Non-destructive inspection of critical infrastructure with no high-risk person-entry required, reducing cost and risk while providing highly accurate data-rich results.
Murphy Geospatial has been instructed to carry out remote access GPR surveys within nominated sections of the A Sewer Main. The purpose of these surveys was to determine the presence and location of voiding within the grout, between the Glass Reinforced Plastic (GRP) liner and original concrete materials.
This report highlights the ability of remote access GPR for the purpose of identifying and analysing the subsurface condition of post remedial works within the A Sewer Main.
Murphy Geospatial (MGS) specialises in pipe and tunnel services, by means of mechanical and technological knowledge, can provide remote access to otherwise unsafe spaces.
This drastically reduces the risks and hazards in comparison to human entry, as well as associated costs.
Previous surveys carried out by Murphy Geospatial have utilised a remote pipe inspection vehicle (PIV), fitted with a ground-penetrating radar (GPR) antenna. An Utsi GV3 GPR system, using a 4GHz antenna, was used to collect the data monitored by a CCTV system. A robotic arm attached to the crawler allowed for the remote positioning of the GPR against the surface at the correct locations.
Data processing, analysis, and reporting of the survey and GPR data has been carried out by Murphy Geospatial’s Specialist Engineering Department, who specialise in providing repeatable, reliable information to inform owners of the condition of their assets.
For previous surveys, the GPR data has been processed and analysed using dedicated software (Geolitix); applying several filters and processes to the raw data allowing for different combinations of the interpretation.
From the analysis of the remote access GPR results, several features were found. These features have been previously highlighted, detailed, and reported.
The GPR data presented below highlighted notable reflections indicative of voids.
The subsequent intrusive survey results verified the ability of the GPR to determine the presence of voiding and give credence to the survey method.
GPR results post-remedial works:
The Figure below has been taken from shaft 17-18 post remedial works. The scan was taken along the length of the pipe at 90degrees.
From analysing the data, much of the scan shows relatively ‘clean’ data (i.e. no significant variations or features). Within the grout layer, the GPR signal is of low amplitude with few features present in-between the joints. This is typical for homogeneous material such as concrete or grout.
Analysis of the data collected at 0 degrees, following the remedial works, the data contains significant noise, indicative of heterogeneous and/or voiding in the grout. In the Figure below, it is possible to see this higher amplitude response, addition to the presence of multiple features. These features are caused by a change in velocity in the GPR signal and are a result of the change in material. The data in the grout layer here is typical for a less homogeneous, more porous material. The change in grouting material can therefore be detected via remote access GPR.
It should also be noted that the previous void reflections are not present in the post-remedial GPR data. It is therefore possible to verify the repair and removal of voids that have been mapped.
The remote access GPR survey carried out on the A Sewer Main was successful and subsequently verified through intrusive works, enabling the client to know the repairs have been completed as required.
From the results presented above, it is clear that GPR can be used to accurately identify the presence of voids within the shafts as well as other defects. Additionally, the same method can be used to verify the extent and quality of repairs, the coverage of repair grout, and confirm that voids have been filled.
For more information on this project, please contact Andy Kitson at firstname.lastname@example.org or +44 203 598 3775