Investigating Subsurface Failure Mechanisms and Mud Pumping in Rigid Airfield Pavements Using Ground Penetrating Radar: A Collaborative Study at Heathrow Airport

The condition of airfield pavements plays a central role in ensuring the safety and efficiency of airport operations. Compared with highway pavements, those on runways and taxiways are exposed to far heavier and more repetitive dynamic loading from aircraft. Over time, these loads can trigger complex deterioration processes that are not easily identified through surface inspection. Among these, mud pumping is particularly damaging, as it accelerates the structural deterioration of rigid concrete slabs and reduces their service life.

Mud pumping develops when water accumulates at the interface between a concrete slab and its sub-base or subgrade. Under repeated high-magnitude loads, a slurry of water and fine soil particles is expelled through joints and cracks. This movement of material results in subsurface voids, uneven support, increased slab deflection, and, eventually, cracking or differential settlement (sinking) of concrete bays. Previous studies have highlighted that knowing the location and extent of these voids is critical for effective slab stabilisation [1]. At Heathrow Airport, this mechanism has led to several cases of significant cracking and premature pavement distress, prompting a detailed investigation into its causes and distribution.

This study presents a collaborative research framework between academia and Heathrow Airport’s asset management team to assess the capability of Ground Penetrating Radar (GPR) as a primary non-destructive method for detecting early-stage pavement decay. Although Heathrow has identified specific areas of concern, such as the Charlie taxiway, the failure mechanisms often remain hidden until surface damage becomes advanced. By utilising GPR, this study aims to characterise the dielectric contrasts associated with moisture accumulation and subsurface voids that typically precede active mud pumping. The effectiveness of GPR for mapping these internal condition variations has been well-documented, particularly in the characterisation of pavement layer interfaces and moisture content [2].

The methodology focuses on high-resolution subsurface imaging to map the internal condition of concrete bays showing unexpected deterioration patterns. The flexibility of GPR enables the use of different frequencies to balance penetration depth with the resolution required to identify features such as thin delamination layers and incipient voids [3].

The long-term goal is to support a shift from reactive maintenance to a proactive, data-driven management strategy. By identifying the geophysical indicators of mud pumping and structural voids, the study aims to provide a diagnostic approach that can help forecast future failure areas, enhance maintenance planning, and extend the operational lifespan of critical airfield infrastructure.

 

Keywords: Ground Penetrating Radar (GPR); Airfield Pavement Management; Mud Pumping; Non-Destructive Testing (NDT)

 

References

[1] Maser, K. R. (2013). Use of GPR for Subsurface Pavement Investigations of 23 Airports in South Carolina, Proceedings Ninth International Conference on BCRRA, Vol 1.

[2] Al-Qadi, I. L., & Lahouar, S. (2005). Measuring Layer Thicknesses with GPR – Theory to Practice, Vol. 19, 10, 763-772.

[3] Benedetto, A., Tosti, F., Bianchini, L., & D’Amico, F. (2018). An Overview of Ground-penetrating Radar Signal Processing Techniques for Road Inspections, Vol. 32, 201-209.