In an effort to produce sustainable infrastructure and preserve valuable land for more beneficial use, cities require underground infrastructure solutions for roads, transit, and waste/water utilities. The big dig projects in Boston and Seattle have opened up urban waterfront spaces and reconnected the city by moving the urban highway underground. Most of us have seen the benefit of tunnels in society; who hasn't ridden in a subway or a tunnel through a mountain pass at some point in their lives?
Yet for some there are many misconceptions about tunneling.
Myth 1: Tunnels are more expensive than other forms of construction.
Fact: The total lifetime cost of tunneling is the same or cheaper than equivalent surface infrastructure.
The construction cost of tunnels may be relatively high, but when maintenance and durability are considered, the total cost is frequently less than the equivalent surface infrastructure. Tunnels are a practical, reliable, and cost-effective solution for many applications. For example:
- Keeping traffic moving through the mountains using tunnels rather than high mountain passes. The Eisenhower tunnel and the Gotthard base tunnel in Switzerland are great examples.
- Elevated or surface rail in an urban area becomes a blight and separates neighborhoods. Underground transit and rail in our towns and cities are more reliable and superior in every way.
- Any trench for water, sewer or other utilities greater than about 20 feet are typically more expensive than a tunneled alternative. When surface interference is considered, the tunnel alternative is always more attractive. Cities such as London require trenchless solutions.
- A tunnel is the best option for cities where the smart use of underground space will significantly reduce real estate,right-of-way, and social/environmental impacts.
Myth 2. Tunnels are dangerous and unsafe to build.
Fact: Safety statistics for underground construction are equal to or better than other forms of surface or building construction.
- Modern tunneling equipment and methods make tunnel construction as safe today as any other construction method.
- The U.S. Bureau of Labor Statistics reports the average recordable incidence rate for all construction as 2.5 (this number means 2.5 incidents per 100 workers per year)
- A sample of the 15 major tunnel contractors in the U.S. over the last three years shows an incidence rate of 0.84, or about one-third of the full construction industry average.
- The safety culture in modern tunneling firms plays a major role in this improvement.
- Working on and around a modern tunnel boring machine (TBM) is comparable to work in a high-end manufacturing facility and workers are not exposed to dangers from the soil, rock and groundwater behind the TBM shield.
Myth 3. Tunneling is a grey solution that is not environmentally friendly.
Fact: Tunnels provide clean water supply, disposal of wastewater, and transit systems that remove millions of cars from the road. Tunnels enable us to live a greener and more sustainable life.
- Tunneling contributes to a sustainable world. A great example is the use of Combined Sewer Overflow systems in older cities.
- During times of heavy rainfall, these combined systems dump raw sewage into our rivers and lakes. Deep storage tunnels capture this excess sewage and take it to treatment plants for cleaning. Tunnels are used to keep hundreds of billions of gallons of raw sewage out of our waterways.
- The Washington DC transit system (WMATA) carries over 28,000 passengers per day, which translates to nearly 19,000 cars that would lead to over 70 miles of traffic congestion relieved everyday.
- Tunnels connect communities that have been separated by elevated or at-grade rail or highways. Seattle recently removed an elevated viaduct along its waterfront and replaced it with a highway tunnel. This has reconnected the city with the waterfront for tourism and commerce and removed a seismic safety risk. (A nearly identical bridge collapsed in the 1989 San Francisco earthquake.)
Myth 4. Tunnel construction is a slow, dirty and antiquated business.
Fact: Tunneling has undergone a revolution in technology and innovation that has improved speed and efficiency of tunnel construction.
- Many tunnels today are mined with gleaming, multi-million dollar TBMs with onboard technology more akin to rocket ships than the donkey carts of 100 years ago.
- Tunnel advance rates of more than 200 feet per day are achievable using these marvels of modern engineering.
- Modern tunnels resemble other industrial or manufacturing facilities in many cases.
- Through the combined efforts of everyone in the tunnel industry, we have made incredible strides, making tunneling one of the safest and most reliable forms of construction for all the world's infrastructure needs.
- Ongoing innovation continues this trend so we are able to extend working opportunities to the next generation of engineers, mechanics, electricians, and craftspeople of all kinds. The opportunities are endless
Myth 5. Tunnels are unsafe during operation or natural disasters.
Fact: During most natural disasters, tunnels are the safest place to be.
- Modern tunnels are designed with ventilation systems, lighting, and clearly marked emergency egress points so that people can safely escape from a fire or other emergency in the tunnel.
- During an earthquake, tunnels are the safest place to take refuge, away from falling glass or other building damage. During most events, transit operations will continue without serious interruption.
- Water and sewer systems are designed to be robust and remain operational during and after major earthquakes. Historically, water systems were unreliable, and the inability to fight fires led to disaster following the 1906 San Francisco earthquake. Modern water tunnels make this scenario a thing of the past.
