Onsite Assembly on the Banks of the Black River

Project Overview

In 2000, the Ohio EPA ordered the City of Lorain to address overflows that violated the City’s National Pollutant Discharge Elimination System (NPDES) permit. After studying options, including the construction of an equalization basin in downtown Lorain, a deep tunnel option was selected. In order to construct the tunnel, the city required the assistance of a USD $65.87 million loan from the Water Pollution Control Loan Fund through Ohio EPA’s Division of Environmental and Financial Assistance. The major components of the Black River Tunnel include the launch shaft and reception shaft – approximately 11 m (36 ft) in diameter and 50 m (165 ft) deep – and the main 1.7 km (1.0 mi) long tunnel with a finished diameter of 5.8 m (19 ft). The project route runs along city property roughly parallel to the Black River, beginning at the launch shaft near the Black River Wharf and terminating near the Black River Wastewater Treatment Plant.

Geology

Ground conditions consisted of soft Cleveland shale, at times layered and laminated in the tunnel crown area.

Onsite First Time Assembly

The mammoth 7.0 m (23 ft) diameter Double Shield machine was built using Onsite First Time Assembly (OFTA)–a Robbins-developed method that saves contractors in shipping time, costs, and man-hours worked.  Using the OFTA approach, individual systems are tested prior to delivery but the machine is never fully assembled in the shop. Robbins field service technicians work on location with the contractor to assemble the machine and provide support. Launch of the TBM took place on November 18th, 2013 — approximately three months after assembly began.

Excavation and Breakthrough

Construction of the main tunnel began in late autumn 2013 with both the Double Shield TBM and continuous conveyor system running at the site. Robbins supplied an in-tunnel continuous conveyor system and space-saving J-type vertical conveyor to provide more open area in the launch shaft.
The Double Shield machine was used in a unique manner during boring. The soft shale was excavated with minimal cutter wear, and rather than concrete segments, ring beams were erected within the tail shield for installation as the machine passed. The lagging was spaced at 45 cm (18 inch) intervals with wire mesh panels.

Cleveland shale made for speedy excavation; so fast that it was challenging for the continuous conveyor system to keep up at times. The contractor confirmed that the TBM was mining so fast it could not excavate at its maximum rate. Rehak explained that the fairly soft ground also made for minimal cutter wear, with only seven cutters changed during course of the bore—four of them as a precautionary measure only.

About 13 sections of bad ground 30 m (100 ft) across were encountered during tunneling, or about 25% of the soft shale geology, which made ground support difficult at times. Those sections consisted of layered and laminated rock that broke from the tunnel crown before ring beams could be expanded, requiring extra chipping and rock relief to expand each rib to the correct diameter. Once workers fine-tuned the technique, they were able to do 12 to 14 rings per day–compared to just one or two rings before the process was refined–even in the sections of bad ground. In more stable sections production averaged 18 to 20 rings per day—a rate the contractor considered very good considering they were erecting steel ribs. Now that tunneling is complete, a final monolithic pour will solidify the lining.
By the time of the machine’s breakthrough on April 29, 2014, the TBM was averaging 21 m (70 ft) per day, and getting up to 24 m (80 ft) per day for multiple days in a row. After tunneling was completed, a final monolithic pour solidified the tunnel lining.