There are many types of piles. Classified by load-bearing behavior, piles include end-bearing piles and friction piles. An end-bearing pile transfers the load of the superstructure through the pile to a deeper, hard soil layer. In Guangzhou, Shenzhen, Hong Kong and other places in China, high-rise buildings generally use end-bearing piles, with the pile tip supported on bedrock. The settlement of end-bearing piles is extremely small, and the side friction of the pile can be neglected. A friction pile transfers the load of the superstructure to the foundation through the friction around the pile shaft. In coastal areas such as Shanghai and Tianjin in China, the foundation soil is often silty, clayey or sandy, and friction piles are generally used. To control the settlement of the building, the tip of a friction pile should rest on a relatively good soil layer (called the pile tip bearing stratum). The bearing capacity of a friction pile consists of two parts: pile side friction and pile tip resistance. Pure friction piles generally cannot be used in high-rise buildings.
　　Classified by pile material, there are timber piles, lime-soil piles, gravel piles, concrete piles and steel piles. Timber piles, lime-soil piles and gravel piles are often used for foundation treatment of multi-story buildings and are rarely used in high-rise building structures. Concrete piles are widely used in China because materials are easily available and the price is moderate. According to different production or construction methods, concrete piles can be divided into two major categories: precast piles and cast-in-place piles. Precast piles include precast reinforced concrete square piles and precast prestressed concrete pipe piles; cast-in-place piles include bored cast-in-place piles, punched cast-in-place piles, driven-tube cast-in-place piles, excavated cast-in-place piles and large-diameter belled cast-in-place piles. Steel piles are often in the form of steel pipe piles, and wide-flange I-sections are sometimes used. Steel piles have large bearing capacity, small soil displacement, and are convenient to lift, transport and drive, but the supply of steel pile materials is tight and the price is high, so they are rarely used and generally only used in important or super high-rise buildings.
　　A relatively hard soil layer should be selected as the pile tip bearing stratum. For a pile with diameter d, the depth to which the full cross-section of the pile tip enters the bearing stratum should not be less than 2d for cohesive soil and silt; not less than 1.5d for sand; and not less than 1d for gravelly soil. In seismic design, the depth to which the pile enters gravelly soil, gravelly sand, coarse sand, medium sand, dense silt and hard cohesive soil should also not be less than 0.5 m, and for other non-rock soils should not be less than 1.5 m. When a weak underlying layer exists below the pile foundation, the thickness of the hard bearing stratum below the pile tip should preferably not be less than 4d, and the bearing capacity of the weak underlying layer foundation must be checked.
　　The selection of pile types for high-rise buildings should take into account factors such as geological conditions, superstructure type, load magnitude and design bearing capacity of a single pile, construction conditions and pile driving equipment, and the building site environment, and should be determined through comprehensive analysis and technical-economic comparison.