Use of resistivity tomography in underground excavation and tunneling Hideo KOMINE Central Research Institute of Electric Power Industry, Japan Panelist Presentation by Komine, 11 th Asian Regional Conference on ISSMGE, Seoul in 1999

Chemical grouting 4 Chemical grouting is widely used as an auxiliary method when underground structures such as shield tunnels are constructed in large cities. 4 The main purposes are to reinforce the ground and to reduce the ground permeability.

Use of chemical grouting

Weak point 4 It is difficult to evaluate the improved region. In chemical grouting, a method to evaluate the region improved by the grouting has not yet been established. 4 This weak point has been a major obstacle to the enhancement of reliability of chemical grouting.

Electrical resistivity 4 The electrical resistivity of chemical grout is much lower than that of the ground and ground water. 4 The resistivity tomography can measure the resistivity distributions of ground before and after chemical grouting in the field.

Advantage of resistivity Resistivity Grout << Ground, Ground water (0.6)(50-300)(20-80) (): Rough value of resistivity, Unit : m The resistivity of grout material is one tenth and/or one hundredth of ground and ground water. It is easy to watch the grouted region by electrical eyes

Resistivity tomography Apparent resistivities corresponding the electrodes arrangement. FEM analysis

Resistivity of grouted sand Test apparatus with copper electrodes There is a close connection between Grout/Void ratio and resistivity. Grout/Void ratio is the volume ratio of grout occupying the void space of ground. It is a representative characteristic of the quality of grouted soils.

Resistivity model 4 We proposed the resistivity model of ground before and after chemical grouting on the basis of laboratory test results. 4 We investigated the validity of the evaluation proposed. In Komine (1992, 1997)

Validity of resistivity model 4 The evaluation of Grout/Void ratio, which is the representative characteristics of the quality of grouted ground, by electrical resistivity was proposed on the basis of the electrical resistivity models of ground before and after chemical grouting. 4 The validity of the evaluation was demonstrated by the comparison of the evaluation results with the laboratory test results.

In Komine & Nishi (10ARC, 1995) We proposed the evaluation of chemical grouted region using the resistivity model proposed and resistivity tomography. Evaluation using resistivity model and resistivity tomography

Apparatus in the laboratory

Example 1 of evaluation

Example 2 of evaluation

Resistivity contrast of grout and ground water

Applicability In Komine & Nishi (IS-Tokyo96, 1996)

Resistivity of commonly used grouts The resistivity ratio between grout and ground water is generally less than 1/10. Therefore, the evaluation method of improved region by resistivity tomography is available in most cases except near the sea.

Verification by field test In Komine (11ARC, 1999)

Evaluation by resistivity model In this site, the region of resistivity ratio, which is less than 0.1, can evaluate the improved region.

How to measure in the field

Results

Another site (Takenaka Corp.) This site is gravel ground. Average diameter is 40-50mm Site condition

Results Distance (m) Depth (m) By Uchida et al. (1998, Proceedings of the symposium on underground space Vol.4, JSCE)

Conclusions 4 We proposed the evaluation of chemical grouted region using the resistivity model proposed by author and the resistivity tomography. 4 We investigated the validity and the applicability of this method by laboratory tests. From the laboratory test results, improved regions evaluated by the proposed method almost agreed with the solidified regions. If the resistivity ratio between grout and ground water is less than 1/10, we can confirm the improved region by this evaluation. 4 We verified this evaluation by field test. From the field test results, we confirmed the availability of the evaluation method in practical fields.

References (in English) 4 Komine, H Estimation of chemical grout void filling by electrical resistivity. Grouting, Soil Improvement and Geosynthetics Proceedings, ASCE. New Orleans: Komine, H. and Nishi, K Evaluation of grouted region by resistivity changes. Proceedings of the 10th Asian Regional Conference on Soil Mechanics and Foundation Engineering, Vol. 1: Komine, H. and Nishi, K Applicability limit of resistivity to evaluate improved region. Proceedings of IS-Tokyo 96 (Grouting and Deep Mixing), Vol. 1: Komine, H Evaluation of chemical grouted soil by electrical resistivity. Ground Improvement, Vol. 1: