By Samantha HeiligOctober 31, 2015
For more than a decade, members of the Rock Island District have been working to design and implement one of the largest civil works projects ever completed in the District. The project, known as the Lockport Lock and Dam Upper Pool Project, is a multi-stage, multi-year and multi-million dollar rehabilitation effort that is now in its final stages and is nearing completion.
The Lockport Lock and Dam is a unique facility, designed and constructed by the state of Illinois, as part of the Chicago Sanitary and Ship Canal (CSSC). It includes a number of structures including a lock, operated by the Corps; a powerhouse operated by the Metropolitan Water Reclamation District of Greater Chicago (MWRD); controlling works that regulate the water level in the CSSC; and an approach dike and guide walls that surround the elevated Lockport pool.
According to Michael Tarpey, project manager for the Lockport Upper Pool Project, a memorandum of agreement signed in 1984 between the U.S. Army Corps of Engineers and the MWRD transferred primary maintenance responsibilities of the structures that create the Lockport pool, to the Rock Island District. These structures, which hold the canal pool at a level roughly 40 feet above the surrounding communities, have served their purpose for more than 100 years, but reliability and safety concerns in the late 1990s and early 2000s prompted the Corps to begin investigating needed repairs.
In 2004, a major Rehabilitation Evaluation Report (RER) was completed by the District to examine the condition of the Lockport facility. An RER is an evaluation of the present condition, past construction history and problems, present and future reliability, alternative solutions, and investment strategies for a needed project. The Lockport RER identified four major areas of concern: the approach dike, concrete guide wall, controlling works, and powerhouse and dam.
In 2005 a group of senior engineers from across the Corps conducted additional inspections of Lockport as part of a large investigation of lock and dam facilities around the country. During this inspection, a Dam Safety Action Classification (DSAC) rating of two out of five was given for the Lockport facility. According to Tarpey, this low DSAC rating meant the facility was identified as being highly urgent. Dams with a DSAC rating of two could fail during normal operations or a failure could be initiated as the consequence of an event. The rating also meant the likelihood of failure from one of these occurrences, prior to remediation, was too high to assure public safety or that the combination of life or economic consequences with probability of failure was very high.
"The DSAC rating was a significant factor in this project receiving funding," said Tarpey.
With the level two DSAC rating in place and funding allocated to continue work on the project, the District began moving forward on developing ways to improve the safety and stability of the Lockport structures. A large-scale project consisting of five stages was created and since that time, four of the five stages have been completed.
Stage 1, which involved constructing a 4,300-foot cut-off wall within the embankment of the approach dike that leads to the powerhouse and Stage 4, which stabilized the powerhouse structure and cleared overgrown embankments were completed in FY09. Stage 2, which included repairing concrete bulkheads and replacing brick, limestone and granite facades in the controlling works and Stage 3, which consisted of constructing two miles of precast concrete panel wall to replace the original walls of the canal were both completed in FY12.
The fifth stage, known as Stage 1-C is the last and final step in the project. This stage, currently underway, includes construction of a new forebay wall behind the existing wall and is scheduled for completion in early FY17.
"It was extremely important that the final product for the Lockport Lock and Dam Upper Pool Project would address the safety issues and mitigate the risks identified in 2005 that led to the DSAC two rating," said Josh Cackley, Dam Safety Program Manager for the Rock Island District. "Upon completion, the objectives will be met and the surrounding communities will have a more reliable and safer CSSC."
The major concern with the final stage of the Lockport rehabilitation project was the integrity of the forebay wall leading up to the Lockport powerhouse. The wall, which is made of both concrete and earth, is approximately 40 feet high and separates the water in the CSSC from the water in the Des Plaines River.
"For years, the Corps has had concerns about water leaking through this wall," said Cackley.
Each week, thousands of gallons of water slowly work their way through the wall potentially carrying bits of soil and concrete that have eroded from within. This gradual seepage has, over time, reduced the stability of the wall and could eventually lead to failure.
To address the issue of the leaking wall, engineers involved with designing the project recommended building a new forebay wall using roller-compacted concrete (RCC). Unlike traditional concrete walls that use forms to hold material in place, RCC uses a different process which allows layers of concrete to be laid one on top of the other until a desired height is obtained.
RCC has the same basic ingredients as conventional concrete including cement, water and aggregates, such as gravel or crushed stone. But, unlike conventional concrete, it is a drier mix that is placed, much like asphalt, and then compacted in place with vibratory rollers. Using the RCC process, the new 40-foot high, 1,500-foot long wall, will have been built 12 inches at a time, by a contracted construction team in about two months.
"This was the perfect application for the use of RCC because it was a large scale project that would have otherwise needed a great deal more time and funding to complete," said Andrew Goodall, project engineer for the forebay wall. "Using RCC we made building the wall simple, fast and economical."
Once the RCC wall is complete, the old forebay wall, currently holding the water back from where the new wall is being built will be removed. In the end, the goal of the $150 million project is that the major rehabilitation work will result in a reclassification of the Lockport facility to a higher DSAC rating.
"Much credit goes to the design team for producing a very good design under challenging site constraints and to the construction team for their dedication to the project," said Goodall. "Thanks to the excellent working relationship between engineering and construction this project has been a great success."