Sinkhole Locating and Corrosion Quantification with Pipe Penetrating Radar

摘要

Pipe penetrating radar (PPR) is the underground in-pipe application of ground penetrating radar (GPR), a non-destructive testing method that can detect defects and cavities within non-ferrous (reinforced concrete, vitrified clay, PVC, HDPE, etc.) pipes. The key advantage of PPR is the unique ability to map pipe wall thickness and deterioration including voids outside the pipe, enabling accurate predictability of needed rehabilitation or the timing of replacement. This paper presents recent advancement of PPR inspection technology together with selected case studies. The century old Broadway sewer main in Everett, WA, is a combination of a 30” reinforced concrete (RC) pipe and a 36” brick pipe. Little information is known about the condition of these pipes and the owners needed structural information beyond the usual closed circuit television (CCTV) in order to plan long term management of these critical assets. Over 16,000 ft of high resolution PPR line data were collected via robotic inspection. Due to the highly complex nature of the geophysical data, data processing and interpretation was a critical component of this project. The PPR results revealed that there are variations in the rebar cover in segments of the RC pipe. Although the average minimum rebar cover (depth of the first layer of rebar measured from the inner surface of the pipe wall) in almost every pipe segment appears to be sufficient (more than 0.75"), local anomalies occur along the pipe. No voids were detected outside the concrete pipe. In the second case study PPR was used for the condition assessment of asbestos cement (AC) pipes. AC pipes form a significant component of the water distribution and sewer collection systems in many cities. A majority of these pipes appear to be approaching the end of their useful life. The ability to accurately and cost-effectively assess the wall thickness of asbestos cement pipe has become a critically important issue for pipe owners. A new, high resolution PPR system, the SewerVUE AC Pipe Scanner (ACPS) was developed and successfully deployed in a live 10” AC pipe in Surrey, BC, Canada. Using new, high frequency antennae, the PPR inspection accurately mapped the remaining wall thickness.