What is pile drivability?
It is the ability of the pile to be driven to a designated depth without suffering without sustaining damages. The ultimate resistance of soil against a pile, which is driven without suffering any damages using suitable driven equipment, specify a limit for pile drivability.
Fig.1: Pile Driving
Factors Influencing Pile Drivability
There are two major drivability features that a pile need to meet namely pile stiffness and pile strength. The pile need to have adequate stiffness to be able to transfer sufficient driving force that overcomes soil resistance. Regarding pile strength, it should be large enough so as the pile can withstand the driving force without suffering any damages.
Pile impedance (EA/C) is the major factor that controls pile drivability. The modulus of elasticity (E) of pile is specified based on the material used for the construction, (C) is the pile wave speed, and (A) is the cross-sectional area of the pile which seems to be the only parameter by which pile drivability can be improved.
The improvement of pile drivability though increasing cross sectional area can be clearly observed when steel pile is selected. For example, the increase of the thickness of steel pipe pile will enhance the pile drivability. However, when the area of reinforced concrete section is increased, the soil resistance would also increase.
Pile driven system features such as speed, stroke, ram weight, and real performance of pile driving system on the construction site would influence pile drivability to a certain extent.
Methods to Assess Pile Drivability
There are three methods used to evaluate pile drivability which include:
- Wave equation analysis
- Dynamic testing and analysis
- Static loads tests