introduce
As early as the early 1950s, the static piling method was adopted in China's coastal areas. In 1980s, with the development of piling machinery and the enhancement of environmental awareness, it was further popularized. By the 1990s, pile drivers have been serialized, and the pile drivers with the maximum piling force of 6800KN have come out, which can press both prefabricated square piles and prestressed pipe piles. Applicable buildings are not only multi-storey and medium-high-rise buildings, but also high-rise buildings and large structures with 20 or more floors. At present, it is used in Hubei, Guangdong, Shanghai, Jiangsu, Zhejiang, Fujian and other provinces and cities in China, especially in Shanghai, Nanjing, Guangzhou, Pearl River Delta and other places.
Pile sinking mechanism
Static pressure precast pile is mainly used in soft soil foundation. In the process of pile sinking, the pile tip directly causes the punching failure of soil, which is accompanied or preceded by the direct shear failure of soil along the pile body. The pore water is squeezed by this punching and shearing to form an uneven water head, which generates excess pore water pressure, disturbs the soil structure, reduces the shear strength of a part of the soil around the pile which is about twice the diameter of the pile, causes serious softening (cohesive soil) or thickening (silty soil and sandy soil), and causes the soil to become plastic, so that the static pressure pile can be easily and continuously sent into the deep foundation soil layer. If the pile pressing process stops, part of the pore water pressure disappears, and the soil around the pile consolidates radially, which increases the compactness of the soil around the pile and the side friction of the pile, especially the strength of the remolded soil at the pile end is restored, which leads to a greater increase in the resistance at the pile end. The longer the pause time, the more the disturbed soil strength will recover. Therefore, static pressure pile driving should not stop halfway. When pile connection must be stopped, shallow pile connection should be considered to avoid pile connection at a depth with good soil. Static pressure pile is a kind of soil compaction pile, which will increase the density of soil around the pile in the process of compaction, and its soil compaction effect depends on the geometry of pile section, pile spacing and soil layer performance.
application area
Static pressure method is usually suitable for high compressibility clay layer or soft clay layer containing light sand. When a pile needs to pass through a sandy interlayer with a certain thickness, its applicability must be comprehensively considered according to the piling force and final pressure of the pile driver, the shape, thickness and density of the soil layer, the mechanical indexes of the upper and lower soil layers, the type of the pile, the structure and strength of the pile, the size and arrangement of the pile section, the level of the groundwater level, the time and times of stabilizing the pressure before the final pressure, etc.
Pile drivers with piling force greater than 4000kN can cross medium-dense and dense sand layers with a thickness of 5 ~ 6 m, while medium-sized pile drivers (piling force ≤2400kN) have limited ability to cross sand layers, so it is necessary to judge the feasibility of piling.
Static pressure piles are also suitable for karst areas with thin overburden. It is difficult to drill holes with bored piles in these areas; Punched pile is adopted, which is easy to jam the hammer; The driven pile breaks easily. Only the static pressure pile can be pressed in slowly, and the compressive capacity of the pile can be shown. However, in karst areas where caves and ditches are developed, and areas where there are many boulders and obstacles in the soil layer, static pressure piles should be used with caution.
Small pile driver (piling force ≤600kN) is used to press precast small piles, which is suitable for bearing layers (such as hard plastic silty clay layer, silty soil layer and medium dense silty sand layer). )/kloc-within 0/0m.
The above is the introduction of anchor static pressure pile provided by Zhong Da Consulting for builders. For more knowledge of architectural terminology, please pay attention to the architectural knowledge column of Zhong Da Consulting.
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