1. Introduction: Contamination of soils with petroleum products, in addition to being an environmental problem, also makes it difficult from the point of view of geotechnical engineering and doubts the use of this soil following structures, road pavements, and other constructed structures. Sridharan et al. (1981) reported an increase in soil settlement due to contamination of the region's soil with hydrocarbons, resulting in damage to industrial buildings. In recent decades, due to the importance of studying the geotechnical behavior of contaminated soils with petroleum products, many studies have been conducted on the physical and chemical properties of these soils. Much research has been done on the geotechnical properties of fine-grained and coarse-grained soils contaminated with petroleum products (Shin and Das, 2001, Ratnaweera and Meegoda, 2006, Rahman et al., 2010, Al-Aghbari, 2011, Kermani and Ebadi, 2012, Karpuzcu et al., 2018). In this study, the emphasis is on the evaluation of the polluting effect of gas oil as a pollutant with a specific gravity less than water on the finegrained and coarse-grained behavior of soil. For this aim, a set of geochemical (including XRD and XRF analyzes), geotechnical tests (including grain size distribution, gas evaporation, Atterberg limits, and unconfined compression strength), as well as observation by scanning electron microscopy on contaminated Clayey Sand by gas oil was done. . .

Clogging occurs during mechanical tunneling with a Tunnel Boring Machine (TBM) because of adhesion of clayey soils to the cutter head and conveyor system. The present study examined the effects of water and sand contents on clogging in Montmorillonite clayey soil. Testing was carried out using an adhesion test device on 28 samples with different water and sand contents to determine adhesion stress and degree of clogging. The results indicate that the consistency index (Ic) of the samples decreases as the sand and water content increases. The results for variation of adhesion stress versus water content at different sand contents formed similar bellshaped curves. In all graphs, an increase in sand content decreased adhesion stress. Adhesion stress increased until the water content increased to 138%, at which point it began to decrease. The results show that adhesion of the soil to the surface of the metal piston did not occur in samples having a sand content of >40% and in samples with >133% water content having a sand content of <40%, Ic>0.5 adhesion occurred.

Observation of such phenomena as liquefaction and flow behavior generally occurring in loose and saturated sands have stimulated extensive investigation into sands and the parameters involved in their critical state behavior. Most studies conducted so far have mainly focused on clean sand or its mixtures containing non-plastic fines, with not much attention paid to the soil mechanics of the critical state of clayey sands. The reason for this neglect may be the misconception that plastic properties in clay prohibit flow behavior and liquefaction. However, the studies of the Northridge 1994, Kokaeli 1999, Chi Chi 1999, and Niigata 2004 earthquakes have indicated that notable settlements occur in soil containing considerable amounts of clay, resulting in great destruction. Researchers have emphasized that more detailed investigation is needed to determine the critical state behavior of clayey sands. The critical state behavior of clayey sands has been investigated using cyclic and static triaxial tests. Based on the results, in low ne content, more density will result in a significant increase in steady state strength, while, at high ne content, the effect of density on the steady state strength would be insignificant. Also, increasing ne content results in more instability, but the trend reverses after a threshold value. This threshold value is independent of cyclic or static loading.Comparing the results of different plasticity fines under similar conditions shows that increasing plasticity leads to more instability under the threshold value, while the effect of plasticity will be more significant with an increase in fine content Firooz-kooh crashed silica sand (sand 161) was used in the experiments due to its desirable properties. Specimens were prepared using the wet tamping method. Having obtained the appropriate blend, it was poured into a special mould and compacted in 6 layers to prepare specimens 50 mm in diameter and 100 mm in height.

This study was undertaken to determine the mechanical behavior of lime- stabilized clayey sands. The variations of compressive and tensile strengths of materials were investigated. Uniaxial and indirect tensile tests were performed and the results of stress-strain diagrams were used to present a simple nonlinear elastic model. The results show that a simple parabolic elastic model can predict the stress-strain relation before failure. A matrix of elastic coefficients is then presented based on the suggested model and the stress level.  

Large pullout test is used to investigate the geogrid pullout behavior in the anchorage zone. When the pullout load is applied to the geogrid, this force is gradually transmitted along with the sample until it reaches the end of the geogrid. In order to more accurately investigate the soil-geogrid interaction mechanism, the pullout behavior of geogrid should be evaluated based on the active length. In this study, by performing a series of large-scale pullout tests, the distribution of shear stress and pullout interaction coefficient of a PET geogrid embedded in clean sand and 20% clayey sand were investigated based on active length. The results showed that the value of the pullout force to start the movement of the last geogrid transverse member increased with increasing vertical effective stress in both geogrid embedded in two soil. In all pullout tests, minimum active interaction coefficient was obtained at the conversion of transfer force stage to pullout stage.

In cases where the soil normally has undesirable properties and it is not possible to replace the soil, it is necessary to use methods such as compaction, injection, stabilization, reinforcing and other methods for soil improvement. Recently, due to the advancement of engineering science and since many soils and minerals are among the nano materials, their chemical reactions occur at nano scale. In this regard, nano materials are used to improve the geotechnical properties of the soil. Also, the self-healing of clay as one of the positive properties of clay in recent years has been considered by researchers. In this study, in order to investigate the effect of iron oxide nanoparticles on the behanior of clayey-sand soil, three soil types were selected for laboratory tests, including soils with 10, 20 and 30 percentage of clay. The results show that the peak strength of soil stabilized with iron oxide nanoparticles is increased especially sandy soil with lower percentage of clay. Also, the effect of curing time was obvious on the strength development in the restoration process of the soil. The effect of nanoparticles on the peak strength and self-healing characteristics of clayey sand has been shown with a series of SEM images.

Soil in cold regions experiences repetitive freeze-thaw cycles that are considered as one of the most significant phenomena in cold region engineering. Approximately 30% of soil all around the world and a large portion of fertile lands are exposed to daily or seasonal freeze-thaw cycles. These cycles cause considerable changes in water content, solute movement, permeability, strength parameters, erosion rate, and other physical or chemical characteristics of soil. Nowadays, one of the approaches to improving the physical and mechanical characteristics of the soil is to incorporate geosynthetic material as a layer between the embankment and the ground surface. This paper presents the results of California bearing ratio that tests clayey sandy soil. Moreover, the effect of freezethaw cycles on the compressive strength of geotextile-reinforced soil was investigated. The geotextile layer was placed in five positions at different depths of 1. 3, 2. 6, 3. 9, 5. 85, and 7. 8 cm beneath the surface of the mold and then, the sample was exposed to freeze-thaw cycles. It was found that the optimum depth of the geotextile layer was 3. 9 cm. In addition, it could be observed that reinforcing the soil could decrease the weakening effects of freeze thaw cycles by up to 41. 7%.

Currently, chemical stabilization with various additives is a common method for improving the engineering properties of different soils. However, environmental and financial factors are also crucial in determining the types of additives used. The present study evaluates the effects of activated carbon (AC) as an environmentally friendly and cost-effective material on the geotechnical and microstructural properties of a clayey sand (SC). For this purpose, the AC as a stabilizer was added to the SC specimens at mass contents of 1, 2, 3, 4, and 5% and unconfined compressive strength (UCS) and pH tests were performed at curing ages of zero, 7, 14, and 28 days. Direct shear and permeability tests were also conducted on the specimens immediately after addition of the AC contents. Results showed that increasing the AC content upto 4% and extending the curing age to 28 days enhanced the UCS of SC by up to 196%. All the stabilized specimens showed a significant decrease in pH level compared to the non-stabilized specimen, with increasing curing age from zero to later stages. However, the curing age had no significant effect on the pH of the stabilized specimens. The shear strength increased with the addition of up to 1% AC, then decreased. The permeability of SC decreased as the AC content increased. Also, microstructural analyses were conducted using scanning electron microscopy (SEM) on both non-stabilized and stabilized specimens with 4% AC at curing ages of zero and 28 days. SEM revealed a flocculated microstructure in the stabilized specimens, mainly due to ion exchange, particularly at the 28-day curing age.

The improvement of soil treatment by additives is one of the most critical issues in geotechnical engineering. Typical additives such as cement, lime, fly ash, and bitumen have been investigated in the past. Nanomaterials have unique features. The application of this type of material has led to a significant development in other branches of engineering. However, in geotechnical engineering, the investigation of the effects of this type of material is a new subject. Hence, in the present research, the effects of nano clay on geotechnical parameters of clayey sand are investigated. The principal purpose of investigation in this scale is the creation of new compounds with changes in ingredients and the detection of a new class of materials with new functions. These types of researches can make an appropriate base for future researches in this context. The Atterberg limits test and direct shear tests were carried out on different types of clayey sand. Various percentages of nano clay were used in the study. Ball mill was applied for uniform dispersion of nanoparticles. Also, in order to obtain optimum water content and maximum specific weight for prototyping, a standard compaction test was carried out on samples without nano clay particles. Based on the results, in general trends of tests, liquid limit and plastic limit are increased by increasing nano clay. The plasticity index has decreased when the percentage of the nano clay is increased by up to 1%. The plasticity index has increased again in a higher percentage of nano clays (more than 1%). Also, the shear strength of clayey sand in direct shear tests is improved in a specific percentage of nano clay. The optimum percentage of the nano clay for the friction angle φ is 1% in the direct shear test, and its best percentage for the cohesion C is 4%. Also, nano clay has a negative effect on the shear strength of pure sand. Therefore, according to the results of experiments, nanoparticles can be an acceptable choice for improving the geotechnical properties of clayey sand soils.