FPrimeC was was engaged by the client to perform comprehensive non-destructive assessment of cracks in wind turbine foundations in Quebec, Canada. Concrete foundation was a circular map foundation of approximately 6 m diameter, and 2.5 m thick anchored to the bedrock using post-tensioning anchor rods.
Cracks in Wind Turbine Foundations
Cracks were observed on the top surface of the wind turbine foundation. It is understood that cracks are a common observation in these foundations. Wind turbine foundations are subject to a significant cyclic loads from the vibration of the turbine, and oscillation of the tower. Although the majority of cracks in wind turbine foundations remain stable throughout their service life without significantly affecting safety and reliability, there are instances where these cracks can indicate more serious underlying issues (i.e. structural cracks). Non-destructive testing and evaluation can play an important role in evaluating the safety and reliability of existing wind turbine foundations.
The main objective of this assessment was to evaluate the extent of potential cracks in the area between the embedment ring inside the concrete foundation and the steel plates under post tensioning system on top of the concrete mat.
Assessment of cracks in Wind Turbine Foundations
A multi-technology approach was adapted for the Non-destructive evaluation of cracks in win turbine foundations. Two test methods based on stress wave propagation was used to study the cracks.
Spectral Analysis of Surface Waves (SASW)
The Spectral Analysis of Surface Waves (SASW) method uses the dispersive characteristics of surface waves to determine the variation of shear wave velocity at different depths across the test area. The technique utilizes the propagation of stress waves (shear waves) generated by a hammer impact to analyze the mechanical properties of concrete, evaluate the integrity and uniformity, and identify potential defects. The shear wave was determined at various depths; Certain assumptions and equations were used to estimate the compression wave speed in concrete. The wave speed was used to determine presence of major anomalies such as cracks.
Impact-Echo
The Impact Echo (ACI 228.2R-13 and ASTM C 1383)) test method is a non-destructive evaluation technique widely used for assessing potential cracks in wind turbine foundations. This method involves generating stress waves by impacting the surface of the foundation with a small, controlled impact. The waves travel through the concrete and reflect back when they encounter discontinuities such as cracks or voids. By analyzing the reflected waves’ patterns and velocities, engineers can accurately determine the location, depth, and extent of any internal flaws. The IE method is highly effective for identifying subsurface defects without causing any damage to the structure, ensuring the continued safety and reliability of wind turbine foundations while minimizing downtime and maintenance costs.