This paper investigates the effect of recycled polyester fiber, produced from polyethylene （PET） bottles, in combination with nano-SiO2 as a new stabilizer to improve the mechanical properties of ...soils. We intend to study the effect of adding nano-SiO2 and recycled polyester fiber on soil engineering properties, especially the shear strength and unconfined compressive strength （UCS）, using clayey soil with low liquid limit. Three different combinations of fiber-soil ratios ranging between 0.1% and 0.5% as well as three different combinations of nano-soil ratios ranging between 0.5% and 1% are used. The shear strength and UCS of treated specimens are obtained from direct shear test and unconfined compression test, respectively. Results of this study show that the addition of recycled polyester fiber and nano-SiO2 increases the strength of soil specimens. Both the shear strength and UCS are improved by increasing the contents of recycled polyester fiber and nano-SiO2 in the soil mixture. The increase in the nano-SiO2 content leads to a reduction in failure strain, but the increase in the content of recycled polyester fiber leads to an increase in failure strain. The increase in the contents of recycled polyester fiber and nano-SiO2 leads to an increase in elastic modulus of soils. Based on the test results, the addition of recycled polyester fiber improves the mechanical properties of soils stabilized with nano-SiO2 as well as the recycled polyester fiber has a positive effect on soil behaviors.
A destructive landslide occurred in spring 2019, in Hosein Abad Kalpush Village, Northeast of Iran, after an unusually rainy period. Significant damages were observed in buildings and roads located ...on the slope failure zone. This paper represents a preliminary reconnaissance report prepared through the site visit done by the authors, a few days following the landslide occurrence. Then, the geotechnical and geophysical properties of the sliding area are reported using the site investigation tests. Subsequently, the rainfall data are incorporated for numerical slope stability analyses. This study shows the variation of the failure mechanism of the slope before and after rainfall. The results confirm that the factor of safety decreases 1.78 times after a 3-month period of rain with rainfall intensity about 6 times the long-term average. Finally, the performance of two slope stability improvement strategies is evaluated to mitigate the landslide hazard. The results of the study can provide a perspective on the climate change impacts in Iran for future geosystem designs, geohazard prediction, and the selection of rainfall-induced landslide mitigation strategies.
Climate change is considered the major environmental challenge for the world. Cement and lime production is a highly energy-consuming, heavily polluting process, and the CO
2
emissions are very ...substantial. Alkaline environment, high temperature, and long processing time lead the researchers to work on alternative soil improvements. Microbially induced calcite precipitation (MICP) has been introduced as a technique for modification of geotechnical properties of sand. The main purpose of the present study was to focus on the efficiency and environmental impact of conventional and microbial grouting. Samples were treated with three chemical stabilizers, namely Portland cement, lime, and cement and lime. The stabilizers were injected with flow gravity and constant head which are almost the same as microbial grouting. Then, the results of conventional grouting were compared with the results of biocement samples which were gathered from previous studies to discuss the efficiency and environmental impacts. The results for treated samples were discussed and compared based on 1 m
3
of soil and a final target of 700 kPa. It was found that in order to obtain the same compressive strength, the cost and calcium carbonate consumption of the cement injection method were 2.5 times more than those of the microbial method. Biocementation has some advantages over existing technologies, such as less calcium usage in the same unconfined compressive strength (UCS).
Electrokinetic (EK) treatment is an effective method in accelerating the consolidation and improving the geotechnical properties of fine-grained soils. This method stabilizes the soil and increases ...the bearing capacity of piles by improving the soil shear strength. Changing the soil pH, due to the occurrence of chemical reactions of electrolysis in the soil, can increase its shear strength. However, the electrodes used in this method corrode due to the change in the soil pH, which in turn reduces the electrical potential. Electrode corrosion and loss of electrical potential can significantly reduce the efficiency of the EK method. In addition, when using the EK method to increase the bearing capacity of piles, changing the pH can cause corrosion and damage to the piles. One of the most important factors influencing the change in the pH of soil is the voltage applied during the EK process. It was reported that increasing the voltage affects the intensity of chemical reactions and electroosmotic flow and thus increases the efficiency of EK. However, very limited research has been conducted on the effect of voltage on the performance of EK method. In the present study, the effects of three voltages on soil pH and corrosion resistance of four types of electrodes including iron (Ir), stainless steel (St), copper (Co), and aluminium (Al) were studied. In addition, the effects of pH variations on the corrosion rate of three types of piles including steel pile (SP), reinforced cement concrete pile (RCCP), and reinforced lime-cement concrete pile (RLCCP) were investigated. It was observed that increasing the voltage from a specific limit had no effect on the intensity of electrolysis reactions and the soil pH adjacent to the electrodes did not change more than a specific limit. Moreover, increasing the voltage to higher than 35 V (i.e. 45 V) did not increase the volume of drained water from the soil, but caused more electric current than the allowable current for Ir, St, and Al electrodes, and the corrosion intensity of these electrodes increased significantly. RCCP reduced the soil pH to 2.4 within 7 d of curing due to severe corrosion (13% corrosion rate). The soil pH values adjacent to RCCP and RLCCP within 28 d of curing reduced to 3.7 and 3.8, respectively, but the two piles were not damaged. In general, the results of this research showed that selecting an optimized voltage had a significant effect on the efficiency of EK, and increasing the voltage did not always lead to increase in the efficiency of EK process.
Underground structures are susceptible to float and move upward during earthquakes when located in a liquefiable soil deposit. There are examples of this phenomenon in past major earthquake events. ...In this study, the uplift of circular tunnels in a liquefiable sand layer was investigated with a series of shaking table tests. The research has focused on the buried depth of the tunnel, tunnel diameter, tunnel weight, liquefaction extent, uplift mechanism, and factor of safety against liquefaction-induced uplift. According to the test results, the shallow buried depth, larger diameter, and lower weight can intensify the tunnel uplift, so the displacement in post-liquefaction time continues at the same rate as during the shaking time. Due to the shear-induced dilation, pore water pressure generation around the tunnel was reduced compared with that of the free field. The excess pore water pressure dissipation in the soil overlying the uplifted tunnel was significant, which leads to suction in the soil deposit. Furthermore, the acceleration response of overlying soil with the uplifted tunnel was similar to that of the free field. However, the soil acceleration response around the tunnel without uplift was similar to the base motion.
One of the issues pertinent to drainage columns is their clogging. In drainage columns, the pores are gradually clogged due to the entrance of fine particles of the surrounding soil to inside the ...column. Using recycled materials, e.g., tire granules, in these columns can improve their performance. According to laboratory investigations, the column's performance was improved by the substitution of tire granules instead of coarse soil particles. The special cell with a diameter of 9 cm and a height of 22.5 cm is designed and fabricated to investigate the clogging performance in drainage columns. In this investigation, 22 drainage columns were tested using the fabricated cells, including columns containing materials used alone, sand or tire granule, those with separate layers of sand and tire granule, and those containing a mixture of sand and tire granule. Eight tests were conducted on each sample, for a total of 176 tests. The materials used in these columns have three different sizes of sand and cubic tire granule with average diameters of 0.5, 0.75, and 1 cm and dimensions of 0.5, 0.75, and 1 cm, respectively. The volume of the input water is considered 5 and 10 L to compare these columns’ performance. In order to examine the clogging performance, water and sand were mixed with fine particles with a mixing percentage of 0, 5, 7.5, and 10% of water weight. In all tests, water flowed into the drainage column with a head of 1 m and left the column after passing through it. The tests indicate that the void ratio in 1-cm tire granule was 30% greater than that of 1-cm sand, permeability increased by 15%, and sedimentation level decreased by 23%. Increasing the ratio of tire granules in drainage columns increases porosity and permeability in columns, improving the drainage performance.
Subgrade soil stabilization is one of the primary and major processes in the construction of any highway. This paper evaluates the use of glass fibers in combination with nano-clay to improve the ...soil engineering properties. We intend to study the effect of adding nano-clay and glass fiber on soil mechanical properties, especially Shear parameters, using clayey soil with low liquid limit. The both ratios of glass fiber and nano-clay added to the soil are between 0.5% and 1.5%. Results of this study showed that nano glass fibers and nano-clay can be very effective in improving mechanical properties of clay. Adding nano particles in clay negatively affects the failure strain, but the increase in the glass fibers contents is connected with the increase in failure strain. Also, binary usage of fiber and nano- particles had a remarkable improvement appearing in clay strength than using the single type of fiber. It was found that a considerable shear strength increase up to 84% could be achieved depending on both the ratios of glass fiber and nano-clay that is used to improve the soil. In addition, the experiment results show that, binary usage of fiber and nano-clay can increase the unconfined compression strength of soil.
Growth of human societies and the development of industries produce many waste materials, including various types of polymeric waste. The facilities used by organizations to recycle the waste do not ...seem to be enough, and entering them into the environment may lead to significant problems. Use of polymeric waste, such as plastics, rubbers, and tires in geotechnical projects is a geo-environmental approach. In this laboratory study, the effect of waste polyamide chips on the shear strength properties of granular soil was investigated. A series of direct shear tests were carried out to achieve this goal. In the tests, sandy soil specimens were reinforced by waste polyamide chips with the lengths of 5, 10, and 15 mm, in addition to different mixing ratios of 0%, 0.4%, 0.8%, and 1.5% by dry weight of soil. The results indicated that the existence of waste polyamide chips as reinforcement in sandy soil would improve the shear strength parameters. Finally, the optimal mixing ratio and the length of polyamide chips were determined.
This paper presents an experimental study aiming to understand the impacts of nanomaterials on collapsible soil Behavior. Collapsible soils are among problematic soils from the perspective of ...geological and geotechnical engineering. These soils under constant stress present volume decrease related to the increase in moisture content. The reason is due to the weakened bond between particles under a constant stress. Collapsible soils exist in different parts of the world. In this study, samples used in experiments were collected by opening a trial pit from the sub-tropical areas of Iran. The soil samples were examined using standard geotechnical tests. The assessment of collapsibility potential of soil samples was carried out using the standard ASTM (2003). An appropriate sample with collapsible potential was employed to assess the effects of nanomaterials selected. Samples were treated with four types of nanomaterials (nanoclay, nanocopper, nanoalumina, and nanosilica) and combined under different percentages of the total dry weight of the soil. Soil tests were carried out in natural water content and density. The results showed that using various nanomaterials had different effects on the behavior of collapsible soils.
With the reduction of available land resources, the construction of civil engineering structures is carried out on soft soil, which leads to the development of ground improvement techniques such as ...soil stabilization. This research is intended to study the effect of adding nano-SiO
2
on soil engineering properties, especially the shear strength and the unconfined compression strength and maximum dry unit weight, using clayey soil with low liquid limit (CL). Nano-SiO
2
was mixed with soil in three different percentages (i.e. 0.5, 0.7, 1.0 % by weight of the parent soil). The shear strength, unconfined compression strength and maximum dry unit weight of treated specimens were measured by direct shear test, unconfined compression test and compaction test. It was found that increase in nano-SiO
2
content resulted in increase in the angle of internal friction, the cohesion, the unconfined compression strength and maximum dry unit weight of the clayey soil. Based on the obtained results, in order to reach the maximum increase in strength parameters, the optimum nano-SiO
2
content occurs at 0.7 %.
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