Nearly 20 years ago the Environmental Protection Agency (EPA) issued a policy requiring municipalities to make improvements to reduce or eliminate combined sewage overflow (CSO) related pollution problems. In 2000, Congress amended the Clean Water Act to require the cities to comply with the EPA policy.

CSOs are found in older combined systems that predate the Clean Water Act. Greater Cleveland’s earliest sewers – primarily within the city and its inner-ring suburbs – are combined sewers. Built around the turn of the 19th century, these sewers carry sewage, industrial waste, and stormwater in a single pipe, and heavy precipitation can overtake capacity. When this happens, control devices may allow some of the combined wastewater and stormwater to overflow into area waterways, such as Lake Erie, which is one of the largest lakes in North America.

The Euclid Creek Storage Tunnel (ECT) project is part of a larger network of underground tunnels that are being constructed in order to drastically reduce CSOs. It is the fourth and last that the Northeast Ohio Regional Sewer District has developed over the past eight years. Currently, CSOs in the Euclid Creek area overflow more than 60 times a year. "This project is part of the system that includes three projects," says Tom Szaraz, project manager at McNally. "The Euclid Storage Tunnel; the Tunnel Dewatering Pump Station, which is under contract and work has just started adjacent to our site; and the Dugway Storage Tunnel, a 24ft (7m) diameter storage tunnel extending approximately 16,000ft (4,877m) in length from its connection to the ECT, which is to be completed in three years time."

When the system is completed, overflows should be reduced to two or less in a typical year of rainfall within the affected service areas. "In addition, Euclid Beach, is only open about 50 per cent of the warm weather days because of the bacteria levels in the water due to the overflows," says Szaraz." This project will help clean that portion of the lake tremendously and end these closings."

A McNally-Kiewit joint venture secured a USD 198.6M contract in December 2010 to excavate the 17,750ft (5.5km) tunnel with an internal diameter of 24ft (7.32m). The finished tunnel will have the capacity to hold 70M gal (318.2M litres) of combined stormwater and wastewater. The project is due to be completed in 2015.

The alignment
The tunnel will start in Bratenahl, south of Interstate 90, and continue northeast to the District’s Easterly Wastewater Treatment Plant. There the tunnel will continue under Lake Erie for about 3,000ft (914m), and pass under the shoreline near Green Creek at East 152nd Street.

It will then head east, following Lake Shore Boulevard and Nottingham Road, and end at Saint Clair Avenue. The ECT depth will vary between 190 – 220ft (58- 67m) through chagrin shale bedrock.

"The alignment of the tunnel is very curvy," says Szaraz. "We’re in an older area of Cleveland, the area spawned in the late 1800s, so although it has changed significantly over the years there are still a lot of old structures in place. I think the alignment was the biggest challenge for us during design. About 70 per cent of the project is curved, it averages about 200ft (61m) in depth and that’s expected for this kind of project. The chagrin shale bedrock geology has an average compression strength of 10,000psi (69MPa), which is also typical for the tunnel alignment."

The project faces tough time restrictions, which Szaraz says will be challenging. "There are several time constraints with access to certain sites," Szaraz explains. "We don’t have access to ECT-3 [where the tunnel cuts under the lake] until November this year. There’s a structure that’s out on East 152nd street and once we start that we have one year to complete the work and open that road back up."

The most noticeable feature on any map of the planned tunnel is the 3,000ft (914m) long section parallel to the shoreline that will be buried deep under the surface of the lake, which is the first construction project on record under the lake.

However, digging 200ft (61m) below the surface through rock is not expected to be any different under the lake than under Lakeshore Boulevard. "The geology is going to be the same – we’ll still be mining through chagrin shale bedrock – and we’re not anticipating any serious challenges with that," says Szaraz.

There are roughly 30 structures that the team has to construct as part of the tunnel work. "A lot of those run along Lakeshore Boulevard, which runs the project length," says Szaraz. "The biggest hurdle that we’ve had is unknown utilities that weren’t identified in the project; we identified them early on and we’ve been meeting with the owner on a bi-weekly basis along with the utility companies and the engineers on the project to work out those utility conflicts. It has pushed back some of that work a little bit, the open cut work and the microtunnel work, but none of the work is critical. It has not been a big impact on the schedule."

TBM arrival
"Notice to proceed was issued in April 2011," says Szaraz. "So we’re just over a year into the project right now. The TBM has been manufactured in Herrenknecht’s plant in China. It arrived at the port of Philadelphia last week and is currently being loaded and transported to the project site. Over the course of the next several weeks we will be receiving all the components of the TBM.

The main drive installed power of the 27ft (8m) diameter TBM will total 4,224hp drawn from nine 470hp motors. The closed mode cutterhead, equipped with 52 no. 17inch disc cutters, will achieve a maximum advance speed of 5inch (127mm) per minute at full speed.

Szaraz explains that as the TBM advances on its one pass drive a vacuum erector will place the precast steel-fibre reinforced concrete segments, which are then bolted in place. Gaskets between the segments help prevent water ingress or egress from the sewer.

The segments are erected within the TBM and as the tail shield passes over the segments a two part grouting system is used to fill the annular space. The advantage of a two part system is the setting time. It usually takes around eight seconds for the grout to set once the part B accelerator is added. It is injected from the tailshield and helps prevent any settlement.

From within a closed TBM it can be hard for operators to know what is happening in the ground around them. Szaraz says that the TBM will be equipped with extensive monitoring systems to keep it on track and ensure nothing untoward happens.

"[The TBM] will be equipped with a data acquisition system capable of retrieving historic and real time data. All of the communication systems are tied to the programmable logic controller and includes a diagnostic and fault tracing package. The system will display cutterhead direction, torque, speed, and thrust; main bearing lubrication pressure, flow, and temperature; grouting pressure and volume; power consumption and motor temperature; ram pressures and extension; date and mine time; stroke; TBM position, line level, correction values, pitch, lead, roll and stationing."

The TBM will thurst itself forwards using hydraulic rams launching from the previously placed segments. A thrust frame will be used for the initial launch of the machine.

"It is expected that we will complete the assembly of the TBM in March 2013; in June we will launch and then we’ll have approximately 15 months of mining."

Muck out
Removing the masses of rock excavated from the tunnel will be managed by a conveyor system. A coveyor belt wlll carry the much from the TBM, through the tunnel and into a vertical conveyor through the launch shaft.

The muck will then be carried via an overland conveyor to a stacker conveyor. "We started receiving the conveyors about two months ago and of the eight conveyors we have one of them completely assembled and one of them partially assembled on the surface.

Aside from the main drive the project also consists of five tunnel access shafts – including a 50ft (15m) diameter mining shaft and 50ft (15m) diameter surge chamber – and four tunnel flow drop shafts, as well as multiple diversion structures, regulators, gate and gate control structures and over 5,600ft (1,707m) of near-surface consolidation sewers constructed by a combination of open-cut, microtunneling and open-shield pipe jacking.