May I ask, how are pile foundations classified?

For more details, visit the website: http://www.jhtvu.net/upload/download/2008723101623.doc. Some of the images that can be downloaded have not appeared here; please go and download them yourself! ! Classification of pile foundations and manufacturing of precast reinforced concrete piles I. Working characteristics of pile foundations Pile foundations are a foundation type that is both ancient and modern, and they are widely used in the construction of high-rise buildings and important structures. The function of a pile foundation is to transfer the large loads from the superstructure, through the piles, to deeper layers of solid soil, thereby overcoming the problems of insufficient bearing capacity and excessive deformation associated with shallow foundations. As shown in Figure 2-1. Pile foundation with high cap; Pile foundation with low cap. Figure 2-1: Pile foundations. Pile foundations feature high bearing capacity, low and uniform settlement, as well as a slow settlement rate. It can withstand vertical loads, horizontal loads, uplift forces, as well as the vibrations or dynamic forces generated by machinery, and is widely used in projects such as building foundations, bridges, and water conservancy structures. II. Classification of pile foundations In engineering, pile foundations are usually composed of several piles, with cap beams placed at the top of these piles to connect them together and to distribute the loads from the superstructure evenly across the piles. Figure 2-1 1. Classification according to the height of the cap: ① Pile foundation with a high cap – the bottom surface of the cap is above ground level, and its stress and deformation characteristics differ from those of pile foundations with a low cap. It is generally used in bridge and dock projects. ②Low-capital pile foundation – the bottom surface of the cap is below ground level, and it is generally used in building construction projects. 2. Based on the nature of the load-bearing capacity: ① End-bearing piles – these are piles that pass through soft soil layers and transfer the loads of the building to the hard soil or rock layers at the pile ends. The frictional force exerted by the softer soil on the side of the pile on the pile body is very small, and this friction can be considered negligible. ②A friction pile is a pile that is driven to a certain depth into soft soil layers; through the friction between the pile side and the soil, the loads applied to the upper part of the pile are distributed throughout the soil surrounding it. The soil at the pile tip also provides some support. When the soil supported by the pile tip is not very compact and there is a certain relative displacement between the pile and the soil, then the pile functions as a friction pile. 3. Depending on the material of the pile shaft: ① Reinforced concrete piles can be prefabricated or cast in place. According to the design, the length and cross-sectional dimensions of the piles can be chosen arbitrarily. ②Common steel piles include steel pipe piles with diameters of 250~1200 mm, as well as wide-flange I-shaped steel piles. Steel piles have high load-bearing capacity, making them convenient for lifting, transporting, driving, and connecting, but they require a large amount of steel and result in high costs. At present, it is only used in a few key projects in our country. In the project of Shanghai Baoshan Iron and Steel Complex, for the foundations of important and high-speed operating equipment as well as column foundations, a large number of steel pipe piles with diameters of 914.4 mm and 600 mm and lengths of around 60 mm were used. ③Piles are now rarely used, only in certain reinforcement projects or temporary constructions where materials can be obtained locally. When below the water table, wood has good durability, but it is highly susceptible to corrosion in an environment with alternating dry and wet conditions. ④Sand and gravel piles are mainly used for foundation reinforcement and soil compaction. ⑤Lime-soil piles are mainly used for foundation reinforcement. 4. Classified by the functional purpose of the pile: ① Vertical compressive piles; ② Vertical uplift-resistant piles; ③ Piles designed to withstand horizontal loads; ④ Piles subjected to combined stresses. 5. Classified by pile diameter: ① Small-diameter piles, with d ≤ 250 mm; ② Medium-diameter piles, with 250 mm < d < 800 mm; ③ Large-diameter piles, with d ≥ 800 mm. 6. Classified by the method of hole formation: ① Non-displacement piles, such as piles formed by slurry shielding and pouring, or by manual excavation followed by pouring – these methods are widely used. ②Some soil displacement piles are drilled first and then driven in. ③Soil displacement pile, driven pile. 7. Classified by manufacturing process: ① Precast piles. Reinforced concrete precast piles are fabricated in factories or at the construction site, and are driven into the ground using methods such as hammering or vibration. ②Cast-in-place piles, also known as poured piles, involve drilling holes directly in the ground at the designated pile locations; a rebar cage may or may not be placed inside the hole, and then concrete is poured into the hole to form the pile. Compared to precast piles, it saves steel, and when the bearing stratum is uneven, the pile length can be designed according to actual conditions. 8. Classified by cross-sectional shape: ① Square-section piles are convenient to manufacture, transport, and store; the side length of their cross-section is generally between 250 and 550 mm. ②Circular hollow piles are prefabricated in factories using the centrifugal rotation method; they feature material savings, low self-weight, and a large surface area. The domestic railway industry already has standardized products, with diameters of 300 mm, 450 mm, and 550 mm, a wall thickness of 80 mm, and section lengths ranging from 2 m to 12 m. I. Production, lifting, transportation, and stacking of piles 1. Reinforced concrete solid square piles The cross-section of reinforced concrete solid piles is generally square. The cross-section of the pile shaft generally remains constant along its length. The cross-sectional dimensions of solid square piles are generally 200×200 mm to 600×600 mm. Length of the reinforced concrete solid pile shaft: Limited by the height of the pile driving rig; the length of piles prefabricated on-site is generally within 25 to 30 meters. Due to transportation constraints, precast piles manufactured in factories generally have a length of no more than 12 meters; otherwise, they must be precast in sections and then joined together during pile driving. There should not be more than 2 joints. Advantages of reinforced concrete solid piles: The length and cross-section can be selected within a certain range according to requirements; since they are prefabricated on the ground, their quality is easy to ensure, they have high load-bearing capacity, and good durability. Therefore, it is widely used in engineering. A reinforced concrete solid pile consists of a pile tip, a pile shaft, and a pile cap. Figure 2-2. Figure 2–2 Precast concrete piles – Material requirements: The strength grade of the concrete used for solid reinforced concrete piles should not be lower than C30 (30 N/mm2). When using the static pressure method for pile driving, the strength grade can be reduced appropriately, but it should not be lower than C20. The strength grade of the concrete used for prestressed concrete piles should not be lower than C40. The number of main reinforcement bars is determined based on the size of the pile cross-section and relevant lifting calculations; generally, there are 4 to 8 bars, with a diameter of 12 to 25 mm ； It should not be less than Φ14; the diameter of the stirrups is 6–8 mm, with a spacing of no more than 200 mm. The stirrups should be denser within a length range of 2–3 times the height of the driven pile, and rebar mesh should also be installed. The thickness of the concrete cover for the longitudinal reinforcement of precast piles should not be less than 30 mm. At the pile tip, the main reinforcement bars can be welded together to the auxiliary reinforcement bars at the pile tip; in compacted sand and gravelly soils, a steel sheet pile shoe can be used around the pile tip to reinforce it. 2. Reinforced concrete pipe piles: Concrete pipe piles are generally produced by centrifugation in prefabrication plants. The pile diameter ranges from Φ300, Φ400, Φ500 mm, etc., and the length of each section is 8 m, 10 m, 12 m, etc. When connecting piles, the number of joints should not exceed 4. The pipe wall is equipped with 10 to 20 main rebar bars of Φ12mm to Φ22mm, surrounded by Φ6mm spiral stirrups, and is usually made of C30 concrete. The connection between various sections of concrete pipe piles can be achieved through welded angle steel or flange bolt connections. Due to the forming process using centrifugation, the excess water in the concrete is expelled by centrifugal force; as a result, the concrete is dense, has high strength, and exhibits good resistance to groundwater and other forms of corrosion. Concrete pipe piles must reach 100% of the designed strength before they can be transported to the site for pile driving. The number of stacking layers shall not exceed three; the edges of the pipe piles on the bottom layer should be secured with wedge-shaped wooden blocks to prevent rolling. 3. Production, lifting, transportation, and stacking of piles ① Production of piles: Shorter piles are generally manufactured in prefabrication plants, while longer piles are usually prefabricated outdoors near the construction site. The ground of the precast site must be level and compacted, and protected from sinking due to water infiltration. For piles with more than two lifting points, when prefabricating them on site, the orientation of the pile tip must be determined based on the order in which the piles are driven. This is because the pulley systems on the pile jacks are arranged on the left and right sides; if the orientation of the pile tip is incorrect, it becomes very difficult to adjust it temporarily. When precasting prefabricated piles in layers, a separation layer should be placed between the piles (such as soap scum, used engine oil, or clay lime paste) to ensure that they do not stick together during lifting. The number of pouring layers should be determined by the load capacity allowed by the ground and the construction requirements; generally, it should not exceed four layers. The concrete for the upper layers of piles can only be poured after the concrete of the lower layers has reached 30% of the designed strength grade (Figure 2–3). Figures 2–3: Staggered construction using the overlap method; 1 – side formwork ； 2—Isolant or isolation layer ； 3—Clamp ； Ⅰ—First batch of poured piles ； Ⅱ—Second batch of poured piles ； Ⅲ—Third batch of poured piles ； The upper end of the main reinforcement bars in the pile should extend below the top layer of reinforcement mesh, and they should be arranged in a “┏─┓” shape; this allows for better absorption and transmission of the impact force from the pile hammer. The main reinforcement must be in the correct position, and the concrete cover around the pile shaft should be uniform; it must not be too thick, as this can lead to delamination during pile driving. The thickness of the pile shaft’s protective cover should not be less than 30 mm. For the connection of the main reinforcement bars in the reinforcement framework of precast reinforced concrete piles, butt welding is preferred. The number of main reinforcement joints in the same section shall not exceed 50% when flash butt welding and arc welding are used ； The distance between two joints of the same rebar bar should be greater than 30d, and not less than 500 mm. The concrete pouring for precast piles should be carried out continuously from the top of the pile to its tip, with no interruptions allowed. After completion, the piles should be kept moistened with water for at least 7 days. The completed precast piles should have their numbers and date of production marked on each pile. If the design does not provide lifting rings, the location of the binding points should be indicated. The allowable deviation for the geometric dimensions of precast piles is: side length of the cross-section ±5mm ； Difference in pile top diagonals: 10 mm ； Concrete cover thickness ±5mm ； The deflection vector height of the pile shaft shall not exceed 0.1% of the pile length ； 10 mm from the centerline of the pile tip ； The flatness of the pile top surface is less than 2 mm. The quality of precast pile fabrication shall also comply with the following requirements: (1) The surface of the pile shall be smooth and dense, with the depth of any chipped areas being less than 10 mm; the total area of local honeycombing or chipping defects shall not exceed 0.5% of the total surface area of the pile, and such defects shall not be concentrated in excessive amounts ； (2) Cracks caused by concrete shrinkage, with a depth of less than 20 mm and a width of less than 0.25 mm ； The length of transverse cracks shall not exceed half of the side length ； ②Lifting, transportation, and stacking of piles: Precast reinforced concrete piles should be lifted only when the concrete has reached 70% of the designed strength grade; they can be transported and driven into the ground once they have reached 100% of the designed strength grade. If lifting is to be carried out in advance, measures must be taken and the operation can proceed only after verification shows it is satisfactory. When lifting, the lifting points must be selected properly to prevent damage from bending during the lifting process. Figure 2-4 on page 58 of the textbook shows the appropriate location for the lifting points of precast piles. When the number of lifting points is 3 or less, their positions are determined based on the principle that the positive and negative bending moments are equal. When there are more than 3 suspension points, their positions are determined based on the principle of equal reaction forces. Piles that are 20–30 m long generally use 3 lifting points. Figures 2–4: Lifting point locations of the pile (a) and (d) – lifting from one point ； (b) Lifting from two points ； (c) Lift at three points ； (e), (f) Lifting of pipe piles at one point and two points