What is a pile foundation?

Pile foundation, referred to as pile foundation, is a kind of foundation type, which is mainly used in situations with poor geological conditions or high building requirements.

Basic introduction

The deep foundation consisting of piles and caps connecting the top of piles is called pile foundation for short. Pile foundation has the characteristics of high bearing capacity, small and uniform settlement, which can be applied to almost all kinds of engineering geological conditions and various types of projects, especially to heavy buildings built on soft foundation. Therefore, pile foundation is widely used in coastal and soft soil areas.

As early as 7000 ~ 8000 years ago in the Neolithic Age, people planted wooden stakes in lakes and swamps to build platforms to build settlements in order to prevent the invasion of wild animals. This kind of settlement is called residence on the lake. In China, the earliest pile foundation was found in the site of primitive society in Hemudu, Zhejiang. In the Song Dynasty, the pile foundation technology was relatively mature. In the "architectural style", there is a section about building a foundation by the water. By the Ming and Qing Dynasties, the pile foundation technology was more perfect. For example, the book Record of Ministry of Industry in Qing Dynasty stipulated the selection, arrangement and construction method of pile foundation. From the Northern Song Dynasty to the present, Longhua Pagoda in Longhua Town, Shanghai and Notre Dame de Jinci in Taiyuan City, Shanxi Province are both existing ancient buildings with pile foundations in China.

Pile foundation is an ancient foundation type. Piling technology has experienced thousands of years of development. Nowadays, great progress has been made in pile foundation materials and pile types, piling machinery and construction methods, and a modern foundation engineering system has been formed. In some cases, the use of pile foundation can greatly reduce the workload and material consumption on the construction site.

main feature

Piles are supported on hard or hard bearing layers, which have high vertical single pile bearing capacity or pile group bearing capacity, enough to bear all vertical loads of high-rise buildings.

The pile foundation has a large vertical single pile stiffness or group stiffness, which will not cause excessive uneven settlement under the influence of self-weight or adjacent loads, and ensure that the inclination of the building does not exceed the allowable range.

Using the huge lateral stiffness and overall anti-overturning ability of single pile or pile group foundation, it can resist horizontal load and bending moment load caused by wind and earthquake, and ensure the anti-overturning stability of high-rise buildings.

Piles pass through liquefiable soil layer, supported on stable solid soil layer or embedded in bedrock. In the case of shallow soil liquefaction and earthquake subsidence caused by earthquake, the pile foundation still has enough compressive and uplift bearing capacity depending on the deep and solid soil layer, thus ensuring the stability of high-rise buildings without excessive settlement and inclination. Commonly used pile types mainly include precast reinforced concrete pile, prestressed reinforced concrete pile, bored pile, manual digging pile, steel pipe pile and so on. Its applicable conditions and requirements are stipulated in the Technical Specification for Building Pile Foundation.

Basic classification

According to the stress principle of foundation, it can be roughly divided into friction pile and bearing pile.

Friction pile: It uses the friction between stratum and foundation pile to bear the structure, which can be divided into pressure pile and uplift pile, and is generally used in stratum with no hard bearing layer or deep bearing layer.

End-bearing pile: the foundation pile is located on the bearing layer, so that it can bear the structure.

According to the construction method, it can be divided into precast pile and cast-in-place pile.

Precast piles: precast reinforced concrete piles are driven into the ground by pile drivers. Its advantages are material saving and high strength, and it is suitable for buildings with high requirements. Disadvantages are high construction difficulty and long construction time limited by the number of machines.

Cast-in-place pile: firstly, drill a hole in the construction site, and after reaching the required depth, put the steel bar into the poured concrete. The advantage is that the construction difficulty is low, especially for manual digging piles, which is not limited by the number of machines. All pile foundations are constructed at the same time, which greatly saves time. Disadvantages are low bearing capacity and high material consumption.

What is a pile foundation? What pile foundations are generally included?

Pile foundation is a kind of deep foundation which connects several pile tops into a whole through pile caps and bears static load and dynamic load together. Pile is a vertical or inclined foundation component set in soil.

Generally, it includes vertical compressive piles, vertical uplift piles, horizontal bearing piles and composite bearing piles.

Pile foundation is a foundation form with high bearing capacity, wide application range and long history. With the improvement of production level and the development of science and technology, the type, technology, design theory, calculation method and application scope of pile foundation have been greatly developed and widely used in high-rise buildings, ports, bridges and other projects.

The function of pile foundation is to transfer the load to the deep soil layer with good bearing capacity to meet the requirements of bearing capacity and settlement. Pile foundation has high bearing capacity and can bear vertical load, horizontal load, uplift load and vibration load. It is the most widely used form of deep foundation.

Extended data

Application scope of pile foundation: when the upper soil layer is weak and cannot meet the requirements of bearing capacity and deformation, and there is a good soil layer at the lower part. Piles are used to pass through soft soil layers and transfer loads to deep hard soil layers. There is no ideal bearing layer in a certain depth range, and the load is gradually transferred along the pile rod through the side friction of the pile.

The foundation needs to bear the upward force, and the pile relies on the negative friction around the pile to resist the upward force, that is, uplift pile. When the foundation needs to bear the horizontal component, it can bear it by bending the straight pile. Pile foundation can be used when the hardness or load distribution of foundation is uneven and the natural foundation can not meet the requirements of uneven deformation of structures.

Consider the influence of adjacent buildings, ground stacking, construction excavation and piling. When the shallow foundation will cause excessive inclination or settlement, pile foundation will be used. There are unstable soil layers under the building, such as liquefied soil, collapsible loess, seasonal frozen soil and expansive soil. Pile foundation is used to transfer load to deep dense and stable soil layer.

Refer to Baidu Encyclopedia-Pile Foundation

What is a pile foundation?

Pile foundation consists of foundation pile and cap connected to the top of the pile. If the pile body is completely buried in the soil and the bottom of the pile cap is in contact with the soil, it is called low pile cap pile foundation; If the upper part of the pile body is exposed to the ground and the bottom of the cap is exposed to the ground, it is called high cap pile foundation. Pile foundation can be roughly divided into friction pile and end-bearing pile according to the principle of foundation stress, which is widely used in high-rise buildings. Building pile foundation is usually a low pile cap pile foundation. With the more and more extensive application of pile foundation in architectural design, static load test technology of pile foundation has also begun to develop.

Pile foundation is an ancient foundation type. Piling technology has experienced thousands of years of development. Both pile foundation materials and pile types, piling machinery and construction methods have made great progress and formed a modern foundation engineering system. In some cases, the use of pile foundation can greatly reduce the workload and material consumption on the construction site.

In 1970s, several major earthquakes occurred in China. Take the Tangshan earthquake as an example, the buildings with pile foundations are generally slightly damaged. This shows that the pile foundation has small deformation and good stability under the action of earthquake force, which is an effective measure to solve the seismic problems of weak foundation and earthquake liquefaction foundation in earthquake area.