Pile driving behaviour for wind farm in Bruce County, Ontario

摘要

As part of a wind farm project in Bruce County in Ontario, over 40 wind turbines had to be supported by piled foundations due to the presence of thick soft soil strata overlying dense soils. Over 1500 steel HP 310 x 110 piles were driven, some more than 30 m deep, to achieve the design pile axial capacities in both compression and tension. Prior to driving the piles, the pile capacities were evaluated by static pile capacity analysis using the borehole data obtained at each wind turbine location. The subsurface soil conditions were investigated by Standard Penetration Test and Dynamic Cone Penetration Test. The minimum pile embedment depth (i.e., anticipated pile lengths) at each wind turbine location was established in order to achieve the design pile compression and tension capacities. Pile driving criteria based on Hiley formula were then developed. During actual pile driving, a number of piles had to be driven much deeper than the anticipated pile lengths as indicated by the resistances from Standard Penetration Test (SPT) and Dynamic Cone Penetration Test (DCPT), particularly when no hard soil layer (e.g., thick layer of hard clay or very dense sand, bedrock, etc.) was present at anticipated pile tips. This paper describes the behaviour of pile driving in comparison with the results of Standard Penetration Test (SPT) and Dynamic Cone Penetration Test (CPT). A suggestion for estimating pile lengths from static pile capacity analysis and SPT / CPT results is provided.