Resistivity and IP Tomography to determine Overburden-Bedrock Interface: A case study of Ilam Embankment dam

Document Type : Research Article

Authors

1 M.Sc. Student, Department of Earth Physics, Institute of Geophysics, University of Tehran, Tehran, Iran

2 Assistant Professor, Department of Earth Physics, Institute of Geophysics, University of Tehran, Tehran, Iran

3 Professor, Department of Earth Physics, Institute of Geophysics, University of Tehran, Tehran, Iran

Abstract

Determination of the overburden-bedrock interface with fine-grained sediments in a high-fold sedimentary environment is a challenging geophysical issue. Electrical Resistivity Tomography (ERT) is considered one of the most effective geophysical approaches for mapping subsurface layers based on the conductivity distribution of materials. The surveys are often performed in two dimensions to investigate lateral and depth variations of resistivity and chargeability values of subsurface layers. The resistivity method, influenced by the volumetric properties of empty spaces, is defined by the ability to transfer charge in subsurface medium, but the induced polarization method depends upon the geometric properties of the pore spaces (grain surface size). Despite the advantages of geo-electrical methods in imaging subsurface structures, due to the high dependency of resistivity and induced polarization parameters on the physical and hydrogeological conditions of the layers, it is not possible to fully match the geological and geo-electrical sections.
One of the applications of geophysical studies is to determine the contact zone between overburden and bedrock in engineering structures such as embankment dams. In cases where the conductivity contrast between the overburden and the bedrock is low, the exact determination of this boundary with the help of geo-electrical methods confronts high uncertainty. In this study, the efficiency of electrical resistivity tomography and induced polarization is investigated by measuring several parallel profiles with the aim of imaging the boundary between overburden and bedrock and determining the possibility of a water escape zone at the left bank of the Ilam embankment dam. According to the results obtained from the inversion of the field measurements, rechargeable sections would be ascribed to the shale region as well as marl limestone containing pyrite particles.
The main objectives of this study include determining the general condition of the overburden concerning the bedrock, geometric imaging of the bedrock, and identification of parts of the bedrock eroded over time. The significant challenge of this geophysical study is the low conductivity contrast between clay and silt overburden and limestone bedrock interbedded with shale and marl. Due to the size of the study area, the studies were performed based on tomographic measurements of electrical resistivity and induced polarization. The field surveys were conducted using four almost parallel profiles (according to the topographic conditions of the area) and with relatively different lengths and through a Pole-Dipole array in forward and reverse measurements.
Geological data as well as borehole information are used to validate the geo-electrical sections to better interpret the models obtained from the collected data (i.e., geo-electrical measurements). Finally, due to the high topography of the area and to better show the trend of subsurface structures using two-dimensional models obtained from electrical resistivity tomography and induced polarization as well as drilled boreholes, a three-dimensional view of sections and boreholes has been prepared. Based on the models obtained from the geo-electrical data, it can be concluded that geophysical studies (electrical tomography) have been able to successfully determine the eroded region of the bedrock surface as well as the bedrock-overburden contact which correlates well with boreholes drilled in the area.

Keywords

Main Subjects


گزارش بررسی نشت و پایداری شیب تکیه­گاه چپ سد شهدای ایلام، شرکت سهامی آب منطقه ای ایلام، 1396.
Amaya, G. A., Dahlin, T., Barmen, G. and Rosberg, J. E., 2016, Electrical Resistivity Tomography and Induced Polarization for Mapping the Subsurface of Alluvial Fans: A Case Study in Punata (Bolivia). Geosciences, 6(4), 51.
Arjwech, R., Sriwangpon, P., Somchat, K., Pondthai, P. and Everett, M., 2020, Electrical resistivity tomography (ERT) data for clay mineral mapping, Elsevier. Amsterdam.
Benes, V., Tesař, M. and Boukalová, Z., 2011, Repeated geophysical measurements of the basic principle of the GMS methodology used to inspect the condition of flood control dikes. River Basin Management, California, USA.
Chambers, J. E. and Wilkinson, P. B., 2012, Bedrock detection beneath river terrace deposits using three-dimensional electrical resistivity tomography, Geomorphology, 177–178, 17–25.
Chavez, R., Tejero, A., Cifuentes, G., Hernandez, E. and Aguilar, D. A., 2015, Imaging fractures beneath a residential complex using novel 3-D electrical resistivity arrays. Environmental and Engineering Geophysics 20(3), 219–233.
Cheng, P. H., 2000, Imaging the subsurface structure of the northern tip of the 1999 Chi-Chi earthquake fault in central Taiwan using the electric resistivity method. Terrestrial, Atmospheric and Oceanic Sciences. 11, 721–734.
Cheng, P. H., Ger, Y. I. and Lee, S. L., 2008, An electric resistivity study of the Chelungpu fault in the Taichung area, Taiwan. Terrestrial, Atmospheric and Oceanic Sciences. 19, 241–255.
Crook, N., Binley, A., Knight, R., Robinson, D. A., Zarnetske, J. and Haggerty, R., 2008, Electrical resistivity imaging of the architecture of substream sediments. Water Resources Research, 44, 13.
Ding, H., and Weiwei, J., 2016, Application of Geophysical Methods in Tunnel Exploration. Proceedings of the 5th International Conference on Civil, Architectural and Hydraulic Engineering (ICCAHE), 188–192.
Fiandaca, G., Auken, E., Christiansen, A. V. and Gazoty, A., 2012, Time-domain-induced polarization: Full-decay forward modeling and 1D laterally constrained inversion of Cole-Cole parameters, Geophysics, 77, E213-E225.
Hauck, C., Muhll, D. V. and Maurer, H., 2003, Using DC resistivity tomography to detect and characterize mountain permafrost. Geophysical Prospecting, 51(4), 273–284.
Hunter, J. A., Pullan, S. E., Burns, R. A., Gagne, R. M. and Good,R. S., 1984, Shallow seismic reflection mapping of the overburden–bedrock interface with the engineering seismograph some simple techniques. Geophysics, 49, 1381-1385.
Ikard, S. J., Revil, A., Schmutz, M., Karaoulis, M., Jardani, A. and Mooney, M., 2014, Characterization of focused seepage through an earthfill dam using geoelectrical methods. Groundwater, 52(6), 952–965.
Ikard, S. J., Revil, A., Jardani. A., Woodruff, W. F., Parekh, M. and Mooney, M., 2012, Saline pulse test monitoring with the self-potential method to non-intrusively determine the velocity of the pore water in leaking areas of earth dams and embankments. Water Resources Research, 48, 1–17.
Jones, G., Sentenac, P. and Zielinski, M., 2014, Fissure detection using 2-D and 3-D electrical resistivity tomography on a flood embankment. Journal of Applied Geophysics, 106,196–211.
Loke, M., 2007, Rapid 2-D Resistivity and IP inversion using the least-squares method, Geo-electrical Imaging 2D and 3D. Geotomo Software, Malaysia.
Li, S. C., Liu, B., Xu, X., Nie, L., Liu, Z., Song, J., Sun, H., Chen, L. and Fan, K.,, 2017, An overview of ahead geological prospecting in tunneling. Tunneling and Underground Space Technology. 63, 69–94.
Liu, P., Wang, K. and Wang, Q., 2021, Data acquisition method and the effectiveness of multichannel analysis of surface waves for defect detections on small earthen dams. Arabian Journal of Geosciences, 14, 631.
Lin, C. P., Hung, Y. C., Wu, P. L. and Yu, Z. H., 2014, Performance of 2-D ERT in investigation of abnormal seepage: a case study at the Hsin-Shan earth dam in Taiwan. Environmental and Engineering Geophysics 19(2), 101–112.
Loke, M. H., Chambers, J. E., Rucker, D. F., Kuras, O. and Wilkinson, P. B., 2013, Recent developments in direct current geo-electrical imaging method, Journal of Applied Geophysics, 95, 135-156.
Maurya, P. K., Fiandaca, G., Christiansen, A. V. and Auken, E., 2018, Field-scale comparison of frequency-and time-domain spectral induced polarization, Geophysical Journal International, 24(2), 1441-1466.
Milson, J., 2003, Field Geophysics, the Geological Field Guide Series, John Wiley & Sons.
Oldenburg, D. W. and Li, Y., 1994, Inversion of induced polarization data, Geophysics 59, 9, 1327-1341.
Planès, T., Mooney, M. A., Rittgers, J. B. R., Parekh, M. L. and Snieder, R., 2016, Time-lapse monitoring of internal erosion in earthen dams and levees using ambient seismic noise. Géotechnique, 66(4), 301–312.
Perri, M. T., Boaga, J., Bersan, S., Cassiani, G., Cola, S., Deiana, R., Simonini, P., Patti, S. and 2014, River embankment characterization: the joint use of geophysical and geotechnical techniques. Journal of Applied Geophysics, 110, 5–22.
Raji, W. O. and Adedoyin, D. O., 2019, Dam Safety Assessment Using 2D Electrical Resistivity Geophysical Survey and Geological Mapping, Journal of King Saud University, 32(1), 1123-1129.
Reynolds, J. M., 2011, An introduction to applied and environmental geophysics. John Wiley & Sons Ltd.
Seigel, H. O., 1959, Mathematical formulation and type curves for induced polarization, Geophysics 24, 3, 547-565, DOI: 10.1190/1.1438625.
Sentenac, P., Benes, V., Budinski, V., Keenan, H. and Baron, R., 2017, Post flooding damage assessment of a historical pond and earth dam by non-invasive geophysical techniques. Journal of Applied Geophysics, 146, 138–148.
Sentenac, P., Jones, G., Zielinski, M. and Tarantino, A., 2013, An approach for the geophysical assessment of fissuring of estuary and river flood embankments: validation against two case studies in England and Scotland. Environmental Earth Sciences, 69(6), 1939–1949.
Sumner, J. S., 1976, Principles of Induced Polarization for Geophysical Exploration, Elsevier, Amsterdam.
Yang, C. H., You, J.I. and Lin, C. P., 2002, Delineating Lake Bottom structure by resistivity image profiling on water surface, Terrestrial Atmospheric and Oceanic Sciences,13(1), 39-52.
Yuval, and Oldenburg, D. W., 1997, Computation of Cole-Cole parameters from IP data, Geophysics, 62, 436-448.