Due to environmental problems of desert expansion as well as dust storms, looking for more efficient and comprehensive methods to stabilize dune sands seems to be an essential necessity. Microbial-induced CaCO3 precipitation (MICP) is an innovative technique that harnesses bacterial activities to modify the physical and mechanical properties of soils. This method produces calcium carbonate precipitation in the soil pores by fracturing urea in the presence of calcium ions. An important factor in achieving uniform calcite deposition (and hence consistent enhancement of geotechnical properties) throughout the treated soil mass is the protocol adopted to inject the reagents of ureolytic bacteria, urea, and calcium. In this study, an urease microorganism was prepared in the laboratory and injected into cylindrical dune sand samples. After required and appropriate curing time, the samples were subjected to unconfined compression and falling-head permeability tests. The test results showed a significant strength improvement and the reduction of permeability of the treated samples in comparison with those of untreated soil. The research results verified the capability of the biological treatment of dune sand which may be regarded as a potential technique to control desert expansion and dust storms.

Foam injection is becoming a standard conditioning agent when tunnelling with an earth-pressure balanced shield, resulting in an increasing interest in this technique. The tech-nique is mostly based on empirical rules and experience. To be able to determine what foam and how may foam has to be injected for different soils, it is necessary to knowthe mechanical parameters of the foam-water-soil mixture. This paper describes a comprehen-sive set of tests that hasbeen performed to evaluate the effect that foam, foam types, and foam parameters have on the shear strength of Sandysoil. Four different foam agents and one type of polymer were used during the tests. The foam production processwas per-formed by a foam generator, which was constructed by the authors. Shear strength tests were carried out in aconventional direct shear box measuring 60x60 mm. The test results show a decrease in the internal friction angle andan increase in soil compressibility for foamed soil, where the changes are functions of soil gradation, foam types, andfoam pa-rameters. It appears that another agent (such as bentonite slurry) needs to be added to coarse-grained soils tocondition the soil effectively by increasing the fine content and re-ducing the number of large voids. The test resultsalso show that the effect of different foaming agents on the shear strength of fine sand is not noticeable.

Geoelectrical resistivity, hydrogeochemical and soil properties analysis methods were used for chemical fertilizer monitoring in Sandy soil at a palm oil plantation in Machang, Malaysia. The time lapse monitoring was done using these methods five times within a three-month period. The hydrogeochemical analysis was conducted over three auger holes to a depth of 1 m and sampled at 25 cm intervals. Chemical fertilizer was applied to the 21 x 21 m2 area after the first data set measurement. The areas outside of this fertilized zone are considered a nonfertilized zone. The other four data sets were acquired at about equal time intervals, thus giving a four-post fertilization data set. The hydrogeochemical measurements indicate that the cations content are relatively similar for every time lapse measurement. However, relatively higher changes of anions content occur at the surface level to a depth of 1 m. The nitrate concentration above the limit for safe human consumption as it returns to the initial value about 100 days after fertilization. The geoelectrical model prior to fertilization showed similar resistivity values at near surface to a depth of about 75 cm with no significant occurrences of low resistivity values. Lower resistivity values were obtained during the second, third, fourth and fifth measurements within the chemically fertilized zone. In the last measurement, the resistivity values in the fertilized zone are almost similar to the nonfertilized zone. This indicates that the contaminant has dissolved into the surrounding environment within this time period.

Successful use of geosynthetics is ensured in a given geotechnical application, as it is not only compatible, but also effective in improving the soil properties when appropriately placed. This study investigates the behavior of unreinforced and reinforced Sandy soil with nonwoven geotextile using CBR tests. The soil used, has poor CBR value due to its low compaction and moisture percent. In a series of tests, Geotextile is placed in various depths from the top of samples. The effect of thickness of dense layer (with 97% compaction) on the soft subgrade is also investigated, and the results are compared with reinforced condition. To study the effect of embedment depth of reinforcement, the geotextile layer is placed in depths of 1, 1.5, 2, 3, 4, 6 and 8 cm from the top of the sample. Furthermore, a comparison between reinforced samples with one layer and two layers of geotextile is done. The results of the CBR tests demonstrate clearly considerable amount of increase in CBR value of soil with geotextile reinforcement. It is also shown that the maximum increase in CBR value is obtained when one layer of geotextile is placed at depth of 1.5 cm. The rate of increase in CBR value was reduced with increase in the placement depth of reinforcement layer. The thicker dense layer leads to more increase in CBR. In the same density and thickness of the replaced soil layer, the highest increase in the CBR value was achieved when the sample was reinforced by two layers of geotextile. To achieve a specified design CBR value, using less depth of replaced soil layer in the reinforced subgrade is possible as compared with unreinforced subgrade. For example, using a depth of 1.5 cm and 3 cm of replaced soil, CBR value equaling 6 is achieved for reinforced and unreinforced subgrades, respectively. Although the replacement of compacted soil layer or the use of reinforcement layer could increase the bearing capacity, achieving a certain capacity needs to consider the details of economic issues and performance limits.

One of the most common methods of soil improvement is to use additives in order to improve strength properties and permeability of the soil. Cements or chemicals are usually used as binders for soil particles, which lead to increase the soil shear strength and reduce its hydraulic conductivity (i. e. permeability). Nevertheless, these materials are not suitable for soil improvement in the long term because they require significant natural resources. The use of cement and chemicals for soil improvement is expensive and time-consuming. Management of renewable natural resources (microorganisms and their products) could lead to solve geotechnical and environmental problems and achieve great economic benefits in the building industry. In addition, the application of microbial biotechnology in the building industry make easier some of the existing methods of construction. Using the latest microbial biotechnology, a new type of building materials, namely biocement, has been produced as an alternative to cement or chemicals. Biocementation is the improvement of strength and stiffness of rock and soil by using microbial activity and their products. The process of the formation of precipitates or biocement in the presence of microorganisms is called microbialy induced calcium precipitation (MICP). Biocement can be used in solid and liquid states. In the liquid state, biogrout can flow like water with very low viscosity. Therefore, compared to cement and chemicals, it will be transmitted into the soil, more easily. Naturally, biocement is formed in the presence of microorganisms in ambient temperature and thus, it requires less energy. Because of the abundance of microorganisms in the nature and easy to reproduce with low cost, this type of cement is sustainable. The Microorganisms that are suitable for the production of biocement are usually non-pathogenic and environment friendly. In addition, unlike cement, soil can be improved without disturbance of ground and the environment; since microorganisms can penetrate into the soil and grow in it. This dissertation aims to realize the effect of ground condition on the MICP process in non-cohesive soils. Since this method is still in the laboratory stage, for being used in practical projects, it is required to carry out laboratory experiments, including relative density and particle size distribution, to evaluate the performance of this method in different ground conditions. For this purpose, it was used from Sandy soil with different silt contents of 0%, 5%, 10%, 15% and 20% in two states of Loose (Dr = 40%) and dense (Dr = 100%) conditions in this research. The high urease activity and non-pathogenic bacteria S. Pasteurii was also used in the MICP process. In order to consider the soil conditions on the efficiency of this type of improvement method, uniaxial compressive test parameters and precipitated calcium carbonate content were investigated. According to the results, increasing of silt content from 0% to 20%, leads to reductions of 40% and 46% in precipitated calcium carbonate content, increases of 57% and 41% in the uniaxial strength and increases of 79% and 71% in the elasticity modulus of the samples in two loose and dense conditions, respectively. It seems that these changes were resulted from shrinking of the empty space and increasing of the contact area between the soil particles.

Introduction: In many areas of the world, the mechanical properties of soils for utilization of land are not sufficient. For improvement of these lands, soil stabilization such as compacting, installation of nails, elders of piles, mixing soil with lime or cement before or during constructions on the surface or inside of the ground can be useful. Microbially induced carbonate precipitation (MICP), due to its versatility and stable performance, has been recently attracted the attention of many researchers in the field of the geotechnical engineering around the world. MICP is a biological technique that is naturally caused to create a cementation agent, which is known as calcium carbonate or calcite by controlling the metabolism of bacteria. Although there are many biological processes that can be lead to MICP, but the using of urea hydrolysis by bacteria is commonly used more. In this method, aerobic bacteria with the enriched urease enzymes inject into the soil. Hydrolysis of urea occurs when the bacteria speeds up the hydrolysis reaction to produce ammonium and carbonate ions. In the presence of soluble calcium ions, carbonate ions are precipitated and formed the calcium carbonate crystals. When these crystals are formed on a grain of soil or like a bridge between them, they prevent the movement of grains and thus improve the mechanical and geotechnical properties of the soil. Material and methods: In the present study, the effect of increasing fines on the improvement of Anzali Sandy soil, and soil resistance parameters for improving the clean sand and its mixtures with a fine grained cohesive soil and a fine grained cohesionless soil separately in a percentage weight of 30 by MICP and using a small scale of direct shear test (6×6) have been investigated. In the present study the Sandy soil was collected from the coast of Bandar Anzali Free Zone and for the preparation of samples of clayey sand and silty sand, Kaolinite clay soils and Firouzkooh broken silt were used, respectively. Anzali sand is poorly graded and had a rounded corner with an average particle size of 0. 2 mm, somewhat, sharpening cores are also found in its granulation. In addition, its fine grained content is very small (less than 1%). The Kaolinite clay is also labeled with a liquid limit of 40, a plastic limit of 25, and a plasticity index of 15 as an inorganic clay (CL). The used microorganism in this study is urease positive Sporosarcina pasteurii, which is maintained with the number of PTCC1645 at the Center Collective of Industrial Microorganisms of Iran Scientific and Research Organization. The bacterium was cultured in a culture medium containing 20 g/l yeast extract and 10 g/l ammonium chloride at pH 9 under aerobic conditions in incubator shaker machine at 150 rpm and temperature of 30 ° C. The organism was grown to late exponential/early stationary phase and stored at 4 ° C before injection in samples. A solution of calcium chloride and urea with a molar ratio of one is also used as a cementation solution. With the direct shear test (6cm×6cm) as a benchmarking of the shear strength in the before and after improvement steps, molds fitted with a shear box made of the galvanized sheet with a thickness of 0. 6 mm and it consists of two main parts, the body, in the middle of which an exhaust pipe was embedded in the injector waste fluid. At the bottom of the samples, a layer of filter paper was placed in order to prevent soil washes, and then all samples with a thickness of 2 cm, with a relative density of 30% at the same weight and height were pressed. In the upper part of the samples, a layer of filter paper is similarly used to prevent the discontinuity of soil particles when injected biological materials are used. Biological solutions are injected from the top to the specimens and allowed to penetrate under the influence of gravitational and capillary forces in the sample and discharge the inhaled fluid from the exhaust pipe. The criterion for determining the volume of the solution to inject into each sample is the pure volume (PV) of soil. The preparation process of the samples was initiated by injection of a PV water unit, followed by a two-layer mixture of bacterial suspensions and cementation solutions, each with a volume of one PV, and then for biological reactions, 24 hours to the sample at laboratory temperature (25 ± 2) is given. After the time of incubation, the solution of cementation is injected into the sample for a period of three days and every 24 hours. The processing time of samples is also considered 28 days. In this study, optical density (OD) was selected as a benchmark for estimating the concentration of bacterial cells in the culture medium, and in all stages of development, and precisely before injection of bacteria suspension into soil samples, it was measured by a spectrophotometer device at 600 nm (OD600) wavelength, which was obtained for all bacterial suspensions in the range of 1. 7 to 2 before the injection. To determine the activity of urea bacteria, 1 ml of bacterial suspension was added to nine milliliters of 1. 11 molar urea solution, and by immersing the electrode of the electrical conductivity in the solution, its conductivity was recorded for 5 minutes at 20 ± 2 ° C. The rate of urea activity in the pre-treatment stage for all specimens was in the range of 0. 8 to 1. 23 mS min-1. In order to evaluate the shear strength parameters of soil samples, before and after the improvement operations, a direct shear test was used based on the ASTM D3080 standard. This test was performed for all samples under stresses of 50, 100 and 150 kPa in undrained conditions at a loading speed of 1 mm/min up to a strain of 15%. Also, samples of soil with a moisture content of 7% and a relative density of 30% (as already mentioned) have been restored. SEM analysis was carried out to determine the distribution of sediment between soil particles and EDX analysis in order to identify carbonate calcium sediment formation elements in improved soil samples, by scanning electron microscopy on Anzali Sandy soil samples in before and after improvement conditions. Conclusions: The effect of the increasing cohesive and cohesionless fines on the bio-treated process of Sandy soil is the main subject of this research. For this purpose, three samples of clean sand, sand containing 30% clay and sand mixture with 30% silt in a relative density of 30% were treated with MICP method and their shear strength parameters were evaluated by direct shear test after 28 days of processing. Using the direct shear test and analyses of SEM and EDX data, the results are represented as below: 1. The microbial sediment of carbonate calcium has greatly improved the resistance properties of all three soil samples. 2. A sample of clayey sand, in spite of a higher improvement compared to the other samples with an average shear strength of 113. 7% in comparison to to its untreated state, it has the lowest shear strength among the three improved samples. 3. Increasing the clay content of 30% increases the soil voids. On the other hand, it reduces the friction angle and shear strength of the soil in the pre-treated state and also facilitates easier movement of the bacteria between the pores in the soil. More favorable distribution of sediment calcium carbonate was occurred and, as a result, increased adhesion between soil particles. 4. The increase of cohesionless fine particles creates more bonding points between sand particles and, therefore, calcium carbonate crystals form shorter distances between the soil bridges. As a result, with the end of the improvement process, the shear strength parameters of the Sandy soil containing 30% of the silt compared to the clean sand have a higher value. 5. SEM images of the clean sand in both before and after improvement show that the calcium carbonate precipitation occurred with a uniform and thin layer that surrounds sand grains and another part of the sediments formed in the joint of grains. 6. Cube-shaped crystalline sediments confirm that the sediment formed in the soil is a stable type of calcite and that the relative increase in the friction angle of the improvement samples can be attributed to solid particles and multifaceted sediments. Also, the elements of carbon, oxygen, and calcium, which are the main components for the formation of calcium carbonate deposits, have been found in the EDX analysis of improvement sand samples.

soil hydraulic properties are key soil physical characteristics that are required to conduct soil and water related studies such as irrigation and drainage. In this study, three indirect methods: inverse modeling, pedo-transfer function, and the semi-physical method of Arya et al., were compared in a Sandy loam soil to estimate soil moisture retention and unsaturated hydraulic conductivity curves. Subsequently, they were applied to simulate soil moisture in irrigated furrows. In the indirect methods, soil hydraulic properties were estimated from easily measured soil data. Using the neural network-based pedo-transfer function of ROSETTA code, soil hydraulic parameters were obtained from soil textural fractions (percentage of sand, silt and clay), bulk density, and two water retention points as input. In the inverse method, the most sensitive soil hydraulic properties were estimated using the Levenberg-Marquardt optimization algorithm in combination with the HYDRUS-2D numerical code. In the semi-physical method, both soil retention and unsaturated hydraulic conductivity curves were predicted from a particle size distribution curve. The predicted soil hydraulic properties were applied to simulate soil moisture below the irrigated furrows during two subsequent irrigations. The results showed that the inverse modeling and Arya et al. methods predicated the soil water content well in the experimental furrows while the pedo-transfer function of ROSETTA overestimated soil water content.

Sandy alluvial soils contaminated with crude oil were investigated with a view to understanding the effects of crude oil contamination on their engineering properties. Bulk samples of alluvial soils compacted in layers were admixed thoroughly with 10% by volume of the contaminant and were cured for 63 days under room temperature in the laboratory and outside in the open to simulate field conditions. Mineralogical and chemical compositions of soils were obtained using X-ray diffraction and X-ray fluorescence analyses, and specific gravity, hydraulic conductivity, and compaction tests were conducted on the soils before and after contamination. Results show that the soil is silica-rich with SiO2 content of 96. 24g/g. This is corroborated by the high quartz content (96. 62%) observed from the mineralogical composition with minor amounts of kaolinite (6. 04%), and trace amounts of haematite (0. 02%). The addition of crude oil resulted in an increase in maximum dry density (MDD) with a corresponding decrease in hydraulic conductivity, optimum moisture content (OMC), and specific gravity for both laboratory and outside cured samples. Hence, crude oil contamination can be said to modify the engineering properties of Sandy soils, and the environment of samples’,emplacement also contributed to the alteration pattern observed.

soil pH is a measure of the acidity and alkalinity in soils, ranging from 0 to 14 that measured in a slurry of soil mixed with water. soil pH normally falls between 3 and 10, with 7 being neutral, acid soils have a pH below 7 and alkaline soils have a pH above 7. Ultra-acidic soils have pH value less than 3. 5 and very strongly alkaline soils have pH value more than 9 which are rare. Extremes in acidity or alkalinity may affect mechanical behaviour physical properties of soil. Recently, the rapid development of cities and the industrial revolution have caused enormous environmental impacts and become a serious environmental problem. About 80% of the pollutants in the atmosphere, including suspended particles and gases, result from vehicular traffic and industrial activities. Precipitation acts as a significant natural cycle to clean up atmospheric pollutants such as gases and particles in the air. The major sources of acid water are strong presence of SO2 and NOx gases in the atmosphere. One of the most important effects of acid water is its effect on soil, including washing nutrient cations, releasing toxic elements, and acidifying the soil. Also, acid mine drainage and the contaminants associated with it, is a common occurrence in waste dumps of mining sites results in acidic conditions with a pH of less than 4 develop over time. On the other hand, mineral deposits, over liming in some parts of the land and the use of limestone to improve the different soil natural and control the pH in waste dumps leads to alkaline conditions (pH more than 7) at mine sites. One of the most important effects of air pollution is acid rain. The increasing expansion of cities, the rapid growth of urbanization and the industrial revolution have caused enormous environmental impacts in and around cities. Industrial activities, production of energy and fuel, the use of fertilizers and pesticides cause significant amounts of contaminants to the atmosphere. The entry of metal contaminants and acidifying compounds such as sulfur, nitrogen compounds or their reaction to the atmosphere in the rain will increase the acidity of the rain which can change the quality of atmospheric precipitation. In general, it can be stated that the meaning of acid rain is a rain that has a pH of less than 5. 5 which is a lower natural pH. In the current study, the effect of acid rain on the mechanical behavior and physical properties of lime stabilized sand with respect to the eastern regions of Isfahan has been investigated. At first, the various lime content was added to the soil and the specimens were tested after treatment and saturation under various pH values. The results show that adding lime increased the optimum moisture content, shear strength of the specimens, the cohesion and the friction angle of the soil. On the other hand, reducing the pH value results in continuously decreasing the shear strength parameters of the soil specimens. Finally, based on the scanning electron microscopy (SEM) image from the specimens, the effect of pH and lime content on the bonds between the sand grains was investigated.