Kery did her job, once again. A Robbins main beam hard rock TBM bored the Albany Park Stormwater diversion tunnel and broke through at the end of August 2017. Kery has been owned by project contractor Kenny Construction since the 1990s and has been used on several projects prior. “The machine holed through into the inlet shaft,” says Clay Spellman, project manager for Kenny Construction. “We excavated the shaft as part of the project. The machine has since been disassembled and removed.
“We rebuilt Keri with size modifications designed by Robbins, which took an existing cutterhead, repaired it, and then added segments, taking it from 17.2ft [5.2m] to 20.4ft [6.2m] in diameter. “Extensive modifications were also made underground to the machine to be able to install rock dowels and stand the ring steel under the roof shield,” adds Spellman.
The Albany Park Stormwater diversion tunnel will soon reduce flooding near the Chicago River. Some storm events in 2008 and 2013 showed the relevant flood risk and following the April 2013 flood, mayor Rahm Emanuel along with local, state, and federal agencies developed a plan to divert excess floodwater from the Chicago River to the North Shore Channel.
The cost of the project is USD 70M. The project is being undertaken by the City of Chicago. The Chicago Department of Transportation (CDOT) is the lead city agency in charge of the project.
The project is using a combination of funds from the City of Chicago, the Metropolitan Water Reclamation District of Greater Chicago (MWRD), Illinois Department of Natural Resources and U.S. Department of Housing and Urban Development.
Kenny Construction is the construction contractor and WSP –USA is CDOT’s construction management consultant.
Work started in June 2016 and the substantial completion is scheduled for June.
Tunnelling begun in late fall 2016 and continued through late 2017.
CDOT project manager Vasile Jurca explains that during the initial phase of planning, the City evaluated the overburden tunnel.
“When the geophysical feasibility study was performed, the City chose to build a rock tunnel,” Jurca says. “Due to geological conditions, the study showed that overburden might be a risk here for facilities’ foundations where the tunnel would be built. The tunnel needed a more stable predictable excavation method to excavate in rock, so the City of Chicago compared the traditional method with drill and blast and also the mechanized method. Many experts chose the TBM as it is more efficient.”
Resident Engineer for WSP management consulting team Frank Jaramilla explains that the cutterhead was refurbished in Solon, Ohio, at Robbins’ workshop while the rest of the entire machine, including the main beam, grippers, cutterhead mount, main bearing, seals, and trailing gear, was assembled and tested in Milwaukee, Wisconsin. “The cutterhead and the rest of the entire TBM arrived to the Outlet Shaft on-site in March of 2017 and was loaded in and assembled in pieces at the outlet shaft bottom in the starter tunnel,” Jaramilla says. “TBM mining commenced from the Outlet side of the tunnel in April 2017. The TBM holed through at the inlet shaft bottom in late August 2017; it was necessary one month to assemble the TBM on-site, and nearly five months to mine the tunnel. Both curves of the tunnel have aligned to a 1,500ft [457m] radius, the TBM with assistance of the TAC guidance system and Kenny’s expertise handled the curves proficiently. The holing through at the inlet shaft was within one-quarter inch of the centre target for alignment and grade. The grade of the tunnel, by design, is 0.12 per cent and the TBM’s performance and precise operation provided this requirement.”
Robbins project engineer Mike Lewis explains that they manufactured a new outer cutterhead and fully reconditioned all other aspects of the cutterhead. “Specifically we cleaned it, cut off partially burned off housings (were partially burned off when removing the old outer cutterhead) and machined the OD back to a precise size. Replaced missing cutter housings and provided new water spray plumbing,” Lewis says. “Additionally we provided drawings so Kenny could modify the gripper shoes, rear support legs, roof and side supports as well as the vertical front support.”
Robbins also reconditioned the main bearing, supplied new ring gear and pinions of upgraded design as well as updated drawings for the service manuals including weights and measures and critical lift drawings.
Regarding the process to add segments, adding 1m diameter to the machine Lewis says: “Once we made a new outer cutterhead with the latest technology in terms of scraper, back scraper and grill bar design, we manufactured a new cutter housing to fit the old style V-mount cutters that Kenny had in stock. We included four cutterhead access doors, openable from both inside and out, for maximum worker safety. The existing cutterhead is of a domed design so new outer cutterhead had to be designed to properly blend into the existing dome – allowing cutters to be mounted across the split line.
“Since two of the four segments would never be taken off during the project, Kenny requested that all of the cutters crossing the split line do so on these two segments. That way those housings would not have to be welded on underground and then burned off at machine removal. This work was all completed in the Cleveland area.”
Lewis adds: “Because the machine is 38 years old, the original drawings were pencil drawings. To use our present day solids modelling program with FEA capability, we first had to transcribe all the relevant parts into solid models from the old pencil drawings. That was to create the parts as they were originally made in 1980. However, many modifications had been made over the intervening years, sometimes with incomplete documentation. Therefore the existing supports had to be fully measured to have a sound basis for the new design. The Robbins team took what measurements were possible of the equipment as it laid in the yard but only so much was possible.
“To get sufficiently accurate measurements, Kenny contracted the In-Place Machining company to bring their laser tracker to measure the parts. This was mostly sufficient but such devices are not adept at measuring less than complete diameters. Since the support surfaces are all of this shape the dimensions we incomplete.
“Ultimately we had to rationalize the electronically measured dimensions with the tape measured dimensions we took at site by doing a bit of mathematical detective work. In the end we got the information we needed to proceed. These dimensions were critical because of the geometrical nature of the side support wedge design. Small errors can have a big effect on the wedge cylinder stroke and the resulting side support movement range. A similar condition existed with the old-fashioned “parallel link” design roof support design. Small errors could mean a lot in terms of movement so the accuracy of the measurements was important.
“Where possible we wanted to make the modifications reversible so in the case of the parallel link connections, we made spacers that can be taken back out rather than modifying the links. It seems pretty likely this won’t be the last time the diameter gets changed.”
On the rebuild work Robbins interfaced with Kenny mostly by phone or email. Lewis adds: “We had a very good working relationship. The Kenny personnel are very experienced and knowledgeable which tends to make things go smoothly.
The final machine diameter with diameter kit installed was 20.4ft (6.2m) diameter. It was 17.8ft (5.41m) diameter prior to the modification. The whole refurbishment process took roughly eight months.
GEOLOGY
Geology investigations have been undertaken by Stantec Inc.
The top layer of the overburden at the site consists of glacial soils from the Pleistocene epoch (30,000 to 10,500 years ago), made up of silty/sandy clay, varying in depth to approximately 70ft (21.3m) deep. Below the overburden layer is a zone of dolomite limestone from the Paleozoic Age, Silurian Period (435 to 410 million years ago).
The city used existing geotechnical boring data generated by MWRD from the 1970s through the 1990s, when MWRD constructed the deep tunnel project in the vicinity (seven borings). The project team then filled in the data gaps with additional borings along the proposed tunnel route and inlet/ outlet shaft locations.
CONSTRUCTION SITES
The 5,800ft- (1,767m-) long tunnel is located under Foster Avenue. There are two construction sites, both located on Chicago Park District property. The main construction site is located at the north end of River Park, immediately south of Foster Avenue on the east bank of the channel. This site includes the outlet shaft and structure while the inlet structure site is located north of Foster Avenue.
WSP’s Jaramilla explains, “The first thing we did was to mobilise and set up site parameters in two parts of land on Chicago park district property, one is the inlet shaft and the other is the outlet shaft and they are almost a mile a part. “We commenced with installation of support excavation, and we begun overburden excavation, first in the outlet side and then in the inlet side.”
The shafts were excavated vertically through approximately 70ft (21.33m) of soil and 75ft (22.86m) to 100ft (30.48m) of rock.
“Sheet piling or other earth retention systems were used to support the surrounding soils throughout construction. The rock was excavated using controlled blasting overseen by an Illinois licensed blaster and an independent blasting consultant. The contract includes strict specifications regarding safety, vibration and noise limits, vibration and settlement monitoring as well as a public awareness program to inform the community of blasting activities.”
Jaramilla adds: “When we blasted down in the outlet shaft vertically, then we started directional blasting at invert level to provide enough space for assembly of the TBM to begun mining the tunnel. We mined from the outlet shaft to inlet shaft, and when the mining was complete, we removed the TBM and started the lining of the tunnel.”
