Characteristics of Time-Lapse Full-Polarimetric GPR Signals from Seepage Zones of Micro-Fractures with Different Dip Angles

Abstract

Fluid infiltration into porous sandstone relics induces micro-fractures that serve as critical early damage indicators. However, detecting these incipient micro-fractures exceeds the resolution limits of conventional non-destructive testing techniques, thereby posing significant challenges for precise identification and risk assessment. Full-polarimetric ground penetrating radar (FP-GPR) facilitates high-resolution, non-destructive detection of micro-fractures by acquiring and analyzing multi-polarimetric data. This study proposes an FP-GPR method for fracture detection in cave temple relics, leveraging the volumetric effect of seepage within rock fractures. The method is applied to detect micro-fractures in the Beishan Rock Carvings, Chongqing, China. First, numerical models of sandstone containing fractures with varying dip angles were constructed. Hydrological simulations were then performed to obtain time-lapse fluid infiltration states. Subsequently, FP-GPR simulations were conducted on the resulting time-lapse dielectric models. Freeman and H-Alpha decompositions were then employed to quantitatively analyze the polarization responses under different infiltration durations and fracture dip angles. Finally, field measurements were conducted to validate the numerical simulations. The results reveal a high correlation between moisture variation and key polarimetric parameters including surface scattering power, double-bounce scattering power, and entropy. This study demonstrates the capability of FP-GPR for micro-fracture detection, offering valuable insights for the conservation of cave temple relics.