چكيده لاتين :
Introduction: Investigation of water passing through soil is one of the most important problems in soil
mechanics and environmental engineering. It is an important parameter for predicting the movement of water
and contaminants dissolved in the water through the soil and measured on soil samples in the lab and sometimes
tests carried out in the field. Soil permeability generally depends on two factors, the first one is soil
Specifications contains an empty space of soil, surface roughness of solid particles, saturation, and another one is
characteristics of the fluid (water) that passes through soil. Already few efforts have been made to recognize the
characteristics of anisotropy in the geotechnical designs therefore this study has been done. Physical and
mechanical properties of soils and sedimentary rocks are generally heterogeneous and hydraulic conductivity (k)
is not an exception. The anisotropy of hydraulic conductivity of soils has a great influence on the fluid flow and
the transmission of contamination. Knowing the hydraulic conductivity in cases such as flow through dams and
dikes, internal erosion in soil masses, settling of consolidated clay levels, optimal design of water and oil wells,
and the design of drainage systems for roads, airports and agricultural land. Generally, the hydraulic conductivity
is more in the horizontal direction than the hydraulic conductivity in the vertical direction, and the hydraulic
conductivity anisotropy is shown with a non-dimensional parameter rk which is equal to the ratio of the
horizontal hydraulic conductivity to the vertical hydraulic conductivity. According to Chapuis et al. (1989), on
more than 100 measurements of hydraulic conductivity along with the results of the experiments of Chapuis et
al. (1990), Rice et al. (1970) and Leroueil et al. (1990), the anisotropy of the hydraulic conductivity of clays,
sands and sedimentary rocks are almost like each other. The degree of anisotropy may depend on the shape of
the particles, their arrangement, or the orientation of the free space among the particles of the soil, which appears
to be less than 4. Due to the impossibility of preparing intact samples from grain materials, as well as the lack of
suitable measuring instruments for grain samples, there are few valid results for non-sticky materials. As
Chapuis et al. (1989) and Sferlazza et al. (2009) in accordance with most of the experimental results, the
anisotropy of hydraulic conductivity increases with density, and also the degree of anisotropy decreases with
increasing porosity ratio. Materials and Methods: In order to conduct the present research, measurement device was designed and
built. This device is a cube with 150 mm ×150 mm × 173 mm dimensions. The components of the device are:
bleeding valves, inlet and outlet valves, porous plates and the size of the sample respectively. In this study, four
uniform soil samples were selected for test. Samples are prepared in falling manner, with three porosity and
under three different hydraulic gradient were tested. In Table 1 The general pattern of research experiments is
presented. In this study, 36 tests were performed.
Table 1-Pattern of research experiments
Diameter Parameter
particle
Void
rati
o
Water head
The number
of test
To measure vertical permeability, due to large grains samples, according to ASTM D-2434 standard fixedload
test method has been used. First, the porous plate is placed on the bottom of the measuring device to prevent
the soil from entering and exiting the water penetration then The soil is inserted from the fixed height into the
device and the porous plate is placed on the sample. Then place should be located at the top of the device and
close the screws so there should be no water leak. Then the weight of the soil should be measured and connect
the system to the water. Then the outlet tap should be opened and water should be passed through the soil sample
until the sample would be completely saturated and no air bubbles come out of the outlet pipe and fix water
level. Then the water head and weigh the empty container and the duration of the outflow of water for a given
water volume should be measured. After performing the test at a specified head, the elevation of water should be
changed by reservoir adjustment and the permeability coefficient would be measured in other loads.
Results and Discussion:
The effect of hydraulic loads on horizontal and vertical hydraulic conductivity coefficients for uniform
samples
Horizontal and vertical hydraulic conductivity tests were performed on uniform samples including coarse
aggregate materials with a diameter of 0.85, 2, 6.35, and 5.9 mm. In Figures (1) to (3), the effect of hydraulic
load on horizontal and vertical hydraulic conductivity for uniform samples in minimum and maximum
conditions is shown. Figuer1- According hydraulic conductivity to hydraulic gradient for uniform samples with A) vertical hydraulic
conductivity, minimal porosity B) Horizontal hydraulic conductivity, minimal porosity C) vertical hydraulic
conductivity, maximum porosity D) horizontal hydraulic, maximum porosity
Investigations showed that in all cases, with increasing hydraulic load, the horizontal and vertical hydraulic
conductivity decreased and then the process of change was almost constant.
Investigation of the effect of porosity on horizontal and vertical hydraulic conductivity of uniform samples
The results showed that the horizontal hydraulic conductivity coefficient for all samples was higher than the
vertical hydraulic conductivity coefficient.
Also, the results showed that the minimum hydraulic conductivity (e = 0.46) and maximum porosity (e =
0.97) were about 34.33 and 0.35 percent higher than the hydraulic hydraulic conductivity, respectively.
Investigation of the effect of porosity on the anisotropy coefficient of hydraulic conductivity of uniform
samples: The results showed that with increasing porosity, the coefficient of heterogeneity of hydraulic
conductivity for uniform samples was reduced and this coefficient was for uniform samples in the range of 0.89
to 1.35.
Conclusions: The final results can be summarized as follow:
1. The permeability in the horizontal direction is often greater than the permeability in the vertical direction.
2. The anisotropy permeability for uniform sample is between 0.85-1.35.
3. The anisotropy permeability decreases with increasing porosity.
4. In the uniform samples, maximum permeability occurs at higher hydraulic conductivity.
5. With increasing the uniformity coefficient, the amount of hydraulic conductivity decreases.
