Deviation limit is a vital factor during installation. It is impossible to install a pile, whether by driving, drilling or jacking, the only mathod is installing piles in groups, which cause horizontal ground movements deflecting the piles . Therefore, contralling the positions of piles is necessary since misalignment affacts the design of pile caps . Accurate calculation of deviation limit of pipe piles are the guarantee of high quality of construction.
Factors affacting pile deviation limit
Specifications in different countries
How to calculate out deviaton limit
Because the spatial piles are usually used, it is possible to have single pile coordinates deviating from the twist angle, rake angle and plane. In addition, the plane coordinates have the largest deviation and the largest amplitude. This is the major factor causing the pile foundation different from the design value.
Non-human factors may cause more plane coordinate deviations. It results in a large deviation of pile quantity, direction and deviation quantity in a single pile cap. This shows that it is difficult to cover the different situations of actual piling engineering to determine the maximum allowable tolerance of pile by estimation.
Judging from the material of the pile, the steel pile is obviously better than the spun pile. The former has better adaptability if deviation occurs. However, the water of steel pipe pile zone are deeper and the steel pile body is longer. It makes the deviation control of steel pile mor difficulat than that used in spun pile. It is estimated that the tolerance of the deviated steel pile can be larger than that of the spun pile.
Although the deviation varies according to the requirements of the constrution project, many countries develop their own standard specifications.In the Hong Kong General Specification, both the installation tolerances for marine and land bored piles are given. The tolerances are 150mm and 75mm for marine and land piles respectively. In China, The specifications clearly specifies the operating conditions for offshore piling of different pile foundations in different areas with different deviations. At present, similar projects in China strictly comply with the requirements of "Coastal Water without Cover" to the deviation of control piles. In British, both standards specify the deviation of land piles is 75mm, and allow appropriate greater tolerance of deviation for marine piles. In BS6349, it is specified atolerance 150mm for piles in jetty or access trestles.
The calculation process is as follows:
Step A. select the appropriate estimated deviation;
Step B. select the unfavorable pile deviation direction;
Step C. external control load condition factors are selected to analyze and evaluate the results.
These three factors are not related to each other and accurate calculations should take into account envelope-value factors from these three different combinations. However, due to the large number of constraints, the actual combination and calculation results may not show any scale, so only the three factors of disadvantage can be considered separately with the actual situation analysis conditions.
In summary,The calculation process of the deviation limit of pipe piles is very complicated and delicate, involving various factors like earthwork, design level of engineers, customer requirements and local landscape. Therefore, accurate and accurate mathematical model is crucial, and a good design team is the guarantee of quality.