Fly ash, a by-product of coal combustion, enhances the geotechnical properties of soil, primarily through its two types: class F and class C, known for their pozzolanic and cementitious properties, respectively. Numerous studies have explored the benefits of both types offly ash in stabilizing problematic expansive soils, which are characterized byweak strength, high compressibility, and significant volume changes that can damage infrastructure. However, direct comparisons between class F and class C fly ashes in improving expansive soils are limited. This study aims to fill this gap by conducting a critical review of research from the past 20 years, focusing on the impact of class F and class C fly ashes on the geotechnical properties of expansive clayey soils. Key parameters examined include Atterberg limits, free swell, unconfined compressive strength (UCS), and California bearing ratio (CBR). The findings indicate that both fly ash types reduce liquid limits and plasticity indices of clayey soils, with class C fly ash showing more pronounced effects. Additionally, class C fly ash significantly reduces soil swelling and enhances UCS and CBR, especially due to its higher CaO content. The study provides novel formulas to aid future researchers in predicting the behavior and performance of clayey soils stabilized with these specific fly ash types, offering a comprehensive examination of their geotechnical parameters.

Stabilizing and improving weak and poorly graded soils in road construction projects is a widely used and highly interesting technology. This research study utilizes paper sludge ash (PSA) residues as a geopolymer waste material to stabilize loose and poorly graded sands (SP), improve mechanical properties, and support sustainable pavement development. Geotechnical tests using the unconfined compressive strength test (UCS), Young's modulus (Es), California bearing ratio (CBR), and a direct shear test (DST) assessed the performance and strength development of geopolymer-stabilized soil. The stabilized soil's microstructure and chemical mineralogy were also examined using SEM and XRD. Additionally, a laboratory testing apparatus was designed and developed to assess the permanent strain behavior of subgrade soil and geopolymer-stabilized soil layers under cyclic loading. The research analysed variables including curing duration (1, 3, and 7 days), PSA concentration (5, 10, and 15%), and the type and concentration of alkaline activators (NaOH or Na2SiO3). Soil samples treated with PSA and Na2SiO3 geopolymers showed higher UCS, Es, and CBR values, leading to improved strength from increased N-A-S-H and C-A-S-H gel formation among sand soil particles. On the contrary, the NaOH solution enhanced the strength parameter of geopolymer-stabilized soil samples. The results showed that geopolymer-stabilized soil significantly improved its resistance to permanent deformation after applying loads. The mineralogical examination also shows a high concentration of lime and cubic aluminate, which may be active cementitious pozzolanic material. This research reflects that PSA has promising potential to stabilize sandy soil and improve the design and maintenance of roads and infrastructure in areas with weak soils.

Global economic growth leads to massive plastic waste increase, posing severe environmental challenges worldwide. Addressing it demands innovative solutions like repurposing plastics for construction. Extensive engineering and environmental assessments can accelerate their adoption. This study explores the potential incorporation of plastic waste (in flake and pellet forms) into a cement-treated fine-grained soil through a comprehensive geotechnical experimental testing program and Life Cycle Assessment (LCA) study to assess their environmental sustainability. Experimental investigations were conducted on four distinct plastic types, namely polypropylene (PP), high-density polyethylene (HDPE), polylactic acid (PLA), and polyethylene terephthalate (PET), with varying weight percent inclusions of 2 %, 4 %, and 6 %. Results revealed a decreasing trend in maximum dry densities and strength (both unconfined compressive strength (UCS) and split tensile strength (STS)) with increasing plastic content. Sorptivity of soil generally increased with plastic inclusions, yet in the case of PET, for plastic content > 4 %, a notable drop in the rate of increase was observed. California bearing ratio (CBR) test results indicated a reduction in the CBR values by up to 18.33 % for 6 % plastic inclusions. LCA study findings favoured plastic flakes over pellets as a more sustainable material choice, exhibiting a lower environmental impact across all assessed indicators. This research findings offer insights into the potential utilization of plastic waste and promote sustainable geomaterial choices in road pavement construction.

The Baiyun Canyon area on the Northern Slope of the South China Sea is a potential hotspot for oil and gas resource development, but the sediment characteristics and sedimentary environment in this region present challenges for offshore engineering. This study comprehensively analyzed the physical, and mechanical properties of sediments in the area using geophysical exploration, engineering geological investigation, fixed-point sampling and hydrological observation. The engineering geological characteristics and sedimentary environment of surface sediments in the Baiyun Canyon area were studied, and the relationship between physical and mechanical properties and sedimentary environment was explored. The study revealed that the sediments in this area consist mainly of organic soft clay with high water content, low density, high pore ratio, high liquid limit, high plasticity and low strength. The physical and mechanical properties of the sediments vary, with the mechanical properties exhibiting higher variability than the physical properties. The research findings offer a scientific basis for understanding the seabed soil properties for designing submarine engineering structures in the deep waters of the northern South China Sea. This study holds significant theoretical and practical implications for oil and gas exploration and offshore engineering construction.

Loess, a Quaternary wind-blown deposit, is a problem soil that gives rise to frequent geohazards such as landslides and water-induced subsidence. The behaviour of loess is controlled by its microstructure, consisting of silt-sized skeleton particles and complex bonding structures formed by clay-sized particles. Achieving a deep understanding and precise modelling of loess behaviour necessitates comprehensive knowledge of the realistic 3D microstructure. In this paper, a correlative investigation of the 3D loess microstructure is performed using X-ray micro-computed tomography (mu XCT) and focused ion beam scanning electron microscope (FIB-SEM). Details of clay structures in loess, such as clay coatings, clay bridges and clay buttresses, are visualized and characterized in 3D based on FIB-SEM images with a voxel size of 10 x 10 x 10 nm(3). The clay structures exhibit a diverse degree of complexity and their impact on the mechanical properties of loess is highlighted. Statistical analysis of the skeleton particles, including size, shape and orientation, are derived from mu XCT images with a voxel size of 0.7 x 0.7 x 0.7 mu m(3). The findings provide insights into the collapse mechanism and particle-scale modelling of loess. The combination of mu XCT and FIB-SEM proves to be a powerful approach for characterizing the intricate micro-structures of loess, as well as other geomaterials.

This study examined the geotechnical behavior of silty sand soil treated with cement and cement-mineral polymer through a series of static and dynamic tests. Uniaxial Compressive Strength (UCS) and Indirect Tensile Strength (ITS) tests were conducted on specimens with varying amounts of cement and polymer (ie, 5, 7 and 9% by weight). Based on the results of UCS and ITS tests, the optimal combination of 7% cement and 7% cement-polymer was selected. Subsequently, California Bearing Ratio (CBR), Freezing and Thawing (F-T), and Large-scale cyclic triaxial (LCT) tests were performed on the optimal combinations. The results indicate that the treatment improves UCS, stiffness, CBR, and durability. By adding the polymer, the maximum UCS Sof the te cement treated specimen can be achieved in a shorter curing period. Moreover, when exposed to F-T cycles, the cement-polymer specimen exhibited. improvements in weight loss (about 0.6%) as well as compressive and tensile strength (about 200 kPa) compared to the cement treated specimen. In the dynamic tests, the cement-polymer specimen outperformed the cement specimen at low to medium cyclic deviatoric stress levels (up to 275 kPa). However, at higher stress levels, this trend was reversed. This behavior can be attributed to the formation of microcracks and cracks due to growth of needle-shaped microcrystals in cement-polymer specimen. Additionally, the cement-polymer treated specimen experienced lower permanent deformation during cycling loading Overall, the polymer additive proves to be more effective in treating the base layer that withstands low and moderate stress levels, making it a suitable complement to a portion of cement

Civil excavation projects frequently produce significant amounts of excess spoil. Repurposing this spoil into usable backfill material instead of disposing of it offers economic and environmental benefits. This study explores the prospect of converting red-bed mudstone construction waste, a type of soil frequently found at shallow depths, into a ready-mixed soil material (RMSM). It assesses the fresh mixture's workability characteristics (initial flowability, bleeding rate, and density) and the hardened material's mechanical properties (compressive strength and stress-strain relationship) by adjusting the water-to-solid ratio (W/S) and cement-to-soil ratio (C/S). The study investigates the impact of W/S, C/S and time on RMSM's flowability loss and proposes an empirical formula to provide a scientific reference for RMSM's flowability design in engineering applications. Findings highlight the significant influence of W/S on flowability, bleeding rate, and compressive strength, while showing C/S has a limited effect on flowability and bleeding. A negative exponential relationship is observed between flowability and time for all mixes, with the flowability loss ratio increasing over time, ranging from 22.9% to 35.6% after 1 h and stabilizing after 3 h. These insights are crucial to optimize RMSM's performance and suggest the need to further improve the flowability retention of RMSM. Furthermore, in comparison to soil cement and concrete, RMSM reduces backfill costs by 30.8% and 80.0%, respectively, while also achieving a reduction in CO2 emissions by 25.9% and 69.2%. Therefore, RMSM presents as an economically and environmentally friendly alternative for backfill applications.

In the present research the durability and geotechnical properties of an expensive clayey soil stabilized by two different compositions of additives were investigated and compared. The first composition consisted of environmentally and ecofriendly materials: BOF steel slag ranging from 0-20% as well as rice husk ash (RHA) ranged 0-16%wt of dry soil. The other composition consisted of relatively new generation of materials including nanomaterials: nano-CaCO3 as well as nano-SiO2. Atterberg limits test, free swell percent test, swelling pressure test and unconfined compressive test were used to assess the stabilizers influences upon expansive soil geotechnical characteristics. Also, the recurrent wet-dry cycles test was exerted on experimental and non-experimental samples for estimating stabilizers effects on durability. According to the results, each of the BOF slag and RHA enhances the expansive soil properties individually, while combination of slag-RHA led to better improvement of the soil properties. Also, the composition of nano-CaCO3 and SiO2 dramatically improved the clay soil operation. The optimum values of slag+RHA were suggested as 20% slag+12% RHA to enhance percent of swelling, pressure of swelling in addition to UCS as much as 95%, 96%, and 370%, respectively. The optimum value for the second stabilizer in this study was found to be 2%nano-SiO2+2% nano-CaCO3 which led to 318% increase in UCS and 86% decrease in swelling pressure.

Structured marine clay is commonly encountered in offshore engineering projects and engineers are concerned about its impact on the engineering properties of marine clay as well as its correlation with index properties. Current research has emphasized the role of soil structure in these aspects of marine clay. In this study, we investigated the influence of depositional environment and oxidation-induced evolution of clay microstructure on the formation of clay structure in structured clay from Zhanjiang area, a coastal city located in South China. The distinct soil structure observed in marine-terrigenous clay deposited under different environments exhibited sensitivity ranging from 1.6 to 8.9 at varying moisture content levels. The wide range of sensitivity observed in structured marine-terrigenous clay was attributed to free iron oxide derived from siderite present in an acidic environment. Compared to other regions, Zhanjiang marine clay demonstrated favorable mechanical properties but poor physical properties due to its unique clay structure characteristics. Based on these findings, we proposed a modified approach for correlating index properties with engineering properties that yielded good predictions.

The waste management of plastic has become a pressing environmental issue, with polyethylene terephthalate (PET) being one of the major contributors. To address this challenge, the utilization of recycled PET fibers and strips in geotechnical engineering applications for soil stabilization has gained considerable attention. This review aims to provide a comprehensive study of the geotechnical engineering properties of recycled-PET-reinforced soils. The review examines various factors influencing the performance of PET-reinforced soils, including PET percent content, fiber length, and aspect ratio. It evaluates the mechanical properties, like shear strength, compressibility, bearing capacity, hydraulic behavior, and durability of recycled-PET-reinforced soils. The findings reveal PET reinforcement enhances shear strength, reduces settlement, and increases the bearing capacity and stability of the soil. However, it is observed that the incorporation of recycled PET fibers and strips does not lead to a significant impact on the dry density of the soil. Finally, an environmental and cost comparison analysis of recycled PET fibers and strips was conducted. This review serves as a valuable resource for researchers, engineers, and practitioners involved in the field, offering insights into the geotechnical properties of PET-reinforced soils and outlining future research directions to maximize their effectiveness and sustainability.