Shanghai Construction Group awarded Shanghai Yiqian the foundation work on the satellite terminal currently under construction at Pudong International Airport. The work scope included building a retaining wall, with an outer Soil Mix Wall to ensure water tightness, and an inner wall made of rows of concrete bored piles for strength. As the construction site was situated right next to the airport’s second runway the use of bentonite was restricted. The added benefit of low resonance of a hydraulic vibratory hammer convinced the client to choose to build in-situ concrete piles with the protection of a temporary steel casing. A video of the project can be viewed in the casings application section of this website.

Three construction methods are commonly used for in-situ foundation construction:

1) Double head rotary drilling, concrete is mixed into the soil

2) Vibrator assisted rotary drilling, a casing is vibrated down and the rotary drill excavates the casing, concrete is poured and the casing is extracted and used for the next pile

3) Vibrator assisted bore piling, a casing is vibrated down and the drilling bucket excavates the casing, concrete is poured and the casing is extracted and used for the next pile.

When comparing the above three methods, the third is the most efficient and cost effective choice. This is why Shanghai Yixian chose this method.

During driving there are some potential pitfalls that need to be avoided:

1) The casing isn’t vibrated to the required verticality

2) Too much concrete is used

3) How to lower the steel reinforcement cage into the concrete

Remedies

1) If the verticality is critical we recommend the user to install the hammer on a piling rig such as the PR90, this way the verticality can be closely monitored and the pile guaranteed to be within specification. Alternatively, a two level positioning frame can be built onsite to guide each pile into the soil. 

2) To reduce the amount of concrete used for bored piles in soft soils, some operators choose the outer diameter of the casing as the template for the bore pile, and not the diameter of the drilling bucket. When the casing is extracted the concrete fills the area of the casing wall thickness. The amount of concrete inserted into the pile can be measured and the quality of the pile guaranteed.

3) We will devote a next article to this topic