Recent Advances in the GPR Detection of Grouting Defects behind Shield Tunnel Segments

Abstract

Injecting grout into the gaps between tunnel shield segments and surrounding rocks can reduce ground subsidence and prevent ground water penetration. However, insufficient grouting and grouting defects may cause serious geological disasters. Ground penetrating radar (GPR) is widely used as a nondestructive testing (NDT) method to evaluate grouting quality and determine the existence of defects. This paper provides an overview of GPR applications for grouting defect detection behind tunnel shield segments. State-of-the-art methodologies, field cases, experimental tests and signal processing methods are discussed. The reported field cases and model test results show that GPR can detect grouting defects behind shield tunnel segments by identifying reflected waves. However, some subsequent problems still exist, including the interference of steel bars and small differences in the dielectric constants among media. Recent studies have focused on enhancing the signal-to-noise ratio and imaging methods. Advanced GPR signal processing methods, including full waveform inversion and machine learning methods, are promising for detecting imaging defects. Additionally, we conduct a preliminary experiment to investigate environmental noise, antenna configuration and coupling condition influences. Some promising topics, including multichannel configuration, rapid evaluation methods, elastic wave method scanning equipment for evaluating grout quality and comprehensive NDT methods, are recommended for future studies.

Detection of Sub-surface Delamination and Moisture Penetration in Unlined Rock Tunnels Using Passive Thermography and Tapping

“…However, hidden damage and structural-condition detection cannot be achieved using these methods. GPR detection of grouting defects behind shield tunnel segments was studied for tunnels constructed in soft soil, such as saturated soft clay, silty soft soil, saturated sandy silt and silty sand (Peng et al, 2021). GPR was also employed to identify areas of delaminated and deteriorated concrete, voids behind the liner and areas of high moisture concentration within and behind the liner (Nako, 2018).…”

Application of Impact Elastic Wave Method in Quality Inspection of Concrete Lining

“…Due to its advantages of non-damage, fast and simple, the detection results are universal, and it is widely used in concrete quality testing at present [3,4]. The GPR method has a good effect in grouting defect detection after shield tunnel segment [5], but the interpretation of radar image results is more dependent on professional technicians. The impact elastic wave method uses elastic wave to carry a large amount of defect information in the propagation process and is not affected by other interference factors.…”

MV-GPRNet: Multi-View Subsurface Defect Detection Network for Airport Runway Inspection Based on GPR

“…Therefore, it is necessary to develop automatic subsurface object detection methods for GPR data analysis. In recent years, several studies have been conducted on the automatic detection of subsurface defects with GPR via traditional machine learning techniques [6,7], and deep learning methods [8,9]. However, all of the proposed algorithms for detection are mostly based on B-scan images only and primarily designed to detect subsurface regular targets with hyperbolic properties [10,11].…”