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.

The shield construction is a mature tunnel construction technology. Grouting behind segment wall synchronously during shield construction is an important measure to control stratum deformation, reduce ground settlement and prevent tunnel water seepage. The quality of grouting can significantly affect the quality of tunnel construction. The method of grouting quality judgment in early tunnel construction is inefficient and uncertain. To ensure the safety of tunnel structure, it is an urgent technical innovation to study the non-destructive testing technology for grouting effect of shield segment wall. Nowadays, the general Non-destructive testing methods include ground penetrating radar detection and seismic wave detection. These two methods can meet most of the needs of grouting defect detection behind the wall, but also have their own advantages and disadvantages. Therefore, this study proposes the combination of ground penetrating radar and seismic wave method of shield tunnel wall after grouting defects Non-destructive detection method, first, ground penetrating radar is used for scanning probe shield wall after grouting, and then according to the seismic wave method is used to further verify the results for some suspected injury, while ensure the detection efficiency to improve recognition accuracy. Finally, the defect detection and verification of the proposed method was carried out based on the shield segment model test platform, and this proposed method was successfully applied to the actual project of a metro line in Foshan.

Erecting underground structures in regions with unidentified weak layers, cavities, and faults is highly dangerous and potentially disastrous. An efficient and accurate near-surface exploration method is thus of great significance for guiding construction. In near-surface detection, imaging methods suffer from artifacts that the complex structure caused and a lack of efficiency. In order to realize a rapid, accurate, robust near-surface seismic imaging, a minimum variance spatial smoothing (MVSS) beamforming method is proposed for the seismic detection and imaging of underground geological structures under a homogeneous assumption. Algorithms such as minimum variance (MV) and spatial smoothing (SS), the coherence factor (CF) matrix, and the diagonal loading (DL) methods were used to improve imaging quality. Furthermore, it was found that a signal advance correction helped improve the focusing effect in near-surface situations. The feasibility and imaging quality of MVSS beamforming are verified in cave models, layer models, and cave-layer models by numerical simulations, confirming that the MVSS beamforming method can be adapted for seismic imaging. The performance of MVSS beamforming is evaluated in the comparison with Kirchhoff migration, the DAS beamforming method, and reverse time migration. MVSS beamforming has a high computational efficiency and a higher imaging resolution. MVSS beamforming also significantly suppresses the unnecessary components in seismic signals such as S-waves, surface waves, and white noise. Moreover, compared with basic delay and sum (DAS) beamforming, MVSS beamforming has a higher vertical resolution and adaptively suppresses interferences. The results show that the MVSS beamforming imaging method might be helpful for detecting near-surface underground structures and for guiding engineering construction.

At present, “The Belt and Road” initiative has risen from the China initiative to an international consensus and has become a popular international public product and a high-profle international cooperation platform. As the soul of the “Belt and Road”, culture’s leading advantages can promote the all-round and multi-feld exchanges and cooperation between China and various countries along “The Belt and Road”. As an important carrier for spreading Chinese culture, domestic flms play an important role in further expanding the international communication practice of Chinese cultural influence. This paper takes the flm “Xuan Zang” as an example, explores the new international communication practices of domestic flms under the framework of “The Belt and Road”, sums up the new path of domestic flm international communication, and looks forward to the new opportunities and bright prospects of cooperation in the feld of flm and television art under the framework of “The Belt and Road”.