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    Comparative Study of Swelling Pressure in Expansive Soils considering Different Initial Water Contents and BOFS Stabilization
    (Hindawi Ltd, 2023) Keskin, Inan; Salimi, Mahdi; Ateysen, Eylem Ozge; Kahraman, Selman; Vakili, Amir Hossein
    In terms of geotechnical engineering, swelling soils are among the most important soil groups whose characteristics should be determined in detail before design studies. These types of soils cause significant damage to engineering structures. For this reason, it is expected that the swelling behavior of the soils will be known in advance to minimize the damage that may occur in the structures. Within the scope of this study, the swelling pressures of bentonite clay with 10 different water content were determined by keeping all conditions the same to reveal the effect of water content on soil swelling behavior. In this context, bentonite-type (montmorillonite content) clay, which has a very swelling property when it comes in contact with water, was used in the experiments. The fixed volume swelling pressure test method was used in the experiments and all samples were compressed at the same rate and placed in the swelling test device. In all samples left to swell with pure water, measurements were made for 10 days and the effects of swelling pressures on the initial water content were discussed. Thereafter, another swelling soil was stabilized using basic oxygen furnace slag (BOFS) during different curing times, and after performing the swelling pressure test, the results were compared with the findings obtained from different initial water contents. According to the results, while the swelling pressures increase in the regions close to optimum water content, significant decreases are observed in swelling pressure values in wetter and drier regions than in optimum water content. Finally, the results indicated that the application of BOFS, albeit small, after the proper curing time can significantly affect the swelling behavior of bentonite, even more than changing the initial water content.
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    Dynamic response, durability, and carbon footprint analysis of the marl clay treated with sodium lignosulfonate as a sustainable-environmentally friendly approach
    (Pergamon-Elsevier Science Ltd, 2024) Vakili, Amir Hossein; Keskin, Inan; Salimi, Mahdi; Kol, Hamiyet Sahin; Onur, Mehmet Inanc; Abdullah, Abdulhadi Imhmed Abdulsalam; Awam, Awass Hamad Mohamed
    In the current study, the marl clay was improved by different contents of sodium lignosulfonate (NLS) and cured at different times and then, all samples were subjected to Bender Element (BE), Unconfined Compressive Strength (UCS), and Brazilian Tensile Strength (BTS) tests considering two different dry condition (DC) and wet condition (WC). The durability of the samples was further controlled by a special technique, namely the soaking test. The carbon footprint analysis was undertaken for a low-volume trench project to address the sustainability benefits associated with replacing cement and lime as traditional stabilizers with NLS. The results show that the reuse of NLS as a non-traditional alternative for stabilizing marl soil can play an influential role in improving dynamic parameters as well as sustainable development. It has been observed that the CO2 emission decreases up to 5.6 and 4.4 times compared to lime and cement, respectively. Additionally, the use of NLS enhances the UCS by 249%, BTS by 208%, and small strain shear modulus by 117%. Furthermore, reducing the adverse effects of the WC on soil properties, among others, was the main finding of utilizing the NLS in marl stabilization with curing time. NLS-treated marl samples were able to preserve the integrity of their particles even after being soaked in water for a period of 3 weeks. In contrast, the particles of the untreated sample started to disintegrate within a few seconds of initiating the soaking test. Finally, possible equations correlating the dynamic and static moduli were reported in this study.
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    Effect of polypropylene fibers on internal erosional behavior of poorly graded sandy soil stabilized with the binary mixtures of clay and polyvinyl acetate
    (Springer, 2023) Vakili, Amir Hossein; Rastegar, Shahram; Golkarfard, Hossein; Salimi, Mahdi; Izadneshan, Zahra
    Internal erosion refers to the mechanism of separation and movement of soil grains owing to water flow from a porous environment that may cause significant damage to the structures involved. In the present research, an environmentally friendly approach was used to improve the mechanical strength and erosion resistance of a poorly graded problematic sandy soil (SP) sample with a high degree of erodibility and negligible strength. For this purpose, polypropylene fibers (PP) (0, 0.35, 0.5 and 1%) were added to the studied sandy soil stabilized with different contents of clay (0, 5, 10 and 20%) and polyvinyl acetate (PVAc) resins (0, 1.2, 1.5 and 2%). The main goal of this study was to fully replace traditional stabilizers such as cement with durable and sustainable substitutes. The results revealed that the development in the strength of the samples by increasing the curing times was attributed to the time-dependent performance of PVAc content. Furthermore, the poorly graded sandy soil (PGSS) treated with PVAc and clay showed the highest mechanical strength equal to 2580 kPa after 28 days of curing. In terms of the Erosion Rate Index (ERI), the combination of 20% clay and 0.5% fiber along with 1.2% PVAc had the best performance, which was reported as 4.28 after 28 days. Among different samples reinforced by fiber, the highest ERI is related to the samples with 0.5% fibers at the 28-day curing time. The strength of the samples with clay inclusion was significantly higher than that of the samples with either PP fiber or PVAc inclusion, indicating the high potential of clay addition in developing the strength of the poorly graded sandy samples as confirmed by Scanning Electron Microscopy (SEM) analysis. SEM observations revealed that the treated sand sample became denser as the content of the amendments increased.
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    Effects of polyvinyl acetate content on contact erosion parameters of pavement embankment constructed by dispersive soils
    (Springer Heidelberg, 2023) Vakili, Amir Hossein; Salimi, Mahdi; Keskin, Inan; Abujazar, Mohammed Shadi S.; Shamsi, Mohammad
    This study deals with the contact erosion investigation and mechanical properties of both the un-stabilized and polyvinyl acetate (PVAc)-stabilized dispersive embankment layer. To this end, in addition to performing the specific dispersivity identification tests, i.e. pinhole and double hydrometer tests and contact erosion test for measuring the contact erosion parameters, a series of basic geotechnical tests was carried out. The microstructural changes with the aid of scanning electron microscopy (SEM) test and financial analysis were studied respectively to understand underlying mechanisms of stabilization and to estimate the economic benefits owing to PVAc addition. The results indicated that 2% PVAc content was the most effective proportion such that it decreased the dispersion potential, mass loss, and settlement of the dispersive soil by 69.6%, 70.5%, and 68.5% respectively, and at the same time, the strength of the samples increased by 107.4% only after 7 days of curing. The reaction between the polarity carboxyl hydrophilic group of PVAc and the hydroxyl group of the soil led to form the strong hydrogen bonds, and therefore, the structure stability and strength of the soil were enhanced. The formation of reticulated membrane structures and stronger bonds between soil particles, as documented by SEM images, testified to the excellent efficiency of PVAc in dispersive soil stabilization. Finally, the accuracy of available correlations between soil dispersivity and contact erosion parameters was examined, and then, the correlations were developed to cover a broad range of soils by using the results of this study.
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    Experimental investigation of the effect of landfill leachate on the mechanical and cracking behavior of polypropylene fiber-reinforced compacted clay liner
    (Springer Heidelberg, 2023) Falamaki, Amin; Salimi, Mahdi; Vakili, Amir Hossein; Homaee, Mehdi; Aryanpour, Marzieh; Sabokbari, Maryam; Dehghani, Reza
    This paper aims to investigate the effect of leachate on the geotechnical parameters and the cracking behavior of compacted clay liners (CCLs) containing different percentages of polypropylene fibers. Accordingly, 200 compacted clay samples were reinforced with different percentages of fiber contents (FC) (i.e., 0, 0.5, 0.75, and 1%) and prepared with water or leachate to conduct different laboratory tests. First, the physical properties of the clay were determined. Then, the shear strength parameters (i.e., cohesion and friction angle), unconfined compressive strength, and the hydraulic permeability were determined subjected to water or leachate. Notably, the cracking behavior was modeled using visual images of the samples. The leachate increased desiccation cracks in the natural soil from 0.425 to nearly 1.111%. However, the addition of 0.5% (in the case of water) and 1% (in the case of leachate) fiber to the soil reduced the surface desiccation cracks in clay liners to about 0.185 and 0.352%, respectively. In both water- or leachate-prepared samples, the addition of fibers significantly increased the cohesion and friction angle. The shear strengths of the unreinforced leachate-prepared samples were lower than those of the water-prepared samples. The shear strength and unconfined compressive strength of all specimens increased with increasing fiber percentage. The presence of fibers in all samples caused more ductile behavior. The required amount of energy to achieve the maximum strength in the samples increased with increasing FC. By increasing the percentage of fibers, the permeability of the natural soil and the leachate-prepared samples increased. However, the highest permeability was observed in the leachate-prepared samples containing 1% fibers of 8.3 x 10(-10) m/s, which is less than 10(-9) m/s (maximum allowable permeability for clay liners). Finally, the obtained results were satisfactorily confirmed by scanning electron microscopy (SEM) analysis.
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    Investigating the efficacy of nanoclay particles in controlling the contact erosion behavior of dispersive clays
    (Springer Heidelberg, 2024) Vakili, Amir Hossein; Khajeh, Aghileh; Salimi, Mahdi; Patino, Juan Pablo Ocampo; Yaghoubi, Saeed
    Erosion behavior at the interface of different layers is a critical consideration in pavement design and construction. Especially, this issue poses a particular challenge in dispersive clays, which are prone to excessive erosion. The current paper focuses on evaluating the effectiveness of nanoclay in stabilizing and mitigating the contact erosion behavior of dispersive clays. To do so, a range of experimental testing, including double hydrometer, pinhole, contact erosion and unconfined compressive strength (UCS) tests was employed. The findings revealed that incorporating 0.75% nanoclay content yielded significant results, leading to a remarkable 391% increase in the UCS, a notable 58% reduction in dispersivity potential (DP), a 53% decrease in eroded soil mass, and a 29% decrease in the dispersive clay settlement after a 28-day curing period. Additionally, new exponential correlations were successfully developed between soil dispersivity and contact erosion parameters (CEPs) with high coefficients of determination using over 50 contact erosion test results. To facilitate the estimation of CEPs, the values were made dimensionless including the ratios of eroded soil mass (m/m0), settlement (S/H), and void ratio (ef-e0/e0). Finally, scanning electron microscopy (SEM) and microstructural image processing (MIP) confirmed the filling between soil particles and the reduction of the number of voids due to nanoclay incorporation into dispersive clays.
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    Strength and post-freeze-thaw behavior of a marl soil modified by lignosulfonate and polypropylene fiber: An environmentally friendly approach
    (Elsevier Sci Ltd, 2022) Vakili, Amir Hossein; Salimi, Mahdi; Lu, Yang; Shamsi, Mohammad; Nazari, Zeynab
    Lignosulfonate is one of the by-products in the paper and pulp industry that is widely produced around the world and its improper disposal or storage can pose irreparable risks to human health and the environment. Sustainable reuse of this industrial waste as a stabilizing agent not only provides a novel approach in the construction industry, but also prevents the loss of natural resources. In this study, an environmentally friendly strategy involving lignosulfonate as a binder along with the polypropylene (PP) fiber as a reinforcing material was adopted to enhance the characteristics of marl soils from detrimental impacts of freeze-thaw (F-T) cycles. To this end, the pure marl specimens were improved by various contents of lignosulfonate and polypropylene fiber solely and simultaneously and cured for different time intervals. The variables assessed in this study were lignosulfonate content, polypropylene fiber content, curing period as well as the number of F-T cycles. The results showed that the greatest improvement was observed in the samples containing 1.5% lignosulfonate and 0.6% PP fibers, showing the least amplitude of fluctuations in MR reduction upon the F-T cycles. Moreover, freeze-thaw weathering transformed the stress-strain pattern of the samples from strain-softening to hardening behavior as well as increased the ductility behavior. It was observed that the simultaneous application of lignosulfonate and PP fibers led to the complete bonding of soil particles and the formation of interlocking zones around the fiber strands, leading to stronger particle bonding. The results of the Fourier transform infrared (FTIR) test also verified the formation of ionic bonds owing to the inclusion of lignosulfonate in the marl soil and the presence of lignosulfonate in the distance between the mineral layers of the soil. Overall, the reuse of lignosulfonate as a nontraditional alternative to marl soil modification can play an effective role in enhancing the durability and mechanical characteristics as well as sustainable development.
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    A systematic review of strategies for identifying and stabilizing dispersive clay soils for sustainable infrastructure
    (Elsevier, 2024) Vakili, Amir Hossein; Salimi, Mahdi; Keskin, Inan; Jamalimoghadam, Mohammad
    Dispersivity has long been a major concern in civil and geo-environmental engineering, as well as in agricultural engineering and soil sciences. Dispersive clay soils are common, but their prevalence and characteristics vary greatly across different regions of the world, especially in arid and semi-arid areas. These soils are highly unstable and prone to erosion when exposed to water, due to their high concentration of exchangeable sodium ions and large specific surfaces. This can cause serious damage to hydraulic infrastructure. However, identifying and stabilizing dispersive clay soils is crucial for infrastructure projects, as the use of untreated soils can result in irreversible and catastrophic failures due to internal erosion and piping. The systematic management of dispersive clays is crucial to prevent the wastage of fertile agricultural land and land designated for engineering construction. Although industrialization has numerous benefits, it often results in large quantities of waste byproducts that must be managed appropriately to reduce their environmental impact. The reuse of these wastes in soil improvement has become an increasingly popular approach to address both environmental pollution and cost-effectiveness concerns. Despite the growing interest in using waste by-products for soil stabilization, there is a lack of a systematic and comprehensive review of the management, mechanisms, identification systems, and improvement strategies for both traditional and non-traditional stabilizers. Therefore, there is an urgent need to review the available literature to provide a comprehensive understanding of the use of waste by-products for soil stabilization. Such a review could aid in the creation of soil stabilization methods that are both efficient and enduring while minimizing the environmental impact of waste by-products.