Underground utility inspection using ground penetrating radar

Underground utility refers to any below-ground line, installation, or structure used by a service or utility provider. Underground utility inspection is a process of examining the designated area that needs to be inspected in detail. The purpose of the inspection is to ensure that the underground utility is in good condition and to check for any faults. By using the ground penetrating radar (GPR), the technology can capture images below the surface of the ground using radio waves. The various data through previous references are used to discuss and analyse the capability of GPR for underground utility inspection to ensure its gives the best performance for the inspection. GPR technology has become an essential tool for locating buried utilities and preventing damage and accidents during construction projects. This paper explores various advancements in GPR technology, including data processing methods and scanning techniques, to improve the accuracy and effectiveness of underground utility mapping. The research presented in this paper highlights the abilities of GPR to inspect underground utilities. The GPR data used in this project was collected from the evaluation and verification facility (EVF) in the Malaysia Nuclear Agency. The accuracy of these predicted positions was validated from GPR data and compared with as-built drawings from the contractor. The alternative analysis approaches that could be applied to improve the GPR accuracy when the optimum conditions are not met are also discussed.


Introduction
Urban planning, building, and public safety all heavily depend on the underground utility inspection method.Its significance cannot be emphasized since it helps prevent accidents, reduce construction delays, and decrease service disturbance.Safety is of the highest priority, both for construction employees and for the general public.By spotting potential hazards like gas leaks, live electrical lines, and unstable ground conditions, underground utility inspection helps lower the chance of mishaps, injuries, and fatalities [1].Accurate information of underground utilities is essential for excavation, and the proposed method using ground penetrating radar (GPR) sets a new benchmark for precise location with high accuracy [1].Underground utility inspection helps detect and map existing beneath the surface utilities, such as water pipes, gas lines, sewage systems, and communications cables, before any construction or excavation work is started.This helps avoid unforeseen damage to these important infrastructure parts, which may be expensive to fix and cause disruptions to crucial services.Accurately locating subsurface lines before construction can help avoid expensive delays and IOP Publishing doi:10.1088/1757-899X/1308/1/012021 2 unexpected expenses.Through careful inspection, accidental damage to utility wires can be prevented, preventing project delays, emergency repairs, and fines.
It is necessary to define GPR before digging into its history.To identify structures and changes in material characteristics within lossy dielectric materials, GPR employs electromagnetic fields to probe the materials [2].Measurements of reflection and transmission are used, as shown in Figure 1.Up until now, natural geologic materials have seen most applications, but man-made composites like concrete, asphalt, and other building materials are also widely used where electromagnetic fields can exist in such lossy dielectric materials.A certain depth will be reached by fields before they are absorbed.The electromagnetic fields that are used in GPR spread as essentially nondispersive waves [3].Events comparable to this occur as the signal is transmitted through the material, is dispersed, or is reflected by changes in impedance.to the signal being sent.To put it another way, signal detection is easy because a GPR antenna has two parts, a transmitter, and a receiver [4].The transmitter antenna will generate an electromagnetic pulse that transmits below the ground.While the receiver will pick up the bock scatter and reflected waves that encounter a discontinuity in the dielectric properties (e.g.pipe, cable, sinkhole) [5].The remaining electromagnetic waves keep going and continue to deepen the subsurface levels.The proposed antenna can be used for the detection of artifacts in the deeper ground known as ground-penetrating radar applications [6].
Figure 1.Ground penetrating radar uses radio waves to probe the subsurface of lossy dielectric materials.Two modes of measurement are common.In the first, detection of reflected or scattered energy is used.In the second signal, variation after transmission through the material is used to probe a structure [1].
The objective of this study is to examine the potential of GPR to inspect underground utilities.The GPR data utilized in this investigation was obtained from the Evaluation and Verification Facility (EVF) of the Malaysia Nuclear Agency.The accuracy of the predicted positions was verified using GPR data and compared with as-built drawings provided by the contractor.The experiment aimed to detect a mild steel pipe buried at a specific depth at the EVF facility.Although various underground facilities, such as fiber optic cables, electrical lines, water pipes, and culverts, are buried at this site, this experiment focused solely on detecting mild steel pipes.

Experimental work
This experiment was held at the evaluation and verification facility (EVF) in Malaysia Nuclear Agency.The scanning area was divided into two parts which consisted of 1 st phase and 2 nd phase (Figure 2).The dimensions of the scanning area were 13 m × 6 m with 22 lines profile for vertical scan and 9 lines profile for horizontal scan for the 1 st phase scanning area.For the second phase scanning area was 5.9 m × 14 m with 9 profiles for the vertical scan and 18 profiles for the horizontal scan (Figure 3 -5).The GPR used was a GSSI 400MHz shielded antenna.Data was collected using 3 SIR 4000 and then processed using RADAN 7 software (Figure 6).For comparison, the contractor's as-built drawing has been used for validation purposes.The depth of mild steel pipe has been used as a reference depth (1.15 m).During the investigation, the experiment was divided into two parts, referred to as Experiment 1 and Experiment 2. The main distinction between these experiments was the size of the scanning area.In experiment 1, radargrams were obtained for the initial stage, while in Experiment 2, radargrams were gathered for the subsequent stage.After completing the scans for each phase, the acquired data was transferred to a computer and merged into a three-dimensional model for each phase.

Results and discussion
The data was obtained from radargram by using SIR4000 and then was processed by Radan 7 software.31 radargram was obtained for experiment 1 and 27 radargram was obtained for experiment 2. From the radargram, the average depth was obtained for mild steel pipe.The average depth from the radargram is 1.075 m with a tolerance of ±0.095 m.Compared with the reference depth of 1.15 m, we get the accuracy using GPR is 1.10/1.15x 100% = 95.65%.For comparison, the 3D file from Radan 7 software shows the pattern of mild steel pipe below the ground (Figure 7-8).According to the radargram depicted in Figure 9 and Figure 10, GPR can directly capture images beneath the ground's surface.The radargram presented a depth of approximately 2 meters.Additionally, the distance at which the data is taken makes it easier for the user to identify the targeted area for marking and point reference.As a result, based on data processing, it can be concluded that GPR is a non-destructive, fast, and economical method for evaluating road structures [7].Through various data acquisition and processing techniques, studies have shown significant success in using GPR to gather information for verifying the state and condition of materials [8,9].This technology helps overcome the constraint of insufficient cavity samples for 3D radar detection on intelligent learning model training, reduces algorithm training costs, and improves identification accuracy [10,11].

Conclusion
The purpose of this study was to identify the location of underground utilities made of mild steel pipes using ground penetrating radar (GPR).By transferring the data obtained from GPR to RADAN 7 software, three-dimensional visualizations can be generated that can be viewed layer by layer for detection.This technology is highly effective in guiding inspectors on where to focus their attention and which areas beneath the ground should be avoided, as it provides a reliable and detailed view of the underground infrastructure.As the technology continue to evolve, it is expected that GPR will become even more sophisticated, leading to further advancements in underground utility inspection.

Figure 7 .
Figure 7. (a) The 3D view for 1 st phase scanning area (b) Contractor's as-built drawing for reference 1 st phase.

Figure 7 .
Figure 7. (a) The 3D view for 1 st phase scanning area (b) Contractor's as-built drawing for reference 1 st phase.

6 Figure 8 .
Figure 8.(a) The 3D view for 2 nd phase scanning area (b) Contractor's as-built drawing for reference 2 nd phase.