What is pile drivability?
Pile drivability refers to the pile’s capacity to be driven to a specific depth without experiencing any damage. This ability is determined by the ultimate resistance of the soil against the pile, which is driven using appropriate equipment. When a pile is driven without any damage, it sets a limit for the pile’s drivability.
Fig.1: Pile Driving
Factors Influencing Pile Drivability
To ensure adequate pile drivability, two key features must be considered: pile stiffness and pile strength. The pile must have enough stiffness to transfer the necessary driving force to overcome soil resistance, while its strength must be sufficient to withstand the force without damage. The factor that controls pile drivability is pile impedance (EA/C), where E represents the modulus of elasticity based on the material used, C is the pile wave speed, and A is the pile’s cross-sectional area. Increasing the cross-sectional area is the primary means of improving pile drivability, as seen with steel pipe piles where increasing thickness enhances pile drivability. However, increasing the area of reinforced concrete sections also increases soil resistance. Additionally, the pile driving system’s speed, stroke, ram weight, and real performance on the construction site can also influence pile drivability to some extent.
Methods to Assess Pile Drivability
To evaluate the drivability of piles, there are three commonly used methods. These methods include wave equation analysis, dynamic testing and analysis, and static load tests. Wave equation analysis involves using mathematical equations to simulate the behavior of the pile when subjected to impact from a hammer. Dynamic testing and analysis involves measuring the pile’s response to the impact of a hammer using sensors, and analyzing the data to evaluate its drivability. Static load tests involve applying a static load to the pile and measuring its deformation to determine its bearing capacity. These methods are used to ensure that piles are driven to the required depth and with sufficient capacity to support the load they will be subjected to.