New excavation technologies have arrived stateside and they are making a big impact
By Jesús M. Garcia
Big tunneling is coming to the United States.
The Gateway Tunnel under the Hudson River in New York (www.gatewayprogram.org) will help to solve a longstanding threat to the transit system of the Northeast U.S. The Waterfix Tunnel in the Sacramento-San Joaquin Delta (californiawaterfix.com) will help to mitigate water supply problems in Southern California for decades. In transit, BART’s Extension to Silicon Valley Phase II in San Jose, California (www.vta.org/bart) will answer the growing demand for reliable, cleaner rapid transit and is set to be the first single bore tunnel in North America.
All of these projects are being made possible thanks to new excavation technologies and equipment that allow us to solve infrastructure challenges that, until recently, were beyond our capacities. Around the globe, safe, efficient, and reliable Tunnel Boring Machines (TBMs) are helping deliver projects that leaders of 20th century infrastructure could only dream about. We are tunneling through some of world’s hardest rock, building new transit beneath bustling metropolises with minimal disruption to local business and affairs, and completing miles of tunneling in record time without putting worker safety at risk.
For large infrastructure projects, the drawbacks of drill and blast are being relegated to the past. In its place, we are assembling construction factories where tunnels are bored and assembled, machines are maintained and adjusted, and data is measured and reported. These underground factories are equipped with cutting-edge technology, innovative materials, and awe-inspiring machines that are achieving successes in ever-challenging scenarios.
Pushing TBMs to new limits
The first true tunneling machine was introduced in France in 1845 for a project in the French-Italian Alps. Plagued by technical inadequacies and waylaid by political upheaval, it was largely a failure. However, by the late 20th century, tunnel boring experienced significant evolution as technologies and materials improved, allowing tunneling to be used in a variety of scenarios. These successes launched a diameter “arms race.” In 1994, the first Mega TBM – more than 46 feet in diameter – was used in Tokyo. In 2005, an ACCIONA project in Madrid broke the 50-foot boundary. Today, the world record is a 57-foot tunnel in Hong Kong.
On the performance side, these underground factories are able to build up to 50 yards of tunnel in a day in ideal ground conditions.
Urban construction with minimal disruption
The increased diameter size and versatility of TBMs has brought new opportunities.
For U.S. municipalities and agencies considering infrastructure improvements, mitigating disruptions to daily life is a priority. For projects like the BART expansion, new subterranean transit also means building new stations. With the new Mega TBMs, tunnels can be built to be wide enough to accommodate tracks and stations. So rather than opening up entire streets to build stations, only the access shaft that will eventually be used by transit riders is needed.
This innovative approach was used for the first time during the Line 9 project in Barcelona, Spain, thanks in large part to the vision of the transit agency, Transports Metropolitans de Barcelona. In addition to needing to minimize disruption to daily life in that city, there were strict precautions to tunnel without disturbing Barcelona’s irreplaceable architecture. The highly adaptable nature of modern TBMs made this possible.
Using big data to improve timelines and cut costs
One of most significant recent improvements in TBM deployment has been the integration of real-time data analysis. For U.S. projects, where costs and timelines will receive incredible scrutiny, these developments offer additional appeal.
If there is a drawback with TBMs it is that replacing cutters on the machines can be time-consuming and expensive. ACCIONA has developed a real-time monitoring network that has allowed us to virtually eliminate unplanned equipment outages. The network uses dozens of sensors placed on the cutters of TBMs, which send real-time data to our TBM Data Control Center, where proprietary software is used to identify trouble spots before they cause problems. The entire project team receives these reports, allowing for better management, improved safety, and reduced costs. Big Data is a successful tool with different applications in our projects, providing real value, today.
Construction factories deliver tunnel success
A mega TBM is a giant factory, longer than a football field, taller than a four-story building, and heavier than ten Boeing 747s. Its non-stop, 24-hour performance requires a logistic effort, handling and assembling thousands of tunnel pieces that each weighs several tons, in a safe, efficient environment. The materials, joints, and assembling methods are constantly being improved, pushing the boundaries of these industry marvels.
Recent advancements in tunneling have opened up new opportunities for American infrastructure that would have been impossible in the past. Today, cities across the nation are seeing tunneling as a path to the signature infrastructure projects of the 21st Century.
Jesús M. Garcia is the director of business development for ACCIONA Construction USA. He is based in Miami, Florida.