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1 |
A modified series-parallel electrical resistivity model of saturated sand/clay mixture
A modified series-parallel electrical resistivity model of saturated sand/clay mixture-2021 Electrical resistivity tomography, ERT, is a geophysical method that is used to image subsurface geomaterials for
various geological, environmental and geotechnical engineering problems. The success of ERT depends on the
availability of a robust electrical resistivity model of soils that is able to characterise the different type of soils
using its electrical resistivity measurements. The aim of this paper is to present an electrical resistivity/conductivity model for isotropic saturated sand/clay mixture that considers the effects of sand content, and surface
conduction of clay content. The proposed model is formulated using a modified series-parallel mixing model
theory which uses phase-volumetric and surface conduction model parameters. The phase-volumetric parmeters
describe the configuration of the different soil/water phases in a representative soil unit cell which includes solid
soil particles, free water, diffuse double layer (DDL) water. The surface conduction model parameters are used to
describe the volume fraction of DDL water in the unit cell, and its electrical conductivity compared to the
electrical conductivity of free water. Simple test methods are used in this study to determine the proposed model
parameters. Laboratory experimental programme was also conducted in this study to validate the proposed
model. Two types of clays, namely, kaolin and bentonite, and one type of clean sand were used to constitute five
different sand/clay and clay/clay mixtures. Dynamic compaction method using Standard Proctor tools was used
to constitute the testing samples. The electrical conductivities of different reconstituted soil samples were
measured and compared with the proposed model predictions, and a good agreement was achieved. The small
differences between the model predictions and the experimental measurements could be attributed to the slight
deviation of the laboratory test samples from the model assumptions, which require the soil sample to fulfil fully
saturated and electrical isotropy conditions.
Keywords: Electrical conductivity | Saturated soils | Surface conduction | Series-parallel | Clay | Sand |
مقاله انگلیسی |
2 |
Methods for field measurement of electrical parameters of soil as functions of frequency
روشهای اندازهگیری میدانی پارامترهای الکتریکی خاک به عنوان توابع فرکانس-2021 In this article, the application of four-electrode and two-electrode arrays to measure electrical parameters of soil
as functions of frequency is investigated and its feasibility is evaluated by simulations and measurements. First,
the experimental arrays are simulated using finite element method to solve a rigorous electromagnetic problem.
New geometric factors are presented, which yield correct estimates of resistivity and permittivity even for
reduced spacing. Formulas are proposed for calculating the geometric factors. Then, a series of case studies is
carried out considering different soil representations, geometric parameters and excitation frequencies. It was
found that increasing excitation frequency and distance between electrodes decreases accuracy. However, resistivity and permittivity of soil can be determined for frequencies up to 2 MHz when using reduced spacing. For
the four-electrode array, a discrepancy of less than 3% between estimate and reference is obtained when using
distance between electrodes less than 0.5 m. Next, measurements using four and two electrode methods were
performed, and it was found that the four-electrode method is the most suitable for measuring soil parameters,
given that it was the one that provided consistent results. An analytical equation was also proposed to represent
the electrical parameters measured for this case.
Keywords: Grounding | Permittivity | Resistivity measurement | Soil electrical parameters |
مقاله انگلیسی |