This article shares the case of China Railway Yihong driving a retaining wall for the Suzhou section of the intercity railway to Anhui. The customer’s job is to install steel combi wall piles on both sides of the river to provide waterproofing and support for the construction of the intercity railway. The diameter of the interlocking steel piles used is 630mm, the wall thickness is 14mm, and the pile length is 24 meters.

The customer had started the job with a 135t electric hammer (exciting force of about 80 tons), but the piles met resistance after 6 meters already. The project manager sent a geological soil report to ICE so a pile driving prediction could be made (the soil geology is mainly weathered clay and sand). The modeling showed that ICE 55NF hammer was the right choice for the site conditions (as shown in the figure) and a 55NF was rented from the ICE fleet.

After arriving on site, the 55NF was lifted by 80t crawler crane and moved in place to drive the first pile. The hammer’s vibrations liquefy the soil, overcoming the friction resistance between the soil and the pile, the pile was installed in about 25 minutes. The second pile needed to overcome both the soil friction, as well as the friction resistance with the interlocked pile. The second and subsequent piles needed a little longer driving time then the first, between 40-60 minutes, depending on the verticality of the adjacent pile. The 55NF’s performance validated the pile drive prediction results.

The 55NF hydraulic vibratory hammer has the following features:

1. Small size and light weight (about 5.7 tons), use with a 50-100t crawler crane

2. The pile driving force is large (171 tons of eccentric force, 80 tons of line-pull), and equipped with 600-liter hydraulic pump, with a power output power of 403KW.

3. ICE clamps are fitted with large jaw plates, the large contact area between hammer and pile ensures the safe transfer of amplitude to the pile.

Combi-walls are gaining in popularity for use in high-speed railway and intercity railway projects, as the reusable piles are an environmentally friendly alternative to concrete. To ensure the integrity of the combi retaining wall, but also to protect the piles from deforming during the driving and extracting work, it is very important to choose appropriate piling equipment that gets the job done by properly liquefying the soil with high frequency and amplitude, and not by brute ramming and yanking the piles.