Cemented sandy gravel is often used to enhance the foundation soil of engineering projects. This paper presents results of triaxial tests on cemented sandy gravel specimens. We compared 8 cemented specimens and 4 uncemented specimens. The strength, dilatancy, and stiffness behavior of both cemented and uncemented specimens are compared. The strength of cemented specimens is significantly greater than that of uncemented specimens, and the cemented specimens demonstrate pronounced expansion characteristics. The peak friction angle of the cemented specimen shows a linear relationship with the confining pressure: psi = 68.1-18.2lg(sigma 3/pa). To quantify the structural strength of the cemented specimens, a structural damage parameter is introduced based on the differences in mechanical properties between the two materials. The structural damage parameter first increases and then decreases as shearing progresses, and a hump curve function is used to describe this behavior. In the frame of the generalized plasticity, a novel elastoplastic model is established, considering the structural parameter as a factor of the plastic modulus, loading vectors and plastic flow direction vectors. The calculated values fit well with the experimental results. The model can reflect the characteristics of cemented sandy gravel, in terms of stress softening, residual strength, and volumetric dilation. Finally, the model is used to evaluate the deformation of a sluice dam foundation after being enhanced with cemented sandy gravel. The results show that after treatment, both the settlement of the gate floor and the shear deformation of the waterstops can be reduced by more than 10%.

Freeze-thaw processes can cause slope instability in areas with short-term frozen (STF) soil, resulting in potential safety risks and huge financial losses to a certain extent, as these processes affect the physical and mechanical properties of the soil. However, their adverse effect on the mesoscopic-level mechanical properties of residual soil has not been adequately investigated. To gain an effective understanding in this regard, a laminated-wall approach was adopted to create a flexible boundary for a triaxial-shear test. Simulated stress-strain curves closely matched experimental results, with a maximum relative error of 7.81% at the peak. Moreover, the experimental data collected from real soil subjected to freeze-thaw cycles were used to calibrate the relation between the macroscopic and mesoscopic parameters. The deterioration of the macromechanical and micromechanical parameters of residual soil primarily occurred in the first four freeze-thaw cycles. For eight freeze-thaw cycles, the damage degree of each microparameter remained the same, reaching approximately 0.37. A freeze-thaw damage model of the mesoscopic parameters of residual soil was then constructed through parameter fitting. Using this model, the impact of frost-thaw on slope deformation behaviors was analyzed. A simulation revealed that displacement primarily occurred at the slope toe and the area of influence expanded with an increasing number of freeze-thaw cycles. As freeze-thaw cycles increased, the stress distribution in the X-direction along the top and surface of a slope became more concentrated, impacting mesoscopic parameters. Conversely, the stress in the Z-direction on the slope dispersed across three slopes after four to eight freeze-thaw cycles, with considerable influence during the initial four cycles. The flexible boundary created using the laminated-wall approach and the freeze-thaw damage model of the mesoscopic parameters facilitated an effective understanding of the freeze-thaw effect on residual soil obtained from an STF area.

Subgrade soil undergoes freezing in winter and thawing in summer in seasonal frost areas, which severely impacts the engineering performance of the subgrade soil. In order to enhance the frost resistance of subgrade while mitigating the environmental impact of incinerating industrial solid waste, rubber crumb was added to cementsoil in this study. The static triaxial and mercury intrusion porosimetry tests were conducted on freeze-thawed cement-soil and rubberized cement-soil. The effects of the number of freeze-thaw cycle and confining pressure on peak strength and initial elastic modulus were investigated. The pore size distribution, porosity, and fractal dimension under various numbers of freeze-thaw cycle were obtained based on the MIP test results. The damage parameter of the specimens was determined using the fractal dimension. A constitutive model with damage parameter of rubberized cement-soil was established. The results showed that the pore size distribution of the specimens deteriorated after the whole freeze-thaw cycles, with increases observed in macropore proportion, porosity, and damage parameters, while peak strength and fractal dimension decreased. The macropore proportion of cement-soil and rubberized cement-soil increased by 14.9% and 2.0%, respectively. The incorporation of rubber particles suppressed the development of pores and cracks and enhanced the frost resistance of the specimens. The damage parameter of rubberized cement-soil decreased by only 0.0186 by the end of 12 of freezethaw cycle. The established constitutive model was suitable for characterizing the stress-strain behavior of rubberized cement-soil. The findings facilitate the construction and design of subgrade engineering in seasonal frost areas, contributing to the development of sustainable, durable subgrade solutions and reducing the environmental impact of waste rubber tires.

In seasonal frost areas, an organic soil stratum is often encountered during engineering construction due to the widespread existence of organic soils. The soil stratum will experience frost heave in winter and thaw settlement in summer, resulting in a signiflcant variation in its engineering behaviour, especially for organic soil stratum. In this study, with the help of cement, fly ash, and fulvic acid, cement-fly ash stabilized organic soil (CFOS) specimens were prepared and the unconflned compressive (UC) and mercury intrusion porosimetry (MIP) tests were carried out on CFOS specimens. The effects of fly ash content, number of freeze-thaw cycles (FT-N), and curing period on the strength, resilient modulus, and porosity were investigated. Test results revealed that the fly ash content increased from 0% to the optimum content of 5%, the unconflned compressive strength (UCS) and resilient modulus of CFOS with FT-12 increased by 50.30% and 118.92%, respectively. The pore size distribution (PSD) curve and fractal dimension (Dn) of specimens were obtained from the MIP test. The proportion of macropores was the main factor affecting the UCS of CFOS. With the increasing FT-N, the macropore proportion of CFOS with 5% fly ash content increased by 333.33%, and the UCS decreased by 28.25%. Based on a freeze-thaw damage model, the damage parameters of the CFOS specimens were extracted with the Dn as an independent variable. The microscopic pore characteristics and the relationship between the strength, Dn and damage parameter were analyzed. The microscopic pore structure of specimens with different fly ash contents experienced a change subjected to freeze-thaw cycles. The lower the strength, the lower the Dn of CFOS. The damage parameters quantitatively reflected the damage degree of specimens after freeze-thaw cycles on the micro scale. The damage parameter of CFOS with 5% fly ash content increased by 341.57% with the increase of FT-N. The introduction of fly ash was able to reduce freeze-thaw damage to the specimens. The damage parameter and CFOS strength exhibited a signiflcant correlation. The relationships of the strength and microscopic pore structure of CFOS subjected to freeze-thaw cycles were conducive to a better understanding of the freeze-thaw damage mechanism of CFOS on the micro scale. These flndings are beneflcial for engineering construction design in seasonal frost areas.