Quality Evaluation for Synchronous Grouting of Shield Tunnels Based on the GPR Detection

With the accelerated development of China’s intensive urbanization in recent years, the number of shield tunnels is increasing quickly. To study the influence of different grouting conditions on ground settlement and construction safety, this paper takes the Jiangyin-Jingjiang Yangtze River shield tunnel as the engineering background, the Loaded-to-Frame (LTF) system with ground penetrating radar (GPR) was used to carry out nondestructive testing of the synchronous grouting in tunnelling, and the grouting thickness of the first 320 rings of the tunnel was statistically analyzed to evaluate the grouting quality. Finally, the monitoring points for ground settlement were set in key areas to help to evaluate the grouting quality. The research showed that: the promising effect of synchronous grouting optimization based on GPR detection, in which 56.3% of the monitoring lines with a mean thickness of more than 35 cm and 97.8% of the monitoring lines with a mean thickness of more than 33 cm. Except for a few measuring points, the settlement value in the main monitoring area does not exceed 40 mm and the surface buildings had been well protected until the tunnelling finished. The proposed method can provide valuable guidance for the construction safety of shield tunnels in the water-rich stratum.