It is known from the literature that the rheological behavior of soils is largely dependent on the water content in pastes and soil organic matter forming the basis of organomineral soil gels. With an increase in soil moisture, gels can swell. As a result, the viscosity of the soil paste should change. The objective of this study was to assess the effect of soil moisture on the viscosity of soil paste. Arable soil horizons were used in this work: sod-podzolic, gray forest, leached chernozem, and chestnut. During the experiments, the soil moisture was changed, whereas the water content in the pastes in each soil type remained unchanged. The viscosity of the soil paste was determined by vibration viscometry, and the size of organomineral particles in pastes was determined by laser diffractometry. Two paste viscosity peaks depending on the soil moisture were obtained for all samples studied. The paste viscosity peaks were explained from the perspective of changes in the structure of humic substances in organomineral gels upon reaching critical concentrations: micelles-supramolecular formations-fractal clusters. Apparently, the transition between structural forms of humic substances under mechanical action on pastes is accompanied by the disintegration of large gel particles and the formation of a more balanced form of humic substances at a given water content.

The effective stress principle is the fundamental theory of soil mechanics. The effective stress transmitted between particles dominates the mechanical properties of soil, such as strength, deformation, and drainage. However, there remains a paucity of research on the effective stress in the compression of nano-scale clay minerals. This study explored the application of the effective stress principle in the consolidation behavior of kaolinite through the Molecular Dynamics method. The calibration and correction for micro effective stress and pore water pressure were first proposed. Micro-effective stress is the stress on the mineral itself in the contact part of two particles, while micro-pore water pressure always represents that on the weakly bound and free water in the same part. The strongly bound water film between particles can indirectly transmit the micro-effective stress through the electrical double-layer repulsion. The calculation of micro stress has been corrected according to the derivation of macro theory, and the results obtained corresponded well with that in the macro experiment. Moreover, the evolution of effective stress was analyzed by observing the interparticle water film. The increase in effective stress during consolidation was mainly due to the compression of the strongly bound water and the drainage of weakly bound and free water.

Understanding pore water distribution in soil is essential for elucidating water movement and mechanical properties, as it significantly influences soil strength and stability. Accurate assessment of this distribution provides a scientific foundation for civil engineering design, ensuring structural safety and durability. This study examines pore water distribution using plate load tests and Nuclear Magnetic Resonance (NMR). Results indicate that matric suction expels free water first, leaving bound water until a critical suction point is reached. As matric suction increases, the peak value of the T2 relaxation time curve decreases, shifting leftward, reflecting water drainage from larger to smaller pores. Then, water expulsion occurs in three stages, with Stage III primarily indicating bound water content, quantified at 19.23%, including 3.3% as strongly bound water. An equation is derived to calculate the surface relaxation rate of 0.0176 mu m/ms. Thus, the distribution of T2 relaxation time can be transformed into pore size distribution, summarizing the characteristics of pore water distribution during the drying process. Finally, comparative analysis confirms the effectiveness of NMR in measuring bound water. These findings enhance our understanding of soil water distribution and highlight the need for advanced models that incorporate pore connectivity and water retention dynamics.

As a typical special soil, red clay found in Guizhou Province, China, must be improved before it can be used for projects owing to its high plasticity. As a soil curing agent, the Consolid system is applicable to a wide range of soils, has good improvement effects and a simple operation, and is environmentally friendly. The effects of the dosage and curing age of the Consolid system on the unconfined compressive strength and shrinkage properties of the cured red clay-gravel mixture are studied. The results showed that both these properties of the red clay-gravel mixture were significantly improved by the Consolid System, and the higher the dosage of the Consolid system, the better the improvement effect. The thermal methods of thermogravimetric analysis and differential scanning calorimetry were used to determine that the bound water content was related to the amount of Consolid system admixture. With the increase in the dosage of the Consolid system, the weakly bound water content of red clay appeared to be reduced to different degrees, while the strongly bound water content was reduced to a lesser extent. The reduction in the weakly bound water led to an increase in the molecular gravitational force between the soil particles. This promoted the agglomeration of the soil particles to form a stronger agglomerate structure, thereby enhancing its mechanical properties. The physical phase analysis of cured soils with different amounts of Consolid system admixture was carried out by X-ray diffraction analysis. No chemical reaction occurred during improvement, but the crystal spacing was reduced. This phenomenon could be a factor improving the shrinkage properties. In addition, the shrinkage properties of the soil improved because of the low number of exchangeable cations on the mineral surface, allowing the cured soil to enter a charge equilibrium state quickly.

For engineering structures with saline soil as a filling material, such as channel slope, road subgrade, etc., the rich soluble salt in the soil is an important potential factor affecting their safety performance. This study examines the Atterberg limits, shear strength, and compressibility of carbonate saline soil samples with different NaHCO3 contents in Northeast China. The mechanism underlying the influence of salt content on soil macroscopic properties was investigated based on a volumetric flask test, a mercury intrusion porosimetry (MIP) test, and a scanning electron microscopic (SEM) test. The results demonstrated that when NaHCO3 contents were lower than the threshold value of 1.5%, the bound water film adsorbed on the surface of clay particles thickened continuously, and correspondingly, the Atterberg limits and plasticity index increased rapidly as the increase of sodium ion content. Meanwhile, the bonding force between particles was weakened, the dispersion of large aggregates was enhanced, and the soil structure became looser. Macroscopically, the compressibility increased and the shear strength (mainly cohesion) decreased by 28.64%. However, when the NaHCO3 content exceeded the threshold value of 1.5%, the salt gradually approached solubility and filled the pores between particles in the form of crystals, resulting in a decrease in soil porosity. The cementation effect generated by salt crystals increased the bonding force between soil particles, leading to a decrease in plasticity index and an improvement in soil mechanical properties. Moreover, this work provides valuable suggestions and theoretical guidance for the scientific utilization of carbonate saline soil in backfill engineering projects. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

In order to understand the influence of sand content on the secondary consolidation behavior of sand-fine mixtures, a series of one-dimensional creep tests were conducted. These tests used mixtures with sand contents of 0%, 16.67%, 28.57%, 50%, and 60% and were run for 3,000 min. As the sand content increases, the structure of the mixtures transitions from being fine-supported to sand-supported. This results in changes in the time at the end of primary consolidation (TEOP), the proportion of secondary consolidation deformation in the total deformation (PCT), and the coefficient of secondary consolidation. These parameters decrease before the sand content reaches 28.57% and increases after this point. The sand-fine mixtures with a sand content of 28.57% exhibit the minimum TEOP, PCT, and coefficient of secondary consolidation. When the sand content is less than 28.57%, bound water (especially weakly bound water) significantly impacts the secondary consolidation behavior of the sand-fine mixtures. However, when the sand content exceeds 28.57%, the secondary consolidation deformation of the mixtures is primarily governed by particle crushing in the sand grains.

Changes in water content have a significant impact on the consolidation of peat soil. Through the water content test and thermogravimetric analysis test, the water content, and the free water, weakly bonded water and strongly bonded water content of peat soil with different organic content in Yunnan Province (China) at different load levels and consolidation times were studied. The results show that the free water in peat soil samples was discharged when the temperature was less than 60 degrees C; the weakly bound water was released at 60 - 110 degrees C; and the strongly bound water was dehydrated at 110 - 200 degrees C. During the consolidation of peat soil, the water content in different states changed significantly. In the primary consolidation stage, the proportion of free water in the peat soil samples decreased by approximately 20%, while the proportion of weakly bound water increased slightly. In the secondary consolidation stage, the proportion of water in different states did not change considerably. In the third consolidation stage, the proportion of free water increased, and the proportion of weakly bonded water causing creep decreased by approximately 11%. For the undisturbed and deformed peat soil, the contents of free water and bound water increased with increasing total water content, but the ratio of free water to bound water remained relatively stable at approximately 1:2.