News & Views

FPS issues New Guidance on Specifying Crosshole Sonic Logging

The Federation of Piling Specialists (FPS) has issued guidance on Specifying Crosshole Sonic Logging (CSL) in an effort to reduce harm to site personnel.

The guidance has been published following the FPS’s examination of the overall viability of sonic logging in foundation piles, to address some of the safety issues inherent in the placement and jointing of the logging tubes in piles, which have resulted in several injuries in recent years, and anomalous results.

Specifically, the guidance states that “In accordance with their duty under Construction Design and Management Regulations, specifiers must eliminate, substitute or reduce safety risks and must do this when specifying CSL. This can be achieved in the following ways; CSL should be avoided in dry stable rotary piles and small diameter piles where the sonic logging tubes have <300mm clear separation. Consider alternative integrity testing methods; Where CSL must be used, limit its use to the top of the pile within a single cage length to eliminate the need to splice tubes, reduce testing frequency, limit the number of tubes (tube spacing as great as 1.5m is acceptable) and where applicable reuse inclinometer or base grouting tubes.”

Further explanation and considerations can be found in the guidance note, which is available for free download to FPS members here.

Involved in the industry review were Arup, Bachy Soletanche, Franki Foundations, Cementation Skanska and SOCOTEC, led by Toby Hayward of Expanded Piling. The joint industry working group investigated how many genuine defects were identified, versus innocent anomalies and their causes, the sustainability cost of the methodology, and any correlation possible between sonic logging results and results from alternative methods such as Thermal Integrity Profiling (TIP) testing.