Cost-effectiveness, fast performance, and relatively long service life have made geosynthetics widely used in geotechnical structures such as road pavement, retaining walls, slope stabilization and foundations, bridge abutments, embankments or at the boundary between embankments and subgrade to be used. The soil geocomposite used in this research, which is made in Iran under the brand name of GC Soil 40/40, is a combination of geogrid and geotextile and is used in various projects such as embankment bed reinforcement and separation to implement embankment on fine and loose subgrade. In general, in the design of geosynthetics, including soil geocomposites, interaction mechanisms including slip and pullout as well as interaction coefficient between soil and geosynthetic should be considered. Accordingly, to evaluate the soil-geocomposite interaction, direct shear and pullout tests were performed in one-layer soil (sand-geocomposite and gravel-geocomposite) and two-layers soil (sand-geocomposite-gravel) under different vertical stresses. The results of direct shear tests showed that reinforcing the soil with geocomposite reduced the angle of friction and increased soil adhesion. Despite the increase in shear stress and pullout resistance with increasing vertical stress, the interaction coefficients decrease with an increase in the vertical stress. This issue can be related to the nonlinear behavior of pullout force and soil-geocomposite shear stress with vertical stress. Vertical stress is an effective factor to increase the pullout resistance and type of mode geocomposite rupture and also has a significant effect on the displacement at the maximum pullout resistance. The results showed that under the same loading conditions, the placement of the geocomposite on the common surface of the two layers soil changes the pullout behavior compared to the one-layer soil. In general, it can be stated that the soil-geocomposite interaction, in addition to vertical stress, is sensitive to the type and size of soil particles, one- and two-layers of soil. For sand-geocomposite and gravel-geocomposite interfaces, the average coefficients of interaction(𝑐𝑖 ) for direct shear are 0.8 and 0.91, respectively. Also, the average pullout interaction coefficients(𝑓𝑏) for sandy and gravel soils reinforced with geocomposite (one-layer) are 0.35 and 0.47, respectively, and this coefficient is obtained as the average of 0.51 for sand-geocomposite-gravel (two-layer).

Mining activities are one of the most persistent causes of soil degradation due to the destabilization of the physicochemical structure of the soil. In this research, quantitative data of soil stability indicators were used to assess the effect of sodium sulfate extraction on soil properties and protective behavior of the earth's surface. The research method was based on tranformations in soil stability indicators, namely, acidity (pH), electrical conductivity (EC), exchangeable sodium percentage (ESP) and sodium absorption ratio (SAR), for natural surfaces (undisturbed topsoil), stripped topsoil layer (displaced soil layer) and sodium sulfate extraction layer. The results show that the concentration of exchangeable sodium percentage and the exchangeable calcium to magnesium ratio in the layer of displaced soil and the extraction layer of sulfate is reduced compared to the natural soil. While the organic matter content of soils does not change in all layers, and the value of electrical conductivity in the sulfate extraction layer is higher than all layers. The results of the soil stability data value show the instability of the displaced soil layer compared to the other two layers. Based on the presented results, it has been shown that the soil instability potential increases due to sodium sulfate extraction.

In this paper, approximate and exact equivalent circuits for grounding electrodes buried in horizontally two-layered soils are introduced. In the approximate one,  two-layer soil is approximated with equivalent resistivity and then the grounding electrode is modelled with RLC equivalent circuit, while in the exact one, the input impedance of the grounding electrode is first computed in the frequency domain via numerical solution of Maxwell’s equations. Then the input impedance is replaced with rational functions and finally the equivalent circuit in time domain is achieved. In order to extract the validity range of the approximate circuit in two-layer soils, transient analysis of overhead line terminated to arrester in the presence of two-layer soils is carried out where the grounding electrodes are modelled with approximate and exact circuits. The simulation results show that when the thickness of the first layer is less than 1 meter or greater than 40 meter, the approximate circuit yields acceptable results. In addition, sensitivity analysis is carried out on the thickness of the first layer with respect to the single-layer soil. The simulation results show that when the thickness is greater than 40 meter, the two-layer and single-layer soils have the same behavior.

Hydraulic conductivity is one of the important physical properties of the soil used extensively in water and soil science. Most of the soil processes take place in unsaturated soil conditions. This study was conducted in order to evaluate the effect of soil layering and water table on saturated and unsaturated hydraulic parameters using a tension disc in five suction heads, i.e. 0, 5, 10, 15, and 20 cm. The experimental tests were done on three same samples with 56 cm diameter and 85 cm height in three compacted layers with soil bulk densities of 1.18, 1.38 and 1.68 gr.cm-3 and water table depths of 85 (no water table) 50, and 25 cm. Additionally, we considered a one-layered sample to investigate the effect of bulk density. The experimental results showed that soil layering caused changes in the values ​​of saturated and unsaturated hydraulic conductivity. Also, sensitivity of the saturated hydraulic conductivity to soil layering was more than that of the inverse air entry suction(α). Compared with the treatment with no water table, the saturated hydraulic conductivity of the layered soil in treatments with water table depths of 25 cm and 50 cm decreased by 52 % and 27.6 %, respectively.

This study aims down to evaluate the ability of chloride magnesium- aluminium- layered double hydroxides (4:1) for nitrate adsorption from the soil solution in successive cropping periods. The study was conductedunder long-term cropping periods, including first crop): bell pepper; second crop: mentheae; third crop: cherry tomato; and fort h crop: wheat), absorption of soil mineral nitrate in fallow periods and nitrate absorption from plants by layered double hydroxides. The effect of layered double hydroxides on qualitative and quantitative characteristics of plants was also studied. Results indicated that layered double hydroxides were able to induce long-term nitrate exchange in crop and fallow sequences. Layered double hydroxides can adsorb soil excessive nitrates in cropping periods and reduce nitrate concentration in the soil solution. Compared to control, the treatment with 16 gram layered double hydroxide/kilogram soil could reduce nitrate concentration in the soil solution by 95%. During two-week fallow periods, the amount of nitrates mineralized in the soil solution was increased, but layered double hydroxides treatments could adsorb them well and maintained the N-nitrate concentration in the soil solution at a low level. Additionally, Results indicated that application of 2, 4, 8 and 16 gram layered double hydroxides/kilogram soil led to 34%, 44%, 58% and 69% reduction in N-nitrate concentration of soil leachates, respectively, compared to control. By increasing nitrogen availability, layered double hydroxides improved the quantitative and qualitative properties of plants. Application of 2, 4, 8 and 16 gram layered double hydroxides/ kilogram soil increased the plant height (cherry tomato) by 14%, 26%, 50% and 80%, respectively. It is concluded that the layered double hydroxides has a potential to be used as a long-term nitrate exchanger to control the movement of nitrate in soil, and thereby reduce risks of nitrate leaching in crop production in sensible areas.

This is a study of the seismic behavior of earth slopes exposed to vertical Ricker shear waves. Two-dimensional FLAC2D software based on the finite difference method was used for modeling. Layering in earth fill exists in natural situation, and the seismic response of the earth fills is mostly dependent on these different soil layers. When the situation of the weak layer changes in height of the earth fills, we expect to see different responses in seismic behavior of the system. The Mohr-Coulomb criterion is used to investigate the nonlinear soil behavior. To investigate the effects of the input wave frequency on the horizontal acceleration amplification coefficient (considered in this study as the response), four different frequencies, to investigate the effects of the input movement level on the response, four acceleration amplitudes, to investigate the effects of angle, three slopes with various angles and five layering modes are considered for the layering effects. This study presents the results of a numerical study on the seismic behavior of two-dimensional semi-sine shaped hills that were subjected to vertically propagating incident SV wave of the Ricker wavelet. The finite difference software is used to model and analyze the different sizes of the hills. Concentration is on topographic effects, so parameters such as shape factor (the ratio of the height to half width of the hill) and the type of ground took into account in this research. Another variable is the soil type that the difference being in ρ and vs. Therefore, according to the by Code 2800, three soil types have been investigated, each of which has been affected by the Ricker wave. The results show that the horizontal acceleration amplification coefficient overlay decreases with increasing movement and angle. Four different frequencies 1, 3, 5 and 10 Hz are studied in input motion Ricker wave. These different input motion frequencies are selected to evaluate the response of system to these frequencies when natural frequencies of soil layers differ. The effects of the frequency and the layering of the soil are also correlated so that if the input wave frequency is close to the natural frequency of the soil, in each layering mode, that layering mode reports the maximum value for the horizontal acceleration amplification coefficient. Generally, in the presence of a relatively weak layer (with Type III material), the response decreases. However, the high frequency does not follow this trend and offers significant responses. The highest amplification in horizontal acceleration happens in high frequency of soil layers or frequencies like them. The obtained responses are sharply dependent on input motion frequencies and also natural frequencies of soil layers. As it can be seen, when natural frequencies of soil layers and input motion frequencies are near each other, the highest responses are evaluated, which we can say that the resonance is happened. In this case, the highest horizontal acceleration in response results is evaluated. When weak layer exists in different soil layers, the de-amplification happens. The results show that the most de-amplification happens due to the weak soil layer. Also, results show that this high de-amplification happens in weak soil layer, and refers to the horizontal acceleration response.

To study the effect of irrigation water salinity on soil chemical characteristics¡ a randomized complete block design experiment was conducted with four treatments of irrigation water salinities of 2¡ 6¡ 9 and 12 dS/m with three replications for each treatment in a corn field under drip irrigation system (T-Tape). The study was carried out in an arid region with high initial soil salinity and soil texture of loam. Results of soil chemical analysis from different soil depths of 0-30¡ 30-60 and 60-90 cm showed that in each layer of soil with increase in irrigation water salinity the salinity of soil saturated extract increases and the salinity of soil saturated extract in deeper layers was higher than upper layers. During the growing season¡ for each of three soil layer profiles¡ with uniform irrigation with water salinity of 1dS/m the value of the ECe¡ SAR¡ HCO3¡ Cl and ESP were decreased. However¡ irrigating with different irrigation water salinities caused that the above values increase after the crop stage of four leaf corn and the maximum increase occurred at the end of growing season. In regions with lack of fresh water¡ irrigating with saline water under drip irrigation will result in uniform distribution of water and soil salinity in soil profile.

This paper describes the reinforcing eects of multiple layers of a rubber-soil mixture in sand, using small scale and large scale static plate loading tests, respectively, at diameters of 113 mm and 300 mm. The small scale test and large scale plate load tests were conducted in a testing tank measuring 800800800 mm, and in an outdoor test pit dug in natural ground measuring 20002000 mm in plane and 700 mm in depth, respectively. According to previous studies of Moghaddas Tafreshi et al.[12], the optimum embedded depth of the rst layer of the rubber-soil mixture was found to be approximately 0.2 times the footing diameter, and the optimum percentage of rubber replacement was found to be around 8% the weight of the soil mixture. The thickness of the rubbersoil mixture, hrs, in terms of hrs=D (D: the loading surface diameter), the vertical spacing of the rubber-soil mixture layers, h, in terms of h/D, and multiple layers of rubber-soil mixture (N) in the foundation bed were the main parameters aecting the bearing capacity and settlement of the foundation bed. The optimum thickness of the rubber-soil mixture and the optimum vertical spacing of the rubber-soil mixture layers were 0.4 and 0.2 times the loading plate diameter (i:e:; hrs=D = 0:4) and h/D=0.2). Results show that reinforcement eciency decreases as the number of rubber-soil mixture layers increases. For example, in the small scale loading plate at a settlement ratio of 4%, the bearing capacity was obtained at about 89, 102, 110 and 112 kPa for the unreinforced and reinforced beds with one, two and three layers of rubber-soil mixture, respectively. Furthermore, the reinforced bed with two layers of the rubber-soil mixture with optimum thickness located at optimum vertical spacing, shows more eciency than one layer of the rubber-soil mixture in increasing the bearing pressure of the foundation bed, whereas the total thickness of the mixture is the same.

Soils, which show a large amount of volume reduction and cause a series of sudden settlements on the surface of the earth, due to the increase of moisture, are referred to as collapsible soils. In many different countries, the immediate settlements of these soils, especially in warm and arid areas, have caused the formation of subsidence and sinkhole. These soils always create inappropriate conditions for the construction of structures such as buildings, road projects, foundations, water channels and other civil engineering projects. The occurrence of such sinkholes in parts of Iran and other parts of the world is one of the geotechnical problems of the above problematic soils. Several sink holes have formed in the northern sector of Hamedan. The soil types in this area include sandy and clayey soils which have low dry density. Generally, collapsible behaviour of soils can be evaluated by the use of odometer test. According to the ASTM standard (D5333-03), the collapse index (Ie) is used to determine the magnitude of collapsible possibility during saturation at 200 kPa in a simple odometer device. The purpose of this study was to investigate the effect of changing the order of clay and sand layers on the collapsible behavior mechanism of collapsible soils and on the changes in the collapse index. To achieve the above mentioned objective, the sandy soil was used from the northern areas of Hamadan and kaolinite clay (Super Zenouz of Tabriz) used to make the samples in three single-layer, two-layer and three-layer systems in specific molds made to a height and diameter of 5 cm in the odometer apparatus. Accordingly, in the present laboratory study on these two types of soil, considering the different arrangements of clay and sandy layers, at each stage of the specimen preparation, specimens were prepared in three different series with a dry unit weight of 1.3, 1.5 and 1.7 g per cubic centimeter in a odometer metal molds. By carrying out a series of odometer experiments, it was found that the sandy soils of the study area alone did not have a high percentage of the collapse index. However, with the presence of clay layers in such soils, the collapse index increases, so that collapse index at a unit weight of 1.3 g per cubic centimeter in the sample made in a single-layer system (fine-grained sand sample) reached from 3.8% to 8.7% in the sample made in the presence of a clay in the two-layer system, (the lower layer of the fine-grained sand and the upper layer of clay). Based on the results obtained from this study, the mechanism of collapse can significantly being influenced by the order of layering in that with increasing dry unit weight, the effect of the ordering of the layers on the value of the collapse index decreases. The results of this paper shows that in specimens made with a density of 1.7 g per cubic centimeter, the collapse index of all samples are almost similar values. In other words, the collapsible behaviour of soils is a function of soil dry density.

In agriculture, cow manures are used to enhance soil fertility and productivity. Escherichia coli is the most common fecal coliform in cow manure and considered as an index for microbial contamination of groundwater resources. The objective of this study was to investigate the transport of Escherichia coli (released from cow manure) through the field soil. Lysimeters (with internal diameter of 20.5 and height of 50 cm) were inserted into an in situ clay loam soil. Unsaturated soil water flow was controlled at an inlet matric potential of –5 cm using a tension infiltrometer. When the steady-state flow was established, air-dried fresh cow manure was applied on the lysimeters at a rate of 10 Mg ha-1 (dry basis) and the soil-manure leaching started. Soil solution was sampled at 1, 2, 4, 6, 12 and 24 h after leaching initiation using plastic samplers installed at depths of 20 and 40 cm. Concentrations of Escherichia coli in the soil solution (C) and the influent (C0) were measured using the plate count method. Impacts of soil depth, sampling time, and their interaction on C and C/C0 were significant (P<0.01). In all leaching times, relative adsorption index (SR) was lower when both soil layers were considered and the filtration increased with soil depth. When the concentration was corrected for the second layer (i.e. 20–40 cm), the SR values in this layer were considerable and greater than those in the first layer at 4 and 6 h. The influence of surface layer was substantial in bacterial filtration; however, the preferential flows especially in the initial leaching times resulted in bacterial movement towards the second layer. Temperature drop reduced bacteria release from the manure, increased viscosity of the flowing water, and consequently diminished significantly the bacteria concentration in the soil solution at 24 h. Overall, it was found that similar to surface layer, subsurface layer might have great role in bacterial filtration due to its higher clay and carbonate contents