What are the functions of a pile hammer and a pile driver? ?

Pile jacks: Most pile hammers or drilling equipment require a pile jack for support and guidance. There are many different types of pile jacks; here, we focus on the universal pile jacks, those that can be used with various pile hammers or drilling devices. Currently, there are two basic types of universal pile driving rigs: one is a universal pile driver that moves along tracks, and the other is a pile driving rig mounted on a crawler chassis. Universal pile drivers are rarely used these days because they need to operate on pre-laid horizontal tracks, have a large structure that occupies much space at the construction site, and are difficult to assemble and transport. The crawler chassis-type pile driver has developed quite rapidly. Only this type of pile driver is introduced here. 　　1) Suspended crawler pile driver As shown in the figure, the suspended crawler pile driver uses a crawler crane as its chassis; the pile driver’s vertical column 6 is suspended by a boom 2, and the column 6 is connected to the vehicle body 1 via support forks 7. Due to the large weight of the pile driver and hammer, as well as their high center of gravity and forward position, it is easy to cause the crane to become unstable. So, usually, some counterweights are added to the vehicle body. Installing the column at the end of the boom is relatively simple. To facilitate the adjustment of the verticality of the columns, the lower end of these columns is usually connected to the vehicle frame using telescopic mechanisms such as screws or hydraulic systems. http://www.21-sun.com/expedite/hyzc/images/p1875-1-6.gif 　　The disadvantage of the suspended piling frame is its poor lateral stability, as the suspension of the columns fails to maintain a proper vertical position. This limits suspended pile jacks from being used for driving inclined piles. 　　2) Three-point track piling frame The three-point track piler also uses a track crane as its chassis, but numerous modifications must be made when using it. First, the boom must be removed, and two diagonal braces must be added. The lower ends of these diagonal braces are supported by ball joints on the crossbeam of the hydraulic legs, ensuring that the lower ends of the braces are kept at a considerable distance apart horizontally, thus forming a stable three-point support structure, as shown in the diagram. 　　The three-point pile driver is relatively ideal in terms of performance: it has a small working range and good stability. Additionally, the columns can be tilted by adjusting the length of the diagonal braces, thereby meeting the needs of driving inclined piles.

Pile-driving machinery that uses impact force to drive piles into the ground. It consists of a pile hammer, a pile driver frame, and auxiliary equipment, etc. (see color illustration). The pile hammer is attached between two parallel vertical guide rods (commonly known as girders) at the front of the pile driver, and is lifted using a lifting hook. The pile driver is a steel structural tower, equipped with a winch at its rear for lifting piles and pile hammers. In front of the tower, there is a guiding frame composed of two guide rods, which is used to control the direction of pile driving so that the piles are driven into the ground layer accurately according to the designed orientation. The tower and guide frame can be tilted together to drive inclined piles. The guide frame can also extend downward along the tower to be used for driving underwater piles along embankments or docks. The pile driver can rotate as well as move. The basic technical parameters of a pile driver are the weight of the impact mechanism, the impact kinetic energy, and the impact frequency. Pile hammers can be classified according to the source of power for their movement into drop hammers, steam hammers, diesel hammers, hydraulic hammers, etc. 　　Drop hammer pile driver: The pile hammer is a steel weight that is lifted by a winch using a hook; once the hook is released, it falls freely along a guide frame to drive the pile into the ground. 　　Steam hammer piling machine: The pile hammer consists of a hammer head and a hammer base, and is powered by steam or compressed air; there are single-acting steam hammers and double-acting steam hammers. A single-acting steam hammer uses a plunger or cylinder as the hammer head; steam drives the hammer head upward, after which it falls along the guide rod in the hammer holder to drive piles. A double-acting steam hammer generally uses a weighted plunger as the hammer head, with the cylinder serving as the hammer seat; steam drives the plunger upward and then causes it to descend for driving piles. The fast back-and-forth speed and high frequency cause vibration as the pile penetrates the strata, which can reduce frictional resistance and result in better pile driving performance. The differential steam hammer with bidirectional unequal acting forces features a light hammer base, allowing for an increase in the effective impact weight and thus better performance. The direction reversal of the inlet and outlet valves of the steam hammer can be controlled manually, or automatically by a flange lever mounted on the side of the hammer head and moving up and down with it; both methods allow for adjusting the impact stroke of the steam hammer. 　　The diesel hammer piling machine also consists of a cylinder and a plunger; its working principle is similar to that of a single-cylinder two-stroke diesel engine. The powerful pressure generated by the combustion of the atomized diesel injected into the cylinder’s combustion chamber, under high pressure and temperature, is used to drive the hammer head in action. Diesel hammers are classified into rod-type and barrel-type according to their structural design. The rod-guided diesel hammer uses a plunger as the hammer seat pressed against the pile cap, with the cylinder serving as the hammer head that moves up and down along two guide rods. During pile driving, the pile is first lifted and placed into the gantry of the pile driver. Then, a diesel hammer is placed on top of the pile; the hook is lowered to lift the cylinder, after which the hook is released allowing the cylinder to drop and fit over the plunger. The air trapped inside the cylinder is compressed, and the cylinder continues to descend until the pressure pin outside the cylinder presses against the rocker of the fuel pump located on the hammer seat. At that point, the fuel pump sprays fuel mist into the cylinder. This fuel mist comes into contact with the high-temperature gases above their ignition point, resulting in an explosion. The force generated by this explosion pushes downward, causing the pile to sink, while at the same time it pushes upward, lifting the cylinder back up. Once the cylinder falls again along the guide rods, another cycle of impact begins. The barrel-type diesel hammer uses the cylinder as the hammer seat and is directly guided by the inner wall of the extended cylinder barrel, eliminating the need for two guide rods; the plunger serves as the hammer head and can move up and down within the cylinder. During pile driving, the pile cap at the bottom of the hammer seat is pressed against the top of the pile; the plunger is lifted using a hook, and then the hook is released to drive downward, compressing the air trapped inside the cylinder. And it carries out processes such as fuel injection, detonation, impact, and gas exchange. A diesel hammer operates by compression ignition of diesel; therefore, it is necessary to ensure that the gas trapped inside the cylinder reaches a certain compression ratio. When driving piles into soft soil, the reaction force is often too low and the compression level insufficient to initiate ignition, so it is required to lift the hammer head multiple times using a hook in order to break the connection and generate impact, thereby starting the hammer. The hammer seat of the diesel hammer is equipped with a fuel injection pump, fuel tank, cooling water tank, and pile cap. The moving clearance between the plunger and the cylinder barrel is sealed by an elastic plunger ring. 　　Hydraulic hammer piling machine: Powered by hydraulic pressure, it allows the hydraulic pressure to be adjusted according to the properties of the soil layer, so as to achieve the appropriate impact force for piling; it is a new type of piling machine.

(1) Pile hammer The pile hammer is the main tool used to apply impact to the pile in order to drive it into the ground. Pile hammers mainly include drop hammers, steam hammers, diesel hammers, and hydraulic hammers; among these, diesel hammers are the most widely used at present. ①Hammer: The hammer has a simple structure, is easy to use, and allows for arbitrary adjustment of the hammer’s height. Light hammers are generally lifted and dropped using a winch. The drop hammer has low production efficiency, and the pile shaft is prone to damage. The weight of the falling hammer is generally 0.5 to 1.5 tons, while heavy hammers can weigh several tons. ②Diesel hammer: A diesel hammer utilizes the energy from fuel combustion to drive the piston back and forth, generating impact forces that are used for driving piles. The diesel hammer has a simple structure and is easy to use; it does not require external power supply. However, in overly soft soil, due to excessive penetration, the fuel does not ignite easily; as a result, the pile hammer fails to rebound, causing the working cycle to be interrupted. Another drawback is that it causes public nuisances such as noise and air pollution, so construction in cities is subject to certain restrictions. The weight of the impact part of the diesel hammer comes in various options such as 2.0t, 2.5t, 3.5t, 4.5t, 6.0t, 7.2t, etc. The number of hammer strikes per minute is approximately 40 to 80. It can be used for large concrete piles and steel pipe piles, etc. ③Steam hammer: A steam hammer uses the power of steam to deliver blows. Based on their operating mode, they can be further divided into single-acting steam hammers and double-acting steam hammers. In a single-acting steam hammer, the impact element consumes power only during its upward movement; it relies on its own weight to move downward ； In a double-acting steam hammer, the lifting and lowering of the impact element are both driven by steam. A steam hammer requires a set of boiler equipment. 　　Single-acting steam hammers possess considerable impact force, enabling them to drive various types of piles; the common weight of such hammers ranges from 3 to 10 tons. The number of hammer strikes per minute is 25 to 30. 　　The casing (i.e., the cylinder) of a double-acting steam hammer is fixed to the pile head, while the hammer moves up and down inside the casing. Due to the high impact frequency (100–200 times/min), it offers high work efficiency. It is suitable for driving various types of piles, can also be used for pile driving underwater, and for pile extraction. The weight of the hammer is generally 0.6 to 6 tons. ④Hydraulic hammer: A hydraulic hammer is a new type of piling equipment, whose impact cylinder is raised and lowered by hydraulic oil. The lower part of the impact cylinder is filled with nitrogen; when the impact cylinder descends, first the impact head exerts pressure on the pile, and then the compressible nitrogen applies pressure to the pile as well, thereby prolonging the time during which the impact cylinder exerts pressure on the pile. As a result, each impact achieves a greater degree of penetration. The hydraulic hammer does not emit any exhaust gases, is noise-free, has a high impact frequency, and is suitable for pile driving underwater; it is an ideal impact pile driving device, but its structure is complex and its cost is high. 　　When driving piles by hammering, to prevent the piles from being damaged due to excessive impact stress, it is important to use a \"gentle strike with a heavy hammer\". If a heavy hammer is used, a large portion of the impact force is absorbed by the pile body, making it difficult to drive the pile in, and the pile head is prone to breaking. The weight of the hammer can be selected by referring to the table below based on factors such as soil type and pile specifications; it would be more scientific to perform calculations of the hammering stress if possible. Hammer weight selection table
Hammer type: Drop hammer, Diesel hammer
20 25 35 45 60 72

Power performance of the hammer
Weight of the impact part, t: 2.0 2.5 3.5 4.5 6.0 7.2
Total weight, t: 4.5 6.5 7.2 9.6 15.0 18.0
Impact force, kN: 2000 2000–2500 2500–4000 4000–5000 5000–7000 7000–10000

Common stroke length, m: 1.8–2.3

Cross-section of the pile
Side length or diameter of precast concrete piles, cm: 25–35 35–40 40–45 45–50 50–55 55–60
Diameter of steel pipe piles, cm: 40 60 90 90–100

bearing stratum
Clayey soil, silt, soil
Typical penetration depth, m: 1.0–2.0 1.5–2.5 2.0–3.0 2.5–3.5 3.0–4.0 3.0–5.0

Average static cone penetration test value, MPa: 3 4 5 >5
Sand, soil
Typical penetration depth, m: 0.5–1.0 0.5–1.5 1.0–2.0 1.5–2.5 2.0–3.0 2.5–3.5

Standard penetration blows, N (unadjusted): 15–25 20–30 30–40 40–45 45–50 50

Typical controlled penetration rate, cm/10 blows: 2–3 3–5 4–8

Design ultimate bearing capacity of a single pile, kN: 400–1200 800–1600 2500–4000 3000–5000 5000–7000 7000–10000

(2) Pile driver
A pile driver is a device that supports the pile shaft and the hammer, guides the direction of the pile during driving, and ensures that the hammer can strike in the desired direction. There are various types of pile driving rigs. The commonly used universal pile driving rigs (those capable of being used with various pile hammers) come in two basic forms: one is a multi-functional rig that moves along tracks ； Another type is a pile driver mounted on a crawler chassis. ①The multi-functional pile driver (shown in the figure below) consists of columns, diagonal braces, a rotating worktable, a chassis, and a transmission mechanism. It has great mobility and adaptability; it can rotate 360° in the horizontal direction, its vertical column can tilt forward and backward, and it is equipped with iron wheels under the chassis that allow it to move along tracks. This pile frame can be adapted to various precast piles, and it can also be used for the construction of cast-in-place piles. The downside is that the structure is relatively large, making on-site assembly and dismantling rather troublesome. http://www.xauat.edu.cn/jpkc/jzgcsg/2zZhuang/image2/2-3.gif ② The crawler-type pile driver (as shown in the figure below) uses a crawler crane as its chassis, with additional columns and braces added for pile driving. It offers good performance, with a flexible pile driving frame that is easy to move, allowing it to be used for various prefabricated pile construction projects; it is currently the most widely used type. http://www.xauat.edu.cn/jpkc/jzgcsg/2zZhuang/image2/2-4.gif (3) Power unit The configuration of the power unit depends on the pile hammer selected. When a steam hammer is used, a steam boiler and a winch must be provided.