Longqi Liu

In alignment with global carbon neutrality goals, this study investigates the regulatory role of magnesium oxide (MgO) content on the macro–micro properties of carbonation-cured collapsible loess from the Hohhot region. While MgO carbonation is established for soil stabilization, the quantitative influence of MgO dosage on the specific phase evolution pathways and mechanical enhancement within the unique macro-porous fabric of aeolian loess remains poorly understood. Addressing this, we systematically examined loess specimens amended with varying MgO contents (10% to 30%) over carbonation periods up to 24 h. Unconfined compressive strength (UCS) tests, X-ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to correlate mechanical performance with mineralogical and microstructural evolution. Results indicate that MgO content acts as a primary regulator of the carbonation process. Higher MgO dosages substantially increased CO₂ uptake, resulting in a significant relative mass gain—up to more than a two-fold difference between the highest and lowest content samples—and culminated in a compressive strength of 10.48 MPa for the 30% MgO specimen. Microstructural analysis revealed a distinct temporal evolution interpreted to be governed by MgO-mediated supersaturation levels. Initially, Mg(OH)₂ agglomerates provided early strength, which was subsequently enhanced by the formation of a three-dimensional framework of nesquehonite, followed by the development of an interlocking skeletal network of hydromagnesite crystals. These carbonate phases enhanced loess strength via a combination of pore infilling, particle cementation, and the construction of a reinforcing micro-skeleton. This work elucidates the link between MgO content and the microstructural evolution of carbonated loess, providing new insights for the synergistic integration of soil stabilization and carbon sequestration in loess regions. The findings offer a valuable reference for engineering applications in collapsible soil environments under the context of sustainable development.

In order to effectively improve the longitudinal connection stability of prefabricated box culverts for highways, this paper proposes a new type of Z-shaped assembled mortise-tenon splicing box culvert for highway reinforced concrete structures. Using the finite element simulation software to simulate, the maximum deformation and stress concentration position of the side wall obviously appear at the end and armpit of the joint, that is, the connection part of the two culvert joints. Under the same filling condition, the most different mechanical properties between the integral box culvert and the assembled box culvert are located at the joint of the prefabricated culvert. According to the stress and deformation characteristics of culvert body, different joint height and joint length box culvert forms are designed and simulated and compared. It is concluded that the 1.8 m joint height and 0.5 m joint length have the most significant improvement on the mechanical properties of the splice culvert. Finally, a Z-shaped assembled mortise-tenon splicing box culvert with a reasonable structural form and a mortise-tenon structure of 1.25 m length was selected.

Alluvial-diluvial soil-rock mixture (ADSRM) is a special geological material, mainly composed of pebbles, gravel, and soils. Gradation design has a remarkable effect on improving the shear strength of ADSRM. Therefore, the N-method of gradation theory was applied to the gradation design of ADSRM fillers, and the influence of gradation on macro-meso shear properties of ADSRM samples was analyzed. Macro-mechanical test results show that the shear strength, the equivalent cohesion, and the friction angle of the graded sample are much higher than that of the ungraded sample, and the shear dilatancy of the graded sample is more obvious. Meso-shear properties indicate that the percentage of pore area of the graded sample is less than that of the ungraded sample, while the percentage of the number of the small pore to the total pore and the crushed rock blocks under the same normal stress are more than that of the ungraded sample. Pore abundance shows the shape of most pores on the shear plane is oblate, secondly, near-equiaxed, and the least long-strip. Finally, the percentage of pore area decreases gradually with the increase of the shear displacement, while the percentage of crushed rock block area increases first and then decreases, which can reflect the change of shear strength at different shear stages. The number of pores and broken rock blocks mainly affect the strength and equivalent cohesion of the filler, while the abundance, roundness, shape coefficient, and fractal dimension of rock block contour mainly affect the internal friction angle.

The contents of both water and rock particles are important factors affecting the mechanical strength of a soil–rock mixture (SRM) filled subgrade in the western mountainous area of China. Therefore, the purpose of this paper is to study the mechanisms of reconstituted landslide deposit samples with different water and rock particle contents by analysing the characteristics of shear strength, volumetric strain and ‘jumping’ phenomenon via large-scale direct shear tests. The results show that the influence of water content on shear strength is greater than the influence of rock particle content under a lower normal stress, and the results are reversed in the case of a higher normal stress. The effect of water content on the equivalent cohesion is bigger, especially for the sample with a high rock particle content. The friction angle of the specimen with same water content increases with the increasing rock particle content, but when the number of rock particles increases to a certain extent, there is a little effect on the friction angle. However, the friction angle decreases with increasing water content at the same rock particle content. Specimens with the same rock particle content change from dilation to compression with increasing water content. Finally, the continuous stage of the ‘intense jumping’ at different water content has been analysed. The ‘jumping’ phenomenon of samples with low water and rock particle content will first strengthen and then weaken the samples with increasing normal stress.

The migration of groundwater often results in subgrade damage such as fracturing, pavement pumping, and cracking in seasonally frozen soil areas. Indoor tests were performed to simulate moisture migration in different soil types usually found in seasonally frozen soil areas. The results indicate that the moisture migration rate of the wetting front in clay is the fastest, followed by that in fine sand and silt. In addition, the migration height of fine sand is much lower than that of both clay and silt, whereas the water flux is larger than that of clay and silt. Moreover, under a freeze-thaw cycle, the trends of water content change and temperature distribution of the three samples at the initial state and final state were similar. Based on the gravity, matric, and temperature potentials, the moisture migrated continuously throughout the freezing process, and the temperature gradient could cause moisture to migrate faster than usual. According to the mechanism of moisture migration in the indoor tests, a case study and field test of the Jixi–Nehe Highway were undertaken in Heilongjiang Province, China. The field test results show that the moisture migration in the seasonally frozen region is consistent with the results of the indoor tests. Highway construction could significantly increase the water content of soil at the original position in the subgrade. Some measures were put forward to protect the subgrade from damage caused by moisture migration.

To investigate the deformation property of weathered phyllite filling subgrade under the comprehensive effect of water and load, three weathered phyllite soil column models were filled and their deformations were tested through a laboratory test and numerical simulation in this article. The results show that the deformation of the weathered phyllite soil column models were greatly influenced by the water replenishment conditions and load conditions, and the deformation of models increased with the increase of the moisture content and load. Moreover, the larger the load, the longer the time required for the weathered phyllite soil column model to reach stability. In addition, the numerical simulation results were compared with the test results, and it was found that they were similar. Consequently, the numerical simulation can be used to reflect the deformation of weathered phyllite filling subgrade under the effect of water and load and provide some guidance for the design of the weathered phyllite filling subgrade.

The mechanical strength of the landslide deposits directly affects the safety and operation of the roads in the western mountainous area of China. Therefore, the research is aimed at studying the mechanisms of a landslide deposit sample with different rock particle contents by analyzing its characteristics of the stress‐strain behavior, the “jumping” phenomenon, the volumetric strain, and the shear strength parameters via a large‐scale direct shear test. Stress‐strain results show that stress‐strain curves can be divided into 3 different stages: liner elastic stage, yielding stage, and strain‐hardening stage. The shear strength of SRM behaves more like “soil” at a lower rock particle content and behaves more like “rock joints” at a higher rock particle content. Characteristics of the “jumping” phenomenon results show that the “intense jumping” stage becomes obvious with the increasing rock particle content and the normal stress. However, the lower the rock particle content is, the more obvious the “jumping” phenomenon under the same normal stress is. Volumetric strain results show that the sample with a lower rock particle content showed a dilatancy behavior under the low normal stress and shrinkage behavior under the high normal stress. The dilatancy value becomes smaller with the increasing normal stress. The maximum shear stress value of the rock particle content corresponds to the maximum value of dilatancy or shrinkage. We also conclude that the intercept of the Mohr failure envelope of the soil‐rock mixture should be called the “equivalent cohesion,” not simply called the “cohesion.” The higher the normal stress and rock particle content are, the bigger the equivalent cohesion and the internal friction angle is.