محمود وفاییان

In the recent decade, the issue of soil contamination with heavy metals such as nickel and lead is one of the most important environmental problems. According to data from the environmental protection agency, nickel is hazardous at large amounts and a dangerous pollutant and lead is the most important pollutant in the environment. This study was conducted to investigate the soil pollution status of Gachsaran refinery using environmental indicators of pollution coefficient, pollution degree index and modified pollution degree index and to investigate the potential of alfalfa refining plant which is native to Gachsaran region.

From the soil of Gachsaran refinery in 2017 as the center of pollution, were selected four ranges of 0-500 meters, 1000-500 meters, 1500-1000 meters and 2000-1500 meters. In each range, 5 soil samples were taken from a depth of 0 to 30 cm. The ICP-OES device was used to determine heavy metals. Statistical analysis was performed using SPSS software.

The analysis of the environmental indicators of the studied area showed a significant degree of contamination for nickel and a high contamination rate for lead. Comparison of mean concentrations of nickel and lead in cultivated soil samples with alfalfa cultivars showed significant difference with mean nickel and lead concentrations in the studied area.

In general, Alfalfa as a native plant of the region in inappropriate pollution conditions can absorb and extraction nickel and lead from the soil. The final results of this study indicate that ability of alfalfa plant for phytoremediation of nickel in the soil contaminated with petroleum products is higher than that of lead in the Gachsaran refinery.

A laboratory research program was arranged to study the effect of different factors influencing the stability of fine soils against wind action. For this purpose, a laboratory wind tunnel was stabilized and several soil samples were examined by putting the sample trays inside the wind tunnel for different rates of wind velocities. The tray for soil samples was 20´30 cm2 with the depth of 5 cm, and the fine soil samples were chosen with different sizes of particle and porosity. Because the main aim of this research was to investigate the effect of some polymer additives to the soil, many samples were made of the soils improved by different additives in different percentages. Furthermore, the effect of infiltration of the liquid additives was also examined, which could show different infiltration heights as functions of soil type, additive type and the height of pouring. Some of the results were examined by using software. The lab results in this research were compared with some proposed theoretical ones. It was found that as the average diameter of particles increases, erodibility under the same wind velocity decreases, and the applied polymer emulsions decrease the erodibility up to 90% compared to the initial condition. Impacts of dust emission due to the suspended dispersion of fine particles and creeping movements of coarse particles are mitigated as a result of treatment with these emulsions. Variations in erosion of soils at various wind velocities depend on the value of threshold friction velocity with the result that the soil erosion values in case of coarser soils after the increase in velocity would be higher than those of threshold friction velocity. Finally, a relationship is proposed for estimation of soil erosion in terms of wind velocity. The results are consistent with the transport rate relationships proposed by different scholars.

Soil compaction is considered as a major threat to long-term productivity of agricultural soils. Two important mechanical properties which can be obtained from the log (stress) - strain curves of compression are: pre-compaction stress (?pc) which is assumed as a transition point between soil elastic to plastic behavior, while the other is the slope of Linear Virgin Compression (VCL) curve at higher stress, called compression index (Cc). Pre-compaction stress and compression index of a silty clay loam soil under long-term (seven years) application of organic matters (municipal solid waste compost, fresh air-dried sewage sludge, farmyard manure) at four rates (0, 25, 50 and 100 Mg ha-1) and one inorganic fertilizer combination (250 urea Mg ha-1and 250 ammonium phosphate Mg ha-1). These mechanical properties were determined at two gravimetrical Water Contents (WCs) (17.1 and 20.9% WC) on remolded soil samples. The experimental designs consisted of: 1) factorial design (organic manure type? organic manure rate) and 2) orthogonal contrasts: i) control with inorganic fertilizer treatment and ii) control and inorganic fertilizer with factorial group in a completely ranomized design of three replications. With an increase in Organic Carbon (OC), the increase in bulk density (BD) after soil compression and at both WCs was lower. The least increase in bulk density was observed in soil amended with 100 SS ha-1 at WC of 17.1%. At the same WC, the apparent? pc of the soil amended with high rates (50 and 100 Mg ha-1of organic amendments had higher values as compared with control. For high water content (20.9%), a linear and negative relationship was observed between soil OC and Cc, whearas the relationship for 17.1% WC was found as not significant. The decreases in pre-compaction stress and compression index, for the inorganic fertilizer were not significant as compared with control. In general, since with an increase in OC, the stress at compaction threshold is increased and soil susceptibility to compaction decreased at high water contents, therefore, it can be stated that a long-term incorporation of manure into soil at high rates, irrespective of manure type, could be employed as a means to increase soil resistance to compaction in central Iran.

In this research the stability of slopes, made of unsaturated soils, constructed by compacted layers has been studied. The properties of unsaturated soils such as the stability of slopes made of them and shear strength have been investigated, and the priory theoretical backgrounds have been cited from the related literature.In this study the program “UDAM” (which have been already developed by Gatmiri and Nanda for the unsaturated soils) has been specially applied.As the development of pore water pressure and also pore air pressure developed during (and after that) the embankment construction and the major effective factors on the stability, so the computations of the quantities of these pore pressures were one of the main purposes of this research.In order to evaluate the stability of unsaturated slopes, it was necessary to a computer program which be suitable for analyzing the unsaturated soils. Because of this, the program CASSAP which has already been developed by Syrous Aryani, has been modified to be able to catch the pore water pressure and the suction of the soil and compute the stability safety factor.The results of these two mentioned programs (UDAM & MCASSAP) have illustrated in different diagrams and figures the final conclusion revealed some new and interesting results.Following is a brief description of UDAM program:The main concepts in the computations are based on the differential equations governing the equilibrium equations for unsaturated porous media. These equations which represent the relationships between the different affecting parameters of soil, air and water in equilibrium conditions are as follows:where is the porosity; the degree of water saturation; the degree of air saturation; are the densities of soil, water and air respectively; and are the velocities of water and air respectively; and is the acceleration.Furthermore, since the variations of void ratio and saturation degree are functions of some physico-mechanical properties of the medium, these variations should be expressed inside a three dimensional space, which is named as the state surface. In UDAM program, the equations of state surface for void ratio and saturation degree are as follows: (Gatmiri and Delage, 1995; Gatmiri et al., 1993)where and are the air and water pressure respectively; and are the net normal stress and matric suction respectively; is the atmospheric pressure; are parameters. Then the permeability coefficients of water and air as functions of parameters and are calculated by the following relationships, respectively:

For prevention of soil compaction, knowledge of allowable compression stress limit (compaction strength) in soil is important. Pre-compaction stress ( σpc) was introduced as soil compaction strength and often used as a criterion for evaluation of soil susceptibility to compaction. In this research, pre-compaction stress was measured for a sandy loam soil with plate sinkage (PST) and confined compression (CCT) tests. To prepare soil samples with different initial compactness, two soil water contents (17 and 19%db) and six pre-loading stresses (0, 25, 50, 100, 150 and 200 kPa) were used. The effects of soil water content and pre-loading stress on estimated pre-compaction stress were studied using a factorial experiment in a completely randomized design with three replications. The σpcvalues were significantly influenced by loading combination and soil water content. For PST, pre-load increase and higher soil water content resulted in higher and lower values of σpc , respectively. However, predicted σpc value increased with higher soil water content for CCT. The results also showed that the σpc predicted with PST was accurate, whereas the values obtained with CCT were 4.5 (at 17 %db) and 8.5 (at 19 %db) times higher than the applied pre-loads. Overall, the findings indicated that σpc prediction depends on the compression test, and PST could be a suitable method for soil pre-compaction stress (compaction strength) determination in sustainable soil management, i.e., soil trafficability and tillage. The PST method is also suitable to assess the effect of managing factors on pre-compaction stress.