Can You Dig It?
Core Drilling for Indy Deep Rock Tunnel
(home page image courtesy of Robb Williamson/AECOM)
An extensive $444 million construction and improvement project is underway 250 feet below Indianapolis. A 28-mile network of 18-foot-diameter deep rock tunnels is being built to improve the city’s wastewater system. As part of the project, a CSDA member was chosen to drill a series of 6-foot-deep, 18-inch-diameter holes in the walls of the tunnel system for the installation of support beams.
The DigIndy project is the largest public works project in Indianapolis history. The city’s existing century-old sewer system is unable to keep up with a growing population and has become susceptible to overflow in rainy conditions. The new system will store up to 250 million gallons of overflow, which will then slowly be released to treatment plants instead of going directly into the city’s waterways.
A pivotal part of the DigIndy project is the creation of the Deep Rock Tunnel Connector and Pump Station in Southport. For this stage of the work, an overhead crane was employed to lower the floor of the existing connector tunnel by 50 feet. However, this task could not be completed unless 12 support beams were installed in the limestone walls of the tunnel. The beams had to be directly across from each other and perfectly level to support the crane and for the work to proceed.
Renda/Southland Joint Venture was responsible for this part of the project and subcontracted CSDA member Concrete Surgeons, Inc. of Indianapolis to create the required openings to house the support beams.
“This was a very high-profile job for us,” said Diane Serban, corporate secretary for Concrete Surgeons. “Because the beams needed to be perfectly level for the overhead crane to be installed, it was clear that the 12 holes should be core drilled. This method provided Renda/Southland with the amount of precision needed and left a smooth finish for the beams to be slid horizontally into position.”
Operators from the core drilling contractor were lowered in a basket to 230 feet below grade by crane through one of the connector’s drop shafts, followed by all of their equipment. It was important to have all necessary drills, core bits and tripods, plus pipe stands for the longer bits down in the tunnel to avoid lengthy downtime in the event of any failures or breakages. “Having to be lowered so far down into the darkened tunnel was a new and intriguing experience,” remarked Tony Judkins, project supervisor for Concrete Surgeons.
To ensure that the holes lined up perfectly across the tunnel, operators used a tried-and-tested method to level the drills. “Concrete Surgeons and our customer ran a string line, making adjustments where needed, for our base to line up.” Judkins explained. The climate in the tunnel was very different to that on the surface. High moisture counts meant that waterproof cord caps were used and the electrical contractor for the project installed wire restraints on the electrical cords to hold them in position during the core drilling work.
There were six holes created on opposite sides of the tunnel. Each set of six holes was positioned horizontally level between 3.5 and 4 feet from the uneven floor surface and spaced 12 feet apart.
“The first task on this project consisted of drilling 0.625-inch-diameter holes 12 inches deep to epoxy all threads for our drill mounts. The epoxy had to cure for 24 hours,” said Judkins. The core drilling team mounted the drilling rig in place with anchors, though this was a challenge as the limestone surface of the tunnel wall was quite brittle. A Hilti DD500 core drill system was used to create the two 18-inch-diameter holes 6 feet deep in the limestone. Operators began core drilling using a 3-foot-long bit. This portion of the work took around 45 minutes to complete.
Once half the total depth had been achieved, the bit was backed out of the cut before the core was broken out and removed. A 6-foot-long core bit was then employed to complete drilling to the required depth in conjunction with a pipe stand to support the longer bit. It took a further one hour of drilling to reach 6 feet. Each 3-foot, 18-inch-diameter core weighed around 800 pounds.
With the first hole complete, operators repositioned themselves and their equipment at the next drilling location and used the same method to create that hole then the remaining ten, running two drills to expedite the process. The team from Concrete Surgeons spent seven days in the tunnel, working eight-hour shifts to complete all twelve holes to the required specifications and tolerances of Renda/Southland. All work was done within the set time frame and a total of 19,200 pounds of limestone was core drilled and removed from the tunnel.
Safety requirements on the DigIndy project included the provision that all on-site personnel had OSHA 10-hour training and 24 hours of Hazardous Waste Operations and Emergency Response (HAZWOPER) training. One representative from Concrete Surgeons was also required to complete the OSHA 30-hour training program. In addition, Concrete Surgeons, Inc. has previously been certified by the Metro Indianapolis Coalition for Construction Safety (MICCS) program, now known as CCS. “We are known for doing excellent quality work and have a great safety rating,” stated Serban.
All parties involved were satisfied with the outcome and the positioning of the crane went ahead without incident. This allowed the tunnel floor to be lowered 50 feet as planned. Following the success of this core drilling work, Concrete Surgeons has been approached to carry out more tasks across the DigIndy system as and when needs arise. The entire DigIndy system is scheduled for completion by 2025.
Concrete Surgeons, Inc. is headquartered in Indianapolis, Indiana and has been a CSDA member for 18 years. The company has been in business since 1992. Concrete Surgeons, Inc. specializes in concrete slab sawing, core drilling, wall sawing, hand sawing, wire sawing, selective demolition and GPR scanning. The company is in the process of achieving Veteran Business Enterprise certification and is currently expanding its operations.
Renda/Southland Joint Venture
Sawing and Drilling Contractor:
Concrete Surgeons, Inc.
Methods Used: Core Drilling