Integrity Testing of Pile Cover Using Distributed Fibre Optic Sensing.

Area of Science:

• Geotechnical Engineering
• Materials Science
• Structural Health Monitoring

Background:

• Foundation pile integrity is critical in geotechnical engineering.
• Ensuring adequate concrete cover is essential for pile performance and durability.
• Existing methods for assessing pile integrity can be limited or invasive.

Purpose of the Study:

• To investigate the use of Distributed Fibre Optic Sensing (DFOS) for assessing cast-in-place foundation pile integrity.
• To infer concrete cover thickness and pile geometry by analyzing concrete curing temperature profiles.
• To compare the effectiveness of DFOS with the standard Thermal Integrity Profiling (TIP) method.

Main Methods:

• Embedding DFOS cables within a foundation pile during the concreting process.
• Monitoring distributed temperature changes along the pile using DFOS during concrete hydration.
• Utilizing a one-dimensional axisymmetric heat transfer finite element (FE) model to back-analyze DFOS data and estimate pile geometry.
• Conducting a field trial on a 51 m long test pile in London.

Main Results:

• DFOS successfully captured the development of concrete hydration temperature profiles over time.
• Variations in temperature patterns correlated with changes in concrete cover thickness.
• The FE model, using DFOS data, estimated pile diameters ranging from 1.40 to 1.56 m.
• The estimated pile geometry profile showed good agreement with results from the standard Thermal Integrity Profiling (TIP) method.

Conclusions:

• DFOS is a viable technique for monitoring concrete curing and assessing the integrity of cast-in-place foundation piles.
• The method provides valuable data for inferring concrete cover and pile geometry with depth.
• DFOS offers a promising, non-destructive approach for quality control in foundation construction.