The shallow stratum in Shanghai area is weak, with low bearing capacity, large deformation of natural foundation and heavy load. For buildings with strict deformation requirements, pile foundations (friction piles) are widely used. Before the founding of New China, most houses with more than five floors were built with wooden stakes, ranging in length from several meters to tens of meters. The pine pile under the international hotel is 39.8 meters long. Some buildings use composite piles under the foundation. Usually, the pile is driven below the groundwater level, and the top is connected with a section of concrete cast-in-place pile, such as Hengshan Hotel, Dianguanju Building, Changjiang Apartment, Zhabei Power Plant Station A, etc. Some houses have a single cast-in-place pile under the foundation. After the founding of People's Republic of China (PRC), the timber supply was tight. In 1950s, single sinking cast-in-place piles were widely used. Due to the soil squeezing effect caused by continuous pile sinking during construction, adjacent piles that do not meet the strength requirements are squeezed, resulting in displacement and pile breakage. Or due to poor construction management, the pile body appears necking phenomenon. Therefore, this pile type was basically abandoned in the 1970s.

For a long time, reinforced concrete precast pile is the main pile foundation in Shanghai. Precast piles have the advantages of low cost, reliable quality control and short construction period, and they were still widely used in various pile types until the 1980s and 1990s. Due to the construction of high-rise buildings, large factories, blast furnaces, bridges, etc. Higher requirements are put forward for the bearing capacity of pile foundation and foundation deformation, so steel pipe piles are introduced into many projects and prestressed concrete piles are widely used. A series of problems caused by piling in urban dense buildings have attracted much attention. 1985, after the prefabrication plant of No.3 Navigation Bureau introduced the production line of high-strength prestressed concrete pipe piles (PHC piles) from Japan, the prefabrication plant of No.20 Metallurgical Company designed the similar production line by itself. This kind of pile can partially replace the steel pipe pile, which has been applied in Shanghai Grand Theatre and other projects and supplied to Hong Kong and Macao. In the choice of bearing stratum of pile foundation, before 1980s, due to the limitation of hammering energy, dark green cohesive soil was mostly used as the ideal bearing stratum of pile foundation. After 1980s, the extensive use of diesel piling hammers provided more space for the selection of bearing stratum of pile foundation. There are many projects that use No.7 silty sand and No.9 sandy soil as the bearing layer of pile foundation.

A, reinforced concrete precast pile

From 1950s to 1977, precast reinforced concrete pile was the main form of pile foundation. In 1950s and 1960s, except for the 43m long piles used in the cast steel workshop of 10,000-ton hydraulic press of Shanghai Heavy Machinery Factory, most of the piles were between 24m and 26m long. The bearing layer is dark green cohesive soil, and the designed bearing capacity of single pile is 600-800kN (60-80t). Since the late 1970s, various high-rise buildings in Shanghai have been continuously built, and precast piles have also developed greatly. Since 1980, the 45-meter-long reinforced concrete piles have been used in Shanghai Hotel, followed by the Telecom Building and Huating Hotel. No.7 silt or silt as the bearing layer of pile foundation has improved the bearing capacity of single pile and reduced the settlement of buildings, and achieved remarkable social and economic benefits, which has made Shanghai pile foundation develop to a new level. In the dark green cohesive soil layer or the first sand layer is missing or thin, or the underlying layer is weak, build more than 30 high-rise buildings. In order to control the settlement, longer piles are used, such as Hongqiao Hotel designed by Donghua Institute of Technology and Lujia Village Shanghai Office Building (union buildings), with a pile length of 60 meters. Since 1990s, the exploration of super-high-rise buildings above 100 meters must reach a certain depth in the first layer of fine silt (the second layer of sand in Shanghai), which is the basis for studying the possibility of the second layer of sand as the bearing layer of pile foundation.

Precast square piles used in Shanghai, with a cross section of 20-50 cm, a few sides of 60 cm and a length of 5-60 meters. It is convenient for prefabrication, transportation and stacking in factories or construction sites. Because the quality of pile body is easy to ensure, it has high bearing capacity and good durability. The existing pile sinking machinery has complete models, convenient construction, short construction period and lower cost than other pile types, especially after years of practice.

Over the years, the manufacturing technology of precast piles has been greatly improved, and the initial consumption of wood and labor is high. 1956 firstly, in the 10,000-ton slipway project of Jiangnan Shipyard, the overlapping method was used for multi-rib pouring, which reduced the pile-building site, saved the wooden mold and labor, and improved the pile-building speed. This pile-forming technology has been popularized throughout the country and achieved remarkable results.

Precast piles can be manufactured and constructed in sections, and steel pile cap welding method was originally used for pile extension. 1972, through the cooperation of relevant design and construction units, the sulfur cement anchoring method was successfully adopted. After years of engineering practice, this technology can safely bear the stress of hammering construction on the premise of strictly ensuring the quality of operation. Since 1975, it has been used in multi-section precast pile engineering, saving about 70% compared with welding cost. Since the late 1980s, due to the improvement of bearing capacity of pile foundation and the quality control of sulfur cement, this kind of joint has been rarely used.

In terms of piling equipment, before the founding of New China, the pile foundation construction equipment was very backward. There are only two steam hammers weighing 7 tons in the city, most of which are steam or electric drop hammers, and even the original stone or cast iron drop hammers are used for manual lifting and unhooking piling. Since 1958, the task of pile foundation has increased, so a batch of steam piling machinery has been processed and manufactured, with a hammer weight of 10 ton. Before 1977, steam hammer was basically used for piling. After Baosteel 1978 started construction, 3 ~ 7.2 tons of diesel hammer and crawler pile driver were introduced. Later, it developed into more advanced diesel hammers, such as 8-ton hammers in Japan and D60 and D62 with adjustable impact energy in the Federal Republic of Germany. On the basis of introducing German technology, Shanghai Construction Machinery Factory has been able to produce D series diesel hammers. Since 1980s, steam hammers have been eliminated and diesel hammers have been widely used. In 1990s, hydraulic hammer (ZHA-30) was introduced from Britain by Shanghai No.3 Waterway Engineering Bureau, and it was applied in Jinmao Building Project.

In the port reconstruction, 1965 adopts piling construction for the first time, and the equipment capacity is 150 tons and 80 tons. By the 1990s, it had grown to 300 to 500 tons. Since 1972, pressed piles have been used in many industrial and civil construction projects, and the pile length is about 20 meters. 1986, the 7 1 meter long static pressure pile constructed by Shanghai Survey Institute in Jinshan Cement Plant reached 1000 ~ 1200 tons. In recent years, a 500-ton pile driver can press the pile up to 38 meters and enter the No.7 muddy soil, which is applied to two 24-story residential buildings in Shanghai Hailong Huaxin Long Garden. Pile pressing construction has the advantages of no noise, no vibration and little influence on the surrounding environment. However, due to the limitation of equipment capacity, it is impossible to penetrate thick sandy soil or silt.