Evaluating the joint use of GPR and ERT on mapping shallow subsurface features of karst critical zone in southwest China

Abstract

The soils and underlying weathered carbonate rock in karstic regions play an important role in the infiltration, storage, and retention of water and nutrients. Because of significant heterogeneity of the karst, the use of individual geophysical techniques is often not sufficient for unambiguous assessment of the irregular distributions of soils and underlying fractures. In this study, ground penetrating radar (GPR) and electrical resistivity tomography (ERT) are jointly used with additional observations to delineate the shallow subsurface structure in two exposed profiles. The results show that ERT is effective for detecting the soil-rock interfaces, even for irregular terrain and fracture structures, such as a funnel-shaped doline, as the soils and rocks show a large resistivity contrast. Although ERT may be able to sense the presence of extensive fracturing, it cannot detect individual small aperture fractures. Joint use of different frequencies of the GPR antenna (e.g., 100 and 500 MHz in this study) allowed the detection of most fractures at different depths in the study sites. However, forward modeling of typical weathered rock features illustrates that the GPR data cannot resolve any reflection signals of the vertical fractures, so the features of vertically enlarged fractures filled by soils cannot be seen from the GPR images.Moreover, large uncertainties of resistivity at the interface between soils or fractures and bedrock limit the identification of an irregularly distributed subsurface structure. Despite the limitations of individual techniques, the combination of ERT and GPR enhances the delineation of the soil-bedrock interface and identification of the fracture network, which can allow an enhanced geological interpretation of shallow subsurface features in the karst areas. INTRODUCTIONKarst is an important landscape, which covers about 15% of the world's land area or about 2.2 million km 2 (Yuan & Cai, 1988). Twenty-five percent of the global population fully

Combined ERT and GPR Data for Subsurface Characterization of Weathered Hilly Slope: A Case Study in Zhejiang Province, Southeast China

“…The Atterberg limits and particle size distribution of the soil samples were determined following the Chinese National Standards (CNS) GB/T50123-2019 [47] (pp. [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. The bulk mineralogy and clay mineralogy of the rock samples were measured using an X-ray diffractometer following the methods described by Moore and Reynolds [48] (p. 378).…”

“…Given the non-uniqueness of dataset interpretation, and the drawbacks of individual techniques in resolution and penetration depth, GPR and ERT have been jointly used for the investigation of subsurface features thanks to their complementarity [35][36][37][38][39][40][41][42][43]. Jongmans and Garambois [28] concluded that almost all the advantages of the geophysical method corresponded well to the disadvantages of the conventional geotechnical techniques.…”

Evaluation of a Ground Subsidence Zone in an Urban Area Using Geophysical Methods

“…International scientific literature has reported many geophysical applications to areas at risk of subsidence [ 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ].…”

“…This technique discriminates between developing sinkholes and mature sinkholes comprising resistive air-filled cavities. Reference [ 8 ] used ERT and GPR methods to map subsoil in karstic areas. They concluded that ERT is effective for detecting soil–rock interfaces and even irregular terrain and fracture structures, such as funnel-shaped dolines.…”

Imaging of karst cave using ground penetrating radar and electrical resistivity tomography: a case study in Shandong, China

“…The depth of GPR also has certain limitations. In recent years, many case studies of GPR combined with the resistivity method have been reported, and the combination of the two methods and technologies has been proved to be an effective means for imaging and characterization of underground karst [5,6,7,8]. In this paper, GPR and ERT surveys are carried out simultaneously in the research area.…”