Lime stabilization is a traditional method for improving foundation soils, and it also has potential applications for embankments and earth structures. In this study, several experimental techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR), were used to provide a clear picture of the microstructural evolution of a lime-stabilized loess (LSL) from China. SEM micrographs were used not only to qualitatively highlight the dual porosity nature of the material, but also to provide quantitative information using Image-Pro Plus (IPP) 6.0 software. As the lime content increases, the pore area ratio decreases, the shape of the macropores and mesopores flattens, and the pore angle distribution becomes more uniform. The FTIR results show that the functional group strength of the LSL samples first increases and then decreases with increase in lime content, while the pore volume continues to decrease. A non-monotonic evolution of the strength with the lime content is then expected, as also confirmed by unconfined compression tests performed at different lime contents and curing times: at low lime contents, the reduction of the pore volume and the increase in the functional group strength imply an increase in the strength; at high lime contents, the competing effects of the reduction of the pore volume and the increase in the functional group strength lead to an overall decrease in the strength with the lime content. Then, as an intermediate step toward further quantitative predictions of the hydromechanical behavior of LSL, a pore size distribution model inspired by the proposal of Della Vecchia et al. (Int J Numer Anal Meth Geomech 39:702-723, 2015) was developed and used to reproduce NMR experimental data. The pore size distribution model proved to be able to reproduce the cumulative porosity curves for the whole range of lime content and curing time studied, with only four parameters kept constant for all the simulations. The predictive capabilities of the model were also confirmed by simulating experimental data from recent literature.

In order to gain a deeper understanding of the changes in pore characteristics of undisturbed loess under the influence of acid pollution and the underlying microscopic mechanisms, this study investigates the alterations in pore characteristics caused by acid pollution and their relationship with macroscopic strength. Strength tests, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR) tests were conducted on undisturbed loess under various acid pollution conditions to comprehend the evolution of these characteristics. The research findings indicate the presence of a critical acid pollution level in soil. Below this level, increasing acid pollution results in a more uniform distribution of pores, a decrease in the difference between the long and short axes, and a complex edge shape. The arrangement of pores also tends to be disordered. However, when the acid pollution exceeds the critical level, it leads to uneven distribution of pores and an increase in the difference between the long and short axes. The shape of the edges becomes more regular and the pore arrangement becomes more orderly. As the acid pollution intensifies, the total volume of pores between aggregates decreases, while the total volume of pores within aggregates increases. This study examines the impact of acid pollution on the characteristics of loess pores, providing valuable insights into the soil-water-acid properties and deformation management of loess in practical engineering applications. These findings are of practical significance for the construction and protection of loess engineering in loess areas.

This paper investigates the effects on the behavior of a saturated porous material of an evolving microstructure induced by the mass exchange between the solid and the fluid phases saturating the porous network, using two-scale asymptotic expansions. A thermodynamically consistent model of the fluid physics flowing through the porous network is proposed first, describing microstructure variations to be captured implicitly via the level set method. The two-scale asymptotic expansions method is then applied to obtain an upscaled model capable to account for mass transfer. This last is proven to depend not only on the gradient of the macroscopic forces, such as the fluid pressure and the chemical potential, but also on the average velocity of the solid-fluid interface. Numerical simulations are carried out using the finite element method in order to evaluate the relative weight of the new terms introduced.

Deep cement mixing (DCM) piles are widely utilized for reinforcing soft clay foundations, particularly in coastal regions where soil stability is critical. Monitoring the quality and early-stage behavior of cemented soil is essential to ensure the effectiveness of DCM pile projects in meeting design requirements. Innovative methods for on-site monitoring are necessary to enhance the reliability and efficiency of these reinforcement techniques. In this study, a novel approach is proposed utilizing polymer optical fiber (POF) sensors based on physical optical sensing principles to monitor the initial hydration degree and overall quality of cemented soil during the early curing stage. The proposed method relies on the principle of physical optical sensing, where POF sensors are employed to measure changes in reflected light intensity (LI) and temperature in cemented soil. Two crucial variables, namely the initial water content and the amount of cement, are considered in analyzing their impact on the LI and temperature changes over time. Unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) analysis are conducted on cemented soil samples with varying water-cement ratios to investigate their mechanical properties and microstructure evolution. The results of the UCS tests indicate that higher initial water content prolongs the initial hydration reaction time required for cemented soil with different cement contents. Analysis of LI curves reveals a rapidly rising trend as the hydration reaction progresses, particularly evident in samples with higher initial water content. SEM analysis further demonstrates that a stable POF LI corresponds to the completion of the hydration process, with hydrated gel formation resulting in a more compact microstructure and smaller voids. The findings highlight the significant influence of cement quantity and initial water content on the mechanical strength and microstructure of cemented soil. By analyzing changes in reflected LI and temperature, the proposed monitoring method provides valuable insights into the early-stage behavior and quality of cemented soil during the curing process. This innovative use of POF sensors for on-site monitoring offers a novel approach to evaluating cemented soil in DCM pile projects.

The influence of thermal damage on macroscopic and microscopic characteristics of different rocks has received much attention in the field of rock engineering. When the rocks are subjected to thermal treatment, the change of macroscopic characteristics and evolution of micro-structure would be induced, ultimately resulting in different degrees of thermal damage in rocks. To better understand the thermal damage mechanism of different rocks and its effect on the rock performance, this study reviews a large number of test results of rock specimens experiencing heating and cooling treatment in the laboratory. Firstly, the variations of macroscopic behaviors, including physical parameters, mechanical parameters, thermal conductivity and permeability, are examined. The variations of mechanical parameters with thermal treatment variables (i.e. temperature or the number of thermal cycles) are divided into four types. Secondly, several measuring methods for microstructure, such as polarizing microscopy, fluorescent method, scanning electron microscopy (SEM), X-ray computerized tomography (CT), acoustic emission (AE) and ultrasonic technique, are introduced. Furthermore, the effect of thermal damage on the mechanical parameters of rocks in response to different thermal treatments, involving temperature magnitude, cooling method and thermal cycle, are discussed. Finally, the limitations and prospects for the research of rock thermal damage are proposed. (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/).

The hydro-mechanical properties of the vadose zone are strongly influenced by seasonal cycles. The hydraulic behavior of this zone is determined by the coupling of biotic and abiotic factors. The biotic factors are controlled by the physiology and anatomy of the vegetation growing in the area, while the abiotic factors depend on the local soil characteristics, such as water content, void ratio, and matrix structure. In this laboratory-scale investigation, we assess the influence of active biomass, water content, and suction on the particle and pore structure rearrangement. We use x-ray computed tomography and 3D digital image correlation to quantify plant roots at different stages of growth, soil deformation, and water content fluctuations. Our results show that the bulk porosity of vegetated soil is strongly affected by the induced water cycles. The global micro-structure rearrangement due to the double effects of plant water uptake and induced drying-wetting cycles translates into a final bulk porosity increase.