Driving casings next to the subway without disturbance

March 2016, independent measurements prove it can be done: vibrating piles three meters from the subway tunnel without impacting the integrity of the tunnel structure or the operation of the metro. Shanghai ICE 28RF hydraulic hammer proves fast installation methods are safe to use. 

Shanghai Tunnel Foundation Engineering Company won the tender for the Beiheng Corridor No. 2 section and faced the following difficulties:

• Foundation work is required within 6 meters of subway line 13

• The water flow of Suzhou river needs to be unobstructed to avoid flooding

• Part of the piling is underwater

• Working space is limited

The best solution for working under these restrictive circumstances are designs with sheet piles and steel casings using vibratory piling hammers. The most commonly used pile installation methods using low and middle frequency vibratory hammers produce vibrations that may result in damage to the tunnel structures and would therefore require temporary suspension of metro services during foundation work. Choosing a high frequency, resonance free, installation method eliminates the risk of damage and allows the metro services to continue during construction work. Shanghai ICE has been promoting and proving its high 2300 RPM frequency, resonance free, method for five years, with numerous demonstrations and successful projects in urban construction sites across China. This was the first time however, that we had the opportunity to independently verify the RF method as truly resonance free, and receive certified permission from Shanghai Metro Authorities to operate close 3 meters away from its tunnels.

Shanghai Metro stipulates that no foundation work can be carried out within three meters of a tunnel; construction work outside this perimeter must nog cause settlement or displacement greater than 20mm, and vibrations may not exceed 25mm/ sec. Measurements on a test pile were ordered to determine that the ICE RF hammer could work within these boundaries.

In accordance with pile dimensions and soil conditions the client chose the 28RF for the project. This medium sized hammer has a total weight of 6t and 160t driving force; it can work underwater and needs little maneuvering space.

Vibration measurements on the test pile were carried out by Shanghai Huigu Geotechnical Engineering Technology Company. Measurement points were set up at 3m, 6m and 10m distance from the outer diameter of the 28m long, 800m diameter casing pile. Vibrations were monitored with an Instantel Minimate vibration monitoring unit, and displacement with a Sinco unit. The test results showed a three dimensional vector peak value of vibration velocity PPV of maximum 4.72mm/ sec, and displacement lower than 2.03 mm, both well within the permitted range. This performance earned the approval of the Metro Authority

Foundation work with sheet piles and steel casings fit well in the 13th five year plans environmental goals. These materials are reusable and eliminate the need for bentonite and concrete. RF hammers work fast, causing minimal disruption to the surroundings and zero vibration impact to nearby residents. Working with fuel efficient, clean engine technology, and a start-stop system, exhaust emissions from the power pack are minimized. On your next visit to downtown Shanghai lookout for one of our RF hammers, they are rapidly changing the construction landscape! Want to read more, contact us now for your copy of the report.