Cementation, even in small amounts, tends to alter the mechanical properties of soil significantly. Ordinary Portland Cement (OPC) is a widely used binding admixture, but there has been an increasing need for replacement owing to its carbon footprint. One such alternative is Calcium Sulfoaluminate cement (CSA), which has higher initial strength gain and lower carbon footprint than OPC. Since existing strength prediction models available from literature were developed for conventional cement types such as OPC and Portland Blast Furnace Cement (PBFC), those are not applicable for predicting the strength evolution of soil treated by other types of cements (e.g., underpredicting the initial strength of CSA treated sand). It is because the prediction models available are generally either soil-specific or cement-specific. This paper proposes a unified strength prediction model that works irrespective of cement and/or soil types by introducing a slope parameter that controls time-dependent strength gain. The proposed model is validated by data collected from literature on various soils and cement types. The three-parameter model demonstrates strong applicability for predicting the strength evolution over a wide range of water-to-cement ratios.

Utilising recycled materials, such as construction and demolition waste (C&DW), into soil improvement projects offers a promising solution to reduce the environmental impact of the C&DW industry. This approach helps address issues related to waste generation, resource depletion, and environmental degradation, while enhancing the overall sustainability and resilience of soil stabilisation efforts. This study investigates the effectiveness of incorporating recycled C&DW into cement-treated peat and clayey soils to enhance their strength and stiffness. To achieve this goal, laboratory experiments were conducted on over 296 soil specimens to assess their Unconfined Compressive Strength (UCS), small-strain Young's modulus (E0) and shear modulus (G0). These tests included varying curing times (28, 60, 90, and 120 days), different cement and recycled material content, and water-to-cement ratios. Moreover, laboratory testing methods for determining geotechnical parameters are often time-consuming and prone to challenges. In this context, reliable predictive models, such as artificial neural networks (ANNs), offer an efficient alternative for accurately assessing these parameters. The findings of this research reveal that, along with cement content, the water-to-cement ratio (w/c) and curing time are key factors influencing the strength and stiffness of treated soft soils, underscoring their critical role in soil stabilisation. Additionally, while minimizing cement content and increasing RM yield improvements in both peat and clay, the effect is more pronounced in peat due to the time-dependent nature of pozzolanic reactions. This suggests that achieving optimal performance with increased strength and stiffness requires a carefully balanced RM content. Finally, the study demonstrates that ANN-based models can accurately predict the strength and mechanical properties of soft soils, offering a viable alternative to traditional UCS and FFR tests.

Unconfined compressive strength (UCS) and California bearing ratio (CBR) are key indicators of soil strength, particularly in fine-grained soils that often fail to meet project standards for roads and embankments. This study investigates the effects of fly ash on UCS and CBR, demonstrating an increase in both, though not symmetrically, due to varying percentages of chemical oxides in the soil-fly ash matrix. The relationships between UCS, curing time, chemical oxides (silica, alumina, calcium, magnesia, ferric), maximum dry density, and optimum moisture content (OMC) were analyzed. Three mathematical models, pure quadratic (PQ), interaction (IA), and full quadratic (FQ), were used to model UCS for 111 fly ash-treated and 49 untreated soils. While FQ and IA offered excellent predictions, their complexity led to applying geochemical indices like the hydraulic index (HI) and lime modulus (LM) to simplify the equations, with FQ remaining the most accurate. Sensitivity analysis showed that curing time was the most influential factor on UCS, followed by calcium oxide (CaO). When geochemical indices were applied, the hydraulic index (HI) emerged as the most significant factor. These findings underscore the importance of grouped chemical oxides, particularly SiO2, Al2O3, and Fe2O3, in enhancing soil properties, providing valuable insights for geotechnical engineering applications.

Utilizing casein in geotechnical engineering and construction can reduce global dairy waste. Variations in initial water content during sample preparation influence cation and OH ion availability, alkaline additive concentrations, casein binder function, and rheological properties of the casein solution. This study investigates the impact of initial water content and casein solution rheology on unconfined compressive strength in two soil types (coarse and fine) treated with casein, both in dry conditions and after water immersion. The study also assesses the long-term performance of casein-treated soil under bio-decomposition. Results suggest that increasing casein content, beyond the optimal ratio, can enhance strength by adjusting initial water concentration. Notably, calcium caseinate-treated soil shows improved water resistance, with wet strength reaching 833 kPa at 5% casein and 20% initial water content, due to reduced viscosity and better workability, resulting in a more rigid soil structure during preparation. We propose an empirical formula describing the influence of casein solution rheological characteristics on soil strength. Furthermore, artificial neural networks, developed from experimental data, predict casein-treated soil strength, highlighting the significance of initial water content and rheological parameters.

Stabilizing weak clayey soils with lime is an effective method for improving the mechanical properties of soil. However, lime production is an energy-intensive process producing significant CO2 emissions in lime-stabilized soils, which can be counteracted through accelerated carbonation that enhances its engineering performance. The present study evaluates accelerated carbonation of lime-treated soils by adding gaseous (CO2-rich gas), liquid (water-CO2 mixture), and solid (sodium bicarbonate) CO2 sources. Results indicated that samples carbonated with gaseous CO2 exhibited 100% lime carbonation, while samples treated with solid and aqueous sources of CO2 had a mean lime carbonation of 60% and 40%, respectively. All lime-treated-carbonated samples exhibited a mean 50% increase in unconfined compressive strength compared to the untreated samples after a 7day curing period. Durability evaluation through cyclic wetting and drying indicated that the carbonated samples had higher durability than the untreated samples. X-ray computed tomography showed that adding solid and liquid sources of CO2 facilitated the flocculation of montmorillonite, reducing the porosity. However, a higher dosage of solid CO2 induced clay dispersion, increasing the porosity. X-ray diffraction and thermogravimetric analysis verified CO2 sequestration through the formation of calcite, a thermodynamically stable polymorph of calcium carbonate.

Assessing the subsurface geological conditions beneath a structure is crucial, as soils inherently tend to lose intergranular strength when subjected to static or dynamic loads. Applying dynamic loads can result in the propagation of stress waves through the soil, leading to deformation of the soil structure and causing more significant damage than static loads. Extensive research has been conducted on treating dynamic characteristics of clay soil properties using traditional additives such as lime and cement. To achieve better results and address the limitations of conventional materials in soil improvement, there is a growing trend towards using nontraditional stabilizers, referred to as 'recycled and sustainable' materials. These include, for example, silica fume, polypropylene fibers, steel slag, fly ash, rubber tire particles, basalt, and recycled and crushed glass, which are currently being deeply investigated to improve the dynamic behavior of clay soils. The review article compares the effects of traditional and sustainable stabilizers on dynamic engineering properties of soils. It also highlights the engineering significance and innovations in the use of such materials. While traditional stabilizers effectively improve soil strength and durability, they pose environmental challenges, including increased CO2 emissions and brittleness under seismic stress. Innovations focus on refining these techniques and incorporating sustainable alternatives, such as waste-derived materials, to enhance soil properties, improve seismic performance, and reduce environmental impact. The study underscores the need for developing cost-effective, ecofriendly solutions for modern infrastructure. It systematically analyzes recent topics on soil stabilization using these additives, examining parameters that influence the dynamic properties of stabilized clay soils. Furthermore, it reviews microstructural changes due to stabilization and their impact on dynamic properties, offering suggestions for future research.

Investigations on the changes in pore water pressures and stress during the construction of stiffened deep cement mixing (SDCM) piles are scarce, resulting in an unsatisfactory understanding of the bearing capacity formation process. Thus, this paper presents a preliminary field study to investigate the variation characteristics of pore water pressures, total stress and effective stress during the construction of SDCM piles derived from field tests. In the meantime, cone penetration tests (CPTs) were conducted before and after the construction of SDCM piles. The results show that the variation ranges of pore water pressure, total stress and effective stress of soils around piles decreased with increasing distance between the measuring point and piles when the depths of the measuring points were the same. During the piling process, the effective stress increased by approximately 53-103%, and the pile side frictions increased accordingly, while the tip resistance and side resistance values of soils around piles increased by 27-106% and 2-145%, respectively. Additionally, SDCM piles successively formed different load-bearing components with decreasing bearing capacity along the pile diameter direction, which realized a better bearing efficiency than conventional piles made with homogeneous materials. In essence, they were also the source of significant economic advantages of SDCM piles. Through this study, we expect to provide a reference for further studies on the bearing mechanism of SDCM piles in soft soil regions.

The employment of novel biopolymers offers geotechnical engineers a diverse range of materials to choose from, depending on the specific requirements of different projects. Regarding the promotion of environmentally friendly materials in the construction industry, this study introduces carrageenan as a novel biopolymer for soil improvement. The research also includes a comparative study of carrageenan's performance with xanthan which is the most commonly used biopolymer in geotechnical engineering. Unconfined compressive tests (UCS) were conducted to evaluate the performance of biopolymer-treated soil samples over a variety of effective parameters including biopolymer content, moisture content, curing time, soil particle size, and durability under wet-dry cycles. In order to explore the soil size effect, kaolinite silt and sand were combined in various proportions and treated with different biopolymer ratios to enhance strength development. The optimal mix of each biopolymer-treated soil was then exposed to five cycles of wetting and drying. Carrageenan improved the compressive strength of untreated soils in all cases, for example 3.4 times for 0.5% (wb/ws) of biopolymer. In higher proportions of kaolinite, carrageenan performed considerably better than xanthan gum in terms of compressive and shear strength. In addition, with an emphasis on confining pressures, static triaxial experiments were conducted to examine the effectiveness of carrageenan, by which it was shown that carrageenan out-performs xanthan in terms of shear strength especially in the fine-grained soil. The mechanism and chemical interaction behind the significant performance of carrageenan in binding soil grains, increasing mechanical strength and improving durability of the soil was also studied through FTIR analysis and scanning electron microscopy (SEM) images. It can be concluded that carrageenan can be considered as a sustainable alternative to conventional materials such as cement and lime.