Application of the small fixed-loop transient electromagnetic method in detecting grottoes seepage channel

Grotto statues are carved or painted in stone mountain grotto niches, vulnerable to various environmental changes. Seepage channels in grottoes are prevalent, leading to the destruction of cultural relics. Effective treatment should be carried out for these hazards to preserve the cultural relics of grottoes, and the most critical factor is identifying the location and form of the anomalies. The transient electromagnetic method (TEM) is sensitive to low-resistivity targets such as water and has a strong penetration ability to high-resistivity layers. The device configuration limits the traditional TEM, and it isn't easy to implement the detection on the grotto surface. Small fixed-loop TEM is suitable for limited space as a branch of transient electromagnetic detection technology. We deployed it into the grotto detection field. The method's feasibility for detecting seepage channels in grottoes was discussed through a series of numerical simulation analyses and model tests. The results showed this method can well-reflected various hazards' spatial location and spatial form in complex water-bearing structure models. The water-bearing structure detection of the statue of Sakyamuni's Nirvana showed that the method could determine the seepage channel under limited space, guiding the implementation of statue hazard management in the later stage.