrows, and DeGray hydropower plants for the past 6-years.
While preparing to conduct scheduled maintenance for Blakely’s generators, Mr. Packer delved through historical documents, pictures, and reports of how a 16-year cyclical repacking and maintenance of a power tunnel expansion joint was conducted. Despite limited continuity from other USACE employees, Mr. Packer deliberately assessed the problem, identified limitations and constraints, and developed courses of actions to reduce cost and increase safety.
Historical maintenance required a crew of 6-8, that would operate on the 24-foot diameter hydroelectric intake tunnel (named the Power Tunnel) and affix 12-16 chain come alongs to exposed ring girders. Subsequently, in unison, the crew would incrementally operate each chain come along to pry the compression ring back and expose packing material underneath. This task would require 10 – 12-hour shifts, that spanned six days. Re-seating of the compression ring is required to remove old packing material and re-pack the expansion joint. The compression ring is divided into three sections and fastened onto the power tunnel’s frame with 120 bolts, all of which require removal. In order to expose the expansion joint, the compression ring must be pried away from the frame at a minimum of 12-inches. This allows adequate access to the expansion joint and packing material. Portable power tools aided the operation, but a high demand for manual labor, dangers of climbing and maneuvering around the power tunnel, and high cost of overtime prompted Mr. Packer to devise a new plan of attack.
Mr. Packer’s understanding of hydraulics and equilibrium load sharing of fluid mechanics, assisted in designing a hydraulic expansion tool. To mimic simultaneous movements, Mr. Packer engineered a device to distribute hydraulic pressure through a simple hydraulic apparatus. He fabricated two hydraulic manifolds, each with three double-acting hydraulic cylinders, a pump, hydraulic fluid reservoir, pressure gauges, hoses, and fittings. For ease of transport, all components were assembled on a wheeled handcart.
Expanded assembly of hydraulic components.
Handcart of hydraulic components assembled.
However, Ron’s ingenuity didn’t stop there! He fabricated additional utensils for the task. He fabricated specialized hand tools for removal and the repacking for the expansion joint. The packing material is wound tightly around the exterior diameter of the expansion joint. Over time, the packing material hardens and is difficult to remove. Prying, chipping, and picking tools were cut and welded to assist the maintenance crew.
Fabricated hand tools for removal of old packing material.
This operation still proved to be labor intensive, despite the integration of a hydraulic assist. However, there was a significant reduction of overtime pay and reduction of employees needed. The removal of the old packing material required hand and power tools including techniques of chipping, shaving, and prying. The fabricated hand tools were valuable and were archived future use.
Roll of the 1.25” x 1.25” x 80’ graphite impregnated packing material.
The hydraulic mechanical system and deliberate engineering enabled a small crew to remove the compression ring sections with ease. The new method only required two employees to connect hydraulic cylinders to ring sections and pad eyes (attached to the intake tunnel), and one employee to operate the hydraulic pump. This resulted in an even and consistent movement of the compression ring sections along dowel rods spanning the gap.
Hydraulic piston installed and attached to compression ring.
Justin Crowe (MVK Employee) monitors
hydraulic piston as the compression ring is peeled back.
Fabricated tool for pushing new packing material into the expansion joint.
The assembled hydraulic machine proved its worth by cutting man-hours by 22% from ~ $98k to $77k, reduced the crew required in half from 8 to 4, and retained the work in- house eliminating contract overhead costs. Initial maintenance estimate from Tennessee Valley Authority (TVA) totaled ~ $125k. Overall execution cost was ~ $101k resulting in a savings of $24k. Parts for the hydraulic manifold cart cost was ~ $3.6k; along with additional safety equipment and tools cost ~ $4.8k. The expansion joint packing material consisted of 13 rolls of impregnated graphite at 1.25” x 1.25” x 80’ dimensions costing $15.6k.
Future considerations for Ron Packer include manufacturing another hydraulic handcart with the addition of nine cylinders to peel back all sections of the compression ring with redundancy built in. The first iteration proved to be successful, but with only one cart, the crew could only move one section of ring girders at a time. Ron Packer remarked, “Having the ability to extract all three sections at once, will further reduce the time needed...” [to peel back the compression ring]. He plans to upgrade psi (pounds per square inch) gauges to increase accuracy of output from the hydraulic reservoir pump.
Mr. Ronald Packer standing alongside the Blakely Mountain Dam intake tunnel’s expansion joint with his engineered hydraulic apparatus connected, extracting a compression ring section.
As for Ron Packer, his excitement to execute this maintenance again. He expects to perform this operation at least once more during his tenure with USACE. Mr. Packer’s leadership and dedication to improve systems highlights the best from USACE Vicksburg District. He hopes to share his ingenuity as an opportunity for others to think outside the box. Mr. Packer is an epitome of disciplined initiative and professionalism that contribute to the Corps of Engineers.