Round-the-clock construction to start on cutoff wall near Lakeport on Monday

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LAKEPORT – Lakeport residents will see lights on the dike at night starting Monday, Feb. 22 as round-the-clock construction gets underway on a cutoff wall inside the L-50 levee along the Borrow Canal. The project started at Earl Beck’s homestead and will extend 4.1 miles passing under State Road 78 and ending 2,000 feet past the S-131 pump station.

The L-50  is a tie-back levee, north of the Fisheating Creek area. The Herbert Hoover Dike is open in the area near Fisheating Creek, with tie-back levees on either side of the creek and its floodplain.

The work is projected to be complete in February 2022. Building the portion of cutoff wall under State Road 78, which will probably be done in May, will take three to four weeks. During that time, that section of SR 78 will be limited to one lane of traffic. Crossing SR 78 will be relatively quick, explained Project Manager Cyril Sleiman of Bauer Foundation Corp. Set up and removal of the diversion lanes will take part of that three to four week period.

The cutoff wall, designed to prevent seepage of water through the dike, will be 50 feet deep and at least 2 feet wide. As work on each section of the wall is complete, the dike will be restored and sodded.

Work on the cutoff wall is like a 4,000 foot long train, said Sleiman. He said work starts with building up a section of the dike so that the crest of the dike is 45 feet wide, using fill dirt from an authorized site on the Brighton Reservation. This area is stabilized so it can hold the heavy equipment. Next, a pre-drilling rig is used to drill down the center of the line where the wall will go. Pre-drilling breaks up the soil and makes sure the mixing occurs in the right way, said Sleiman. Two passes of the pre-drill rig are completed using GPS monitoring to ensure accuracy. The onboard computer can tell if the pre-drill is off by even a few degrees. Core material brought up by the drill is collected for disposal at an approved site.

The blue flags mark the path for the pre-drilling machine which prepares the site for the Concrete Slurry Machine.
The blue flags mark the path for the pre-drilling machine which prepares the site for the Concrete Slurry Machine.

The Concrete Slurry Machine (CSM) trails after the drill, injecting the grout and mixing it with the soil. A compressor pumps compressed air into the mixture, helping it to mix more smoothly. The CSM operator monitors the progress of the process on a computer, which also uploads data for monitoring by the Corps of Engineers.

The Concrete Slurry Machine injects the grout into the prepared ground and mixes it with the soil.
The Concrete Slurry Machine injects the grout into the prepared ground and mixes it with the soil.

The grout flows from the mixing machine in a pipeline to the CSM. The mixing machine is also computerized, following a recipe that includes water, bentonite (a type of clay from Wyoming), cement, slag and lignosulfonate (an environmentally-friendly product of tree sap.)

A computerized system mixes water, bentonite, cement, slag and ligno into the grout mixture formulated for use on the L-50 levee.
A computerized system mixes water, bentonite, cement, slag and ligno into the grout mixture formulated for use on the L-50 levee.

Testing is conducted throughout the process to make sure the completed seepage barrier will meet the required specifications. That includes testing the grout mixture in the ground. Periodically, samples are taken from the bottom, middle and top third of a section and tested by a third-party lab. If the mixture is off, that panel (a 7.5 ft. section of wall) is removed and redone.

Safety officer Tera Birkhimer said the goal is to complete at least eight panels per 12-hour shift.

When the CSM work is complete in one area, the fill dirt is removed and the dike’s surface sodded to return the outside of the dike to it’s original condition. The fill dirt is transported forward to the next section and the process starts again, on the next 4,000 feet.

On Monday, when the night shifts start, all of the pre-drilling will be done during the 12-hour day shift, Sleiman explained. He said pre-drilling goes faster than the CSM work so they can maintain the 24-hour schedule without drilling at night.

Work on cutoff walls as part of the rehabilitation of the Herbert Hoover Dike has been ongoing since 2007, explained Herbert Hoover Dike Construction Program Manager Ingrid Bon. However, she added, “it has been years since we’ve been so close to homes.” She warned residents will notice the lights and some machinery noise. The backup alarms usually draw the most complaints, she added.

Lakeport is easily visible from the top of the L-50 levee.
Lakeport is easily visible from the top of the L-50 levee.

Bauer was involved in building the cutoff wall in the Reach 1 area (from Port Mayaca to Belle Glade). Sleiman said working in that area was more complicated because they had to replace the peat. The soil in the dike near Lakeport is silty sand, clay and a small layer of limestone, he explained. Working with the sandy soil brings other challenges, he continued. Erosion control is important. As each section is completed, a hydroseed truck comes along to spray the area with a slurry of seeds and mulch.

Monitoring on the project includes on-site safety officers, air quality testing by the Florida Department of Environmental Protection and wildlife and environmental monitoring by CECOS Environmental Consulting Services. Some gopher tortoises had to be relocated with the approval of the Florida Fish and Wildlife Conservation Commission. Drain pipes along the top of the dike keep the work area from getting too wet during rainstorms. Spray trucks keep the exposed soil from drying out too much and prevent dust from getting into the air. Silt barriers protect nearby waterways. Birkhimer said the narrow work area on top of the dike requires strict adherence to safety protocols. On Monday night, she will be the night shift safety officer.

Silt barriers help control erosion from the site.
Silt barriers help control erosion from the site.

“As long as residents have allowed us, we have inspected a large number of the houses (in Lakeport) prior to construction (of the cutoff wall),” said Sleiman. He said they also have sensors to monitor vibrations from the equipment, and to ensure the vibrations stay at a safe level.

Sleiman said in the 13 years they have worked on the Herbert Hoover Dike, Bauer has improved their technology. Bauer builds most of their own equipment, with a factory in Texas as well as in Germany. When engineers find something is slowing a project down, they look for ways to resolve the problem. For example, cleaning the CSM was once done by hand. Sprayers attached to the machine not only make it safer for the humans operating the equipment but also save time.

He said they also found ways to modify the cutters used in the drills and the CSM for different types of soil. The continued improvements allow Bauer to be more cost effective and to ensure quality, he added. The “teeth” used by the CSM to mix the grout with the soil are specialized for the type of soil in that area. There are 30 to 40 different versions of these attachments, each specialized by soil type.

The "teeth" used by the CSM are specialized for the type of soil.
The "teeth" used by the CSM are specialized for the type of soil.

He pointed out the new state-of-the art CSM straddles the pre-drilled area. That makes it possible for the machine to work on a 45-foot surface. Older equipment required at least 85 feet, which required a lot more time and fill dirt to prepare the top of the dike to support the machinery.

“The contracts for cutoff walls require the contractor to build 500 feet of wall first. They test it and we test it before we give the go ahead,” said Bon. “We tell the contractor what the finished product should be. We don’t tell them how to build the wall.”

When the project is complete with the fill dirt removed and the area sodded, it will look just like the dike did before the project started, said Sleiman. “When we reconstruct the dike, the type of sod used is very specific sod.”

“Grass is the first defense against erosion,” said Bon. She said they only have a 36-hour window from harvest to installation for the sod, which comes from local sod farms.

She said the 500 feet of test wall completed by Bauer is near SR 78, which will help speed work in that area.

While the work is expected to be completed in February 2022, weather-related delays could affect the schedule.  The site is required to shut down if lightning is within 10 miles.

The towering metal equipment increases the danger during lightning storms. Safety rules require the construction site be shut down if lightning is within 10 miles.
The towering metal equipment increases the danger during lightning storms. Safety rules require the construction site be shut down if lightning is …

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