Liansheng Tang

Different chemical solutions can significantly change the contact angle (CA) of soil, but few studies have studied the change rule and action mechanism of the CA from the mineral composition of soil essence. In unsaturated soil mechanics, the CA is an important parameter to calculate the wet suction between soil particles in unsaturated soil. When the chemical composition of the soil pore liquid changes, the CA will also change, which will affect the wet suction and other parameters, thus changing the macroscopic mechanical properties of the soil. In this study, the CA of air-solution-mineral phases with different solution components (pH, type and concentration of salt solution) of different minerals (quartz, orthoclase and plagioclase) were measured. The results show that the CAs of quartz, orthoclase and plagioclase all rise first and then drop with the rise of pH. The peak CAs are pH = 5, pH = 4 and pH = 3, respectively. Quartz, orthoclase and plagioclase all have valley values in different concentrations of NaCl and KCl solutions. In CaCl₂ solution, only quartz has valley value, while orthoclase and plagioclase increase monotonously. Quartz in soil plays a main role in the influence of soil CA, followed by orthoclase and plagioclase. The CA of different minerals in different chemical solutions is mainly controlled by electric double layer interaction and functional groups interaction. In different salt solution environment, in addition to the above two effects, the mineral CA is also affected by the surface tension.

A 24 km urban expressway on the Leizhou Peninsula in southern China required the extensive use of different graduation basaltic residual soils nearby as subgrade filler. In order to fully understand the engineering properties of these Leiqiong basaltic residual soils, four different fine granule contents (with 24.26%, 55.72%, 84.50%, and 94.92%) along the expressway construction sites were selected for preliminary analysis of their chemical composition, oxide content, and microstructure. Five cement contents (1.5%, 3%, 4.5%, 6%, and 9%) were used to improve the residual soils based on the results of the unconfined compressive strength test and consolidated undrained triaxial compression test, the cement improvement index, which can both meet the strength requirement of the roadbed and avoid the brittle failure of soil is determined. The relationship between carrying capacity and moisture content of soil samples after outdoor improvement is studied, and explains why the moisture content corresponding to the maximum CBR of outdoor improved basalt residual soil is higher than the optimal moisture content of indoor improvement test. Parameters investigated include consistency limits, unconfined compressive strength, compressibility, shearing stress, California bearing ratio (CBR), and compactness. The relationship between the Leizhou peninsula basaltic residual soils with different granule sizes, recommended water content ratio, rolling cycle times, and compaction degree are studied outdoors, and the application suggestion of different granule sizes of basaltic residual soils in different grade highway subgrade engineering is put forward. The results are as follows: 1) The content of fine granules greatly influences the physical and mechanical properties of Leizhou peninsula basalt residual soil. 2) Due to the special colloidal state, the cement uniformity error of basalt residual soils with fine granule content of more than 85% are plus or minus 3% when it is mechanically modified, and the improvement recommended content of cement is 6% if it needs as subgrade filling materials after disturbance. 3) It is recommended that the soil moisture content before improvement in high-temperature areas should be Opt+2%, and the cement improvement time should be controlled within 50 min 4) After rolling seven times, the maximum compaction degree of residual soil with fine granule content greater than 85% is less than 95%; it is only suitable for filling embankment structures below the roadbed of highway. The results extend the research on the engineering characteristics of basaltic residual soils and provide practical, improved guidance for the use of basaltic residual soils in road foundation engineering.

The southern tropical coastal areas of China are high-temperature and high-humidity salt environments, which hinder the durability and service life of ordinary asphalt pavement. To enhance the durability of asphalt pavement in these areas, modified bagasse fiber combined with nano-TiO₂ was used to improve the corrosion resistance of asphalt pavement in high-temperature and high-humidity salt environments. The micro-morphology, high-temperature oil absorption, high-temperature heat resistance, and hygroscopicity of bagasse fiber modified using three silane coupling agents combined with NaOH were compared, and the best silane coupling agent/NaOH modification scheme for bagasse fiber was found. Based on conventional physical tests (penetration, softening point, ductility), rheological property tests (rotational viscosity, dynamic shear rheological test, multi-stress creep recovery test, linear amplitude scanning test), and a four-point bending fatigue test of the asphalt mixture, the properties of modified bagasse fiber asphalt binder and mixture after cyclic dry–wet erosion under pure water and salt solution (NaCl, Na₂SO₄) were determined, and the effects of the erosion environment and fiber ratio on the basic physical and rheological properties of the asphalt were clarified. Compared with the silane coupling agents KH550 and KH590, the bagasse fiber modified with KH570/NaOH had a better high-temperature oil absorption capacity, heat stability capacity, and matrix asphalt compatibility. The worst erosion environment was Na₂SO₄, but the increase in test temperature and fiber content weakened the sensitivity of the asphalt binder performance in different erosion environments. The erosion capacity order was as follows: Na₂SO₄ > NaCl > pure water. In the worst erosion environment, 0.5% modified bagasse fiber/Nano-TiO₂ asphalt binder (B_{n−570−0.5}) had the best corrosion resistance in a high-temperature and high-humidity salt environment. The penetration, softening point, creep recovery rate R_3.2, non-recoverable creep compliance J_nr3.2, and fatigue life after long-term aging (with 5% strain) of B_n-570-0.5 were, respectively, increased by −16.9%, 37.5%, 37.95%, −27.86%, and 38.30% compared with unblended base asphalt binder (B). In addition, the four-point flexural fatigue life of B_n-570-0.5 was 169.2% higher than that of the unblended base mixture.

The tensile strength of granite residual soil has different changing laws during the wetting and drying process which often appears after rainfall. The microscopic relationship between tensile strength, bond force, and absorbed suction was studied using a self-developed soil tensile strength tester. The results show the following. (1) The change in tensile strength with saturation is a convex curve with a peak; according to the drying and wetting path, there are differences in peak value and amplitude of variation. (2) The sample with a higher fine particle content has a structure that is denser and has fewer pores, while an increase in gravel content will significantly reduce the tensile strength of the soil. (3) Absorbed suction and bond forces are important factors that control tensile strength in the drying process. The bond force contributes more than 70%, the tensile strength is in invariable constant saturation, and the wetting process is mainly controlled by absorbed suction.

Under uniaxial compression, the soil mass may be subjected to transverse tensile splitting or swelling failure. This failure is caused by the tensile stress in the soil; that is, part of the vertical stress is converted into lateral stress. In order to investigate the factors that influence the stress transfer phenomenon, the failure mode of the soil mass can be predicted more accurately, and the internal force of the soil mass can be analyzed. This paper begins with the definition of the stress conversion coefficient and measures it by combining macroscopic mechanical properties with microscopic structure analyses. By carrying out a uniaxial compression test on a large soil sample, an equivalent tensile test was carried out according to the equivalent transverse displacement measured using the S-type tension sensor in order to explore the change law of the stress conversion coefficient. The arrangement and distribution of pores and particles at different positions in the samples before and after compression were further observed and analyzed using the SEM test to explore the formation mechanism of the stress transition phenomenon, and the following research results were obtained: (1) The stress conversion coefficient of the soil under compression is not invariable. An increase in the loading rate and a decrease in water content cause brittleness, and the stress conversion coefficient of the soil decreases. (2) Shear failure is more likely to occur in large samples of brittle soils under uniaxial compression. (3) The tensile stress in the compressed soil is caused by the invasion and extrusion of soil particles.

The parent rock properties, weathering degree and soil formation conditions of soil in different regions and different levels are different, which results in the obvious difference of grain size composition of soil. At present, the research on granite residual soil often ignores the mechanism of its grain size composition on engineering properties. In this study, a series of soil samples with different grain size composition were configured based on the content of gravel grain in the granite residual soil. This paper mainly studies the influence of the content of gravel grain group and fine grain group of the compaction and strength of granite residual soil. The results show that the optimal moisture content and cohesion of granite residual soil are mainly controlled by the content of fine grain, and the maximum dry density and internal friction angle are mainly controlled by gravel grain. For each 1% increase in the fine grain content of the soil, the optimal moisture content of the soil will approximately increase by 0.11%, and correspondingly, the cohesion of the soil will approximately increase by 0.27 kPa. In addition, the engineering properties of granite residual soil with different grain size composition are also affected by soil structure. Finally, based on the microstructure characteristics of granite residual soil, three different aggregates are proposed, and seven micro models with different structural characteristics are established. Micro models established by different aggregates can control different engineering properties of soil. The research results are helpful to understand the relationship between the engineering properties and grain size composition of granite residual soil and provide reference for the refinement of its engineering classification.

The physical and mechanical properties of soil are crucial in engineering construction, but conducting extensive experimental tests can be time-consuming, laborious, and subject to uncertainties due to the heterogeneity of the soil and variations in experimental conditions. Soil is composed of various minerals, and the mineral composition is the fundamental determinant of various physical and mechanical properties of the soil. The purpose of this study is to establish a convenient and reliable soil property prediction model based on mineral composition. To achieve this end, a dataset comprising the percentage content of different minerals in the soil, as well as the soil’s mechanical and physical properties, was collected. Using artificial neural network methods, prediction models for liquid limit, plastic limit, internal friction angle, and cohesion of the soil were developed based on mineral composition. Each model’s performance was evaluated through deviation analysis, and models with poor prediction accuracy were optimized using a genetic algorithm. The results demonstrate that the neural network model based on mineral composition can accurately predict soil properties with high applicability. This research provides a method for accurately predicting the majority of engineering properties of soil using experimental data on mineral composition, which is significant for cost savings and improving work efficiency in engineering projects.

High liquid limit soil has unfavorable engineering geological characteristics, such as strong disintegration, dry shrinkage and easy cracking, and easy uplift when encountering water, which will cause various problems to the engineering. At present, the relationship between the physical and mechanical properties of high liquid limit soil and the characteristics of water-soil interaction is still not clear enough. In this study, the high liquid limit soil of Zhanjiang Avenue was selected to explore the influence of different ratios of three kinds of industrial waste residues (blast furnace slag, carbide slag, and tailing sand) on the high liquid limit soil. Aiming at the common adverse engineering geological phenomena of high liquid limit soil, such as easy disintegration, dry shrinkage crack, and easy uplift in water, the effects of different industrial waste residues on the water-soil interaction characteristics of high liquid limit soil are explored through disintegration and crack tests. In addition, the effects of different kinds and ratios on the free expansion rate, pH, unconfined compressive strength, and shear strength parameters of high liquid limit soil were studied. The improvement mechanism of different industrial waste residues on the engineering properties of high liquid limit soil is discussed in terms of mineral composition and microstructure. Based on the experimental results of this study and considering the cost and engineering practice, it is suggested that the modified carbide slag optimal ratio of high liquid limit soil of Zhanjiang Avenue is 8%. The results can provide certain guidance for the improvement and application of different industrial waste residues on high liquid limit soil to achieve the effect of sustainable development.