Mackenzie, the 1,500-ton tunnel boring machine drilling the 3-mile long Euclid Creek Tunnel 200 ft under Cleveland, Ohio, broke through the shale at Shaft 5 on Aug. 21, marking the end of her journey. On Sept. 9, the Northeast Ohio Regional Sewer District, the project owner, hosted an event at which the 27-ft diameter cutterhead was hoisted back to the surface after mining 18,000 ft.
The Euclid Creek Tunnel project is the first of seven tunnels for the sewer district as part of Project Clean Lake, a 25-year program to reduce pollution to Lake Erie and its tributaries. The Euclid Creek Tunnel was mined using a Herrenknecht one-pass, hard-rock TBM excavating a 27-ft diameter tunnel, 3.4 miles in length. The tunnel will be segmentally lined to an ID of 24 ft. Segments were by CSI Hanson in Macedonia, Ohio. The tunnel represented the district’s first use of a hard-rock TBM with segments.
Ground conditions consisted predominantly of thinly bedded shales and interbedded siltstone of the Chagrin shale formation at an approximate depth of 200 ft. A launch shaft, reception shaft and three intermediate shafts were built as part of the contract. A portion of the alignment extends under Lake Erie – a first for the District.
McNally/Kiewit JV was the low bidder at $198 million and was given NTP in April 2011. The JV sunk the launch shaft to invert using steel liner plate support in overburden and rock bolts, mesh and shotcrete in rock. Crews used an Alpine Tunnel Miner 105 to excavate a 300 ft tail tunnel and a 120 starter tunnel for the TBM, which arrived in March 2012.
Hatch Mott MacDonald provided tunnel design and construction engineering services for the District. The four-year project is on pace to finish in April 2015. The launch shaft will be used as part of the Dugway Storage Tunnel, which is the next tunnel component of Project Clean Lake, which was the result of a consent decree.
A 160-mgd pump station, to be built under a separate concrete, will be constructed adjacent to the launch shaft to bring flows from the Euclid Creek and Dugway Storage tunnels into existing interceptors that pass through the area, carrying them to the Easterly Treatment Plant, which will be renovated as part of the consent decree. Walsh/Atkinson JV was awarded the $70 million pump station contract.
A Northeast Ohio First
Prior to the Euclid Creek Tunnel, the District’s tunnels have been built using two-pass lining systems consisting of combinations of rock reinforcement and steel rib and lagging, in conjunction with a cast-in-place lining. However, a number of these projects have had to deal with the occurrence of gas, localized tunnel instability due to rock wedges and blocks, and time-related rock deformations associated with slaking, overstress or both.
Because relatively high horizontal in-situ stresses are expected to exceed the rock mass’ compressive strength, spalling behavior is anticipated during tunnel excavation. Recently, the Niagara Tunnel endured delays and cost over-runs because the design-build team’s two-pass construction method was not able to cope with overstressed ground. To avoid similar risks on the ECT, as well as address potential gas infiltration concerns, HMM designed the tunnel with a one-pass, bolted and gasketed lining system.
“The reason behind using the one-pass tunneling method is to manage and mitigate risks associated with the subsurface geology,” said Kellie Rotunno, NEORSD’s Director of Engineering and Construction. “There were some problems encountered with the two-pass system on the Mill Creek tunnel – namely methane gas was encountered and we had some issues with overbreak. Considering that we are going to be tunneling through the same rock on the Euclid Creek Tunnel, we felt we should take steps to mitigate those potential issues. The single-pass system allows us to get the tunnel grouted and sealed more quickly as we mine, and hopefully will help manage the overbreak and gas issues should they be encountered. In addition, we are hopeful that the one-pass system will provide schedule benefits to the completion of the Euclid Creek Tunnel. Since this project is part of the District’s CSO Consent Decree, it carries the potential for stipulated penalties if we do not complete it on-time.”
HMM specified a tailshield grouting system that utilized a fast-set, two-component grout to immediately grout the annulus and support the segment rings as mining advances. As this application involves an open face, rock TBM, the quick set time of the grout is also needed to mitigate grout travel forward of the shield toward the TBM cutterhead. Contact grouting through segments will be performed to fill any gaps or voids behind the tunnel lining.
“We tried to anticipate and avoid grouting issues by grouting through the tail shield and using a two-part accelerated grout with a rapid gel time,” Rotunno said. “However, there was a bit of a learning curve at the beginning of the project. The contractor had some issues in getting the grout to gel, which was discovered by drilling check holes through the segments as part of our QA/QC program. As it turned out, there were issues with the accelerator. Once the contractor made modifications to the delivery system and changed accelerators, we’ve been humming right along and there haven’t been any issues with the grout.”
In order to deliver the grout, the contractor selected a grouting system manufactured by Hany and supplied by DSI Underground Systems. The system delivered grout the entire distance (18,000 ft) from a ZMP 726 Dual Plunger Pump located on the surface near the batch plant to a holding tank on the TBM.
The high-shear colloidal mixers are designed to weigh the mixing components and to efficiently prepare a high-quality suspension. Besides water, up to three dry components and three liquid additives can be automatically batched, mixed and transferred to a holding tank.
Water is fed to the mixer either by a direct water line of through a special water tank. The dry components are dosed one by one from the silos through screw conveyors. Individual components are weighed precisely in the mixer. When the mixing process if over, the mix is transferred to the holding tank. The mixing plants are consumption controlled, meaning new batches will be mixed automatically as needed.
Additionally, the system comes with a PLC and touch screen control unit that automates and optimizes batching. Meanwhile, a batch record and consumption record are stored on a memory card for future reference.
While the tunnel boring operations are finished, the Euclid Creek Tunnel still has much work ahead. The tunnel will not be complete until 2015 as the lining and ongoing preparation is complete. When finished, the Euclid Creek Tunnel will hold 60 million gallons of sewage and stormwater and reduce combined sewer overflow entering Lake Erie by more than 300 million gallons annually.
Project Team Owner: Northeast Ohio Regional Sewer District
Designer: Hatch Mott MacDonald
Equipment/Supply: Herrenknecht (TBM), Alpine (road header), Hany (grout plant), CSI Hanson (segments)