- journal_title：Geophysics
- Contributor：Etienne Rey ; Denis Jongmans
- Publisher：Society of Exploration Geophysicists
- Date：2007-
- Format：text/html
- Language：en
- Identifier：10.1190/1.2399453
- journal_abbrev：Geophysics
- issn：0016-8033
- volume：72
- issue：1
- firstpage：F9
- section：ELECTRICAL AND ELECTROMAGNETIC METHODS
Surficial heterogeneous soils such as till, alluvial fans, or slope deposits are difficult to characterize by geotechnical tests because of the presence of decimeter- to meter-sized pebbles or rocks. The effective resistivity of such two-component media composed of a percentage of resistive particles embedded in a conductive matrix is given by the Bussian's equation. The application of this equation allows the concentration of resistive particles to be determined if the resistivity values of each component and of the mixture, as well as the cementation exponent m, are known. However, previous theoretical and experimental studies have shown that the effective resistivity is affected by the shape of the particles. The objective of this study is to numerically determine the 2D effects of particle shape and orientation on the resistivity. Two configurations have been considered in the finite element (FE) modeling: laboratory-like measurements and field layout. For circular particles, the numerical results fit the Bussian's equation with an exponent m of 2. Aligned elongated particles induce an anisotropy which can raise or diminish the exponent m, depending on the particle orientation and the tortuosity of the current paths. Field experiment simulations showed that m varies between 2.5 and 3.1 for an aspect ratio of 5 and that anisotropy resulting from the particle shape has little effect (m close to 2) when this ratio is lower than 2.5. This increase of m with the aspect ratio is in agreement with both theoretical models and experimental studies. For laboratory measurement simulations, m values vary between 1.3 and 4 for a particle aspect ratio of 5, whatever the resistivity contrast between the particles and the matrix. The difference in results between the two configurations is explained by the paradox of anisotropy.