Invention and Development of Silent Piler
Necessity is the mother of invention. Invention, however, does not emerge from necessity alone. Invention can only emerge through a person with rich creativity and solid determination. Invention of the “Silent Piler” is no exception.
Akio Kitamura, the inventorofthe Silent Piler, started his business in the construction industry in 1967 with the idea of its being an anti-pollution company. During the 1960s to the early 1970s when Japan was enjoying high economic growth, Kitamura, who had ample experiences of handling a variety of construction machinery, was running his business mainly with piling contracts for foundation works using construction machinery such as the vibratory hammer.
One day, an incident occurred where an operator in his company was chased by local residents near the construction site due to complaints of noise and ground vibration caused by a vibratory hammer. He came to encounter the frequent occurrence of damage caused by pile driving works, such as roof tiles slipping down, doors unable to open, and walls cracking. He then realized that he himself had become a source of pollution in spite of his ambition to develop an anti-pollution company. He made up his mind to devote himself to inventing and developing pollution-free piling machines.
Luckily enough, he became acquainted with an experienced mechanical engineer, Yasuo Kakiuchi, as a working partner for design and manufacture. The first prototype of the Silent Piler was completed in 1975, as a piling machine offering a noise- and ground vibration-free machine. This was the point of departure for the development of the walk-on-pile-type press-in piling.
From original concept to design, manufacture, and selling of the Silent Piler
When he started developing the ideas, a scene recurred in his mind from, when he was watching with keen interest an operation to extract an embedded H-shaped steel pile (hereinafter called H pile) used for retaining walls in a building project. Many workers on the construction site were trying hard to pull up the H pile with a manual pulling system using timbers installed around the H pile as the required reaction. The resistance of the H pile was so strong that the pile could not easily be pulled out.
While he was recapturing the past scene, an idea flashed in his mind. A pile could be statically jacked in (hereafter “pressed-in” is used, with the same meaning as
“jacked in”) without noise and ground vibration, if the piling machine were designed to firmly grip the tops of existing piles previously installed in the ground, utilizing the pullout resistances of these piles as a reaction force. A clear image of piles gripping the Earth occurred to his mind.
Figure 2.7 presents a conceptual sketch of such a piling machine, where the piling machine was mounted on the top of installed piles while statically pressing a new pile into the ground by a hydraulic pressure.
Design of the first prototype commenced in 1973, and after 2 years of development, the first prototype was completed in 1975. The prototype machine had a capability of jacking a 400 mm width U-shaped steel sheet pile into the ground using hydraulic pressures. The machine was named the “Silent Piler”, implying that the piling machine could install a pile in the ground quietly. Figure 2.8 shows a view of the first prototype, and Figure 2.9 presents the corresponding design drawings.
The first prototype had a designed maximum press-in force of 100 tons and the weight of the machine was 13 tons (a ratio of maximum press-in force to machine weight of 7.7). Based on a number of trial-and-error experiences on the first prototype, Kitamura and his partner improved the original design and manufactured the second prototype in 1976, as shown in Figure 2.10.
The second prototype had a designed maximum press-in force of 120 tons and a machine weight of 6 tons (a ratio of maximum press-in force to machine weight of 20), achieving high-operating performance with light weight. The second prototype had a capability of pressing-in a 6m long steel sheet pile at a penetration rate of 0.8~2.5 m/min.
Figure 2.1 A conceptual sketch by Akio Kitamura.
Figure 2.8 First Silent Piler.
Figure 2.9 Design drawing of the first Silent Piler.
Figure 2.10 Second prototype.
The first practical application of the Silent Piler was in 1976, for excavation works near a residential area, thanks to the bravery and resolution of the project engineer, in Kochi City Waterworks Bureau, adopting this newly developed technology for the first time.
In Chapter 5, a set of the measured data of noise and ground vibration during piling operations at construction sites is presented, confirming that the levels of noise and ground vibration are far below the allowable levels specified in various regulations or standards.
Soon after the first practical application, the Silent Piler gained a high reputation throughout Japan as a noise- and ground vibration-free piling machine. While Kitamura’s company, Giken Seisakusho Co. Ltd. (currently known as GIKEN LTD.), used its Silent Piler units for their own piling projects, a purchase order from another company arrived. Sales of the Silent Piler then started in 1977. Figure 2.11 plots the accumulated number of the Silent Piler sold from 1977 to 2018, totaling more than 3,400 machines up to the present time.
Repetitive Upward and Downward Motion
During the course of development of press-in operational technique on-site, a unique technique called “repetitive upward and downward motion” was developed for maintaining the required alignment and verticality of the pile and for reducing the penetration resistance by repeating up and down motion of an installing pile controlled
Figure 2.11 Accumulated number of sold units of Silent Piler from 1977 to 2018.
by operating a hydraulic pressure in the set of cylinders mounted on the Silent Piler. The repetitive upward and downward motion further provides the merits such as adjustment of distortion and rotation of piles and prevention of interlock separation.
The repetitive upward and downward motion is characterized by penetration length lp (downward motion) and extraction length le (upward motion), practically penetration length lp is equal or longer than extraction length le.
The upward and downward motion turns to be one of the important on-site operational techniques with respect to quality control of piles installed, thus structures to be completed. Evidence will be presented of the effectiveness of the upward and downward motion in reducing the penetration resistance, and geotechnical interpretations on the upward and downward motion will be described in Chapter 5.
The concept of the Silent Piler stems from the idea of using the installed piles as a source of reaction force, with the machine mounted on the top of the previously installed piles which it grips. The machine then grips the next pile to be installed and statically presses the pile into the ground. This function of “Grip” forms one of the two key functions in Silent Piler.
Another key function is the “Self-Walking” function, which significantly widens the application ranges of press-in piling works. The self-walking machine means that a crane is no longer required for relocating and positioning the machine to install the next pile.
The idea of the self-walking function was already in Kitamura’s mind since the design of the first prototype. To achieve this function, reducing the machine weight was essential. A unit of Silent Piler with the self-walking function was completed in
1980, by reducing the maximum press-in force to 80 tons with the machine weight limited to 5.8 tons (a ratio of maximum press-in force to machine weight of 13.8).
The main body of the Silent Piler is fundamentally composed of four parts: Leader Mast, Chuck, Saddle, and Clamps as shown in Figure 2.12.
Figure 2.13 illustrates how the Silent Piler can walk on the continuously installed piles. Once the pile © is completely pressed-in to the ground, the leader mast is slid forward for pitching the next pile © into the chuck. The next pile is pressed-in to the ground to a certain embedment depth, until the pile being pressed-in becomes stable enough to support the machine weight. While gripping pile © firmly with the chuck, open the clamps and lift the machine upward. And then move the saddle forward to the new clamp position. After lowering the machine down and closing the clamps, the press-in process of the pile © proceeds to the designed embedment depth. The machine can walk and move forward by repeating these processes.
Steel tubular piles (hereinafter called tubular piles) are also commonly used for construction works such as retaining structures and foundations, where higher lateral rigidity is required. From the mechanical points of view, pressing-in tubular piles requires some modifications onto the machine itself as well as the operating mechanisms for grip and self-walking functions to accommodate the tubular shape of the pile, while achieving a larger penetration force.
For tubular piles, two modifications are required. One is that the machine has cylindrical feet attached to the saddle, instead of clamps. The cylindrical feet are made to fit to the inner diameter of tubular pile and have a capability of expanding when firmly holding the tubular pile and of contracting when detaching from the pile. The other is the use of a driving attachment for holding the main body to move forward as illustrated in Figure 2.14.
The biggest advantage of the self-walking function is to simplify the construction procedures, that is to say, to eliminate the process of crane operation for relocating and positioning the piling machine for the next pile installation. The self-walking
Figure 2.13 Self-walking function (sheet piles).
function is vital, in particular, for construction projects where only a very narrow working space is available, for example, piling works in densely populated residential areas as well as in areas near busy roads or where headroom clearance is limited, such as piling works under existing bridges.
Figure 2.15 presents various examples of piling works carried out in a narrow space, including a case where horizontal space is just over the machine width, while Figure 2.16 shows a view of piling works under an existing bridge without disturbing active traffic, where the headroom clearance was as low as 1.0 m.
These “Grip” and “Self-Walking” functions have further extended to the idea of the so-called the Non-staging system shown in Figure 2.17, where all the necessary piling work procedures, including pile transportation, pile pitching, and press-in operations can be carried out on the top of the aligned installed piles. This means that piling works can be carried out without temporary structures or temporary works, which has significant implications for widening the applications of press-in technology.
Figure 2.17 illustrates the typical configuration of the Non-staging system, also known as GRB (Giken Reaction Base) system, consisting of Silent Piler, piler stage, power unit, unit runner, clamping crane, and pile runner. Figure 2.18 shows several examples of Non-staging piling works. Chapters 3 and 4 compile case histories of
Figure 2.15 Pile installation in narrow working space.
Figure 2.16 Pile installation in a narrow working space.
Figure 2.17 Non-staging system.
Figure 2.18 Examples of Non-staging piling works.
piling works where the piling projects could not be carried out without using these unique features of the Silent Piler.