There are three types of prestressed pipe piles: PHC, PC, and PTC. It is a very mature construction technology and is widely used in industrial plants and civil buildings in the Yangtze River Delta, Pearl River Delta, and Bohai Bay. It has simple technology and easy construction quality. control. There are two pile driving techniques: static pressure and hammering. At present, the Yangtze River Delta region is dominated by static pressure piles. As far as Shanghai is concerned, the vertical bearing capacity of a single pile of PHC-500 (100) pipe piles can reach more than 2000KN. The price of PHC-A500 (100) pipe piles is 105 yuan/m, and the construction cost is about 15 yuan/m.

The following technical solution is provided to you:

Use ultra-high-strength prestressed concrete pipe piles (PHC piles). Before piling, you need to select pile hammers and pile frames, and determine the pipe piles. During the pile age period, corresponding technical measures have been taken during pile insertion, hammering, pile connection, and pile delivery. In this project, the characteristics of PHC piles such as high single pile bearing capacity, good hammer resistance of the pile body, strong penetrating power, and low cost are all well reflected.

The main building of Tongzhou Jiangong Building is 36m long from east to west, 18m wide from north to south, with 20 floors above ground and 1 floor underground, with a construction area of ??12,000m2. Adopt frame shear wall structure. The total load of the building is about 200000kN, and the maximum single column load is 6700kN. The foundation is a raft foundation, and the piles are ultra-high-strength prestressed concrete pipe piles (PHC piles) with a specification of ф600×110 and a pile length of 24m (two 12m proof joints). A total of 93 piles were installed in the main building, with a designed single pile bearing capacity of 3100kN.

1 Characteristics of PHC piles

(1) Produced in strict accordance with the national standard GB13476-92 and Japanese JISA 5337 standards, its concrete strength grade is not lower than C80.

(2) Single pile has high bearing capacity and wide design range. In the same building foundation, pipe piles of different diameters can be used, which can easily solve the problem of pile placement and fully utilize the bearing capacity of each pile.

(3) Single schools can be connected to any length and are not limited by the capacity of construction machinery and construction conditions.

(4) The pile quality is reliable, and the pile length and pile body quality after sinking can be monitored by direct means.

(5) The pile body has good resistance to hammering and cracking, and has strong penetrating power.

(6) Low cost. Its unit bearing capacity price is only 1/3-2/3 of steel piles, and it saves steel.

(7) The construction speed is fast and the construction is civilized.

2 Pile driving preparation

2.1 Selection of pile hammer

When selecting a pile hammer, the shape, size, weight, length of the pile, and length of the pile must be fully considered. Structural form, soil quality, meteorological and other conditions, and master the characteristics of various hammers. The ramming energy of the pile hammer must overcome the penetration resistance of the pile, including overcoming the pile tip resistance, pile side friction and energy loss caused by pile rebound. If the energy of the pile hammer cannot meet the above requirements, it will cause local buckling of the pile head, making it difficult to bring the pile to the design elevation. In view of the fact that this project has soft and hard soil layers, a steam hammer was selected with a hammer weight of 8t.

2.2 Selection of pile frame

The setting, installation and preparation of pile frame have a great influence on the efficiency of piling. The pile frame is a D-308S crawler-type pile frame. Its biggest feature is flexible movement and easy use. The operating mechanism is crawler and has relatively low requirements on the road surface.

2.3 Construction organization design and pile location Measurement and design

According to the geological conditions and foundation geometry in the piling construction area, the piling sequence must be reasonably selected and preventive measures must be taken for surrounding buildings. Conduct pile position measurement and design according to pile foundation construction drawings.

2.4 Storage and Lifting

Pipe piles generally need to be designed with two fulcrums (Figure 1), and their lifting points must meet the location requirements shown in Figure 2. Pipe pile storage requires the use of soft mats (wooden mats). Pipe piles should be protected from vibration and collision during lifting and transportation.

2.5 Determination of the age of pipe piles

The interval from manufacturing to piling construction of pipe piles should be as long as possible, and the concrete strength should be above the standard value of the design strength grade ( If it is manufactured in a factory, it usually leaves the factory at 80% of the standard value of the design strength level), so a certain amount of piles are required to be stored on site, and the principle of "first in, first driven" is used to meet the strength requirements of pipe piles.

2.6 Inspection and Repair

Before construction, the pipe piles should be inspected one by one again, that is, the concrete piles should be checked for serious quality problems, and both ends of the pipe piles should be cleaned and welded. If there is paint contamination on the surface, it should be cleaned.

3 Technical measures during the pile driving stage

3.1 Pile insertion

It is difficult to correct the angle of the pile during the pile driving process, so it should be placed correctly when in place . When the first pipe pile is inserted into the ground, try to keep the position and direction correct. Start laying it down gently, check carefully, and correct it in time if there are any deviations. If necessary, pull it out and hit it again. The vertical angle of the check pile can be used, that is, theodolite in two directions (90° to each other) is used to keep the guide frame vertical. Adjustment is made through the rotation, sliding and stopping of the pile driver guide frame. The theodolite should be set up where it will not be affected by piling and should be leveled frequently to keep it vertical.

3.2 Hammering

Because the ground is soft, there may be a large amount of sinking during the initial driving. It is advisable to use a low-lift hammer and hammer lightly. As the pile sinking deepens, the sinking will begin. Slow down the speed and gradually increase the lifting height. During the entire pile driving process, the pile hammer, pile cap, and pile body should be kept on the same axis as much as possible. If necessary, the direction of the pile hammer and pile frame guide rod should be adjusted according to the direction of the pile body. Care should be taken to prevent the pipe pile from being eccentrically hammered to prevent the pipe pile from bending.

When piling is difficult to sink, check the sinking