A review on innovative approaches to expansive soil stabilization: Focussing on EPS beads, sand, and jute

2.1 Bibliometric analysis

Bibliometric studies strengthen the connection between academic research and practical engineering, bridging gaps in technology transfer and knowledge sharing. By analysing highly referenced articles, engineers gain crucial insights for problem-solving and innovation. Using bibliometrics helps identify key technologies and methods with a significant impact in engineering. In the present study, we have focused only bibliometric analysis on keywords to support the current work and restrict the bibliometric analysis up to author keywords and occurrence.

2.1.1 Bibliometric analysis based on author keywords distribution

Keywords act as markers to the core themes and subjects of research. In this segment, we dissect the author keywords to uncover the pivotal areas of interest within soil stabilization research. The data were extracted from the Web of Science Core Collection Database, ensuring a comprehensive grasp of academic discourse. Each research entry was tagged with its respective author keywords. This metadata formed the foundation for our analysis. With a plethora of topics encapsulated within soil stabilization research, our analysis spotlights the dominant themes and materials. It is clear from Figure 1 that the larger nodes in the visualization likely represent the dominant themes or terms that emerged from the analysis. Where large nodes labelled “stabilization,” “EPS beads,” “jute,” and “sand,” it suggests that these are the primary focus areas within the dataset. Links between nodes, especially between dominant themes, suggest that there are publications or works that discuss these themes together. Such as link between “EPS beads” and “stabilization,” it could imply that EPS beads have been frequently discussed in the context of soil stabilization. Similarly different colours indicate different clusters or groups of related terms. As there is a cluster around “EPS beads” or “jute,” it means that there is a significant amount of literature or discussion around these specific topics, and they have their own set of associated sub-themes or keywords. Moreover, smaller nodes or those on the periphery might represent emerging themes or those that are not as dominant but are still present within the dataset. These could be potential areas of future research or lesser-explored areas within the field. Additional to it links between seemingly unrelated nodes indicate interdisciplinary research or collaboration between different fields. Such as a link between “jute” (a natural fibre) and a term from another domain might suggest an innovative application or study. Areas with a high density of nodes and links can be seen as “hotspots” in the research area. These are areas with a high concentration of related works and can be considered significant or dominant sub-fields within the broader domain.

Figure 1

Keyword analysis map depicting the connections between them.

2.1.2 Findings

In the realm of soil stabilization research, several keywords emerge as central themes. “Soil stabilization” leads the way with 110 mentions, underscoring its foundational importance. “Stabilization” and “UCS” further highlight the methodologies and testing mechanisms inherent to this field with 60 and 56 mentions, respectively. Materials like “cement” and “sand” also play pivotal roles, as indicated by their 50 and 35 mentions. Other significant keywords include “lime,” “strength,” and “microstructure,” each painting a picture of the diverse facets of soil stabilization studies. The data in Figure 2 provide a clear roadmap of the core themes in soil stabilization research. While “soil stabilization” stands as the overarching theme, the presence of other keywords indicates the diversity of methods, tests, and materials that researchers delve into. Recognizing these keywords is crucial as they not only guide researchers to the most relevant studies but also hint at potential areas for future exploration.

Figure 2

Top 20 author keywords in soil stabilization research.

The “Keyword Plus” section in research databases typically consists of author-independent keywords that emerge from the titles of the references cited in articles. These keywords provide additional insights into the thematic elements or underlying themes of the research.

On the basis of our analysis of the occurrences of the specified keywords in the “Keyword Plus” data, we found the further mentioned findings. For the keyword “Stabilization,” it had the highest occurrence, signifying its overarching relevance in the dataset. It suggests that a significant portion of the research is focused on methods, techniques, or innovations related to soil stabilization. Keyword “sand” indicates that many research works delve into stabilization techniques or challenges specifically related to sandy terrains or materials. This could mean studies around desert regions, beachfronts, or areas with loose, sandy soil. In the same way, the Materials & Techniques indicated that “Lime & Fly Ash” are traditionally used materials in soil stabilization. Their frequent mention underlines their continued importance and possibly their combinations or innovations in usage. Additional to it usage, “EPS Beads & Jute” indicated as emerging areas of research. EPS beads and jute could be alternative or novel materials being tested or applied for stabilization purposes. Although “geofoam” indicate that it might be an emerging or less-explored material or technique in the context of the dataset. “GGBS,” with no mentions, it might either be a very nascent topic or could be represented under a different term or abbreviation in the dataset.

The frequency of these keywords as depicted in Figure 2 indicates areas of focus in the research community. For instance, while traditional methods like using lime for stabilization might be well established and continue to be a focus, newer methods or materials like EPS beads or jute might be in the experimental or validation stages. Areas with fewer mentions can be goldmines for researchers looking for less-trodden paths or innovative topics. In summary, the occurrences of these keywords in the “Keyword Plus” data offer a snapshot of the prevailing trends, focus areas, and emerging topics in soil stabilization research. They highlight the materials, techniques, and areas that are garnering attention, thus providing a compass for researchers, students, and professionals in the domain.

2.2 Materials

Similarly, studies that push a little more to stabilize the expansive soil sand in the present study are as follows: Premalatha and Sabarishri [49] presented a case study where lime sand piles were used to stabilize an expansive soil, resulting in improved strength and reduced volume change characteristics. Bahia and Ramdane [46] conducted an experimental program and found that adding sand to expansive soil improved soil consistency and reduced swelling. Hussein et al. [50] reviewed different methods for stabilizing expansive soil and mentioned sand as a material to enhance engineering properties. Garg et al. [51] investigated the use of industrial waste products, including sand, for stabilizing expansive soil and concluded that these materials can improve the engineering characteristics of the soil. Therefore, the papers collectively suggest that sand can be an effective additive for stabilizing expansive soil.

Recent research has shifted towards sustainable and eco-friendly materials. Among these, sand, EPS beads, and jute fibres have garnered attention due to their unique properties and potential environmental benefits. Sand being granular and non-cohesive, which aids in reducing the plasticity of the soil, thereby increasing its shear strength. EPS beads are lightweight and versatile, which can reduce the weight of the soil, making it suitable for applications where weight is a concern, such as embankments. Similarly, jute is a natural fibre that not only aids in soil reinforcement but also contributes to sustainability, being biodegradable and eco-friendly.

2.3 Soil stabilization

Soil stabilization refers to the process of improving the physical properties of soil, enhancing its ability to support infrastructure. The process involves the use of various methods and materials to enhance the soil’s strength and durability. Soil stabilization processes are influenced by various factors, including flooding intensity and edaphic factors, although vegetational properties can also influence soil aggregate stability [84]. The stabilization of expansive soils presents a significant challenge in geotechnical engineering, with the efficacy of stabilization methods being heavily influenced by environmental factors such as humidity and ambient temperature. These factors, which can markedly affect soil behaviour and the performance of stabilizing agents, underscore the need for innovative approaches that consider local climatic conditions. Recent studies, such as those conducted by Adin [85], have emphasized the importance of ambient conditions in affecting the mechanical properties of stabilized soils. These studies have shown that humidity and temperature have intricate effects on these properties. Thus, it is crucial to develop adaptable stabilization techniques that can effectively respond to varying environmental conditions. Outlook on types of stabilization is shown in Figure 3. Mechanical stabilization involves physical methods like compaction, prewetting, reinforcement, blending, vibration, and dynamic compaction. It aims to densify the soil and rearrange particles to improve shear strength and load-bearing capacity. The combined influences of soil organic compounds binding and coating soil particles, retarding water wettability, and modifying soil porosity are significant mechanisms of mechanical stabilization in soil [86]. Mechanical stabilization is faster but alone may not treat highly expansive or weak soils.

Figure 3

Types of soil stabilization.

Chemical stabilization involves adding binders like lime, cement, fly ash, bitumen, and polymers that alter the soil properties through physio-chemical reactions. It reduces plasticity and swelling potential while increasing strength and stiffness. Chemical stabilization is more effective but involves complex design and testing [87,66].

Some key advantages of soil stabilization include the following:

• Allows use of locally available soils rather than importing stronger soils, reducing costs.

• Accelerates construction schedules since site soils can be treated quickly.

• Improves strength and performance characteristics of weak soils.

• Controls erosion and dust.

Soil stabilization is applied in subgrade preparation for roads, airfields, building foundations, slope stabilization, embankment construction, dust control, etc.

Over the years, numerous methods and materials have been explored to improve soil characteristics, making it more suitable for construction and infrastructure projects. Traditional methods like lime and cement stabilization are often effective but come with environmental concerns and cost implications.

The past studies explore various methods for stabilizing expansive soils, soils that drastically change volume with changes in moisture. Multiple studies (which can be noted from Table 1) found that adding lime and fly ash, industrial by-products, to expansive soil reduces swelling and increases strength. Ji-ru and Xing [88] found that adding 4–6% lime and 40–50% fly ash decreased swelling potential, increased coarse particles, and improved CBR. Similarly, Wubshet and Tadesse [89] concluded that adding 3% lime and 15% bagasse ash, a sugar cane waste product, increased CBR and decreased plasticity. Some papers studied alternative stabilizers. Cementing material of rice husk ash and calcium carbide residue decreased swelling, increased strength, and improved workability in expansive soil [79]. Mohanty [90] discovered that fly ash addition decreased plasticity, increased CBR, and changed grain size in expansive soil. 5% tire rubber powder and 10% cement kiln dust reduced plasticity and increased strength [91]. A few studies looked at more novel stabilizers. Zhang et al. [92] revealed that polyvinyl alcohol and potassium carbonate combination stabilized expansive soil, increased strength, and allowed for surface application. In the research, a 1 m tall soil column was built, where polyvinyl alcohol (PVA) and K₂CO₃ solutions were sprayed on the soil surface to mimic field application. Swelling and strength reduced with depth but remained in the satisfactory range even at 90 cm depth showed potential for direct surface application to stabilize expansive soils to considerable depth. Sugarcane straw ash addition over time increased CBR and UCS in expansive soil [93]. In summary, multiple industrial by-products such as lime, fly ash, and bagasse ash improve the engineering properties of expansive soils. Alternative stabilizers such as rice husk ash, calcium carbide residue, tire rubber powder, and sugarcane straw ash also effectively stabilize expansive soils. Polyvinyl alcohol and potassium carbonate have potential as surface-applied stabilizers for expansive soils. In addition to the materials discussed earlier, several other innovative composite materials have gained attention in various engineering applications due to their unique properties. Other innovative composite materials include basalt fibres, geosynthetic clay liners, shape memory alloys, aerogels, self-healing concrete, graphene, piezoelectric materials, magnetorheological fluids, and biomimetic materials [52,94]. These materials have unique properties and potential applications in various engineering fields, showcasing the versatility and importance of composite materials in addressing complex challenges. Recent studies have also explored the potential of CFRP as a sustainable construction material, focusing on its eco-friendly production processes and the possibility of recycling and reusing CFRP components [95].

Soil stabilization has been an active area of research to improve the properties of problematic soils for construction. Researchers have explored both traditional and innovative techniques for stabilizing soils. Traditional chemical stabilizers like cement, lime, and fly ash have been widely used to treat expansive and soft soils [96]. However, these stabilizers can react adversely with sulphate-rich soils, leading to pavement failure [96]. To address this, researchers have investigated alternative stabilizers like quarry dust and fibres. Kumar and Kumar [97] found that adding quarry dust and Recron 3S fibres to expansive soils improved their properties. Polymers have emerged as promising eco-friendly stabilizers. Different polymers like geopolymers, biopolymers, and synthetic polymers can enhance soil strength, reduce permeability, and inhibit swelling [98]. The interactions between polymers and soils depend on the type of polymer and soil. Cationic and neutral polymers stabilize soils through electrostatic forces and entropy increase, while geopolymers form aluminosilicate gels that bind soil particles [98]. Nanomaterials are an innovative class of stabilizers that are still being explored. Majeed and Taha [94] reviewed how nanoparticles could improve soil properties, though more research is needed on their long-term effects. In addition to chemical stabilizers, mechanical stabilization techniques like deep mixing and jet grouting have been developed. These techniques involve injecting grout into soils to bind particles together [99]. Geosynthetics, another mechanical technique, are synthetic materials that can reinforce and improve drainage in soils [100]. While soil stabilization has advanced, challenges remain. There is a need for standardized testing of stabilized soils, evaluating their in situ properties, improving their durability, and understanding their stabilizing mechanisms better [98]. With the continued research, soil stabilization can be further enhanced to support infrastructure development sustainably.

Overall, the past research shows that many stabilizers can enhance the strength and the volume stability of troublesome expansive soils.

3.1 Materials and properties

The NS used in this study was sourced from Bhopal, India, itself. The soil type has its distinct engineering properties, which form the baseline for understanding the effect of stabilization techniques. Standard construction-grade sand sourced from the local market was used, characterized by its granulometry and non-cohesive nature. The inclusion of sand aims to reduce the plasticity of the soil, thereby improving its shear strength. Table 2 presents the index properties of the host sand utilized in this study. The determination of specific gravity was conducted under the guidelines outlined in ASTM D 854 [101]. The determination of maximum and minimum dry unit weights was conducted using the methods outlined in ASTM D 4253 and ASTM D 854 [102,101], respectively. The material under investigation exhibited a specific gravity of 2.63. Its dry unit weight was determined to be 16.5 kN/m³, corresponding to a void ratio of 0.57. These values were obtained through rigorous experimentation and analysis. The sand sample exhibited a coefficient of uniformity measuring 1.54, indicating a moderate range of particle sizes. In addition, the coefficient of curvature was determined to be 1.1, and the uniformity coefficient was found to be 1.87, suggesting a slightly well-graded particle distribution. Following the Unified Soil Classification System, the sand was classified as SP, denoting poorly graded sand. Similarly, under the AASHTO Soil Classification System, the sand was categorized as A-3. In the present study, sand was mixed at around 20% by weight with the soil.

EPS beads were obtained from a regional EPS block molding company “Shree Insupac Pvt. Lmtd.,” which specializes in the production of EPS geofoam blocks. The beads observed in the study were found to be uniformly white, exhibiting a spherical shape. The size of the beads ranged from 2 to 7 mm. The dosage of EPS beads to be mixed in soil was kept at 1% by volume.

The determination of the unit weight and specific gravity of the EPS beads was carried out using a modified procedure based on a standard test method for fine aggregates, specifically ASTM C128 [103]. In this experiment, a 1-L hydrometer was utilized to investigate the behaviour of beads. The beads were carefully inserted into the hydrometer until it reached a point where the volume appeared to be completely occupied. To achieve a moderate compaction state, the beads were introduced into the hydrometer without any discernible application of compaction force. The determination of the unit weight of the beads can be conveniently achieved by proportionally scaling the net weight of the beads that were employed to fill the bottle. The unit weight of EPS beads was determined to be 16 kg/m³ in this study. The specific gravity (G _s) of the beads was determined through a method involving the filling of voids between EPS beads with distilled water. By calculating the net volume of the beads and subsequently determining the specific gravity, a value of 0.98 was obtained.

Jute is a natural fibre known for its tensile strength and biodegradability. For jute admixture preparation, the jute fibres were cut into 10 mm lengths. Before mixing with the soil, the jute fibres were treated with a 5% NaOH solution for 48 h to enhance their bond with the soil particles. In this study, jute fibres with a length of 10 mm was used. Jute fibres of approximately 10 mm length were added at a concentration of about 0.5% by weight. The specific values for these properties, as obtained from preliminary tests, serve as a reference for evaluating the effects of admixtures. All the optimum dosage of sand, EPS beads, and jute were taken as per the past literature survey as mentioned in the literature review of all three admixtures within the material section.

3.2 Sample preparation

The soil samples used for this study were collected from a depth of 1.5 m below the ground surface to ensure a consistent quality. The NS had a liquid limit of 120%, a plastic limit of 40%, and a natural moisture content of 35%. For all the tests, the NS was air dried, pulverized, and sieved through a 2 mm sieve. The specific gravity of the soil was found to be 2.65, and the particle size distribution was as follows: gravel (5%), sand (20%), silt (40%), and clay (35%).

For compaction test the soil samples were first air dried and sieved through a 2 mm sieve (IS 2720 Part 4 [104]) to remove any large particles. For specific proportions, the dry soil was thoroughly mixed with individual admixtures: sand, EPS beads, and jute fibres. The proportions ranged 1, 20, and 0.5% by weight for EPB beads, sand, and jute, respectively. Water was added incrementally to determine the OMC as per IS 2720 Part 7 [105]. Standard Proctor’s Compaction Apparatus with cylindrical molds of 100 mm diameter and 1,000 cm³ volume was used.

Compacted samples from the compaction test were extruded into cylindrical molds of standard dimensions (38 mm diameter and 76 mm height). The samples were cured for 28 days in a controlled environment. After the curing period, the samples were subjected to unconfined compression using the Universal Testing Machine as per IS 2720 Part 10 [106].

For the CBR test, the soil was compacted in five layers in the CBR mold using a standard compaction hammer. Each layer was given 56 blows using the standard hammer. The standard mold had an internal diameter of 150 mm and an internal effective height of 175 mm as per IS 2720 Part 16 [107]. The sample was then soaked in water for 4 days, allowing it to swell. The soaked sample was subjected to a penetration test using the CBR apparatus.

In case of swelling pressure test sample preparation, the cylindrical specimens with a diameter of 50 mm and a height of 20 mm were prepared. The soil samples mixed with varying proportions of the admixtures were compacted in three layers. Each specimen was then placed in a consolidation ring and subjected to a seating pressure of 5 kPa. The swelling pressure was recorded as the change in vertical stress required to maintain a constant specimen height.

3.3 Tests performed

A series of tests like liquid limit, plastic limit, compaction, UCS, swelling pressure, and CBR tests were conducted to assess the properties of the NS and the stabilized soil. In addition, these tests were performed based on the combination of admixtures to understand their combined effect on soil properties.

The compaction test was conducted to determine the relationship between the moisture content and dry density of the soil when compacted under controlled conditions. For the compaction test, the soil samples were first air dried and sieved through a 2 mm sieve (IS 2720 Part 4) to remove any large particles. For specific proportions, the dry soil was thoroughly mixed with individual admixtures: sand, EPS beads, and jute fibres. The proportions ranged 1, 20, and 0.5% by weight for EPB beads, sand, and jute, respectively. Water was added incrementally to determine the OMC as per IS 2720 Part 7. Standard Proctor’s Compaction Apparatus with cylindrical molds of 100 mm diameter and 1,000 cm³ volume was used. This relationship helps in identifying the OMC at which the soil achieves its MDD. The compaction characteristics can be significantly influenced by the addition of admixtures, and as such, the test was also performed on soil samples stabilized with sand, EPS beads, and jute fibres. Various models have been proposed in the literature to describe the compaction behaviour of soils. One of the widely recognized models is the modified Proctor compaction test [108], which offers a more aggressive compaction effort compared to the standard Proctor test, suitable for larger projects such as highways. Another model, the Zero Air Voids Curve, describes the relationship between the dry density and moisture content of soil when it is fully saturated. This curve is often used as a reference to compare the compaction characteristics of different soils [109].

Past research has shown that materials like EPS beads, being lightweight, can shift the compaction curve to the left, indicating a reduction in the OMC. Jute fibres, being organic, can absorb water and potentially influence the moisture–density relationship differently [110]. In the context of our study, where we are using admixtures like sand, EPS beads, and jute, it is essential to understand how these materials influence the standard compaction curves.

4.1 Engineering properties of soil

Table 3 presents a comprehensive overview of the engineering properties of the original soil. The soil is highly clayey, as evidenced by its liquid limit of 120% and plastic limit of 40%, indicating its ability to hold water. The natural water content and specific gravity of the NS were measured to be 35% and 2.65, respectively. The particle size distribution of the soil, as shown in Figure 5, demonstrates that it contains 5% gravel, 20% sand, 40% silt, and 35% clay. This distribution indicates that the soil has a higher proportion of silt and clay particles, which is typical for clayey soils.

Figure 5

Engineering properties of soil.

4.2 Compaction

Table 4 presents the results of a compaction test carried out on the NS and its various mixtures with different stabilizing agents. The natural soil without any additives, referred to as NS, showed an MDD of 1.48 g/cm³ and an OMC of 22%. These results indicate that the soil attains its maximum density at a relatively high moisture content, which is typical for clayey soils.

Sand, being coarser, tends to increase the density but reduces the required moisture content. This is evident from the results obtained – an MDD of 1.58 g/cm³ and an OMC of 20%. EPS beads, being lightweight, tend to reduce the overall density of the mix. The resulting MDD is 1.52 g/cm³ with an OMC of 21%. Jute fibres, on the other hand, may slightly increase the density due to their binding effect. However, they would not significantly affect the moisture content. The MDD is 1.54 g/cm³, and the OMC is 21.5%. When all the admixtures are combined, there is a balancing effect. The resulting MDD is 1.62 g/cm³, and the OMC is 19.5%. This combination may provide the best compaction properties among the samples tested.

4.3 UCS

The UCS test is used to measure the strength of soil under compression. Compacted samples from the compaction test were extruded into cylindrical molds of standard dimensions (38 mm diameter and 76 mm height). The samples were cured for 28 days in a controlled environment with a temperature of 27 ± 2°C and a relative humidity of 65 ± 5%. After the curing period, the samples were subjected to unconfined compression using the Universal Testing Machine as per IS 2720 Part 10. According to Table 5, the NS had a certain UCS value, which served as a baseline. The UCS value of 72.25 kPa, as shown in Figure 6, indicates that the NS has moderate strength. When admixtures were added, a noticeable increase in UCS was observed. Sand aids in particle interlocking and reduces the soil’s plasticity, resulting in improved compressive strength. As a result, UCS increased to 102 kPa. The UCS of EPS beads-stabilized soil was 93.5 kPa, showing a slight decrease. Since EPS beads are lightweight, they may not contribute significantly to the soil’s compressive strength. However, the weight reduction can be beneficial in certain applications. Jute fibres contributed to a moderate increase in UCS of 89.25 kPa. The fibres likely form a network within the soil matrix, providing additional reinforcement, but the strength contribution is less than that of sand. When all admixtures were combined, the UCS increased to 119 kPa. This suggests that the combination of all admixtures provides superior strength enhancement than any single admixture. Although the combination of all three admixtures with soil gave a marginal increment in UCS value, further mixing of sand, EPS beads, and jute in two additional proportions other than 20, 1, and 0.5% was done, resulting in 21 and 19% for sand, 0.9 and 1.1% for EPS beads, and 0.6 and 0.4% for jute, respectively. When the UCS test was performed on these new proportions, it resulted in 110 kPa for the first new proportions and 124 kPa for the second new proportions of all three admixtures.

Figure 6

UCS of different samples.

4.4 Swelling pressure

The swelling pressure test measures the soil’s expansion potential when exposed to moisture. This parameter gauges the potential of the soil to expand when exposed to moisture. A higher value signifies a greater expansion potential, which can cause significant engineering problems such as pavement heave, building foundation uplift, and pipeline ruptures. For the swelling pressure test, cylindrical specimens with a diameter of 50 mm and a height of 20 mm were prepared. The soil samples mixed with varying proportions of the admixtures were compacted in three layers. Each specimen was then placed in a consolidation ring and subjected to a seating pressure of 5 kPa. The swelling pressure was recorded as the change in vertical stress required to maintain a constant specimen height. The admixtures played a crucial role in moderating this behaviour. With a swelling pressure of 42 kPa as noted in Table 6, the NS exhibits a high swelling potential. This is expected given its high clay content (as indicated by a liquid limit of 120%). Sand introduction reduces the swelling pressure to 36 kPa. Sand particles, being larger and non-cohesive, dilute the clay fraction, thereby reducing its ability to absorb water and expand. EPS Beads had a neutral effect, with minimal changes observed in the swelling pressure. The swelling pressure drops slightly to 34.8 kPa with EPS beads. These beads, being lightweight and porous, might reduce the density of the soil matrix, leading to a slight reduction in swelling potential. However, the inclusion of jute results in a swelling pressure of 37.2 kPa, shown in Figure 7. Jute fibres might provide some binding effect, restricting the free movement of clay particles and thereby slightly reducing swelling. Also given their organic nature and moisture absorption capacity, jute fibres reduced the swelling pressure of the soil. A combined addition of all admixtures leads to the lowest swelling pressure of 32.4 kPa. This suggests a synergistic effect where the combination of all admixtures provides better swelling control than any individual component.

Figure 7

Swelling pressure test results.

4.5 CBR

The CBR is a critical measure used to determine the load-bearing capacity of soils, particularly in the realm of road construction. Higher CBR values indicate that the soil has a better capacity to bear loads, making it a preferable choice for constructing road subgrades. For the CBR test, the soil was compacted in five layers in the CBR mold using a standard compaction hammer. Each layer was given 56 blows using the standard hammer. The standard mold had an internal diameter of 150 mm and an internal effective height of 175 mm as per IS 2720 Part 16. The sample was then soaked in water for 4 days, allowing it to swell. The soaked sample was subjected to a penetration test using the CBR apparatus. The test was conducted in a controlled environment with an ambient temperature of approximately 25°C. The CBR value for the NS is 5%. This relatively low value suggests that the soil in its untreated state possesses a limited load-bearing capacity. Such soils might not be suitable for heavy-duty applications without stabilization. The introduction of sand increases the CBR to 7% sand and can be seen in Table 7, and being granular and non-cohesive provides better interlocking between particles, leading to enhanced load distribution and resistance to deformation. The CBR value drops to 4% with EPS beads. While EPS beads can reduce the overall density of the soil, they might not significantly enhance its load-bearing capacity. The decrease suggests that while EPS beads can be beneficial for certain properties (like reducing weight), they might not be the best choice for enhancing bearing capacity. Incorporating jute gives a CBR of 6%. Jute fibres can create a binding effect, leading to better cohesion and a moderate increase in the load-bearing capacity of the soil. Combining all admixtures results in a CBR of 6.5%. This value is higher than most individual additives but not as high as sand alone. It suggests that while a combination can provide a balanced set of properties, some admixtures might counteract the benefits of others in terms of load-bearing capacity.

The graph depicted in Figure 8 is a spider (or radar) chart that depicts the CBR values for different admixtures. Each axis of the spider chart represents one of the admixtures: ‘NS’ and its combination with all other admixtures. The distance from the centre of the chart to a point on an axis represents the CBR value for that particular admixture. The further out the point is, the higher the CBR value. The blue filled area connects the CBR values for all admixtures, giving a visual representation of the distribution of CBR values across the different admixtures. The area is filled with a light blue colour to make it visually appealing and to easily differentiate between the different sections.

Figure 8

CBR test results.

In summary, the graph provides a visual comparison of the CBR values for different admixtures. From the graph, you can quickly discern which admixture has the highest or lowest CBR value and how they compare relative to each other.

4.6 Comparative analysis research finding

The addition of admixtures resulted in varied effects on the soil’s properties. Sand, for instance, was effective in enhancing the soil’s shear strength, making it ideal for applications demanding higher load-bearing capacities. EPS beads, on the other hand, provided weight reduction benefits. Jute fibres contributed both to strength enhancement and moisture regulation.

A detailed comparison, backed by quantitative data, would offer insights into the optimal admixture proportions and their suitability for specific geotechnical applications.

1. Liquid and plastic limit: The NS had a high liquid limit, indicating a clayey nature. The addition of sand or jute would reduce this limit due to dilution or binding effects, respectively. However, combining all admixtures might produce a synergistic effect, balancing out the soil properties to an optimal range.

2. Compaction (MDD and OMC): Sand improved the MDD due to its granular nature, while EPS beads and jute had a lesser impact. The combination of all admixtures yielded the highest MDD, suggesting that the collective effect of the admixtures was beneficial. OMC was generally reduced with the addition of admixtures, with the combined effect resulting in the lowest OMC.

3. UCS: Sand significantly improved the UCS, demonstrating its efficiency in enhancing the soil’s compressive strength. Jute and EPS beads had moderate impacts. Combining all admixtures yielded the highest UCS, showing that the combined effect offers the most comprehensive strength enhancement.

4. Swelling pressure: Sand and jute reduced swelling pressure due to dilution and binding effects, respectively. EPS beads had a lesser impact. The combination of all admixtures had the most significant reduction in swelling pressure, highlighting their synergistic effect in controlling soil expansion.

5. CBR: Sand had the most significant positive impact on CBR, indicating its efficacy in enhancing the soil’s load-bearing capacity. Jute and EPS beads had moderate impacts. The combination of all admixtures produced a CBR value that, while higher than the NS and most individual additives, was not as high as sand alone.

4.7 Synergy of materials

The combined use of sand, EPS beads, and jute fibres in soil stabilization demonstrated a synergistic effect. Where sand’s granular nature improved inter-particle friction, thereby enhancing the soil’s shear strength. This was evident in the increased UCS values of sand-stabilized soil samples. EPS beads led to a slight decrease in UCS due to their lightweight nature, and their inclusion provided weight reduction benefits, proving advantageous in specific scenarios where reduced soil weight is desired. The biodegradable nature of jute fibres added an eco-friendly dimension to the stabilization process. Their reinforcement mechanism, rooted in the interlocking of fibres with soil particles, showcased a promising avenue for organic soil stabilization. Overall, the results obtained in the current study are in line with the findings of several previous research works. The significant improvement in the strength and load-bearing capacity of the expansive soil due to the inclusion of randomly distributed jute fibres is consistent with the observations of Prasanna and Kumar [57,53]. The optimal jute fibre content range of 1–2% reported by Prasanna and Mendes [57] agrees well with the findings of the present study. Moreover, the reduction in swelling potential and improvement in the geotechnical properties of the expansive soil achieved by the combined use of sand, EPS beads, and jute fibres at optimal dosages are supported by the work of Khajeh et al. [111]. They found that the strength reduction caused by EPS beads alone can be effectively compensated by the inclusion of stabilizing agents like zeolite and cement. Furthermore, the concept of active composition proposed by Khajeh et al. [111] provides a plausible explanation for the synergistic effect observed in the current study, where the admixtures complemented each other in enhancing the soil’s properties. The decrease in swelling potential and improvement in CBR value with the increasing sand content in the clay mixture, as reported by Afriani and Perdana [112], further reinforces the effectiveness of sand as a stabilizing agent in the present study. These collective findings highlight the potential of using sustainable and eco-friendly materials like jute fibres, EPS beads, and sand in combination with traditional stabilizers for the effective stabilization of expansive soils in construction projects.

4.8 Regression analysis

To further substantiate the findings, regression analysis was conducted to study the relationship between admixture proportions/properties and the resulting UCS. The regression models, underpinned by R ² values of 96% for UCS exhibit a commendable fit to the research data. Preliminary results indicate a linear relationship for sand and jute fibre proportions, while a nonlinear relationship was observed for EPS beads.

Detailed regression models, along with coefficients and statistical significance levels, will be provided, adding depth and robustness to the research. In the present study, a regression analysis was performed to investigate the relationship between the UCS of the stabilized soil and the dosages of the three admixtures: sand, EPS beads, and jute.

The regression equation derived for first case is given by:

where β ₀ is the intercept which is equal to 76.5 kPa and β ₁, β ₂, and β ₃ are the regression coefficients for sand, EPS beads, and Jute, respectively, which are equal to 1.31, 18.2, and 12.8 kPa.

The coefficients β ₁, β ₂, and β ₃ provide insight into the relative impact of each admixture on the UCS. A positive coefficient indicates that as the dosage of the admixture increases, the UCS also increases, and vice-versa. R ² value for this case was found to be 0.96 or 96%. This value suggests a strong correlation between UCS and the combination of all three admixtures. The dosages of sand, EPS beads, and jute show a significant influence on the UCS of the stabilized soil. The model can be instrumental in predicting the UCS based on the admixture proportions. Therefore, the model explains about 96% of the variance in the UCS values, which means the model fits the data quite well. However, the equation also satisfied few past research works when compared [113,114,115,116].

The UCS values showed an increase when the soil was stabilized using the admixtures. The regression analysis indicated a positive correlation between the UCS and the combined use of all three admixtures (sand, EPS beads, and jute). This suggests that the combined use of these admixtures enhances the compressive strength of the soil.

Specifically:

• Sand showed the most significant positive impact on UCS among individual admixtures.

• EPS beads and jute also showed positive effects on UCS, but slightly less than sand.

• The combined use of all three admixtures resulted in the highest UCS, indicating a synergistic effect.