Upper Antelope Creek Flood Reduction

Upper Antelope Creek Flood Reduction #135

Customer Name
City of Lincoln and the Lower Platte South Natural Resources District (NRD)

Design / Specifying Engineer
Don Day of Olsson Associates

Block Manufacturer
Workman Precast

Wall Installer
M.E. Collins (General Contractor); Leick Landscaping (Installer)

Project Location
Lincoln, Nebraska

Test

Year Built
2011

Project Scope

THE CHALLENGE: Protecting Homes and Businesses From Flooding.

When the Lower Platte Natural Resources District (NRD) and the City of Lincoln, NE set out to control flooding along the Antelope Creek, they had several objectives in mind. Taking homes and businesses out of the flood plain was a major goal, but preserving and improving a nearby bike path was also a priority.

The Lower Platte South Natural Resources District (NRD) and the City of Lincoln partnered on the $2.5 million project,which included new retaining walls along Antelope Creeks west bank, among other improvements including additional box culverts under a bridge, a “detention cell” to hold water temporarily in a park, two flood-control berms,and a wider recreational trail.

THE SOLUTION: Channelization with Redi-Rock Ledgestone Walls

Finding the right solution for lining the creek channel was a challenge for project designers. Since there was no room to excavate for geogrid, the NRD and City initially considered using a poured-in-place wall and sheet piles.

However, a meeting with local Redi-Rock manufacturer and retailer Workman Precast led the NRD and City to an even better solution. By using massive, one-ton Redi-Rock blocks, engineers were able to design gravity retaining walls up to 16.5 ft. tall to create a channel for the Antelope Creek. Once the owner saw Redi-Rock and the price, the decision was made to specify Redi-Rock with the Ledgestone face (no other options or equivalents allowed).

Several major benefits of the Redi-Rock system in storm channel applications include:

Minimized excavation: The massive size of each Redi-Rock block allows tall walls to be built with minimal excavation. This allows walls to be built closer to property lines—or in the case of this project, the gravity solution preserved space that could be used for widening the bike/pedestrian path.
Fast Installation: Redi-Rock blocks stack like giant Legos, making them quick and easy to install using an excavator and a small crew. Redi-Rock is a product for strong minds and weak backs.
Durable Components: Each block is made of wet cast, 4,000 PSI air-entrained concrete—ensuring that it will stand the test of time.
Superior Aesthetics: Redi-Rocks Ledgestone texture creates walls that look like natural, random stone walls. Ledgestone blocks have the same dimensions and engineered capabilities as other Redi-Rock blocks, but with the look of natural, stacked ledgestone.
THE OUTCOME: 100 Buildings No Longer Threatened By Floods

In total, the project utilized 14,000 sq. ft. of Redi-Rock retaining walls along 2,000 lineal ft. of Antelope Creek. The NRD estimates that when all phases of the project are complete, the flood control measures will take about 100 homes and businesses out of the 100-year flood plain.

The final phase of the project is scheduled for completion in 2012 and includes replacing the South Street Bridge, additional channel stabilization, water main relocation and sanitary sewer construction.

THE REST OF THE STORY:

Even though this was primarily a flood control project, it seems that local bikers and pedestrians are appreciative of the projects other benefit—the improved bike path.

“It’s almost impossible to stop people from using it,” Ed Ubben, project coordinator for the Lower Platte South NRD explained. “We’re almost done. We haven’t had our final walkthrough,” he told the Lincoln Journal Star newspaper in November 2011.

Trail users won’t be the only ones benefiting from the new and improved trail segment. The zoo’s animals will, too. The walls help prevent erosion under the Lincoln Childrens Zoo, plus they help keep vandals from throwing trash and other debris in the animal pens.

“Obviously, we’re always concerned about security and our animals, especially along that perimeter,” said John Chapo, the zoo’s director.

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Schewe Farms (Omaha Royals New Stadium Development)

Schewe Farms

Customer Name
Sanitary and Improvement District No. 290 in Sarpy County, Nebraska

Design / Specifying Engineer
Thiele Geotech Inc. and Lamp, Rynearson & Associates, Inc.

Block Manufacturer
Workman Precast

Wall Installer
Linhart Construction Inc.

Project Location
Papillion, Nebraska

Year Built
2010

 

Hybrid Gravity/Reinforced Headwalls Protect Wetlands

Protecting local wetlands was a high priority when the Omaha Royals AAA baseball team needed a new stadium to call home. Their long‐time stadium in downtown Omaha closed in Sept. 2010 and the team was moving south of town.

CASE STUDY:

Sarpy County broke ground on the $26 million new stadium in 2009. The total cost for the stadium portion of the project was an estimated at $20 million, with the remaining $6 million going towards infrastructure. The 6,000 seat stadium is the anchor for a family entertainment district that is expected to include hotels, shopping, restaurants and recreational activities.

The access road for the 30‐acre development crossed through an area of wetlands, which required special environmental consideration. Initially, engineers considered grading a gradual slope from the roadway down into the wetlands but chose a design using architectural culverts and headwalls instead.

“The objective was to minimize the footprint through the wetlands. Rather than creating a 3:1 slope and destroying or disturbing all that wetland, the vertical headwall saved a substantial amount of wetland,” Dan Thiele, president of Thiele Geotech explained.

A total of three culverts required six headwalls. The headwalls abut the culverts and stand approximately 30 ft. from the centerline of the roadway, on either side.
The project’s civil engineering firm and contractor had both worked with large precast modular wall systems in past and liked the mass of the blocks and their inherent stability in headwall applications. Redi‐Rock was ultimately chosen for the project based on its cost competitiveness and aesthetics.

“The new Ledgestone face looks really good. Aesthetics wasn’t a primary consideration, but once they saw the new face, the deal was sealed,” Thiele explained.

These headwalls have a very different look than large block precast systems of the past. The new Redi‐Rock Ledgestone texture gave these headwalls an incredibly natural look. It’s nearly impossible to distinguish individual blocks within the finished walls, and the colors blend in with the landscape. Ledgestone blocks have the same dimensions and design capabilities as other Redi‐Rock blocks, with an entirely new look.

The design of the Redi‐Rock headwalls was unique—a hybrid of reinforced and gravity structures. The civil engineers for the entire project, Lamp, Rynearson & Associates, Inc., required the top 7.5 to 9 ft. of the headwall be a gravity structure. But since the headwalls stand 28.5 ft. high, the bottom portion of the headwalls needed to be reinforced.

“Creating a geogrid‐free zone in the upper part of the walls helped prevent potential conflicts with utilities that would be installed under the road way—waterlines, sanitary sewers, storm sewers, power, and communications,” Thiele explained.
To meet the design criteria, Thiele designed the bottom portion of the headwalls using Redi‐Rock 28 in. reinforced blocks. Prior to constructing the walls, the installation crew from Linhart Construction Inc. installed leveling pads of compacted stone to ensure the stability of the walls. The crew installed 12 courses of Redi‐Rock blocks, or 18 ft. tall walls—reinforced in every course with geogrid extending 18 to 20 ft. behind the walls.

As specified by Thiele, the crew backfilled using sand and compacted after each course of block and geogrid were installed. Thiele designed the remaining 6‐7 courses using Redi‐Rock 41 in. gravity blocks to allow the top portion of walls to be built without geogrid.

The headwalls feature both inside and outside curves, which were built using standard Redi‐Rock blocks. No cutting was required.

The headwall portion of the project was completed in about a month. Phase 2 of the project will include installing Redi‐Rock Ledgestone columns and freestanding walls, as well as black metal fences atop the headwalls. The scheduled completion date is in the late fall of 2010.

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