Soft Soil Stabilization Using Admixtures From Various Solid Waste Materials
ABSTRACT
Foundations for civil infrastructure built on soft and compressible soils are prone to failure owing to either undrained shear failure or excessive settlement. Therefore, it is essential to improve soft soils by increasing their bearing capacity and reducing their compressibility. Amongst various techniques, addition of specific admixtures to the soft soil is one of the most effective and convenient methods of stabilization. This paper presents a series of experimental studies conducted for soft soil improvement using various admixtures like nylon cord fibers, banana fibers, and plastic waste materials. A comparative analysis of the enhancement of compaction and penetration properties of the treated soil was conducted. It was observed that the values of optimum moisture content, maximum dry density, and California Bearing Ratio of the soil were altered significantly by the addition of admixtures wherein China nylon cord fiber was most effective. An array of concluding remarks were derived from the overall study.
1 INTRODUCTION
Failure of foundations for infrastructure constructed upon soft and compressible soil is evidenced either by undrained shear failure of the supporting soil or excessive settlement (Chang et al., 2008). Therefore, providing a cost-effective foundation for civil infrastructure with the required factor of safety against bearing failure and an acceptable magnitude of settlement is imperative for long-term safety and serviceability (Sánchez-Garrido et al., 2022). Subsoil existing in significant regions worldwide consists of soft alluvial clay or soft marine clay deposits in coastal areas (Basack et al., 2023). Consequently, it is vital to augment the strength and stiffness of the soft soil; this technique is termed as ‘ground improvement’ (Basack et al., 2022a). Various types of ground improvement techniques adopted around the world have been primarily classified as mechanical stabilization, consolidation, and chemical stabilization (Basack et al., 2022b).
In the case of mechanical stabilization, soft soil is subjected to external impact energy such as compaction or blasting, blending, or replacing the poor soil with better quality materials or soil reinforcement, where stiffer materials such as compacted fine or coarse aggregates are used to strengthen the soft soil (Afrin, 2017). The consolidation technique is specifically applicable to soft clay, which includes the application of preloading on the ground surface and allowing the clay layer to consolidate. To accelerate the consolidation process, a series of vertical drains are often used to assist radial consolidation. Stone columns, sand compaction piles, and prefabricated vertical drains are included in this category of soft ground improvement techniques (Basack et al., 2022). The use of chemical additives or admixtures to enhance soft soil performance is termed chemical soil stabilization. Among the particular techniques of chemical soil stabilization are stabilization by cement, lime, and bituminous emulsion (Cabezas et al., 2019).
Using certain admixtures for soft soil has often been considered as a combination of mechanical and chemical stabilization. Apart from acting as stiffening materials to improve the overall strength and rigidity of soft dirt, admixtures often undergo chemical reactions with soil particles to alter their geotechnical properties. The application of bagasse ash, stone dust, or other similar materials used as admixtures has been a few examples of this category (Basack et al., 2021).
2 LITERATURE REVIEW
A brief overview of the concepts and field applications of soil stabilization by admixtures has been discussed by Puppala et al. (2015). The authors described a diverse array of admixture treatment techniques, encompassing the formulation of stabilizers and their respective dosages, together with experimental mix design procedures, field building practices, and quality control evaluations.
A laboratory-based investigation on the influence of fly ash and lime used as admixtures on the geotechnical properties of expansive soil was performed by Ji-ru and Xing (2002). The stabilization was visualized by alteration in soil texture, Atterberg limits, compaction parameters, and CBR. Choobbasti et al. (2010) studied the influence of rice husk ash and lime as admixtures for controlling the swelling potential of soft clay. The method was found to assist in the effective chemical reaction between the admixtures and clay particles and in the enhancement of the geotechnical qualities of soft ground.
Another technique of applying sawdust ash as admixture to increase strength of unstable soil was performed by Butt et al. (2016). This industrial waste material was observed to be a cost-effective and suitable strengthening ingredient for base and sub-base course in flexible pavement construction. Jalal et al. (2020) performed an extensive review regarding the utilization of calcium-based admixtures for expansive soil stabilization. The authors provided an in-depth analysis of the effects of calcium-based stabilizers on the physicochemical attributes of soft soils.
Renjith et al. (2021) studied the improvement of fly-ash-based soil stabilization techniques for highway building. They found that the application of enzymes as an additive improved the strength of the fly ash-treated soil. The utilization of specific industrial waste materials including steel slag, blast furnace slag, and phosphor-gypsum for treating construction residue soil was conducted by Chen et al. (2024). This research examined the engineering features of construction residual soil treated with a specific admixture, studying how organic matter concentration, dose, and curing age affect unconfined compressive strength. The long-term performance was also studied in wet–dry cycle and water stability tests.
It is an innovative approach to address plastic pollution by incorporating solid plastic waste into the subgrade pavement layers. Plastic waste can be used as a sustainable alternative in road construction, thereby reducing environmental pollution and improving waste management practices. By repurposing plastic waste in this manner, this practice contributes to circular economy principles and provides a practical solution for reducing plastic accumulation in landfills and oceans (Amena, 2022).
The application of leftover plastic materials to improve soft soils is an emerging trend. Small-sized strips or pieces derived from waste plastic bottles or other materials, used as admixtures to virgin soil, were found to provide satisfactory results in soil stabilization (Singh and Mittal, 2019; Gangwar and Tiwari, 2021). Attempts have also been made to use strips of plastic-mesh textile bags in combination with fly ash treated soil, which indicated significant increment in shear strength properties of soft clay (Bitar et al., 2024). Other recent techniques include the use of banana fiber reinforcements derived from banana trees and cut into small strips (Gobinath et al., 2020; Bawadi et al., 2020) and China nylon cord obtained from waste rubber tyres (Jafari and Esna-ashari, 2012).
3 MOTIVATION AND RESEARCH METHODOLOGY
Waste plastic materials in various forms are widely used by citizens and are available everywhere in communities (Pilapitiya and Ratnayake, 2024). A similar situation also exists for waste rubber tyres obtained from vehicles (Tian et al., 2024). In addition, banana trees exist in approximately 135 countries around the world (Li et al., 2024). Although waste plastic materials, banana trees, and waste tyres are widely available, their applications for soil stabilization are still not thoroughly investigated. An in-depth investigation of the utilization of large volumes of these waste materials as admixtures for soft soil stabilization is yet to be conducted, although the use of various conventional materials in ground improvement has been studied in detail.
This study seeks to address this research gap. This particular research has aimed to bridge this gap through a set of comprehensive laboratory tests and comparative analyses. The research methodology includes extensive experimental investigation in a geotechnical engineering laboratory with the objective of studying the effectiveness of the above-mentioned waste materials as admixtures for stabilizing soft soil. Various materials were collected in appropriate quantities, including soft soil, waste plastics, banana tree branches, and China nylon cord. Disturbed soil samples were tested to determine their engineering properties. In the next step, various admixtures were cut to the desired shapes and sizes, intimately mixed with the soil samples, and subjected to laboratory testing to observe alterations in the geotechnical parameters of the treated soils. Thereafter, in-depth analyses and interpretations of the test results were obtained, followed by a comparative study.