US Army Corps of Engineers
Nashville District

District Digest News Stories

Concrete placement rolling along at Center Hill’s auxiliary saddle dam

Nashville District Public Affairs
Published April 18, 2019
LANCASTER, Tenn. (April 18, 2019) – The U.S. Army Corps of Engineers recently began placing “roller-compacted concrete” to build a reinforcing berm downstream of Center Hill’s auxiliary dam.  This construction is the final major risk-reduction contract in the ongoing Center Hill Dam Safety Rehabilitation Project.

A bull dozier spreads a special type of concrete, RCC, which resembles more of a solid than a liquid at the Auxiliary dam project.

LANCASTER, Tenn. (April 18, 2019) – The U.S. Army Corps of Engineers recently began placing “roller-compacted concrete” to build a reinforcing berm downstream of Center Hill’s auxiliary dam.  This construction is the final major risk-reduction contract in the ongoing Center Hill Dam Safety Rehabilitation Project.

A Thalle Construction employees tests Roller Compacted Concrete before applying it to the platform. (USACE photo by Mark Rankin)

LANCASTER, Tenn. (April 18, 2019) – The U.S. Army Corps of Engineers recently began placing “roller-compacted concrete” to build a reinforcing berm downstream of Center Hill’s auxiliary dam.  This construction is the final major risk-reduction contract in the ongoing Center Hill Dam Safety Rehabilitation Project.

The USACE team working at the Center Hill Dam Auxiliary dam project. Linda Adcock, U.S. Army Corps of Engineers Nashville District project manager, Bill DeBruyn, Nashville District resident engineer; Alan Malcomb, U.S. Army Corps of Engineers Nashville District resident engineer and contracting officer.

LANCASTER, Tenn. (April 18, 2019) – The U.S. Army Corps of Engineers recently began placing “roller-compacted concrete” to build a reinforcing berm downstream of Center Hill’s auxiliary dam.  This construction is the final major risk-reduction contract in the ongoing Center Hill Dam Safety Rehabilitation Project.

LANCASTER, Tenn. (April 18, 2019) – The U.S. Army Corps of Engineers recently began placing “roller-compacted concrete” to build a reinforcing berm downstream of Center Hill’s auxiliary dam. This construction is the final major risk-reduction contract in the ongoing Center Hill Dam Safety Rehabilitation Project.

LANCASTER, Tenn. (April 18, 2019) – The U.S. Army Corps of Engineers recently began placing “roller-compacted concrete” to build a reinforcing berm downstream of Center Hill’s auxiliary dam.  This construction is the final major risk-reduction contract in the ongoing Center Hill Dam Safety Rehabilitation Project.

The berm is necessary to reduce risk of both a potential saddle dam foundation internal erosion failure and a potential overtopping failure of the saddle dam. The berm is being built primarily of Roller Compacted Concrete with conventional concrete facing. 

Linda Adcock, U.S. Army Corps of Engineers Nashville District project manager, explained that 11 of the planned 137 one-foot layers or “lifts” of Roller Compacted Concrete are already completed at the Center Hill saddle dam reinforcing berm site.  

Adcock said the contractor, Thalle Construction Company, placed a minimum of two-feet of conventional concrete, referred to as “mud matting,” on the 125-foot wide by 800-foot long cleaned bedrock base to allow for a good working surface to begin placement of the RCC.  The stepped downstream face of the berm is being shaped with metal formwork, she added.

The contactor has a concrete batch plant near the construction site with equipment in place to produce and deliver a special type of concrete, commonly referred to as “RCC,” which resembles more of a solid than a liquid.  The concrete is placed on the berm site and compacted into one-foot layers using a vibrating roller. 

Adcock said RCC sections are built lift-by-lift in successive horizontal layers.  Formwork on the downstream slope creates large concrete steps. Once a layer is placed, it can immediately support the earth-moving equipment to place the next layer.

“The RCC is transported by a conveyor belt from the batch plant, dumped onto the surface and spread with vibratory rollers, compacted in lifts to form the gravity concrete structure, which will reinforce the existing earthen saddle dam just upstream,” said Adcock. 

ill DeBruyn, Nashville District resident engineer, said RCC resembles a mixture of dirt and rock more than typical, conventional concrete, due to its low moisture content.

“The advantage of this type of concrete is that it can be put in place using traditional road paving equipment, which is much more efficient than placing typical conventional concrete,” said DeBruyn.

Two non-overflow sections allow access to a grouting gallery that runs along the berm.  The approximate 1,000-foot long structure has an 850-ft wide, 100-ft high overflow section.

DeBruyn said earlier in the year, the Corps blasted and excavated about 65,000 cubic yards of rock to create a solid, notched base for the large 100-foot high by 1000-foot long concrete RCC berm.  About two-foot diameter rocks and smaller stones, recycled from stabilization excavation at Center Hill Dam’s left rim, have been placed between the auxiliary dam and RCC berm.  The rock fill is designed to place pressure on the downstream auxiliary dam embankment and reduce the risk of internal erosion.

Adcock said the last component of the ongoing dam safety effort is the rehabilitation of the 70-year old main dam spillway gate electrical and mechanical components, which is ongoing.  The gate reliability repair is scheduled for completion in the summer of 2019, while the RCC berm is scheduled to be completed by this fall.  The Corps anticipates Center Hill Lake should return to normal operating levels by the end of 2019.

“The berm concrete placement began in March and is estimated to be completed in September,” said Adcock.  Night placements are scheduled to being in late April to mitigate placement, heat production and potential for cracking.”

LANCASTER, Tenn. (April 18, 2019) – The U.S. Army Corps of Engineers recently began placing “roller-compacted concrete” to build a reinforcing berm downstream of Center Hill’s auxiliary dam.  This construction is the final major risk-reduction contract in the ongoing Center Hill Dam Safety Rehabilitation Project.

The berm is necessary to reduce risk of both a potential saddle dam foundation internal erosion failure and a potential overtopping failure of the saddle dam. The berm is being built primarily of Roller Compacted Concrete with conventional concrete facing. 

Linda Adcock, U.S. Army Corps of Engineers Nashville District project manager, explained that 11 of the planned 137 one-foot layers or “lifts” of Roller Compacted Concrete are already completed at the Center Hill saddle dam reinforcing berm site.  

Adcock said the contractor, Thalle Construction Company, placed a minimum of two-feet of conventional concrete, referred to as “mud matting,” on the 125-foot wide by 800-foot long cleaned bedrock base to allow for a good working surface to begin placement of the RCC.  The stepped downstream face of the berm is being shaped with metal formwork, she added.

The contactor has a concrete batch plant near the construction site with equipment in place to produce and deliver a special type of concrete, commonly referred to as “RCC,” which resembles more of a solid than a liquid.  The concrete is placed on the berm site and compacted into one-foot layers using a vibrating roller. 

Adcock said RCC sections are built lift-by-lift in successive horizontal layers.  Formwork on the downstream slope creates large concrete steps. Once a layer is placed, it can immediately support the earth-moving equipment to place the next layer.

“The RCC is transported by a conveyor belt from the batch plant, dumped onto the surface and spread with vibratory rollers, compacted in lifts to form the gravity concrete structure, which will reinforce the existing earthen saddle dam just upstream,” said Adcock. 

Bill DeBruyn, Nashville District resident engineer, said RCC resembles a mixture of dirt and rock more than typical, conventional concrete, due to its low moisture content.

“The advantage of this type of concrete is that it can be put in place using traditional road paving equipment, which is much more efficient than placing typical conventional concrete,” said DeBruyn.

Two non-overflow sections allow access to a grouting gallery that runs along the berm.  The approximate 1,000-foot long structure has an 850-ft wide, 100-ft high overflow section.

DeBruyn said earlier in the year, the Corps blasted and excavated about 65,000 cubic yards of rock to create a solid, notched base for the large 100-foot high by 1000-foot long concrete RCC berm.  About two-foot diameter rocks and smaller stones, recycled from stabilization excavation at Center Hill Dam’s left rim, have been placed between the auxiliary dam and RCC berm.  The rock fill is designed to place pressure on the downstream auxiliary dam embankment and reduce the risk of internal erosion.

Adcock said the last component of the ongoing dam safety effort is the rehabilitation of the 70-year old main dam spillway gate electrical and mechanical components, which is ongoing.  The gate reliability repair is scheduled for completion in the summer of 2019, while the RCC berm is scheduled to be completed by this fall.  The Corps anticipates Center Hill Lake should return to normal operating levels by the end of 2019.

“The berm concrete placement began in March and is estimated to be completed in September,” said Adcock.  Night placements are scheduled to being in late April to mitigate placement, heat production and potential for cracking.”

In a separate contract, a lake access and restored boat ramp are planned just west of the dam, set to be finished by the end of 2019.  Both the berm and access Completion is necessary before Center Hill Lake can return to normal operating lake levels.

(The public can obtain news, updates and information from the U.S. Army Corps of Engineers Nashville District on the district’s website at http://www.lrn.usace.army.mil, on Facebook at http://www.facebook.com/nashvillecorps, and on Twitter at http://www.twitter.com/nashvillecorps. The public can also follow Center Hill Lake on Facebook athttp://www.facebook.com/centerhilllake.)