Introduction

Landfills serve as crucial facilities for the disposal and management of solid waste and the design of effective landfill liners is essential to prevent environmental contamination [1]. Traditional compacted clay liners (CCLs) have historically been widely used as landfill liners due to their effectiveness in restricting the flow of liquids, such as leachate, and providing a barrier between waste and the surrounding environment [2]. However, there are several reasons (Such as: Limited availability of clay, High cost, Environmental Impact and Long term performance) so that traditional CCLs are being reconsidered and alternative liner materials are being explored [3].

Bentonite, a predominantly composed mineral from the smectite group, has found extensive use as the optimal material for constructing landfill liners and barriers [4]. Its widespread adoption can be attributed to its distinctive attributes, including characteristics like high shrinkage, high swelling, compressibility, remarkably low hydraulic conductivity, sufficient absorption capacity, and low shear strength [5]. Likewise, the characteristics of bentonite are remarkably impacted by the presence of explicit monovalent and divalent cations, like sodium (Na+) or calcium (Ca2+) [6]. Research underscores the fact that sodium (Na+) bentonite exhibits superior swelling capacity and markedly lower hydraulic conductivity when compared to its calcium (Ca2+) counterpart [7]. This inherent superiority in modest performance has established sodium bentonite as the preferred choice for landfill liner systems [8]. This strategic selection is made possible by its propensity for optimal swelling behaviour, ensuring effective barrier performance, while its minimal hydraulic conductivity adds an additional layer of security against potential leakage and contamination [9]. While bentonite has numerous favourable properties for landfill liners, there are certain difficulties related with its utilization. One of the main concern is related with its susceptibility to desiccation and subsequent shrinkage, which can prompt cracks and compromise the trustworthiness of the liner [10]. Additionally, the swelling behavior of bentonite can be affected by changes in moisture content, potentially causing uneven expansion and contraction [1, 5]. This can result in uneven stress distribution within the liner material [11]. To address some of the challenges associated with bentonite, the combination of sand and bentonite has been explored. This mixture aims to leverage the strengths of both materials. Sand, being granular and less prone to desiccation, can provide structural stability to the liner, counteracting the shrinkage issues of bentonite [5, 12]. When sand is incorporated into a bentonite mixture, it can enhance the overall mechanical properties, such as shear strength and load-bearing capacity [13]. Depletion in the amount of natural sand has led to exploring the suitable alternative material to be used as a geomaterial alone or, in combination with other materials. For such purposes, various alternatives of sand-like; pond ash [14], lateritic soil [14], crushed shale [15], red mud [16], granular activated carbon [17], industrial waste residues [17] have been explored.

Rajasthan, India, stands as a prominent global hub for marble production, contributing to approximately 95% of the nation’s output and securing its position as the world’s largest manufacturer [18]. This concentrated marble production, while economically significant, inadvertently ushers in a significant environmental challenge. The quarrying and processing operations result in the generation of substantial marble waste, exacerbating environmental concerns due to improper disposal practices on land [18]. Marble dust, a by product of this industry, has found utility in various construction domains. Its role spans diverse applications, including enhancing concrete properties as a filler [19], stabilization in highway construction [19], and participation in brick manufacturing owing to the fine particles in marble slurry [20]. Intriguingly, marble dust boasts favorable geotechnical characteristics, such as elevated shear strength, heightened permeability, and a coarser particle size. This intriguing profile positions it as a prospective material for diverse geotechnical purposes, such as subgrade construction, embankment projects etc [18]. In fact, a handful of studies have even delved into the potential of marble dust to enhance soil properties [18]. Yet, the comprehensive exploration of marble dust’s performance when amended with bentonite remains an detailed research. Investigating this amalgamation is pivotal as it holds the potential to serve as an alternative geotechnical material within sand-bentonite (S-B) blends [21]. Fly ash, which is a by product of coal combustion in thermal power plants. Fly ash possesses pozzolanic properties and is known to exhibit cementitious behavior when mixed with appropriate binders [22]. Soil Stabilization: Fly ash is utilized to stabilize and improve the engineering properties of soils, reducing plasticity, increasing shear strength, and mitigating settlement [5]. Embankment and Road Construction: Fly ash is employed as a construction material for embankments and road bases, providing cost-effective solutions and reducing environmental impact [4]. Due to its abundance and potential beneficial properties, numerous studies have investigated the use of fly ash in geotechnical applications. The combination of bentonite and fly ash to form a composite liner system has shown promising potential in enhancing the physical properties of landfill liners [17, 23]. The high swelling capacity and low permeability of bentonite, coupled with the pozzolanic properties of fly ash, offer the possibility of creating a synergistic composite that exhibits improved hydraulic conductivity, enhanced compaction characteristics, and increased shear strength [23, 24].

However, the promising potential of utilizing marble waste and fly ash as alternatives to sand remains largely unexplored in the context of various geotechnical applications, including their viability as liner materials in landfill liner and their suitability for embankment construction. Despite their untapped potential, comprehensive investigations into the feasibility and effectiveness of these materials in such applications are relatively scarce [8]. The proper design and construction of landfill liners are essential to safeguard the environment and public health by preventing the leachate, a highly polluting liquid formed as waste decomposes, from infiltrating into the surrounding soil and contaminating groundwater resources [3]. Geotechnical properties, such as hydraulic conductivity, compaction characteristics, shear strength, and compressibility, play a pivotal role in determining the performance and longevity of landfill liners [8]. Hence, visualizing the positive impact of fly ash on geotechnical properties of soil, it can be used as landfill liner material as an alternative to sand with bentonite.

The novelty of this study lies in its exploration of marble dust and fly ash as alternatives to sand in landfill liners, particularly in combination with bentonite. While previous research has investigated the individual properties of these materials, their synergistic effects when incorporated into landfill liners remain largely unexplored. By comprehensively assessing the geotechnical properties of these novel blends, this study aims to provide valuable insights into their suitability and effectiveness as sustainable alternatives to traditional landfill liner materials.

The present study is aimed to investigate the geotechnical properties of marble dust and fly ash amended with bentonite for its application as an alternative to S-B mix. Thus, detailed experiments on Sand-Bentonite mixes (S-B) are also conducted to examine the geotechnical properties and, for performance evaluation of Marble dust-Bentonite (MD-B) and Fly ash-Bentonite mixes (FA-B) [25]. The detailed experimental investigations of S-B, MD-B and FA-B mixes include the determination of physical properties (Atterberg’s limits and swell indexes), compaction characteristics [maximum dry density (MDD) and optimum water content (OWC)], California Bearing Ratio, Angle of internal friction and cohesion and physicochemical analysis. However, the comparison on permeability and swelling characteristics of mixes are the scopes for future research [26].

Materials and methodology

Material used

Bentonite used in the present study is collected from the Barmer district, Rajasthan which is predominated with fine particles. Fly ash is collected from the thermal power plant Kota, Rajasthan, whereas the marble dust used in the present study is bring from Makrana, Nagaur, Rajasthan and sand is collected locally near to Poornima University, Jaipur, Rajasthan.

Energy dispersive X-ray analysis reported that bentonite is predominated by silica and alumina, fly ash is predominated by silica, alumina and calcium, marble dust have calcium as major constituents and silica and alumina are major predominated chemicals in sand.

The Table 1 reported that bentonite is predominated with Na (5.24%) as predominant chemical followed by Mg (1.76%) with negligible amount of calcium hence considered as Sodium Bentonite. Further, Fly ash is predominated with Al (17.70) and Ca (13.32%), Marble dust predominated with Ca (14.51%) and negligible amount of Si and Al, Sand is constituents as Si (40.94%) and Al (13.57%).

Table 1 EDAX analysis of Bentonite, Flyash, Marble dust and Sand
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Methodologies followed

Mixture selection and formation of samples

Considering the limited research on the imminent usage of marble waste and fly ash as suitable substitutes for sand when amended with bentonite for landfill liner, This study includes a different combination including marble dust-bentonite and fly ash bentonite mixes [27, 28]. The results got from these marble dust-bentonite and fly ash bentonite mixtures get compared with sand- bentonite combinations. This far reaching approach empowers us to measure the exhibition and expected benefits of these eccentric materials in contrast with conventional sand-based combinations when utilized amended to bentonite for landfill liner material [29].

For notation purpose throughout the manuscript, the selected mix proportions of Fly ash (FA)-Bentonite (B) (%FA +%B), Sand (S)-Bentonite (B) (%S + %B) and Marble Dust (MD)-Bentonite (B) (%MD + %B) are designated as 100FA + 0B, 95FA + 5B. 90FA + 10B, 85FA + 15B, 80FA + 20B, 75FA + 25B, 70FA + 30B, 65FA + 35B, 60FA + 40B, 0FA + 100B, 100S + 0B, 95S + 5B, 90S + 10B, 85S + 15B, 80S + 20B, 75S + 25B, 70S + 30B, 65S + 35B, 60S + 40B, 0S + 100B, and 100MD + 0B, 95MD + 5B, 90MD + 10B, 85MD + 15B, 80MD + 20B, 75MD + 25B, 70MD + 30B, 65MD + 35B, 60MD + 40B, 0MD + 100B, respectively [21, 29].

The selected material for the present study went through an exhaustive and fastidious readiness cycle to guarantee their consistency and dependability. At first, all materials were exposed to a drying technique to dispense with any innate dampness content. In this way, these dried materials were sieved through a 425-micron IS sieve, guaranteeing that they met the predetermined molecule size measures [8]. The amounts of S + B, FA + B and MD + B for various mixtures were meticulously measured using dry weight considerations to achieve a high degree of homogeneity. The dry blending stage followed, where the foreordained measures of S + B, FA + B and MD + B were mixed energetically until a reliable variety and surface were accomplished, ensuring consistency inside the combinations. In order to facilitate a thorough wet mixing process, distilled water was added to each mixture in accordance with its Optimum Water Content (OWC) requirements [23]. After that, the samples were allowed to settle for a period of 24 h to achieve equilibrium and ensure uniform saturation. The samples were used for experiments following this mellowing period, maintaining the desired saturation and uniformity throughout the study. This careful arrangement was urgent in guaranteeing the quality and dependability of the examples utilized, empowering exact and significant trial and error [28].

Physicochemical analysis (pH and electrical conductivity)

The mixtures of FA-B, S-B and MD-B are prepared at the ratio of 1:5 i.e. 20 gm solid: 100 ml distilled water, and are stirred at a certain interval for 1 h. Before performing the experiment, calibration of pH meter is necessary with 4.0, 7.0, and 9.20 buffer solutions, and the pH value of samples is measured after 1.5 h [30]. Thereafter, the electric conductivity of FA-B, S-B and MD-B mixes is determined by same samples [31].

Laboratory works

All experiments in the present study followed the IS code to decide the geotechnical properties of both the parent materials and their different combinations. All experiments were directed carefully under controlled room temperature conditions, decreasing inside the scope of 23 to 31 degrees Celsius [26]. The methodology utilized for finding out the geotechnical properties of the Fly ash-Bentonite (FA-B), Sand-Bentonite (S-B) and Marble Residue Bentonite (MD-B) combinations are detailed in Table 2.

Table 2 Geotechnical properties of materials (Sand, Marble Dust, Fly ash Bentonite)
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Result and discussion

Physicochemical analysis of S-B, MD-B and FA-B mixes

The physicochemical analysis of (pH and electrical conductivity) of MD-B, S-B and FA-B mixtures are presented in Fig. 1. An identical result is observed while visualizing the variation of pH for MD-B, S-B and FA-B in Fig. 1. The pH of Marble dust, Sand and Fly ash increases from 8.35 to 9.91, 8.54 to 9.22 and 8.81 to 11.41 with the addition of bentonite up to 20%, 25% and 35% respectively [21].

Fig. 1
figure 1

pH and EC value of sand, fly ash and marble dust amended with Bentonite content

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The increment in the pH value of marble dust, sand and fly ash can be attributed due to cation exchange and hydrolysis mechanisms. Bentonite releases positively charged ions such as calcium, potassium, and sodium (cation exchange) into the mixture, elevating pH [41]. Hydroxide ions on bentonite’s surface contribute to hydrolysis, leading to the release of alkaline hydroxide ions, further increasing pH [8]. The diffuse double layer get increases with addition of bentonite which ultimately increases the ph of marble dust, sand and fly ash due to the aggregation of clay particles [28]. The buffering effect of bentonite tends to stabilize pH, while at higher bentonite concentrations, potential dilution of alkaline compounds from marble dust, sand and fly ash might influence the observed pH reduction [28]. Moreover, intricate chemical reactions between the two materials, including the formation of new compounds or dissolution of specific minerals, could contribute to the observed pH fluctuations. This falling in pH after certain addition of bentonite is due to decrement in the concentration of salt cations with the reduction in the content of sand, marble dust and fly ash [28, 41].

It is reported from Fig. 1 that the EC value of marble dust, sand and fly ash increased from 0.088 ms/cm, 0.131 ms/cm, 0.07 ms/cm to 0.197 ms/cm, 0.20 ms/cm, 0.108 ms/cm respectively with addition to bentonite content. As the proportion of bentonite in the mixture increases, there is a gradual rise in EC values of marble dust, sand and fly ash. This phenomenon can be predominantly attributed to cation exchange and ionic migration mechanisms [18]. Bentonite’s cation exchange capacity leads to the release of positively charged ions (such as calcium, potassium, and sodium) into the mixture, enhancing the ion concentration and, consequently, EC [18, 28]. The interaction between the released ions and the conductive environment of the mixture contributes to the overall increase in EC. Furthermore, the presence of hydroxide ions on bentonite’s surface, combined with the inherent alkaline nature of bentonite, could promote an increase in ion mobility and conductivity within the mixture [15]. This phenomenon can be accentuated as the bentonite content increases, resulting in the observed incremental trend in EC values. The intricate interplay of cation exchange, ion migration, and hydroxide ion contributions from bentonite shapes the EC dynamics [8].

Index properties of S-B, MD-B and FA-B mixes

The effect of Bentonite on atterberg’s [liquid limit (LL), plastic limit (PL), plasticity index (PI), and shrinkage limit (SL)] of marble dust, sand and fly ash is analysed and compared as shown in Fig. 2, 3 and 4 respectively [42].

Fig. 2
figure 2

Liquid Limit of sand, fly ash and marble dust amended with Bentonite content

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Fig. 3
figure 3

Plastic Limit of sand, fly ash and marble dust amended with Bentonite content

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Fig. 4
figure 4

Plasticity Index of sand, fly ash and marble dust amended with Bentonite content

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Effect on liquid limit (LL)

The influence of varying bentonite content on the liquid limit (LL) of marble dust (MD), sand (S), and fly ash (FA) mixtures demonstrates intriguing trends that can be explained by their distinct properties and interactions is presented in Fig. 2. As the percentage of bentonite increases, a general increment in LL is observed among all mixes [43].

In the case of marble dust (MD), the LL rises from 17.2% at 0% bentonite to 73.45% at 40% bentonite. This significant increase in LL can be attributed to the clayey nature of bentonite, which possesses high water absorption and swelling properties [24, 41, and 28]. The added bentonite particles absorb water and expand, creating a more cohesive and plastic mixture, ultimately leading to an increase in LL. For sand (S), the LL rises from 27.2% at 0% bentonite to 89.92% at 40% bentonite. While sand has relatively low natural plasticity, the introduction of bentonite imparts finer particles that fill voids between coarser sand particles [8]. This increases the water-retaining capacity and promotes cohesion, causing an increment in LL. In the case of fly ash (FA), the LL increases from 38% at 0% bentonite to 110% at 40% bentonite. Fly ash, being a by product of coal combustion, inherently contains fine particles with some natural plasticity. The observed phenomenon can be attributed to the remarkable water retention capacity of Bentonite particles [8, 28]. Upon contact with water, Bentonite particles create a diffused double layer around themselves, leading to an enhanced water holding capacity. Thus, when Bentonite is brought into fly ash blends, this property becomes instrumental in prompting versatility inside the initially non-plastic fly ash particles [44].

The uniform pattern of rising LL across the three mixtures highlights the predictable impact of bentonite on their plasticity and water-holding capacity. This is because of the ability of bentonite to adjust the particle arrangment and enhance cohesion, prompting more prominent water retention. However, it’s vital to take note of that the greatness of the LL increment differs in view of the inherent properties of MD, S, and FA [45].

Effect on plastic limit (PL)

The impact of varying bentonite content on plastic limit (PL) of marble dust (MD), sand (S), and fly ash (FA) combinations uncovers captivating experiences into their plastic way of behaving, affected by the unique properties of bentonite is presented in Fig. 3. As the percentage of bentonite increased, a rising trend in PL is seen across each of the mixtures [46].

In the case of marble dust (MD), the PL increases from 0 at 0% bentonite to 28.11% at 40% bentonite. This substantial increment in PL is attributed to the water retention capacity and swelling characteristics of bentonite. As bentonite particles come into contact with water, they create a diffused double layer around them, enhancing water-holding capacity [28, 44]. This leads to greater moisture absorption by MD particles, increasing their plasticity and thus the PL. For sand (S), which inherently possesses low plasticity, the PL increases from 0 at 0% bentonite to 26.66% at 35% bentonite. Bentonite’s water retention capacity and cohesive properties contribute to filling gaps between sand particles, creating a more cohesive matrix that results in an elevated PL [8, 41]. Similarly, fly ash (FA), with minimal natural plasticity, exhibits an increase in PL from 0 at 0% bentonite to 31.41% at 40% bentonite. The swelling characteristics of bentonite in the presence of moisture induce plasticity in the originally non-plastic fly ash particles, leading to an enhanced PL [47].

Effect on plasticity index (PI)

The impact of varying bentonite content on the plasticity index (PI) of marble dust (MD), sand (S), and fly ash (FA) mixtures unveils insightful patterns that can be elucidated through the unique characteristics of bentonite is presented in Fig. 4. With an increasing percentage of bentonite, a consistent trend of elevated plasticity index is evident across all mixes [48].

For marble dust (MD), the PI increases from 17.2 at 0% bentonite to 45.34 at 40% bentonite. This substantial rise in PI is a result of the interplay between liquid limit (LL) and plastic limit (PL). As bentonite’s water retention capacity and swelling properties trigger an increase in LL and PL, the resultant expanded range between the two parameters leads to a higher PI. This signifies greater potential for plastic deformation and moldability in MD-B mixtures [49]. Similarly, sand (S) exhibits an increase in PI from 27.2 at 0% bentonite to 55.22 at 35% bentonite. The introduction of bentonite enhances water retention, cohesion, and workability, creating a more moldable mixture. The interaction of the cohesive bentonite particles with the originally non-cohesive sand contributes to the observed increase in PI. In the case of fly ash (FA), the PI rises from 38 at 0% bentonite to 78.59 at 40% bentonite [50]. Bentonite’s ability to induce plasticity in non-plastic FA particles results in an expanded plastic range, thereby boosting PI. The rise in liquid limit and plastic limit, as observed previously, underscores the significant role of bentonite in altering PI [20].

Effect on shrinkage limit (SL)

The effect of varying bentonite content on the shrinkage limit (SL) of marble dust (MD), sand (S), and fly ash (FA) mixtures reveals intriguing insights into their behavior under drying conditions, influenced by the unique properties of bentonite as presented in Fig. 5. As the percentage of bentonite increases, a nuanced trend emerges, highlighting the role of bentonite in modifying shrinkage characteristics [51].

Fig. 5
figure 5

Shrinkage limit of sand, fly ash and marble dust amended with Bentonite content

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In the case of marble dust (MD), the SL increases from 0.00 at 0% bentonite to 10.61 at 40% bentonite. This significant increment in SL is attributed to bentonite’s ability to retain moisture and mitigate the drying process [19]. The introduction of bentonite particles, with their water-absorbing properties, acts as a moisture reservoir within the mixture. This hinders rapid moisture loss during drying, reducing the extent of shrinkage and resulting in a higher SL [48, 51].

Similarly, for sand (S), the SL increases from 0.00 at 0% bentonite to 17.45 at 40% bentonite. Bentonite’s water retention capacity and cohesive nature contribute to a more cohesive mixture that retains moisture for longer periods [44]. This cohesive environment limits the extent of shrinkage during drying and leads to an elevated SL.

In the case of fly ash (FA), the SL increases from 0.00 at 0% bentonite to 10.11 at 40% bentonite. Bentonite’s capacity to retain water translates to reduced moisture loss during drying, curbing the magnitude of shrinkage. The cohesive characteristics induced by bentonite further contribute to this effect [28].

These trends illustrate the role of bentonite in enhancing the moisture retention capacity of these materials, resulting in reduced shrinkage during drying. Understanding these changes is crucial for landfill liner applications where drying-induced shrinkage influences material behavior, such as in construction, where cracks and deformations must be minimized [19, 28].

Compaction characteristics of MD-B, SD-B and FA-B mixes

The Fig. 6 presented the compaction characteristics for mixtures of marble dust (MD), sand (S), and fly ash (FA) at different percentages of bentonite. As per the observed data in Fig. 6, there is a consistent decrease in the MDD values as the percentage of bentonite increases. The reduction in MDD with increasing bentonite content can be attributed because bentonite particles absorb water, they become hydrated and expand [24, 28]. This expansion disrupts the packing of adjacent soil particles, leading to increased porosity and decreased soil density [15]. Additionally, the hydrated bentonite acts as a lubricant between soil particles, reducing interparticle friction and making it harder to achieve high compaction densities [41].

Fig. 6
figure 6

Compaction characteristics for marble dust, sand and fly ash amended with Bentonite content

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The decrement in the maximum dry density can also be reported due to water-absorbing property of bentonite causes an increase in the overall water content of the soil mixture as bentonite is added. Higher water content can lead to a reduction in soil cohesion and, consequently, lower MDD values. Excess water can also contribute to the dilation of soil particles during compaction, preventing them from settling into a denser configuration. Further, the addition of bentonite also alters the structure of the soil matrix [52]. It tends to create a more open and less densely packed soil structure, which is less amenable to achieving high dry densities during compaction [17]. The bentonite particles themselves can occupy space within the mixture, displacing soil particles and increasing porosity and bentonite imparts greater cohesion to the soil mixture. While cohesion is essential for soil stability, an excessive increase in cohesion can make it more challenging to compact the soil to higher densities are another reasons behind the reduction in the maximum dry density [8, 44, and 23].

The Fig. 6 presented the Optimum Water Content (OWC) values for mixtures of marble dust (MD), sand (S), and fly ash (FA) at different percentages of bentonite content. Notably, there is a consistent increase in the OWC values as the percentage of bentonite increases. Following are the identified reasons for the increment in the OWC value of MD, S, and FA by increasing the bentonite content are (i) Hydration of Bentonite, (ii) Improved Lubrication, (iii) Increased Cohesion, (iv) Particle Disruption and (v) Optimal Packing of Hydrated Bentonite [52, 53].

Free swell and modified free index of MD-B, SD-B and FA-B mixes

Free swell index and Modified free swell index (MFSI) of Marble dust, Sand and Fly ash increased with addition of bentonite content from 0 to 40% as presented in Fig. 7 [54, 55].

Fig. 7
figure 7

Free swell index and Modified free swell index (MFSI) of Marble dust, Sand and Fly ash amended with Bentonite content

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As the percentage of Bentonite increases from 0% to 100%, both MFSI and FSI for Marble Dust show a significant upward trend. This indicates that the addition of Bentonite has a pronounced effect on the swelling behaviour of Marble Dust [56].

The increase in MFSI and FSI can be due to Bentonite’s high water-retaining ability and its capacity to make a gel structure when hydrated [23]. This gel structure prevent the free movement of water particles, which swells the material and absorb more water. The higher Bentonite results in higher swelling because of the expanded accessibility of Bentonite particles to associate with water.

Like Marble dust, the MFSI and FSI for Sand also increase with the addition of Bentonite. Be that as it may, the increment isn’t quite so steep as reported with Marble dust [57]. Sand has a coarser surface contrasted with Marble dust, and its particles have less surface area for Bentonite to interact with. Consequently, while Bentonite actually improves the swelling behavior of Sand, the impact is less pronounced. The increasing trend in MFSI and FSI proposes that even within the sight of coarser particles, Bentonite can significantly alter the swelling properties of the material [58].

The MFSI and FSI of Fly ash also show a increasing pattern with addition of Bentonite content. Similar to Sand, Fly ash has larger particles size compare to Marble dust, which brings about a less sensational impact of Bentonite on its swelling behavior. Notwithstanding, the vertical pattern in MFSI FSI actually means that Bentonite assumes a part in modifying the water-absorption capacity of Fly ash [48, 58]. This could be especially significant in applications where Fly ash is utilized in construction or environmental remediation, as it shows that Bentonite can be utilized to change its hydraulic properties [59].

California bearing ratio of MD-B, SD-B and FA-B mixes

The experimental result of California Bearing Ration (CBR) in unsoaked and soaked condition of Marble Dust (MD), Sand (S), and Fly ash (FA) at varying percentages of Bentonite are presented in Fig. 8.

Fig. 8
figure 8

Unsoaked and Soaked California Bearing Ratio values for Marble Dust, Sand and Fly ash amended with Bentonite content

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As the percentage of Bentonite increases from 0% to 40%, the Unsoaked CBR of Marble Dust (MD-B) decreases significantly. This decrease can be attributed to the addition of Bentonite, which enhances the fine-grained nature of the mixture [60]. Because of Bentonite (considering its fine content), the mixture become less stable under unsoaked conditions, resulting lowered the CBR value [15, 28]. Additionally, the soaked CBR of Marble dust-bentonite (MD-B) also decreased by increasing bentonite content. This reduction is due to the improved moisture sensitivity of the mixture when Bentonite is added. Bentonite has a high water-absorbing capacity and swells when in presence with water, which can prompt decreased strength and stability in the soaked condition [16, 23, 18, and 41]. Like Marble dust, the Unsoaked CBR of sand decreased with addition of bentonite content. The addition of Bentonite increased the fines content in the sand, making it less stable and resulting a lower Unsoaked CBR. The soaked CBR of Sand additionally decreased with addition of Bentonite content. The fines content of Bentonite makes the mixtures more susceptible to moisture-induced reduction in strength and stability when soaked [23].

Similar with marble dust and sand, the unsoaked CBR of fly ash (FA-B Blends) decreased with addition of Bentonite content. The fines content of bentonite adversely impact the Unsoaked CBR. The soaked CBR of Fly ash also decreased with addition of bentonite content, that is because of the moisture sensitivity of bentonite [61].

In summary, the changes in fines content and the moisture sensitivity introduced by bentonite makes the mixtures less stable under both unsoaked and soaked conditions, resulting in lower CBR values [23, 41].

Effect on angle of internal friction and cohesion of MD-B, SD-B and FA-B mixes

The variation in the angle of internal friction (Φ) and cohesion for three different materials (Marble dust - MD, Sand - S, Fly ash - FA) with varying bentonite content (B) are presented in Fig. 9.

Fig. 9
figure 9

Effect on angle of internal friction and cohesion of Marble Dust, Sand and Fly ash amended with Bentonite content

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Fig. 10
figure 10

Effect on permeability of MD-B, SD-B and FA-B mixes

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As the bentonite content increases from 0% to 40%, the angle of internal friction (Φ) of marble dust decreases from 25.50 to 19.34 [62]. This phenomenon is primarily due to the lubricating effect of bentonite particles. Bentonite is a type of clay with small, plate-like particles that can act as a lubricant between larger particles like marble dust [8, 41]. The addition in bentonite content decreases the frictional resistance between particles, making it simpler for them to slide past one another [16, 23, and 44], resulting decrement in the angle of internal friction. Accordingly, the point of inner grinding diminishes. Cohesion of marble dust increments from 15.60kPa to 28.67kPa as the bentonite content increments from 0% to 40%. This is because of bentonite particles can form a bond between adjoining particles, expanding the strength of the material. The higher the bentonite content, the more bonds are formed, prompting greater cohesion [43, 44].

The angle of internal friction (Φ) of sand decreases from 23.00 to 15.67 as the bentonite content increases. The lubricating effect of bentonite particles which reduced the resistance to particle movement within the sand [45] is the primary reason behind the reduction in angle of internal friction. Cohesion of sand also increases from 17.83kPa to 27.00kPa with bentonite content 0% to 40% respectively. The bonding effect of bentonite particles enhances the cohesion between sand particles, making the material more resistant to shear forces [16].

The angle of internal friction of fly ash decreases from 19.82 to 10.75 as bentonite content increases from 0% to 40% respectively. This decrease can be attributed to the lubricating effect of bentonite particles within the fly ash, allowing particles to move more freely. Cohesion of fly ash increases from 14.00kPa to 28.12kPa as bentonite content increases from 0% to 40% respectively. Bentonite particles enhance the cohesive strength of fly ash by forming bonds between particles, which resist shear forces [63].

In summary, the variation in the angle of internal friction (Φ) and cohesion of these materials with changes in bentonite content is mainly due to the lubricating and bonding effects of bentonite particles. Increasing bentonite content reduces the frictional resistance between particles and enhances the cohesive strength by promoting particle bonding. These effects ultimately influence the shear behavior and mechanical properties of the materials [64].

Effect on permeability of MD-B, SD-B and FA-B mixes

The variation in the permeability of marble dust, sand and fly-ash with varying bentonite content (B) from 0% to 40% are presented in Fig. 10. The experimental results showcase a systematic reduction in permeability with increasing percentages of Bentonite in the mixture of sand (S-B), marble dust (MD-B), and fly ash (FA-B), suggesting a clear trend in the effectiveness of the mixture for a landfill liner application.

The decrease in permeability can be elucidated by the unique properties of Bentonite, a clay known for its exceptional swelling capacity upon hydration. As Bentonite content rises, the clay particles imbibe water and undergo volumetric expansion, effectively reducing the interstitial spaces between the coarser particles of sand, marble dust, and fly ash. This swelling action is particularly prominent in the initial stages (0 to 25% Bentonite content), where the permeability experiences a decline about 85% to 100%.

Furthermore, the intricate interplay of Bentonite with the other components contributes to improved particle packing within the mixture. The fine particles of Bentonite fill voids between the larger particles, leading to a reduction in overall porosity. The establishment of a more compact and cohesive structure is evident from the decreasing trend in permeability.

Due to bentonite content the clogging of pores becomes more pronounced, hindering the movement of water through the composite material. The fine-scale interactions between bentonite and the other constituents manifest as a cumulative effect, creating a progressively impermeable barrier. This property is crucial for landfill liners, where the prevention of water percolation and the migration of contaminants is paramount.

The inclusion of Bentonite at varying percentages showcases its role in transforming the mixture into an effective barrier material for landfill applications. The observed permeability values, highlight the potential of this composite material in mitigating environmental risks associated with landfill sites. In conclusion, the systematic reduction in permeability observed in this study underscores the significance of Bentonite as a key component in the development of landfill liners, providing a foundation for further research and practical applications in environmental engineering.

Influence of waste marble dust and fly ash as landfill liner material

The incorporation of waste marble dust and fly ash as alternative materials in landfill liners, in place of traditional sand, presents intriguing possibilities and challenges. These experimental results demonstrate the significant impact of bentonite content on various properties of these mixtures, shedding light on their suitability for such applications [27, 42, and 8].

The observed increase in pH values with the addition of bentonite, attributed to cation exchange and hydrolysis mechanisms, suggests that these alternative materials may contribute to improved alkalinity in landfill liner systems. Bentonite’s role in releasing positively charged ions and hydroxide ions enhances pH levels, potentially enhancing the liner’s resistance to acidic leachate [51].

Electrical conductivity (EC) values also rise as bentonite content increases, indicating enhanced ion concentration and mobility. This proposes that waste marble dust and fly ash, when blended in with bentonite, can possibly offer better conductivity properties, which might be worthwhile in manging leachate in landfill applications [47, 48].

The increase in liquid limit (LL), plastic limit (PL), and plasticity index (PI) with higher bentonite content suggests that these alternative mixtures exhibit greater plasticity and water retention capabilities compared to sand. This property can be advantageous for landfill liners, as it indicates improved resistance to deformation and cracking [65].

Furthermore, the increased shrinkage limit (SL) with higher bentonite content highlights the potential for reduced shrinkage during drying conditions, which is crucial in maintaining the integrity of landfill liners over time [60, 65].

Compaction characteristics, as evidenced by the decreasing maximum dry density (MDD) and increasing optimum water content (OWC), need careful consideration. While the altered compaction properties could present difficulties in accomplishing desired densities, they additionally recommend that the mixtures become more moisture sensitive with higher bentonite content [61].

The free swell index (FSI) and modified free swell index (MFSI) results represent that waste marble dust and fly ash, with bentonite content, exhibit increased swelling behavior. This property could influence the liner’s performance, particularly under changing moisture conditions [32, 58]. The California Bearing Ratio (CBR) results suggest that the unsoaked and soaked CBR values decrease with higher bentonite content, indicating potential challenges in achieving adequate bearing capacity and stability for landfill liners [49, 52, 59]. The influence of marble dust and fly ash in conjunction with Bentonite on permeability, as indicated by the experimental results, aligns with the EPA’s recommendations for landfill liner materials. The observed decrease in permeability suggests that the composite mixture has the potential to meet or surpass regulatory requirements, showcasing promise for practical applications in landfill engineering while adhering to environmental protection standards.

In conclusion, the incorporation of waste marble dust and fly ash, along with bentonite, as alternative materials for landfill liners offers several advantages, including enhanced alkalinity, plasticity, and resistance to shrinkage [66]. However, the altered compaction characteristics, increased moisture sensitivity, and swelling behavior should be carefully considered in the design and application of these materials [58, 63, and 34].

Conclusion

In this study the detailed experimental investigation are performed on Benonite-Marble dust, Bentonite-Sand and Bentonite-Flyash mixes. Following are the important conclusion can be drawn from the experimental evaluation:

  1. 1.

    The addition of bentonite to waste marble dust, sand, and fly ash mixtures significantly increased pH and electrical conductivity (EC). This rise in pH was attributed to cation exchange, hydrolysis mechanisms, and increased ion concentration due to bentonite. The EC increase was primarily driven by cation exchange and ion migration, highlighting the complex interplay of these mechanisms with bentonite content.

  2. 2.

    The liquid limit (LL), plastic limit (PL), plasticity index (PI), and shrinkage limit (SL) of marble dust, flyash and sand increased with addition of bentonite content. The enhancement in the cohesion, water retention, and moldability of S-B, FA-B and MD-B mixture attributed due to bentonite’s water-absorption and swelling properties. Understanding these modifications is indispensable for different applications, including landfill liners where the control of these properties can be worthwhile for accomplishing desired performance and limiting potential issues, for example, shrinkage-induced cracking. The swelling behavior of marble dust, sand, and fly ash is enhanced by bentonite’s water-absorbing capacity and gel-forming properties. While the impact is most articulated in marble dust, considerably coarser-textured sands and fly ash experience striking changes, proposing the adaptability of bentonite in adjusting water absorption characteristics.

  3. 3.

    A consistent decrease in maximum dry density (MDD) is observed with addition of bentonite to marble dust, sand, and fly ash mixtures due to factors such as water absorption, reduced soil cohesion, altered soil structure, and increased cohesion from bentonite. Conversely, the optimum water content (OWC) increase with addition of bentonite content, influenced by hydration, improved lubrication, enhanced cohesion, particle disruption, and optimal packing of hydrated bentonite.

  4. 4.

    The addition of Bentonite to Marble Dust, Sand, and Flyash mixtures leads to a significant reduction in both Unsoaked and Soaked California Bearing Ratio (CBR) values. This decrease is primarily attributed to the increased fines content and heightened moisture sensitivity introduced by Bentonite. These changes collectively diminish the stability and strength of the mixtures under unsoaked and soaked conditions.

  5. 5.

    The addition of bentonite to Marble Dust, Sand, and Fly Ash mixtures leads to notable changes in their angle of internal friction (Φ) and cohesion. These alterations are primarily driven by the lubricating and bonding effects of bentonite particles, resulting in reduced friction and increased cohesive strength with higher bentonite content.

  6. 6.

    The addition of bentonite to Marble Dust, Sand, and Fly Ash mixtures decreased the permeability. The fine particles of Bentonite fill voids between the larger particles, leading to a reduction in overall porosity. The establishment of a more compact and cohesive structure is evident from the decreasing trend in permeability.

The findings suggest that incorporating bentonite into waste marble dust, sand, and fly ash mixtures enhances their properties such as cohesion, water retention, and plasticity, making them suitable for landfill liner applications. However, it also leads to reduced stability, increased fines content, and heightened moisture sensitivity, necessitating careful consideration to ensure the desired performance and durability of the liners in managing waste containment and preventing environmental contamination.

The utilization of waste marble dust and fly ash as alternatives to traditional sand in landfill liners holds promise for enhancing alkalinity, plasticity, and resistance to shrinkage. However, the altered compaction properties, heightened moisture sensitivity, and swelling behaviour necessitate careful consideration in their application. Further research is essential to assess their long-term performance under specific environmental conditions, highlighting the need for a comprehensive evaluation of these alternative materials in landfill liner systems.