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Discussion of Offshore Steel Pipe Pile Foundation Construction

2016/10/07
Construction of offshore steel pipe pile
With the completion of the main bridge of Hong Kong-Zhuhai-Macao Bridge in the world's largest cross-sea bridge, the construction experience of steel foundation piles as bridge, wind power station, harbor and wharf is mature in China. Based on the successful experience of HHP35 and HHP30 hydraulic piling hammer in Guangdong Hong Kong-Zhuhai-Macao Bridge and offshore wind power project, the construction characteristics of offshore steel pipe pile and the situation in construction are analyzed.

HHP35 hydraulic piling hammer and φ2500mm, 67 meters long steel pipe pile

OVERVIEW OF OCEAN CONSTRUCTION
The sea construction site a number of away from the shoreline without cover outside the sea, wind, wave height, flow and change the flow of more obstacles and other construction difficulties under water conditions, and by the tides and weather, the effective working days less . The traditional diesel piling hammer has been gradually replaced by hydraulic piling hammer because of its low efficiency of energy conversion, low continuous work intensity, and easy to cause marine pollution, and so on, which directly raise the requirements for construction equipment. By fully utilizing hydraulic piling hammer to adapt to the characteristics of long-time high-intensity work, high-impact energy conversion and striking energy infinite control, it can effectively reduce the problems such as slip piles, reject hammer, buckling and other problems in the past pile driving process. Impact on ancillary equipment.

In the pay three-ship piling boat and HHP30 hydraulic piling hammer in Shanghai port of wind power project construction


1. Application status of steel pipe pile and construction characteristics
1.1 Application status of steel pipe pile
The steel pipe pile foundation has the characteristics of quick construction, high safety and mechanized operation. It is often used in the large-scale offshore bridge, harbor and wharf substructure, and has considerable application prospect. In recent years, the bridge steel pipe pile foundation is widely used, the most prominent example of the project is the East China Sea Bridge and Hangzhou Bay Bridge, the temporary platform at sea, the pier also widely used steel pipe pile foundation.

HHP30 hydraulic hammer hammering φ1700mm, 82 meters long steel pipe pile


1.2 The characteristics of offshore steel pipe pile construction
Offshore steel pipe pile construction, positioning difficult to use conventional measurement methods, the need to use GPS measurement and positioning technology, poor natural conditions at sea, less effective operating time.
2. Pile construction
2.1 steel pipe pile processing and transportation
Steel pipe piles by the manufacturers through the drawing of a long processing shape, in the process of sinking does not require the length of pipe joints, steel pipe pile processing in the factory should ensure that straight seam dislocation. When the finished product enters the factory, the manufacturer must provide the steel product certificate, the quality guarantee certificate and the factory product certificate of the steel pipe pile used in the rolled steel pipe pile. Steel pipe pile approach strictly in accordance with the quality inspection procedures for inspection, the main test content, including steel pipe pile welding quality and dimensions. Steel pipe piles are transported to the site by barges.
2.2 Survey Stakeout
The construction of steel pipe pile is measured by total station.
2.3 steel pipe pile plug play precautions
(1) steel pipe pile to pay attention to the top of the pile when the elevation control, pile top elevation should be controlled within a positive error of 10cm. When the steel pipe pile footage is very slow or Shi Shen difficult, you can not force Shen, in order to avoid steel deviation or deformation, to analyze the reasons.
(2) When the pile of steel pipe is hit, if the top of the pile is damaged or local buckling, the part shall be cut off and then be connected to the design elevation.
(3) steel pipe pile construction plane position, tilt must meet the following requirements: plane offset ≤ 300mm, inclination ≤ 1%.
3. Steel pipe pile in the sinking process of quality problems
3.1 steel pipe pile top deformation
3.1.1 Phenomenon
Steel pipe pile in the process of playing, especially the longer pile, the large energy, long time to fight, resulting in deformation.
3.1.2 Analysis of the causes
(1) encountered a hard obstacle, such as large stones, large pieces of concrete and other materials difficult to wear.
(2) encountered a hard hard sandwich, such as thick sand, sand and gravel layer.
(3) the geological description is unknown, fewer exploration points.
(4) the top of the damping cushion material is too thin, the replacement is not timely, the selection is not appropriate.
(5) poor selection of piling hammer, piling order unreasonable.
(6) Steady pile correction is not strict, resulting in hammer eccentric, affecting the vertical penetration.
(7) site roughness deviation is too large, resulting in easy to pile into the pile, so that the pile sink difficult.
3.1.3 Control measures
(1) according to the complexity of the geological survey in detail, encryption hole, if necessary, a probe (especially when playing a long pile).
(2) put the pile, the first drill to find underground objects, timely removal, and then put the pile site.
(3) flat piling site, should be the old base and other objects dug out, the flatness requirements of not more than 10%, and requires the density, can make the normal pile driver walking, if necessary, laying sand and gravel cushion, Layer and other measures.
(4) wear hard sandwich, you can use water jet method, gas blowing and other auxiliary measures.
(5) before the pile, pile cap cushion on the appropriate vibration material, such as sacks, cloth wheels and other objects, at any time for a replacement or a change. Stabilize the pile to two-way correction, to ensure vertical into the vertical deviation of not more than 0.5%.
(6) to break the deformation of the pile, then the pile should be cut off in order to smooth pick pile.
(7) to play long and large diameter pile, should use large-capacity diesel hammer to hammer low hit is better.
3.2 The pile can not reach the design requirement
3.2.1 Phenomenon
Pile design is based on penetration degree and final elevation as the ultimate control of the construction. Under normal circumstances, to a control standard, with another control standard as a reference. Sometimes the pile can not reach the final control requirements of the design.
3.2.2 Cause Analysis
(1) The exploration site is not enough or the exploration data is rough, and the engineering geology situation is unknown. Especially, the undulation level of the bearing stratum is unknown, which makes the design take the force stratum or choose the elevation of the pile tip wrongly, and sometimes the design requirement is too strict. Construction machinery capacity or pile concrete strength.
(2) the exploration work is based on the point of the surface, the local hard sandwich or soft sandwich of the lens can not fully understand, especially in complex engineering geological conditions, as well as underground obstacles, such as large stones, concrete blocks. Piling construction encountered this situation, it is difficult to meet the design requirements of the construction control standards.
(3) With the new sand layer as the bearing layer, due to the instability of the sand layer, the strength of the same layer of soil is very different. When the pile penetrates into the layer, it can penetrate into the bearing layer. degree. However, when pile group construction, the sand layer squeezed more dense, and finally appeared unable to sink phenomenon.
(4) pile hammer selection is too small or too large, so that the pile can not sink or sink over the design requirements of the control elevation.
(5) encountered a thick hard sandwich, through the extremely difficult, or require double control (into the holding force layer more penetration is too small).
(6) then take the pile quality does not meet the design requirements, welding cracking. The soil part of the selected pile, not to avoid the hard layer or hard sandwich layer.
3.2.3 Control measures
(1) in the case of hard sandwich, you can use piling, water jet method or air-blown construction. Pile construction is the first drilling, the hard sandwich drilling through, and then inserted into the hole pile, and then hit the design elevation. The diameter of the drilling requirements, to square inscribed circle, hollow round pipe pile diameter of the tube is appropriate. Regardless of the use of piling, water jet or air-blown construction, the pile tip into the undisturbed soil at least 6 times the pile diameter.
(2) in the construction program, clearly written to meet the thick hard sandwich selection jet method or gas blowing method and requirements. Such as can not meet the requirements of the design of dual control should be designed with the design of an effective way to solve the problem to meet the design requirements.

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