Ground penetrating radar detection of steel fiber reinforced composite linings in shield tunnels: Experimental and field studies

Steel fiber reinforced concrete-reinforced concrete (SFRC-RC) composite linings are popular in shield tunnel construction due to exceptional strength and waterproofing properties. Non-destructive testing methods are essential for assessing the quality of these linings and ensuring tunnel construction safety. This study investigates the potential and parameters of ground penetrating radar (GPR) detection for the composite linings, using the Deep Tunnel Sewerage System-Phase 2 project in Singapore as a case study. The gprMax simulations incorporated the random distribution and precise parameters of steel fibers to conduct preliminary frequency selection studies. The structural setup of the model experiments mirrored that of the actual tunnel, allowing for an analysis of GPR penetration capabilities at various frequencies. Field testing provided authentic GPR data, validating conclusions drawn from simulations and model experiments and examining GPR power attenuation patterns. Findings indicate that GPR is effective for the quality detection of composite linings. The optimal frequency for detecting SFRC-RC composite linings is 300 MHz, which resolves the interfaces of different layered media. Based on single-parameter exponential and power function fitting, empirical formulas for power attenuation quantitatively characterize GPR signal attenuation in SFRC-RC composite linings. This paper offers valuable references for GPR detection of SFRC-RC composite linings.