Post-grouted shafts (PGDS) and stiffened deep cement mixed (SDCM) shafts reinforce the surrounding soils with cement to enhance the bearing capacity of shaft foundations, and their applications are becoming increasingly widespread. Field tests involving two post-grouted shafts and two stiffened deep cement mixing shafts were conducted at the bridge foundations projects, analyzing the vertical bearing performance of the shafts with cement-stabilized soil enhancement. Additionally, numerical simulations were performed to establish calculation models for single shaft and groups of drilled shafts, PGDS, and SDCM shafts, enabling a comparative analysis of their bearing capacity performance within the identical strata. The results indicate that the post- grouted shaft demonstrated significant bearing deformation capacity, as confirmed by field tests. After grouting, the ultimate bearing capacities of DS1 and DS2 improved by 124.5 % and 110.9 %, respectively. In both single and group modeling shaft foundations, the post-grouted shafts demonstrated the highest bearing deformation characteristics, followed by the identical- size stiffened deep cement mixed shaft, while the long-core SDCM shafts and the ungrouted shafts exhibited the weakest performance. Due to interaction effects among group shafts, the total bearing capacity of the group shafts is not simply the sum of the individual shafts. Specifically, the reduction factor for group shaft capacity ranges from 0.68 to 0.79 at the Baoying Large Bridge site, while at the Yangkou Canal Bridge site, it varies from 0.66 to 0.85. The findings of this study provide valuable insights for practical engineering applications.

Fracture toughness and cohesive fracturing properties of two classes of sandy-clay soils, (A) with fine and (B) coarse grains and stabilized with low (2%) and high (10%) cement (as soil stabilizer), were investigated using a chevron-notched semicircular bend (CN-SCB) sample under static and cyclic loads. The samples with coarser grains and higher amounts of cement stabilizer showed higher KIc compared to the soils containing low cement and fine grains. A noticeable reduction in KIc was also observed under cyclic loading compared to the monotonic loading. Load-crack opening displacement (COD) graphs obtained during cyclic loading showed high plastic deformation accumulation before the final fracture. The cycles required for the fatigue crack growth of the Class A soil were noticeably (three to six times) higher than the Class B. The FRANC2D nonlinear simulations, cohesive fracture analyses, and maximum stress theory were utilized for estimating the critical crack length and the onset of cohesive unstable crack propagation.

This paper investigates the durability and long-term bearing behavior of post-grouted piles in sand. Laboratory tests were conducted on cement-stabilized sand exposed to seawater erosion environments to investigate the effects of curing times and cement ratios on soil strength using micro-cone penetration (MCPT), scanning electron microscopy (SEM), and X-ray diffraction (XRD) tests. The strength distribution, microstructure, and phase composition of cement-stabilized soil were analyzed to determine the characteristics of strength changes. Furthermore, long-term field static load tests were performed on the Yinchuan Beijing Road extension and Binhe Yellow River Bridge project to investigate the relationship between the change in strength of cement-stabilized soil under erosion environments and the time effect of post-grouting at the pile tip. The results indicated that erosion damage to the cement-stabilized soil occurs from shallow to deep as the curing time increases, resulting in a reduction in its strength due to the formation of hydration products and products with poor gelation and low strength. Conversely, an increase in cement ratios resulted in heightened hydration products, which subsequently increased strength and significantly reduced the depth of erosion damage. The change in strength of cement-stabilized soil under seawater erosion environment is a combined result of the strengthening effect of hydration reaction and the weakening effect of erosion reaction. This change is the main reason for the time effect of post-grouting at the pile tip, allowing for effective control of pile foundation settlement with increasing time. The research findings provide valuable insights for evaluating the durability and long-term bearing behavior of post-grouted piles in sand.

Extensive research has demonstrated that cement is one of the most effective materials for improving soil properties. Researchers have investigated cement-stabilized soil techniques from various perspectives, including microstructural evolution and mechanical performance. However, studies on cement-stabilized soils in seasonal frozen regions remain limited. This study thus explored the application of cement-stabilized soil in these regions, specifically examining the effects of freeze-thaw cycles on its microstructure and shear strength through scanning electron microscopy (SEM) and direct shear tests. The findings indicate that freeze-thaw cycles induce noticeable microcracks and pores, significantly increasing particle breakage and decomposition, which leads to a loose structure and severely compromises the soil's mechanical properties. Incorporating cement generates hydration products that form cementitious bonds between soil particles, significantly enhancing structural density and overall stability. This cement stabilization effectively mitigates the damage caused by freeze-thaw cycles, enabling the soil to maintain good shear strength even after such cycles. These findings underscore the importance of cement stabilization in improving soil performance under freeze-thaw conditions, providing a theoretical basis and technical support for foundation improvement in cold regions.

Cement stabilization of soils is a common technique to enhance engineering and mechanical properties of in situ soils in the field of road geotechnics. Usually, moderate quantities of cement are used, around 5-10% of the dry material. However, cement manufacturing is one of the biggest sources of greenhouse gas emissions, specifically carbon dioxide. For this reason, reducing cement content by a few percent in geotechnical structures made with cement-stabilized soils (CSS) has a high environmental interest, particularly in view of the involved volumes of material. This work aims to contribute to a better understanding of the mechanical characteristics of lightly stabilized soils. First, the mechanical behavior of a clayey and a sandy soil treated with 3% cement was studied for several curing times. Next, measured mechanical features were correlated. Finally, these measurements were used to characterize the Mohr-Coulomb failure criterion and compared with a conventional approach. Results point out that mechanical enhancement can be quantified in terms of cohesion. Friction angle seems to be independent of curing time. The proposed approach can be adapted in geotechnical applications based on the Mohr-Coulomb yielding criterion such as stability slopes, foundations, and retaining structures.

This study investigates the mechanical enhancement of sandy soils through cement stabilization modified with Consoil, targeting improved pavement substructure performance. Unconfined compressive strength (UCS) tests were conducted on samples with varying cement contents (3%, 6%, 9%), Consoil dosages (0%, 5%, 10%, 15%, 20% by cement weight), and curing periods (3, 7, 28, 90 days). Field Emission Scanning Electron Microscopy and X-Ray Diffraction analyses complemented mechanical testing to understand strengthening mechanisms. Results demonstrated that 15% Consoil consistently optimized strength development across all cement contents, with 9% cement and 15% Consoil achieving peak 90-day UCS of 17.74 MPa, representing a 67% increase over control samples. Microstructural analysis revealed progressive matrix refinement with increasing Consoil content, while XRD indicated enhanced pozzolanic activity through calcium hydroxide consumption. The study introduces Consoil as an effective stabilization additive, establishing optimal dosage rates and demonstrating significant strength improvements through synergistic cement-Consoil interactions. The findings provide new insights into strength enhancement mechanisms in Consoil-modified cement-stabilized soils, offering practical guidelines for designing high-performance pavement substructures. The research contributes to sustainable construction practices by optimizing cement usage through Consoil incorporation.

Cement-stabilized soil in coastal soft soil regions is essential for infrastructure construction. However, under the combined effects of seawater erosion and cyclic loading, cement-stabilized soil often faces issues such as strength degradation, reduced durability, and stiffness softening. To enhance the engineering properties of cement soil, this study utilized nano-Al2O3 as a modifier. The effects of nano-Al2O3 on the dynamic properties of cement soil under various erosion environments were assessed using the GDS dynamic triaxial system. Furthermore, scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests were performed to study the microstructural changes in cement-stabilized soil modified with nano-Al2O3 subjected to seawater erosion. The results indicate that nano-Al2O3 significantly improves the resistance of soil to deformation. As the content of nano-Al2O3 increases, the dynamic strain of cement-stabilized soil initially decreases and then increases, while the dynamic shear modulus first increases and then decreases, showing optimal performance at a 0.25% content. Seawater erosion severely weakens the strength and stiffness of cement-stabilized soil; as erosion concentration increases, dynamic strain increases, and dynamic shear modulus decreases. Nano-Al2O3 improves the strength of cement-stabilized soil and mitigates the negative impacts of seawater erosion through pozzolanic reactions and filler effects.

Cement-stabilized soil is a commonly used pavement base/bottom base material. Adding a suitable curing agent to cement-stabilized soil can effectively reduce the dosage of cement, meet the strength requirements, and also greatly improve its water stability. In this paper, three kinds of cement dosage (6%, 8%, and 10%) of cement-stabilized soil were selected to add a 0.04% organic liquid curing agent, and then compared with high-dose cement (10% and 12%)-stabilized soil. The influence of wetting-drying cycles on the mechanical properties of the five stabilized soils was discussed. The mineral composition of cement-stabilized soils before and after the addition of a curing agent was analyzed by X-ray diffraction (XRD), and the microscopic morphology of 10% cement-stabilized soils with a curing agent was studied by scanning electron microscopy (SEM). The macroscopic test shows that the unconfined compressive strength of solidified cement-stabilized soil can be divided into three stages with the increase in the times of the wetting-drying cycles, which are the rapid decay stage, stable enhancement stage, and stable decay stage. The wetting-drying stability coefficient first increases, and then decreases with the increase in the times of the wetting-drying cycles. The microscopic test shows that the addition of a curing agent can enhance the content of hydration products in the cement-stabilized soil specimen; at the curing age of 28 d, with the increase in the times of the wet-dry cycles, the structure of the solidified cement-stabilized soil gradually broke down. The surface porosity P and pore diameter d showed an overall upward trend but decreased at the fifth wetting-drying cycle. The pore orientation weakened. The results show that the resistance of cement-stabilized soil with a curing agent is obviously better than that of cement-stabilized soil under wet-dry conditions.

Municipal solid waste incineration fly ash (MSWIFA) can be reused as a positive additive to strengthen soft soil. In this study, MSWIFA was initially used as a supplementary solidification material in combination with ordinary Portland cement to prepare fly ash cement-stabilized soil (FACS) with silty sand and silty clay, respectively. The ratio of MWSIFA to total mass was 5%, 10%, and 15%, and the cement content was set as 10% and 15%. The mechanical properties of FACS were evaluated by unconfined compressive strength test. The heavy metal-leaching test was conducted to estimate the environmental risk of FACS. The scanning electron microscope was used to test the micro-structure of FACS. The X-ray diffraction was performed to analyze material composition of FACS. The result indicates that the collaborative solidification of soft soil with MSWIFA and cement is feasible. Regarding the silty clay, the FA had positive effects on the silty clay in the service age (between 50 and 100% with 15% MSWIFA), as the MSWIFA reformulated the initial silty clay structure, resulting in interconnection and pore fill between particles. It can be founded that C-S-H and ettringite are the main products of MSWIFA and cement hydration, which are formed by the hydration of C3S and C2S. Regarding the silty sand, the MSWIFA decreased the peak strength (between 35 and 48% with 15% MSWIFA) but increased the ductility of the stabilized cement. Under the same mix proportions, the leaching toxicities of Zn and Pb in FACS of silty clay were obviously lower than were those of silty sand. Generally, the leaching concentrations of tested metals under all the mix proportions were well below the limit value set by GB 18598-2019 for hazardous waste landfill. Thus, the reuse of MSWIFA in cement-stabilized soil would be one of the effective methods in soft soil treatment and solid waste reduction.