Effects of Landfill Leachate on Mechanical Behaviour of Adjacent Soil: a Case Study of Saravan Landfill, Rasht, Iran

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Urban waste in most cities of Iran is dumped without proper standards of landfill construction. Improper implementation of waste barriers leaks off leachate into the surrounding areas, causing soil contamination and other serious environmental
  Vol.:(0123456789)  1 3 International Journal of Civil Engineering https://doi.org/10.1007/s40999-018-0311-2   RESEARCH PAPER Effects of Landfill Leachate on Mechanical Behaviour of Adjacent Soil: a Case Study of Saravan Landfill, Rasht, Iran Nader Shariatmadari 1  · Behnam Askari Lasaki 2  · Hasan Eshghinezhad 3  · Pourya Alidoust 3 Received: 24 June 2017 / Revised: 13 January 2018 / Accepted: 30 April 2018 © Iran University of Science and Technology 2018 Abstract Urban waste in most cities of Iran is dumped without proper standards of landfill construction. Improper implementation of waste barriers leaks off leachate into the surrounding areas, causing soil contamination and other serious environmental problems. The main goal of this study is to determine the possible effects of leachate on the geotechnical properties of contaminated soils around the dump site and estimating a safe zone for a landfill site. In this regard, uniaxial compression, direct shear, consolidation and permeability tests were carried out on several samples to assess the possible effects. SEM tests were also conducted to precisely assess the geotechnical parameters and clarify the possible changes in soil characteristics. Results showed that by increasing leachate concentration, maximum uniaxial and shear stresses decrease, and the volumetric strain increases. This behavior continues by getting closer to the contamination source. A decreasing trend in the cohesion and coefficient of permeability and a relatively low decreasing trend in the internal friction angle (  )  were also observed as the contamination concentration increased. According to the results, a 600 m distance from the contamination source is proposed as a safe zone, in which the soil holds its initial properties. This study provides additional insight into the effects of leachate on the spoil texture of soil. Keywords  Municipal solid waste · Leachate · Contaminated soil · Geotechnical properties · Safe zone Abbreviations BOD Biochemical oxygen demandCOD Chemical oxygen demandTP Total phosphoruspH Potential hydrogen (  )  Friction angle C   Cohesion°C Centigrade k   Coefficient of permeability  A  Cross-sectional area of the sample Δ Q  Average of inflow and outflow Δ t   Interval of time h  Average head loss across the permeameter/ specimen  L  Length of specimen 1 Introduction The increasing rate of urbanization and industrialization around the world and the uncontrolled growth of popula-tion especially in developing countries have led to the ever-increasing generation of municipal solid waste (MSW) [1]. The worldwide limited space for storing the MSW is bound to cause crucial problems in the near future, greatly affect-ing human life.MSW management involves various steps including col-lection, transportation, processing and disposal [2]. Land disposal or landfilling, despite being uneconomical in the long term, is the most commonly adopted method in the world. Generally, MSW disposal follows two procedures: *  Nader Shariatmadari shariatmadari@iust.ac.ir Behnam Askari Lasaki st151040@stud.uni-stuttgart.de Hasan Eshghinezhad eshghinezhad@civileng.iust.ac.ir Pourya Alidoust p_alidoust@civileng.iust.ac.ir 1  Department of Civil Engineering, Iran University of Science and Technology, Narmak, Teharn 16846-13114, Iran 2  School of Civil Engineering, University of Mohaghegh Ardabili, Ardabil, Iran 3  School of Civil Engineering, Iran University of Science and Technology, Narmak, Teharn 16846-13114, Iran   International Journal of Civil Engineering  1 3 (1) open dumping without any protection and design systems method, a method used mostly by developing countries, in that more than 50% of the collected waste in these countries is disposed without any pretreatment and liner systems [3]; and (2) engineered sanitary landfills, which is widespread throughout the developed countries. Protecting systems are used in engineered landfills to minimize the risks of munici-pal solid wastes on the environment and human health (e.g., lining and capping systems), but the operational problems are still inevitable [4]. Both methods still face, the contami-nation of subsurface soils and groundwater by high amounts of heavy metals, which result from improper disposal prac-tices and accidental spills [5, 6]. The free flow of leachate in landfills causes numerous environmental problems, such as soil and groundwater con-tamination [7]. A large volume of leachate is produced in the process of MSW decomposition due to the high moisture content of municipal solid waste. It should be noted that waste composition changes over time, as a result of weath-ering or biodegradation; hence the quality of produced lea-chate will also change over time, making leachate leakage protection ever more important for nature [8]. The main ingredients of leachate are organic hazardous substances such as aromatic and chlorinated aliphatic compounds, phe-nols, phthalates and pesticides; as earlier mentioned, lea-chate concentration of leachate depends on various factors, such as waste composition of waste and other [9, 10]. Pollut- ants, all of which pollutants have accumulative, threatening, and detrimental effects on the survival of aquatic life forms, ecology, and food chains that lead to public health crisis including carcinogenic effects, acute toxicity, and genotox-icity [11–13]. Leachate, as a chemical substance, takes the constituents of the solid waste mass through which it flows. Thus, there is no typical leachate and the site-specific waste mass must be considered in this regard [14].Besides all the mentioned hazardous impacts, the perco-lation of leachates may cause changes in the geotechnical properties of soils [15]. Extensive research has been done towards better understanding the effects of various con-taminants on the soil profile [16–19]. In this regard, many researchers have studied the impacts of hazardous waste leachate on engineering behavior of soils, especially in clays used as barriers in landfill liners and covers [7, 15, 20–22]. Roque and Didier [23] proposed linear expressions for precise soil selection as cover and liner of landfills, due to possible changes that can occur on the geotechnical prop-erties of soils in contact with landfill leachate (with a focus on hydraulic conductivity changes). Studies by Francisca and Glatstein [24] on the long-term permeability of com-pacted clay affected by leachate proved that permeability was reduced in compacted clays due to the microorganism clog of effective pores. Oztoprak and Pisirici [25] reported significant changes in the micro and macro behaviors of polluted clays in the city of Istanbul. Li et al. [26] conducted several tests including permeability, compressibility, and shear strength on polluted clays to assess the possible effects of pollutants on mechanical behavior of soils. The research results of Zhao et al. [27] indicate that different concentra-tions of landfill leachate during microstructure tests (SEM and MIP) and mechanical tests (direct shear, swelling, and permeability tests) considerably impact polluted clays.This research uses two different methods to study the samples. Laboratory tests, namely uniaxial compression, direct shear, consolidation and permeability tests, were car-ried out to study the impacts of landfill leachate leakage on the strength characteristics of the lateritic soils in the Sara-van landfill. To better understand the mechanical behavior of clays under landfill leachate pollution, several microstructure tests (SEM) were conducted. 2 General Information 2.1 Location of the Case Study The 13 ha saravan landfill is geographically located around 20 km of Rasht, Iran (Fig. 1). Up to 700 tons of waste is produced daily in Rasht and most of them are buried in this site without any pre-treatment methods. The adjacent soil of this landfill is classified as CL based on the unified soil classification system (Fig. 2). In addition, the soil’s Atter-berg limits and compression parameters are listed in Table 1. 2.2 Leachate Characteristics On average, the Saravan landfill site generates 4–5 l of lea-chate per second in dry weather and 18 l/s in rainy weather. A total of 1.5 tons of the solid waste leachate is discharged into the environment on a rainy day, both soil and water. Understanding leachate is therefore crucial to better treat the health of the environment. Table 2 illustrates significant physical and chemical properties of leachate.The important point regarding Table 2 returns to high values of cationic constituents of leachate such as NH 4 –N and NO 3 –N. This is well-established fact that the cationic constituents bear a positive electric charge, while the under-lying clay soil of landfill bears negative electric ones. Hence, ion exchange between cationic and anionic particles results in an inter-particle reaction. Actually, interaction between anionic and cationic particles controls the diffusion of lea-chate particles in a contaminated soil and confines the lea-chate leakage to a specific area. In this regard, this is logical to expect that concentration of leachate in soil decrease the friction between soil particles and increases chemical and electrical interactions among clay particles.  International Journal of Civil Engineering  1 3 3 Sample Preparation For purposes of this study and to investigate the changes in the mechanical properties of soil, two sampling methods were used, namely in-situ sampling and sample prepara-tion in the laboratory. In the first method, samples were taken at distances of 100, 200, 300, 400, 500 and 600 m from the landfill site. In this method, soil samples were collected from the uppermost foot of soil using a sample scoop. Actually, the soil was loosened with a shovel or a spade, and after loosening, a scoop was used to collect the sample. The device used for collecting an undisturbed sample is a thin-walled tube 30–60 cm long and 3–8 cm i.d. This tube sampler is pressed or hammered into the soil and then is pulled out, bringing up a core sample which preserves differences in the soil composition with depth. Based on the conducted tests on collected samples, the distance where the soil is completely out of the contami-nation source, at its maximum strength, was determined. Fig. 1 View of Saravan landfill Fig. 2 Grain size curves of tested soils   International Journal of Civil Engineering  1 3 Shear strength variations were also determined at different distances from the landfill.In the second method, clean soil, which was not exposed to leachate at the site, was placed in the oven at 100 °C for 24 h. Then the leachate which was mixed with distilled water in different weight percentages was added to the dry soil. At this stage, the samples were kept in a sealed container for 3 months. Thereafter, the samples underwent standard proctor compaction, direct shear, uniaxial compression and permeability tests. 4 Experiments 4.1 Uniaxial Compression Test Results To determine the intensity of soil consolidation with dif-ferent percentages of solid waste leachate and the effect of distance from the source of contamination on the uniaxial compression strength of the soils, the uniaxial compression test has been used in accordance with the ASTM D2166/ D2166M-13 standard test, and the tests were conducted on molds that are 5 cm in diameter and 8 cm in initial height [28]. To investigate the stress–strain behavior of soils con-taining different percentages of landfill leachate, the data obtained from the uniaxial compression test have been ana-lyzed in two ways: first, the different percentages of leachate were added to the laboratory samples to study the maxi-mum uniaxial compression strength of the soil and the cor-responding uniaxial strain; and second, the maximum uni-axial compression strength of the soil and the corresponding uniaxial strain were evaluated based on the distance from the contamination source. The obtained data were verified once the maximum distance from the contamination source, where the soil retains its natural strength, was obtained, and the results of both methods were compared with each other. The following results were obtained.Figure 3a and Table 3 show that maximum uniaxial stress in each stage was reduced as the leachate concentration was increased. Increasing the leachate concentration decreased the reduction rate, which made the maximum uniaxial stress for the contaminated soil with 70% leachate approximately close to the uniaxial strength of the soil contaminated with 100% of leachate. Unlike the maximum uniaxial stress, the strain decreases as solid waste leachate increases, but this decreasing trend occurs in a very small strain range.Figure 3b and Table 3 illustrate that by increasing the distance from the contamination source also increases the uniaxial compression strength of the soil. The uni-axial compression strength of the soil reached its maxi-mum value at 600 m from the landfill site, therefore the 600 m distance from the source of contamination is the least required distance for removing the effects of Table 1 Atterberg limits and compaction characteristics of the soilMineralValueSpecific gravity2.64Liquid limit (%)40Plastic limit (%)24Plasticity index (%)16Maximum dry density (g/cm 3 )1.54Optimum moisture content (%)23Nature density (g/cm 3 )1.42Nature water content (%)5.6Sand content (2000–75 µm) (%)3.62Silt content (75–2 µm) (%)41.76Clay content (< 2 µm) (%)54.62 Table 2 The leachate characteristics of Saravan landfillLeachate constituentsAverage valuesPH6.24COD (mg/l)39,683BOD (mg/l)14,900VS (mg/l)–Volatile acids (mg/l)150Fe (mg/l)920Ca (mg/l)310Mg (mg/l)112Mn (mg/l)32Zn (mg/l)11Sr (mg/l)–So 4  (mg/l)150NH 4 –N (mg/l)763NO 3 –N (mg/l)3.1Tot–N (mg/l)432Cl (mg/l)648Conductivity (mmho)310Non-volatile matter (mg/l)4600K (mg/l)220Na (mg/l)–Alkalinity (mg/l)–Tot-P1.6As–Pb0.023Cd–Hg–Cr0.2Co0.05Cu0.079Ni0.09Phenol5  International Journal of Civil Engineering  1 3 leachate from the soil. The uniaxial strain correspond-ing to the maximum uniaxial compression strength was also increased by increasing the distance from the source of contamination. The removal of chemical properties of the contaminants from the soil by increasing the distance of the samples from the source of contamination greatly improves the mechanical properties of the soil. Conse-quently, more strain is needed to fail the soil’s structure and reach to its maximum uniaxial compression strength. As seen in Fig. 3a, b, the changes observed in the uniaxial stress, its corresponding strain and the obtained data from both methods show that the experiments were conducted properly. Mosavat and Nalbantoglu [15] obtained similar results to this study. Their results showed a decrease in the unconfined compressive strength of the soils and an increase in contamination. 4.2 Direct Shear Test Results Direct shear test was conducted according to ASTM D3080-04 on compacted clay samples with different percentages of landfill leachate [29]. The sample preparation was also done according to the aforementioned parts, and the displacement rate was 0.6 mm/min during all tests. The main purpose of this test was first to determine the effects of leachate on the shear strength of contaminated soils, and then find a relation between the contamination percentage and the distance in which the shear stress is at its maximum. The results of this experiment are as follows:Figure 4a, b shows the failure envelopes of clear and con-taminated samples. To describe the cohesion coefficient, the graphs should be divided in two separate intervals: lower vertical stresses (< 200 kpa) and above 200 kPa. While the cohesion values decrease as leachate content is increased, this process is not obvious at a 50% or higher pollution. In other words, it could be considered that the higher con-tamination amounts have a cohesion value of a sample with 50% contamination. In the case of vertical stresses above 200 kPa, however, the decreasing trend of the cohesion coef-ficient value is far more obvious at different percentages of pollution.Figure 4b illustrates minor changes in cohesion for dis-tances that range between the 100 and 300 m from the source of contamination, in low vertical stresses. A comparison of Fig. 4a, b shows that the percentage of pollution in the 100–300 m interval is more than 50%.Figure 4a also illustrates that increasing the pollution content in low vertical stresses brings the curve gradients closer to the horizontal surface. The point to consider is that changes in the gradient of low stresses are negligible. The high stress levels are especially important as increase in the stress, regardless of the pollution percentage, do not change the friction angle, and is relatively equal for all the samples. Results pertaining the friction angle are approximately the same in Fig. 4a, b. Fig. 3 Vertical stress versus uniaxial strain curve in samples with different concentrations of landfill leachate and distances from the source of contamination Table 3 Maximum vertical stress and its corresponding uniaxial strain values in samplesDistance (m)Percentage of pollution    max εChange in stress (%)–Natural clay114.80.057––30% polluted96.20.052− 16.2–50% polluted810.05− 29.4–70% polluted60.80.048− 47–100% polluted500.045− 56.40–45.020.041–100–51.040.04113.38200–61.40.04736.38300–81.190.06180.35400–95.620.065112.39500–109.050.067142.22600–119.10.069164.54
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