Geophysical characterisation of asphalt pavement failure: a case study from the campus of South Valley University, Qena, Egypt

Near-surface seismic refraction tomography and electrical resistivity imaging were used to study the collapse and subsidence of two asphalt roads on the campus of South Valley University in southern Egypt. The roads surround a garden where irrigation water was suspected to be the cause of the damage to the asphalt roads. Two seismic refraction tomography (SRT) lines were measured on the asphalt roads, and a single SRT line and an electric resistivity tomography (ERT) line were measured within the garden. The tomographic inversion of the SRT lines on the road shows several low velocity anomalies indicating areas of weakness beneath the asphalt. The SRT and ERT lines in the garden show a thin surface soil of fine sand and clay overlying a low electric resistivity and low seismic velocity clay layer. Examination of the results suggests that the damage to the asphalt roads could be caused by the presence of loose silt and clay soil that was used as a sub-base for the asphalt. This soil had not been compacted and engineered for use as a strong base layer. Instead, the asphalt was laid directly on top of it, which later led to the failure of the roads.