A Condition Assessment Approach for Highway Filter Drains Using Ground Penetrating Radar

The deterioration of highway filter drains (HFDs) is driven by the intrusion of foreign particles within the drainage trench. Being a porous material that offers high water removal capacity at the beginning of its service life, the drainage performance of the backfill can be significantly reduced in time by the introduced fouling material. This poses a serious safety hazard for road users (standing water on the carriageway), and can potentially have an effect in the structural capacity of the pavement. With currently limited approaches to methodically evaluate the physical condition of such assets, the Ground Penetrating Radar (GPR) offers an effective, non-destructive and continuous way to achieve this at both the project and network level. The laboratory calibration study carried out to support its adoption in a condition assessment system, builds upon the evaluation of a HFD-specific condition index aligned to permeability trials and the extraction of dielectric properties of the granular backfill material at different fouled states. The paper thus discusses what kind of HFD distress information are to be collected (condition data) and how this can be achieved (data collection methods), and defines four distinctive HFD media condition bands (Excellent to Very Poor) based on the proposed free voids ratio ( R FV ) ranges and extracted relative permittivity values.