15This study aims to investigate the ability of using biopolymer (environmental friendly material) to enhance 16 the mechanical characterizations of collapsible soil. Two types of biopolymers were used in this study 17 (xanthan gum and guar gum) because of their stable behaviour under sever conditions and their availability 18 with reasonable prices. The experimental program focused on three major soil properties, which are; 19 compaction characterizations, collapsible potential and shear parameters, these three properties are 20 essential in any soil improvement process. Different biopolymer concentrations were used in this study and 21 the experimental program was performed at two curing periods (soon after mixing the soil with the 22 biopolymer and after one week curing time). shear parameters were measured for the treated specimens in 23 both soaked and unsoaked conditions, while a collapsible potential test was performed under different 24 mixing conditions (wet mix and dry mix). A numerical model was built to predict the behaviour of the 25 treated collapsible soil after and before inundation. The analysis of results indicated the ability of both 26 xanthan gum and guar gum to be used as soil improvement materials for collapsible soil treatment. The 27collapsible potential has been reduced significantly from 9% to 1% after mixing the soil with 2% 28 biopolymer concentration in the wet case. After one week curing period, the cohesion stress has been 29 increased from 8.5 to 105 kPa by increasing the xanthan gum concentration from zero to 2%, leading to 30 overall improvement in the soil shear strength. Also, it proved that the superiority of guar gum over 31 xanthan gum in improving the shear strength is about 30% more than xanthan gum at the same conditions 32 and reduces the collapsible potential by about 20% more than xanthan gum at the same conditions. 33 34 35

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Generating large quantities of contaminated soil annually in all parts of the world poses a great threat to the environment and humans. In recent times there have been multiple sources of soil contamination. One of the most famous of these contaminants is the used engine oil. In this research, the effect of waste engine oilon some geotechnical properties of soil were studied. Laboratory tests including compaction and California bearing ratio (CBR tests were conducted on clean and contaminated soil. Contaminated soil samples were prepared by adding the waste engine oilat ratios of 4%, 8%, 12% and 16% of the dry weight of the samples. The results revealed a positive effect of the waste engine oilon the maximum dry density (MDD) and CBR values, but this improvement continued until the contaminant ratio of 8%. These values were decreased with further increase in the contaminant ratio to 16%.

Underground soft pockets, located in a footing's failure zone, may result in foundation instability and severe super structural damage. Throughout this paper, an experimental study is presented showing the behavior of a model strip footing on both geogrid-reinforced as well as un-reinforced sand slope above a soft pocket. Affecting factors, including the depth of a soft pocket below the strip footing, the setback distance between the crest of a sand slope and the strip footing, the relative density and the various number of reinforcement layers below the footing were all examined. The stress-settlement of the model footing supported on a medium and dense sandy slope with and without a soft pocket were obtained and compared at different studied parameters. Test results indicated that the existence of such a soft pocket within the subgrade layer under the footing has a great effect on the stress and settlement of footing. Furthermore, it has been found that the inclusion of the reinforcement layers in the sand not only significantly increases the stability of the sandy slope itself, but also lessens the settlement. Moreover, two main factors upon which the efficiency of sand-geogrid systems depends are the location of the footing relative to the slope crest, and the depth of the soft pocket below the footing. Variations of the stresssettlement with different parameters are given and discussed, based on the test results.