USE OF GEOPHYSICAL SURVEYS TO ASSESS AND MITIGATE VOID FORMATION OVER A SEWER FAILURE - CHARLES B. WHEELER AIRPORT - TAXIWAY G - KANSAS CITY, MISSOURI

Abstract

Two geophysical methods, ground penetrating radar (GPR) and multi-channel analysis of surface waves (MASW) were used at an airport site in Kansas City, Missouri to identify the potential location of voids beneath a reinforced concrete taxiway. Prior to conducting the geophysical surveys, airport personnel observed a failed joint within a 42-inch corrugated metal pipe (CMP) situated approximately 22 feet beneath the taxiway during a CCTV inspection. Evidence of sand infiltration was observed within the pipe during the CCTV inspection, and the airport was concerned about voids forming beneath the taxiway slab above the pipe. Exploration using GPR and MASW surveying was performed on the taxiway to assist in identifying the location of potential voids, and to help identify locations for invasive exploration methods such as drilling or slab removal. 3D GPR data were collected over the suspected void area using several closely spaced orthogonal 2D GPR survey lines. MASW data were collected over two orthogonal survey lines situated over the survey area. A high amplitude GPR anomaly was observed in the vicinity of the failed pipe joint. The presence of a void was interpreted immediately beneath the taxiway slab, and the bottom of the void was interpreted at approximately nine feet beneath the slab. The 3D GPR data suggested the presence of a cone-shaped void above the failed pipe joint area. Additionally, a zone exhibiting lower shear wave velocities was observed on the MASW profiles to a depth of approximately 25 feet in the area of the 3D GPR anomaly, suggesting the presence of less consolidated soil beneath the interpreted void. A contractor subsequently removed taxiway pavement and exposed a large void and underlying eroded sediment beneath the taxiway as imaged during the geophysical surveys. The damaged sewer was replaced, backfilled, and the taxiway re-paved.