Investigation Of Ground Penetrating Radar For Detection Of Leaking Pipelines Under Roadway Pavements And Development Of Fiber-Wrapping Repair Technique
Nowadays, it has become a common practice to observe urban roadways undergo severe distress characterized by substantial depressions. In some cases, these pavement depressions are caused by leakages in the connecting joints of sewage pipelines laid beneath the roadway pavement. Manual inspection of pipe leakages has become costly and complex since sewage pipes with relative small diameters do not allow inspection from inside and digging may be required. On the other hand, pipes with large diameters, in which inspection can be made from pipe interior, inspector can not remain inside of the pipe for long periods of time because of toxic fumes. In order to overcome this problem, a geophysical technique known as ground penetrating radar (GPR) has been proposed as a candidate to detect the leakages. GPR is a nondestructive reflection technique, which uses high frequency electromagnetic waves to acquire subsurface information. GPR contributes to detect leaks in sewer pipes either by detecting underground voids surrounding the faulty pipe, or by detecting anomalies in the depth of the pipe as the radar propagation velocity varies due to the saturation of the soil near the leak. Once the leakage is detected, on site-repair technique to restore the damaged pipe is not an easy task. In this study, fiber reinforced polymer (FRP) composite created by saturating a fiber sheet with an epoxy resin matrix is proposed to be applied in several layers of overlay to the faulty structure surface. This fiber sheet is typically made of carbon or glass and saturated with the chemical resin matrix and makes the repaired structure even stronger than originally constructed. For the last twenty years, FRP has been used to repair and strengthen concrete columns by employing a practice known as fiber wrapping technique . This method involves the wrapping of unidirectional fiber composite sheets around concrete columns. FRP wrapping approach can be extended to sewage pipelines for repairing and strengthening the distressed pipeline. The purpose of this study is to detect leakages in sewer pipelines using GPR, and develop an on-site fiber-wrapping technique for repairing and strengthening sewage pipes. In detecting sewer leakages, one case study is presented. The case involves the use of GRP for leakage detection in a sewer pipeline overlaid by flexible pavement that already shows signs of subsidence. Moreover, in developing a repair technique, a gypsum cement mold wrapped with carbon fiber composite material is placed around a large-scale faulty pipe joint, and tested using a MTS servo-controlled hydraulic actuator. In addition, both free ends of the pipes are capped and filled with water to determine the effectiveness of the technique in stopping leaks along the repaired joint. During the GPR survey performed in the area of study, no clear indications of leakages were observed along the buried sewer pipeline. This lack of traceable signals from the subsurface was the result of the significant attenuation of the radar signal with depth that made impossible to discern effectively any anomaly along the designated pipeline. Although different antennas having center frequencies of 300 and 80 MHz were used and a variety of settings on the GPR unit were tried, the buried pipeline was barely detectable. Nevertheless, signal reflections generated by buried pipelines in other areas such as stormwater pipes on UCF campus and drainage pipelines at road side of University Boulevard were clearly detected, which makes to believe that the significant attenuation of the radar signal at the area of study is due to the extreme high conductivity of soils which have been severely contaminated by the leakage of sewage from the distressed pipeline. In contrast, favorable results were obtained in the development of the repair technique since the two-component system, Hydro-stone Gypsum Cement and FRP composite material, wrapped around the faulty joint effectively increased its structural capacity even higher than the pipe original strength
