Homemade tunneling machines boost urbanization

A super large tunnel boring machine (TBM) measuring 15.03 meters in diameter has begun an underwater tunneling project in Shantou City, south China's Guangdong Province.

At 130 meters long and weighing 4,800 tonnes, the slurry TBM, with maximum thrust of 25,000 tonnes, can cope with multiple complex terrains such as soft silt and hard granite bedrock, according to manufacturer China Railway Engineering Equipment Group Co. Ltd. (CREG), one of the leading TBM suppliers worldwide.

Under 10-bar pressure from water, air, earth and slurry, the machine will bore a tunnel 3,048 meters long in a depth of 20 meters.

Its cutter head cuts the bedrock into small pieces, which are mixed with stones and sediment and then delivered out of the tunnel.

China's TBM demand has increased with the country's development. Many large infrastructure projects, such as urban subways and railways traversing mountains or waterways, require the technical and operational support of TBMs.

TBMs can excavate tunnels using a circular cross section that drills through a variety of soil and rock strata, and seamlessly lays concrete segments to build tunnels, subway tubes and sewer lines.

According to the China Association of Metros, by the end of June, 34 Chinese mainland cities had subway lines, and Jinan and Lanzhou are welcoming their first metro lines.

The fast expansion of rail transit has boosted demand for TBMs, and domestic demand accounts for 60 percent of the world total, according to CREG.

The 18 manufacturers of TBMs have a combined annual output of about 1,000 units, said Song Zhenhua, of the China Construction Machinery Association (CCMA). TBMs are getting larger as tunnels become wider to integrate utilities including railways, highways, water supply and drainage pipes, telecommunication and power cables.

Safety is the top priority no matter how large or complicated the projects are.

A 4,760-meter-long tunneling project with vehicle ways and subway rails is under construction in Jinan, east China's Shandong Province.

The tunnel is equipped with fire hydrants, broadcasting devices, emergency phones and video monitoring devices to ensure evacuation within 6 minutes in the upper vehicle ways and 30 minutes in the lower subway rails in an emergency, said He Yingdao, designer of the project.

China's largest slurry TBM with a diameter of 15.8 meters started work on a project in Shenzhen, south China's Guangdong Province, in August.

In previous decades, China relied on foreign tunneling expertise, with Beijing bringing in experts for its first subway lines in late 1960s, said Su Zimeng, secretary general of the CCMA.

In 2008, China's first independently developed earth pressure-balanced TBM debuted.

With around 30,000 precision components and mechanical engineering, electric, sensing, information and dynamics technologies, a TBM is considered a gauge of a country's equipment manufacturing level.

In the past decade, China's TBM industry has witnessed great progress, with products exported to more than 10 countries and regions for projects like subways, highways, railways and water conservancy.

About 70 percent of components and parts of Chinese TBMs are domestically made, said Song. "Our products are cheaper than those produced by other countries and excellent after-sale service is also our commitment."

By the end of June, CREG had received 916 orders and manufactured 842 TBMs, five times more than five years ago.

Manufacturers and experts are working to promote the repurposing of TBMs. The machines are specifically tailored in different shapes and diameters for each project.

"It's a pity that such a high-end equipment is hard to be reused," said Su Zimeng. He suggested the tunneling industry agree unified standards, such as a maximum width and height of tunnels, so that the machines can be used in more than one project.