Monitoring of grout material injected under a reservoir using electrical and electromagnetic surveys*

Koichi Suzuki; Takahiro Oyama; Fumiharu Kawashima; Tomoyuki Tsukada; Akira Jyomori

doi:10.1071/EG09051

RESEARCH ARTICLE

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Monitoring of grout material injected under a reservoir using electrical and electromagnetic surveys^*

Koichi Suzuki ¹ ⁴ Takahiro Oyama ¹ Fumiharu Kawashima ² Tomoyuki Tsukada ² Akira Jyomori ³

+ Author Affiliations

- Author Affiliations

¹ Central Research Institute of Electric Power Industry, 1646 Abiko, Abiko-shi, Chiba 270-1194, Japan.

² Tokyo Electric Power Company, 1-1-3 Uchisaiwai-cyou, Chiyoda-ku, Tokyo-to 100-8560, Japan.

³ Neo-science, 2-7-1 Ayumino, Izumi-shi, Ohsaka-fu 594-1157, Japan.

⁴ Corresponding author. Email: k-suzuki@criepi.denken.or.jp

Exploration Geophysics 41(1) 69-79 https://doi.org/10.1071/EG09051
Submitted: 18 September 2009 Accepted: 4 December 2009 Published: 19 February 2010

Abstract

In order to reduce leakage from a reservoir, a large amount of cement milk (grout) was injected from boreholes drilled around the shores of the reservoir, and monitored to establish the infiltration of cement milk into the bedrock under the reservoir. From laboratory tests using rock core samples, it was revealed that the resistivity of cement milk is much lower than that of the groundwater at this location. Therefore, it was expected that the resistivity of the zones filled with cement milk would be significantly reduced. Geophysical surveys are expected to be suitable methods to check the effectiveness of grouting in improving the water-retaining performance of a reservoir. DC electrical surveys (seven in total) and two Controlled Source Audio-frequency Magneto-Telluric (CSAMT) surveys were conducted along survey lines in the reservoir to monitor the infiltration of cement milk during the grouting. Extremely low resistivity zones (10 Ωm or less) were observed in resistivity sections obtained by 2D inversion. The zones are inferred to be fractured zones filled with cement milk. In sections showing the rate of change of resistivity, three zones that showed significant change showed gradual expansion to deeper parts as the grouting progressed. These zones correspond to highly permeable zones detected by Lugeon tests at grout boreholes.

We have confirmed that it is possible to measure the resistivity change by DC electrical and CSAMT surveys from the surface of the reservoir. It seems that such monitoring results could be reflected in future grouting plans.

Key words: cement milk, CSAMT survey, DC electrical survey, grouting, monitoring.

Acknowledgments

The authors thank Dr Daiei Inoue and Dr Kaieda Hidesi of Central Research Institute of Electric Power Industry for profitable advice on the geological interpretation for the results of the geophysical exploration.

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^* ^*Part of this paper was presented at the 9th SEGJ International Symposium (2009).