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Freezing points play a crucial role in distinguishing between salt expansion and frost heave in frozen saline soil. Through a series of cooling experiments, the freezing points of sodium chloride and sodium sulfate saline soils were measured, considering various salt concentrations and ratios of c(Cl−)/2c( SO 4 2 - ). The results revealed a three-stage cooling process: rapid cooling, constant cooling, and decreasing cooling. The freezing point of saline soil decreases with increasing salt concentration ranging from 1.5 to 4.9 times, attributed to the presence of more hydrated water molecules. Furthermore, influenced by the solubility of sodium sulfate, the freezing point of saline soil decreases with an increasing ratio of c(Cl−)/2c( SO 4 2 - ) in the range of 0.7–4 times. The reduction of water content, on the other hand, enhances capillary action and soil particle adsorption, causing the freezing point of the soil to decrease by 0.5 to 1.7 times. To accurately predict the freezing point of saline frozen soil, a prediction model was proposed and validated, taking into account the effects of salt types, salinities, and water contents. This research serves as a valuable theoretical reference for predicting the freezing point of saline frozen soil. [ABSTRACT FROM AUTHOR]

This study illustrates and discusses the physical properties, mechanical behavior, and microscopic characteristics of the South China Sea soft soil, and a comparison with the Bohai Sea marine clay, the Yellow Sea soft clay, and some typical marine soils is presented. In addition, the mechanisms of the difference in the geotechnical properties of these marine soils are revealed. Compared with the soils from other sea areas, the South China Sea soft soil presents remarkable characteristics of higher water content, larger void ratio, higher liquid limit, and higher content of fine particles. Besides, the South China Sea soft soil shows higher compressibility. As shown in the microscopic characteristics, the South China Sea soft soil contains lower content of clay minerals; in addition, due to the depositional and geological environments with higher salinity and higher temperature, there are more macropores, connected pores, and trellis pores in the South China Sea soft soil, so it presents a more open, flocculated structure rather than a granular-connection structure like the Bohai Sea marine clay and the Yellow Sea soft clay. The results presented in this paper will provide an important theoretical basis for revealing the engineering properties of marine soils, and improve the insights for ensuring the safety of ocean engineering during construction and service periods. [ABSTRACT FROM AUTHOR]

The geotechnical behavior of clay is known to be influenced by its external environment chemistry. In this study, a series of experiments were conducted to investigate the geomechanical behavior, mineralogical behavior, and microscopic characteristics of Tianjin marine clay when subjected to an acidic environment. The micro-mechanisms of these phenomena were thus revealed. It is interesting to note that the increasing environmental acidity would promote the illitization in illite–smectite and conversion in part of the smectite component in illite–smectite to chlorite. In addition, our results indicate that a critical pH developed with the increasing environmental acidity, leading to phased variations in strength and compressibility. When the environment pH was greater than its critical value, the increasing environmental acidity led to an increase in strength together with a decrease in compressibility, which was mainly related to the reduced thickness of the diffuse double layer and improved intermolecular force between soil particles. However, with an environment pH lower than its critical value, the geotechnical behavior of Tianjin marine clay was deteriorated as a result of more open, flocculated microscopic structures and low intergranular cementation strength in the marine clay, such that the strength decreased while compressibility increased as the environment became more acidic. [ABSTRACT FROM AUTHOR]

Geotechnical investigation and design show that when evaluating the settlement of ground with soft soil ground, the use of a single stress path results in a larger error than in the case of a multistress path. To understand the influence of a multistress path on the deformation properties and microstructure characteristics of soil, a two-stage stress path (corresponding to three stress states: the in situ state, unloading-loading state, and grouting pressure state) of soil was examined by analytical solution. Then, a series of triaxial tests was conducted to analyze macroscopic deformation properties considering four influencing factors, i.e., the relative distance between the soil and tunnel, stress paths, type of silty clay, and drainage conditions. The results show that axial strain of silty clay caused by the two-stage stress path increases by 31.6% with the relative distance decreasing from 1.67R (R means tunnel radius) to 1.25R on tunnel side, while the volume strain increases by 80% with the relative distance decreasing from 1.21R to 1.06R on tunnel bottom. In addition, the deformation caused by the two-stage stress path (or reconstituted soil or undrained condition) is larger than that caused by the one-stage stress path (or undisturbed soil or drained condition). Finally, through scanning electron microscopy and mercury intrusion porosimetry, the pore size, distribution, shape, and arrangement of silty clay on the bottom and sides of the tunnel were investigated. The research shows that under the two-stage stress path, the number of large pores decrease and that of small pores increase. The probability entropy of pore orientation ranges from 0.834 to 0.971 when silty clay is subjected to a two-stage stress path. This illustrates that the pore order of the soil on tunnel side is better than that on the tunnel bottom. [ABSTRACT FROM AUTHOR]

The properties of a soil, either in situ or at a hydraulic reclamation site, may change if influenced by the chemical status of the surroundings. Acidity, indicated by the pH, and magnesium (Mg2+), sometimes used to reinforce soil, are good indicators of the chemical environment. It is therefore worth investigating how acidity and Mg2+ affect the settling of dredged fill. In this study, a cylinder model test and ethylenediaminetetraacetic acid (EDTA) titration were used to investigate the mechanisms behind self-weight consolidation settlement. The results indicated that the settlement process of the dredged fill occurred in three stages and that the consolidation settlement process of the dredged fill varied as the pH and mass percentage of Mg2+ varied. As the pH increased from an initial low value, the settlement amount and settlement rate of the dredged fill approximated to a quadratic function trend and increased first and peaked when the pH was 4 and then decreased, reflecting the influence of the mineral composition of the soil and the Zeta potential of the soil particles. Under medium pH conditions, the settlement amount and settlement rate increased in an approximately linear manner, reflecting increases in the mass percentage of Mg2+ and changes in the double electric layers on the clay mineral surface. [ABSTRACT FROM AUTHOR]

Core samples to a depth of approximately 50 m and undisturbed soil samples were retrieved from eight locations in the Saga Plain, Japan, to investigate the effects of the depositional environment and post-depositional processes on the engineering properties of Quaternary clays in the Saga Plain. The engineering properties of these soil samples were measured, and the test results showed that the clays in the Saga Plain have a high void ratio, high water content, high compressibility, high sensitivity, and low stiffness. The one-dimensional compression curves plotted above the sedimentation compression line proposed by Burland, and the compression index was high, which indicated that the clays had been cemented to some degree. The clays have high strength sensitivity and high stress sensitivity, indicating that they have strong structures. It was considered that a considerable amount of volcanic ash from the four large volcanic eruptions that occurred during the deposition of these clays settled into the clays, resulting in a certain degree of cementation, which was attributed as the main driver of the strong structure in these clays. Comparisons of the NaCl concentration, pH, and oxidation-reduction potential (ORP) of the clay samples representing the initial depositional environment and the current ground environment showed that salt leaching occurred in the Ariake clay formation, and that the ground environment changed. When the NaCl concentration was less than approximately 2 g/L, the strength sensitivity of the Ariake clay samples with low-activity clay minerals significantly increased due to the decrease in the liquid limit and subsequent significant decrease in the remolded undrained shear strength. Therefore, salt leaching was probably a main cause of the high strength sensitivity of the clays in the Saga Plain. The depositional environment at some locations changed from an alkaline, reducing environment, to an acidic, oxidative environment, with the potential to change into a strongly acidic environment, which could have deteriorated the strength of the cement/lime-treated clays in the Saga Plain. [ABSTRACT FROM AUTHOR]