When Ohio’s massive Project Clean Lake is completed in 2036, Nicholson Construction can take pride in having played its part in improving the water quality in one of North America’s great lakes.
Project Clean Lake is the Northeast Ohio Regional Sewer District’s (NEORSD) 25-year program to reduce the volume of combined sewer overflows into Lake Erie, the fourth largest of the five great lakes, by 4 billion gallons per year. It is a combination of large-scale storage and conveyance tunnels, improvements to wastewater treatment plants and investment in green infrastructure in the city of Cleveland.
The US$3bn program to protect Lake Erie and its tributaries comprises seven large-scale projects – the Euclid Creek Tunnel, Dugway Storage Tunnel, Doan Valley Tunnel, Westerly Storage Tunnel, Shoreline Storage Tunnel, Southerly Storage Tunnel and Big Creek Tunnel – and to date, geotechnical general contractor Nicholson Construction, a subsidiary of Soletanche Bachy, has had support of excavation contracts on three of the projects.
For the US$153m Dugway Storage Tunnel, a 24ft diameter, three-mile tunnel lying 180-230ft below ground and completed in 2020, Nicholson installed secant piles as the temporary support of excavation for a baffle drop structure, and two rectangular gate structures. The work was on two sites that connect to the existing sewer system.
On this section, where the Salini Impregilo (now We Build) Healy JV was the general contractor, Nicholson drilled with polymer to position the 122ft secant wall, one of the deepest secant pile structures in the city of Cleveland.
Project superintendent Steve Davies said the five-month works went to plan but one of the biggest challenges was the confined spaces for the two sites.
“Both shafts were on very tight sites and the second shaft was on a busy intersection, near a school and a church,” said Davies, adding that Nicholson managed the challenge with good planning and logistics.
The Dugway Storage Tunnel is now in operation.
For the US$135m Westerly Storage Tunnel, also completed in 2020, Nicholson’s US$7m contract involved support of excavation systems for three shafts – the TBM’s 50ft diameter entry and retrieval shafts and a vent shaft. On this project, which controls overflows at two locations on the Cuyohoga River, which flows into Lake Erie, the general contractor was JayDee- Obayashi JV.
The original plans outlined secant piles with a rib and liner plate system and de-watering at specified locations but Nicholson proposed an alternative solution using diaphragm walls, which reduced the risk associated with traditional support of excavation. The diaphragm wall provided one continuous system keyed into rock, eliminating the need for the rib and liner plates and allowing the mass excavation of the shaft in a more controlled environment. All three shafts were unreinforced, relying instead on compression and hoop stress.
Davies said Nicholson favours diaphragm walls over secant piling because the job can be done more quickly and efficiently.
Using a mechanical clamshell to dig out the overburden, and a hydrofraise to mill the rock socket, the team constructed a 42in-thick, 152ft-deep unreinforced diaphragm wall, using six triple bite panels, at the drop shaft, as well as a 2ft-thick, 71ft-deep steel-reinforced diaphragm wall for support of excavation of the connecting gate structure. For the 21ft-diameter vent shaft – one of the smallest diaphragm wall shafts built in the US – Nicholson built a 3ft-thick, 175ft-deep unreinforced diaphragm wall.
The retrieval shaft, formed using eight triple bite panels, extended to a depth of 95ft.
Again the crew were working in a tight space, constrained by highways, existing structures, underground utilities and overhead power lines.
They also had to deal with Cleveland’s harsh winter weather. To protect against the freezing conditions, the slurry plant was framed out so concrete blankets could insulate the plant components. Ten portable torpedo heaters were also placed throughout the plant to supply ambient heat for the enclosures. Even with these measures, however, Davies said there was still a problem with freezing, and maintaining the bentonite density, and the company had to stop work for two or three days.
“As soon as we were thawing things out they were freezing again,” he said.
The second shaft was close to the lake shore and so particularly exposed, as was the larger plant required for the hydrofraise.
The Westerly Storage Tunnel is scheduled to come into operation next year.
Now Nicholson is working on its third Project Clean Lake contract – the Shoreline Storage Tunnel, where McNally Kiewit SST JV is the general contractor. This part of Project Clean Lake will control overflows at 11 permitted locations along Lake Erie and reduce overflow volumes by around 500 million gallons each year.
Again, Nicholson is installing three diaphragm wall access shafts along the three-mile tunnel alignment. The work includes cement bentonite mass treatment break in/break out blocks for at the TBM launch and retrieval shafts, and two solider pile reinforced cement bentonite walls for support of excavation systems for two near-surface structures.
On this project the company has avoided the challenges of winter weather by taking a three-month break from the site after completing the first shaft in December last year. The team returned to site in spring, to build the second shaft, and it will finish the third shaft in October, before the coming winter’s weather sets in.
On Shoreline Nicholson encountered more clay – and sticky clay – than on the previous two projects but Davies said it did not create any problems.
“It’s actually nice to dig and come out with a full bucket of clay,” he said.
On Site 1 – the TBM launch shaft – Nicholson built a 66ft internal diameter, 129ft-deep diaphragm wall shaft comprising 10 4ft-thick triple bite panels. On this site a mechanical clamshell removed 15m3 of soils an hour. With the geology comprising clay on shale, this was the only one of the three sites where the hydrofraise was required to anchor the wall. In addition, the team built an 8ft x 37ft break-in using 20 4ft-thick single bite cement bentonite panels.
For Sites 2 and 3, Nicholson used a hydraulic clamshell, which removed up to 20m3 per hour.
On Site 2, which was completed in June, the shaft is 160ft deep with a 56ft internal diameter. Nicholson also built a near surface structure at 74ft below ground to connect to the existing sewer.
Site 3, where Nicholson is currently working and expects to wrap up its project works in October, the 133ft-deep shaft has a 45ft internal diameter. It comprises seven triple bite panels, 3.5ft thick. Near surface structures were completed at a depth of 66ft.
On this site there are also two near surface structures, excavated with mechanical clamshell and formed by 14 single bite panels each, 2ft thick.
The Nicholson team first built the cement bentonite break in/break out structure before moving on to the diaphragm wall shaft.
On the first two sites for Shoreline, Nicholson had the luxury of large working areas, but project manager Jerome Dupront said the third site posed constraint challenges again.
“It is the tightest site so far,” he said.
The site required many phases of work because it impinged on a road, so traffic management was needed, and the main shaft was positioned near a building.
An unforeseen problem was the presence of overhead utilities, which Nicholson had been told would be put underground. This meant changes to the planned jobsite.
“There are overhead communication and electricity lines so we’ve had to work around the utilities. We’ve had to re-plan the project and move everything around,” said Davies.
This included replacing the planned vertical silos with mobile 21,000 gallon tanks.
“We have six tanks in the road to store the bentonite,” said Davies.
As it has worked on each of the three Project Clean Lake contracts Nicholson has maintained a continuity by using the same supply chain partners, said Dupront but, he added, a nationwide cement shortage was a concern, especially in the busy summer construction period.
“It is changing the balance of how you plan jobsites,” he said. “Usually when you are building diaphragm walls the focus is on how fast you can do it. Now the emphasis is on when you can you pour the concrete, so it’s reversing how you pan a job.”
Another challenge has been finding operators for the hydrofraise and mechanical and hydraulic clamshells. In the US there is a shortage of skilled labour for this specialised equipment as many operators are entering retirement but fortunately the unions have allowed Nicholson to bring in operators from its French parent company Soletanche Bachy.
Nicholson, however, is trying to address the shortage by training people on jobs and “spreading the knowledge”, said Dupront.
