The Tianmu Road section of Shanghai's North Cross Passage is a major new construction project. The project runs from Beihong Road in the west to Neijiang Road in the east, crossing Changning, Putuo, Jing'an, Hongkou and other districts, with a total length of 19.1 km. The Tianmu Road elevated section in particular is located in the busy commercial area of Shanghai Railway Station, so how to adopt an advanced and green construction technique for the pile foundation work of the elevated project is particularly important. "To achieve the expected goals of the construction plan, the key factor is that we adopted the resonance-free hydraulic vibratory hammer technique," said Yu Wei, project manager of the Tianmu Road elevated project of Shanghai's North Cross Passage. 　　The resonance-free hydraulic vibratory hammer is a branded product of the Dutch company ICE
　　The resonance-free hydraulic vibratory hammer technique mentioned by Yu Wei is a relatively advanced piece of equipment for pile foundation construction, and the 70RF is the highest-power model in this technique. According to Yu Wei, in order to realize this new technique, they conducted extensive research and ultimately specially introduced the 70RF resonance-free hydraulic vibratory hammer from the Dutch company ICE; this high-power model was the first of its kind in the world. The Dutch company ICE has consistently maintained a market-leading position in China and is an authority in the specialized field of hydraulic vibratory hammers. When discussing why the 70RF was chosen rather than a relatively lower-power vibratory hammer, Yu Wei explained that according to the geological survey report, the sand layer in this area is relatively thick and in places can be twice that of other areas, so the selection of the 70RF was based on rigorous calculation and comparison of schemes. What is commendable is that Yu Wei was also one of the "detailed design" contributors to the 70RF. Since the 70RF's factory configuration did not include moving and positioning accessories, he combined similar foreign equipment to customize a detachable 80-ton crawler-type "mount" for the 70RF, and different matching schemes can be selected according to working conditions. Pile foundation construction can be carried out at night when traffic volume is lower, and the equipment can leave promptly after completion to restore traffic. 　　The 70RF achieves high-speed piling in the S3 expressway project
　　On July 29, 2016, on the Shanghai S3 expressway project, this resonance-free hydraulic vibratory hammer, the world's highest-power unit, drove the first test pile. According to Yu Wei, at the test pile site, the resonance-free hammer 70RF pressed a 25-meter-long pile steadily into the ground in only 4 minutes. No mud was generated on site, vibration could not be felt at all a few meters away, and only a sound similar to a car engine could be heard. It took only two hours to drive 12 pipe piles of 48 meters completely into the ground. With incredible speed, the vibratory hammer miraculously advanced the completion date of construction. Of course, achieving high-speed piling also benefited from the project manager's effective on-site preparations. The 12 casings were positioned in a frame in advance, ensuring verticality and also facilitating the welding of each casing section. The first 31-meter casing section was driven with the light and flexible 20RF vibratory hammer, after which the second casing section was welded on and then driven to the design depth of 48 meters with the 70RF. The lean construction method introduced flow into the construction process, enabling the project department to drive an average of 18 piles per day. In the early implementation section of the S3 highway, the project department used this "new weapon" to complete the construction of about 600 steel pipe piles in just one month, with very rapid construction speed.
　　Construction with the 70RF in densely populated areas has no impact on the surrounding environment
　　The deepest pile foundation of the Tianmu Road elevated project reaches 60 meters, driven into the ground in three sections and connected by welding in between. The interchange at this road has heavy traffic pressure and is surrounded by many buildings and residents. Both the owner and the construction unit hoped to minimize the impact on the surrounding environment and residents during construction. At the construction site, citizens stopped to watch in an endless stream, all praising the fact that such a huge construction operation could be carried out on such a narrow site, and during the daytime the sound of the pile hammer operation was basically imperceptible. The 70RF liquefies the soil through high-frequency vibration generated by the vibratory hammer (avoiding the resonance frequency of the soil), thereby sinking the steel pipe pile into the soil. It not only features fast construction speed, low noise, and no soil resonance, but also does not compress the soil. Compared with conventional bored cast-in-place piles, steel pipe piles have the characteristics of fast construction speed and no mud pollution, with basically no impact on surrounding buildings and the environment, making them especially suitable for densely populated areas in city centers. 　　The resonance-free hydraulic vibratory hammer will lead the future of pile foundation technology
　　The industry knows that traditional vibratory hammers have a constant eccentric moment. During startup and shutdown, when approaching the critical frequency range of surrounding buildings, the constant amplitude can cause disturbing negative vibrations in the crane boom and the soil. It is not limited to the work area but can extend over considerable distances around it. When working in highly urbanized areas or near fragile building structures, this may cause damage to nearby structures. In construction applications, an ordinary-frequency vibratory hammer is not a viable choice, and the contractor will need to choose a high-frequency vibratory hammer. A high-frequency (variable moment) vibratory hammer can adjust its frequency from 0 to 2,300 rpm. The key is that during startup and shutdown it does not generate any vibration. After passing through the critical frequency range, the eccentric weight automatically adjusts and synchronizes to the current eccentric moment. The benefits of using resonance-free technology for construction are: low cost, flexible construction, and it can be installed on lightweight excavators or suspended from cranes. It minimizes interference with the surrounding environment and is an ideal choice under narrow working conditions.
　　As the process of building industrialization and building intelligence accelerates, the state's requirements for green construction in the building industry continue to rise, and people's environmental awareness gradually strengthens, reducing sewage discharge, silent, and efficient resonance-free technology will have great prospects. The resonance-free hydraulic vibratory hammer technique represented by the highest-power 70RF may lead pile foundation technology into a revolutionary era.