Deep soil mixing (DSM) is a widely used ground improvement method to enhance the properties of soft soils by blending them with cementitious materials to reduce settlement and form a load-bearing column within the soil. However, using cement as a binding material significantly contributes to global warming and climatic change. Moreover, there is a need to understand the dynamic behavior of the DSM-stabilized soil under traffic loading conditions. In order to address both of the difficulties, a set of 1-g physical model tests have been conducted to examine the behavior of a single geopolymer-stabilized soil column (GPSC) as a DSM column in soft soil ground treatment under static and cyclic loading. Static loading model tests were performed on the end-bearing (l/h = 1) GPSC stabilized ground with Ar of 9 %, 16 %, 25 %, and 36 % and floating GPSC stabilized ground with l/h ratio of 0.35, 0.5, and 0.75 to understand the load settlement behavior of the model ground. Under cyclic loading, the effect of Ar in end-bearing conditions and cyclic loading amplitude with different CSR was performed. Earth pressure cells were used to measure the stress distribution in the GPSC and the surrounding soil in terms of stress concentration ratio, and pore pressure transducers were used to monitor the excess pore water pressure dissipated in the surrounding soil of the GPSC during static and cyclic loading. The experimental results show that the bearing improvement ratio was 2.28, 3.74, 7.67, and 9.24 for Ar of 9 %, 16 %, 25 %, and 36 %, respectively, and was 1.49, 1.82, and 2.82 for l/h ratios of 0.35, 0.5, and 0.75 respectively. Also, the settlement induced due to cyclic loading was high under the same static and cyclic stress for all the area replacement ratios. Furthermore, the impact of cyclic loading is reduced with an increase in the area replacement ratio. Excess pore water pressure generated from static and cyclic loads was effectively decreased by installing GPSC.

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.

In cold regions' engineering applications, cement stabilized soils are susceptible to strength degradation under freeze-thaw (F-T) cycles, posing significant challenges to infrastructure durability. While metakaolin (MK) modification has shown potential in enhancing static mechanical properties, its dynamic response under simultaneous F-T cycling and impact loading remains poorly understood. This study investigates the dynamic mechanical behavior of cement-MK stabilized soil through split Hopkinson pressure bar (SHPB) tests under varying F-T cycles. The effects of strain rate and F-T cycles on the dynamic failure process and mechanical properties of cement-MK stabilized soil were investigated. Pore characteristics were analyzed using a nuclear magnetic resonance (NMR) system, providing an experimental basis for revealing the degradation mechanism of F-T cycles on the strength of cement-MK stabilized soil. Based on the Lemaitre's strain equivalence principle, a composite damage variable was derived to comprehensively characterize the coupled effects of F-T cycles and strain rate. A dynamic constitutive model is established based on damage mechanics theory and the Z-W-T model. The results indicate that under the effect of F-T cycles induce progressive porosity increase and aggravated specimen damage. At varying strain rates, the strength of cement-MK stabilized soil decreases with increasing F-T cycles, while the rate of strength reduction gradually diminishes. Under impact loading, both strain rate and the number of F-T cycles significantly reduce the average fragment size of fractured specimens. The modified Z-W-T model effectively predicts the stress-strain relationship of the cement-MK stabilized soil under impact loading.

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.

The soil-cement deep soil mixing (DSM) technique has been widely used to improve the bearing capacity of the soft soil under embankment loading. However, utilizing ordinary portland cement (OPC) releases a tremendous carbon footprint. Industrial waste-based geopolymer has emerged as a sustainable and environmentally friendly solution for stabilizing soft soils. This work investigates the behavior of embankment models constructed on geopolymer-stabilized soil columns (GPSCs) under static and cyclic loading conditions similar to transportation routes. A series of static and cyclic loading tests were carried out on the reduced-scale designed embankment model resting on soft soil (cus = 5 kPa) reinforced with end-bearing (l/h = 1) and floating (l/h = 0.75) GPSCs with area replacement ratios (Ar) of 12.7%, 17%, and 21.2% to analyze the vertical stress-settlement behavior of the improved ground. Earth pressure cells were used to measure the vertical stress on the column and the adjacent surrounding soil under static and cyclic embankment loading. A pore-pressure transducer was used to monitor the excess pore-water pressure generated during the loading process. The results indicate that the ultimate bearing capacity (qult) improvement for end-bearing GPSCs was 246.92%, 344.56%, and 418.8%, whereas the improvement for floating GPSCs was 126.9%, 151%, and 181.64% for Ar values of 12.7%, 17%, and 21.2%, respectively. Furthermore, the stress concentration ratio increases and excess pore-water pressure decreases with increasing Ar and l/h ratios. A mathematical equation was also derived to determine the qult value with Ar and l/h ratios. End-bearing GPSCs were more effective than floating GPSCs at the same Ar under static and cyclic loading. For installing floating GPSCs, a higher area replacement ratio is required for better load bearing under static and cyclic loading. In addition, a life cycle assessment of the geopolymer compared to OPC was performed, showing that the geopolymer is a sustainable and eco-friendly construction material.

To improve the utilization rates of soda residue (SR) and fly ash (FA), reduce environmental pollution, and enhance the mechanical properties of marine clay (MC), this study proposes mixing SR, FA, and MC with cement and /or lime to prepare soda residue-fly ash stabilized soil (SRFSS). Using an orthogonal design for the proportions, the study analyzes the compaction performance, unconfined compressive strength (UCS), and shear strength of SRFSS. The influence of various factors on the mechanical properties of SRFSS was investigated through range and variance analyses. The mechanical mechanism was revealed from the perspectives of grading and cementation. The results indicate that SR and FA significantly impact the mechanical properties of SRFSS. The range and variance analysis results are consistent: SR content of 30% and 70% has the most significant impact on compaction performance and UCS, respectively, while 20% FA content has the greatest effect on shear strength. The recommended base proportion is 70% SR + 20% FA + 10% MC. The gradation and cementitious properties jointly influence the mechanical performance and microstructure of SRFSS, G8 has the lowest planar porosity, at only 0.89%. The calcium (Ca) content in SRFSS specimens with different proportions shows significant variation, from 5.0 to 53.6 wt%, while the silicon (Si)/Al ratio (0.76-2.73) shows relatively small fluctuations. The primary hydration products include calcium hydroxide (Ca(OH)2), calcium silicate hydrate (C-S-H), and ettringite (AFt).

Cement soil stabilization is widely used in civil engineering to improve the performance of soils subjected to freeze-thaw (F- T), wet-dry (W-D), and sulfate attack (SA). Due to the negative impacts associated with manufacturing cement, the development of eco-friendly and sustainable additives is highly desirable. Coal-derived char is a cost-effective byproduct of the coal pyrolysis process. In this study, the influence of coal char on mineralogical, microstructural, physical, and mechanical properties of cement stabilized soils (with cement contents of 0%-20% and char contents of 0%-30%) subjected to F-T cycles, W-D cycles, and SA is investigated. Compared to cement stabilized soils, char-cement stabilized soils exhibit up to 60.8% fewer volume changes during F-T cycles and 31.6% fewer during W-D cycles. The compressive strength of char-cement stabilized soils with cement contents of 5%, 10%, and 20% are on average 7.9%, 17.6%, and 11.0%, respectively, higher than that of cement stabilized soil subjected to F-T cycles, W-D cycles, or SA. The inclusion of char promotes cement hydration and results in the formation of more amorphous hydration products that fill voids or cover soil minerals. The findings indicate the promising potential of coal char in enhancing soil performance under a range of challenging environmental conditions.

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.