Construction Background

1. The steel casing (diameter 2 m, length 15 m) had been in the ground for nearly half a year and had a deviation of nearly 50 cm;

2. The steel casing was located beside the river channel next to an old bridge; the bridge had been in disrepair for years, and passing vehicles caused obvious shaking;

3. The other three piles around the target steel casing had already been concreted, and it was uncertain whether grout had overflowed at the pile bottoms;

4. The project party had successively used two vibratory hammers of other brands, but the steel casing did not move at all, and the works were temporarily suspended.

Equipment Selection

1. Based on the geological survey report provided by the contractor, the parameters of the steel casing itself, and various conditions encountered during previous pile driving and extraction, our company calculated and recommended a vibratory hammer with a pile extraction force of no less than 60 t and the necessary amplitude.

Considering the on-site construction conditions, the EP320 resonance-free vibratory hammer with stepless adjustable eccentric moment was recommended.

2. The EP320 vibratory hammer has an exciting force of 0–160 t, a maximum allowable pile extraction force of 90 t, and a working amplitude of up to 6.5 mm that meets the site conditions; it can be operated independently with a 200 t truck crane. (Table: basic technical parameters)

Pile Extraction Operation

1. Smooth start-up: before starting the equipment, the eccentric moment was adjusted to "zero" via the adjusting device, so the equipment started smoothly, and the crane and the bridge deck on which it was operating showed no obvious shaking. (Anecdote: the rented truck crane driver had previously worked with traditional vibratory hammers and had been deeply affected by the "resonance hazard" of traditional vibratory hammers, strongly rejecting vibratory hammers and at one point refusing to carry out the work. Only after being introduced to the working principle of our company's "new generation" resonance-free vibratory hammer and assured that the resonance-free vibratory hammer would not damage the crane did he decide to give it a try.)

2. Fully "liquefy" the soil. After the equipment started successfully, the eccentric moment was gradually increased, and the exciting force and amplitude were adjusted to "maximum." Considering that the steel casing had been in the ground for a long time, had a deviation, and involved other unknown conditions, before starting extraction the vibratory hammer vibrated the steel casing for a sufficient time to fully "liquefy" the soil. (Record: 20 minutes of vibration was planned, but in practice it took only 5 minutes for the pile-soil interface to loosen, and the steel casing visibly sank.)

3. Crane lifting of the pile. After the soil was fully liquefied, the crane seized the opportunity to pull upward, and in less than 20 minutes the entire steel casing was successfully extracted. (Tip: when extracting a pile, do not simply pull upward all the way to the top; the correct approach is to reverse and drive the pile downward for a period after each upward pull, then continue pulling upward, repeating this process, which makes pile extraction more efficient.)

4. "Imperceptible" shutdown. After completing pile extraction, before shutting down the equipment, the eccentric moment was readjusted to "zero," allowing the equipment to shut down smoothly under "zero" exciting force and avoiding the harm of "resonance" to the crane and surrounding environment. (Pride: after the equipment shut down, the crane driver asked the operator whether the vibratory hammer had stopped. After confirming that the vibratory hammer had completely stopped, his previous worries disappeared entirely; he gave a thumbs-up in admiration and even left his contact information to help promote the equipment.)

Reflections on On-Site Service

During the on-site service process, through communication with the contractor's commanding personnel, electricians, crane drivers, and others, feedback revealed that the market still has certain limitations and misunderstandings regarding the selection and use of vibratory pile hammers—for example, simply using the single indicator of "exciting force magnitude" to measure a vibratory hammer's working capacity while ignoring the importance of several other factors. This leads to unreasonable equipment selection and many detours during construction, which not only wastes manpower and material resources but also greatly reduces construction progress. In the next issue, we will discuss common problems in vibratory pile hammer selection with everyone.