Soil Microstructure Research Articles

Effects of initial water and salt content on permeability and microstructure of sodic-saline loessal soils

Effects of initial water and salt content on permeability and microstructure of sodic-saline loessal soils

Automated identification of soil functional components based on NanoSIMS data

NanoSIMS technique allows to investigate the micro-spatial organization in complex structures in multiple scientific fields such as material science, cosmochemistry, and biogeochemistry. In soil biogeochemistry applications, NanoSIMS-based approaches aim to disentangle the interactions of organic matter (OM) and mineral phases in the heterogeneous soil microstructure. Investigating the spatial arrangement of distinct organic and mineral functional components is necessary to understand how these components interact and contribute to biogeochemical processes in soil systems. Identifying soil functional components within NanoSIMS measurements necessitates advanced and efficient data processing tools capable of accessibility and automation. We have developed a pre-processing tool to streamline NanoSIMS data preparation and handling. The tool is provided as an open-source software toolbox (NanoT). In addition, a two-step unsupervised segmentation method was developed to identify soil functional components based on NanoSIMS analyses. To illustrate the segmentation method, here we describe its application to two exemplary NanoSIMS measurements. This allows to distinguish mineral- and OM-dominated regions, as well as different mineral phases. To improve the detection of iron oxides and aluminosilicates, the 56Fe16O− channel was separately processed. The presented NanoSIMS-based processing workflow helps to disentangle functional components within a biogeochemically-diverse microstructure in soils and further warrants applications to a wide range of complex environmental samples.

Microstructural Evaluation and Linkage to the Engineering Properties of Metal-Ion-Contaminated Clay.

The rapid progress of urbanization and industrialization has led to the accumulation of large amounts of metal ions in the environment. These metal ions are adsorbed onto the negatively charged surfaces of clay particles, altering the total surface charge, double-layer thickness, and chemical bonds between the particles, which in turn affects the interactions between them. This causes changes in the microstructure, such as particle rearrangement and pore morphology adjustments, ultimately altering the mechanical behavior of the soil and reducing its stability. This study explores the effects of four common metal ions, including monovalent alkali metal ions (Na+, K+) and divalent heavy metal ions (Pb2+, Zn2+), with a focus on how ion valence and concentration impact the soil's microstructure and mechanical properties. Microstructural tests show that metal ion incorporation reduces particle size, increases clay content, and transforms the structure from layered to honeycomb-like. Small pores decrease while large pores dominate, reducing the specific surface area and pore volume, while the average pore size increases. Although cation exchange capacity decreases, cation adsorption density per unit surface area increases. Monovalent ions primarily disperse the soil structure, while divalent ions induce coagulation. Macro-mechanical tests reveal that metal ion contamination reduces porosity under loading, with compressibility rises as the ion concentration increases. Soils contaminated with alkali metal ions shows higher compression coefficients at all loads, while heavy metal ions cause higher compression under lower loads. Shear strength, the internal friction angle, and cohesion in metal-ion-contaminated clay decrease compared to uncontaminated field-state clay, with greater declines at higher ion concentrations. The Micropore Morphology Index and hydro-pore structural parameter effectively characterize both micro- and macrostructural properties, establishing a quantitative relationship between HPSP and the engineering properties of metal-ion-contaminated clay.

Short-term mechanical properties and microstructure of coastal cement soil modified by sugarcane bagasse ash

Sugarcane bagasse ash is a kind of agricultural waste with a large quantity and good volcanic ash reactivity, it is necessary to find a way to reasonably utilize it to prevent environmental pollution caused by long-term accumulation. In this paper, the effect of sugarcane bagasse ash on the short-term mechanical properties of coastal cement soil were studied, and unconfined compressive tests and triaxial shear tests were carried out. The sugarcane bagasse ash content was set to 0 %, 1 %, 2 %, 3 %, 4 % and 5 %, respectively, the cement content was set to 5 %, and the curing age was set at 7d. The test results show that sugarcane bagasse ash can effectively improve the unconfined compressive strength and triaxial shear strength of cement soil, exhibiting a trend of increasing first and then decreasing with the increase of its content. When the sugarcane bagasse ash content is 1 %, the unconfined compressive strength reaches the maximum value of 2040 kPa, which is 56 % and 8 % higher than that of cement soil with 5 % and 7 % cement content, respectively. Compared with cement soil with 5 % cement content, the triaxial shear strength increases by 12 %∼17 %, the internal friction angle φ and cohesion c increases by 3 %∼8 % and 2 %∼11 %, respectively. The SEM test results show that the addition of bagasse ash can promote the hydration of cement to produce hydrated calcium silicate and other hydration products, fill the internal pores of the sample, and make the microstructure of the modified cement soil tend to be dense. The research results provide a reference for the application of sugarcane bagasse ash modified cement soil in practical engineering.

Soil-water retention capacity of expansive soil improved through enzyme induced carbonate precipitation-eggshell powder

Enzyme Induced Carbonate Precipitation (EICP) has been extensively investigated as a promising approach to improve engineering properties of soil, while Eggshell Powder (ESP) is an agricultural waste that effectively fills soil pores. The ESP provides abundant nucleation at sites for the EICP process, further promoting the effective precipitation of calcium carbonate. The research presented in this paper investigated the Soil Water Characteristic Curves (SWCC), permeability coefficient, and microstructure of expansive soil before and after EICP and EICP+ESP modification. A series of laboratory experiments were conducted, including soil water characteristic tests, permeability tests and Scanning Electron Microscopy (SEM). The results proved that the addition of EICP and EICP+ESP into natural expansive soil resulted in a gradual decline in air entry value, residual water content, and permeability coefficient, indicating an increase in water retention capacity and a decrease in permeability. Furthermore, with the intrusion of EICP and EICP+ESP, the contact between particles becomes smoother, and the soil pores become more equally distributed. Ultimately, there was an enhancement in water retention capacity of the natural expansive soil. This study emphasizes the synergistic potential of combining EICP and EICP+ESP as stabilizing additives to enhance the water retention capacity of expansive soil. Moreover, the reuse of ESP provides a sustainable solution for the resource utilization of agricultural waste and the improvement of expansive soil using bio-inspired methods.

Vegetal layer restoration of contaminated sites from petroleum industry using sewage sludge

Soil is a non-renewable natural resource, extremely valuable for maintaining life on Earth. Large areas of soil are often polluted with petroleum products as a result of various human activities. In this case, it is necessary to remediate the contaminated soils from the oil industry and return them to the natural and economic circuit. In addition, large quantities of sewage sludge are generated daily by sewage treatment plants. The purpose of this study was to use the soil subjected to a bioremediation experiment with sewage sludge as support for the development of a new vegetal layer to restore the natural balance. The grass was sown in the land, which had previously been treated with sewage to monitor its development. Through microbiological analysis, we observed that soil and sewage sludge mixtures have a high content of heterotrophic bacteria and filamentous fungi that could play an important role in seed germination. IR (infrared spectroscopy) analysis revealed a decrease in hydrocarbon concentrations in the petroleum- contaminated soil treated with sewage sludge. By using the combined methods SEM-EDX (scanning electron microscopy – energy dispersive X-ray), we also analyzed the soil microstructure and the distribution of chemical elements to highlight the plants' evolution. The present study considers soil regeneration in areas contaminated with petroleum products and opens new perspectives for the use of sewage sludge in the ecological reconstruction of petroleum-contaminated sites.

Evolution of the Shear Strength and Microstructure of Undisturbed Lateritic Soil under the Influence of Alkali Contamination

Abstract With the progression of industrialization, alkaline contamination has become an increasingly serious issue in soil environments, significantly impacting the engineering properties and microstructure of soils. Undisturbed lateritic soil samples were immersed in sodium hydroxide solutions with pH values of 8.8 and 11.4, as well as in deionized water with a pH of 7.0, for soaking times of 1 day, 7 days, and 28 days. The influence of alkali contamination on the shear strength of the lateritic soil was quantified through consolidated slow shear tests. Additionally, scanning electron microscopy, thermogravimetric analysis, nitrogen adsorption tests, mercury intrusion porosimetry, and laser particle size analysis were employed to thoroughly explore changes in micromorphology, mineral composition, pore structure, and particle size of samples, aiming to establish a microstructural evolution model. At pH = 8.8, the cohesion and friction angle of samples are higher than that soaked in water and increase with the soaking time. At pH = 11.4, the cohesion significantly increases on the 1st day, relatively decreases by the 7th day, but remains higher than that at pH = 8.8. Subsequently, with an increase in soaking time, the cohesion continues to rise. The alkali solution dissolves the kaolinite minerals causing the pore structure to collapse. The elevated shear strength at pH = 8.8 is attributed to smaller particles tightly locking together to form a more stable structure. At pH 11.4, the significant increase in cohesion after 1 day is not only attributable to the reasons mentioned above but also attributed to the aluminum silicate gel’s bonding effect on particles. By the 7th day, gel dissolution reduces soil cohesion.

Investigating the internal erosion behavior and microscopic mechanisms of chemically stabilized soil: an experimental study

IntroductionInternal erosion triggered by water pipeline leaks seriously threatens the stability of the urban ground. Hangzhou, a city in Zhejiang Province, China, is facing critical challenges due to urban ground collapse (UGC) caused by internal erosion. However, there is a lack of research on the prevention of UGC by improving the internal erodibility of underground soil. Addressing this issue is of utmost importance to ensure the city’s stability and safety. This paper proposes to improve the internal erodibility of typical sandy silt soils with chemical stabilisers.MethodsThe effects of three chemical stabilisers, lignosulphonate (LS), lime (LI), and lignin fibre (LF), on the critical shear stress (τc) and erosion coefficient (kd) of sandy silt soils were investigated, which from Hangzhou, Zhejiang, China, by the hole erosion test (HET) at different mixing amounts and at different conservation times.ResultsThe findings indicate that LF mainly improves the erosion resistance of sandy silt by increasing τc, and the maximum increase is 2.38 times; LI mainly improves the erosion resistance by decreasing kd, and the maximum decrease is 2.18 times. After adding LS, τc and kd did not change significantly. The scanning electron microscope (SEM) test revealed that the inclusion of LF led to the formation of larger agglomerates in the sandy silt soil. The microstructure of sandy silt soil remained dispersed even after adding LS. Various chemical stabilisers used to improve sandy silt soils exhibited distinct erosion mechanisms. Sandy silt soils improved with LF exfoliated into agglomerates, displaying high resistance to erosion. On the other hand, the sandy silt treated with LF still lacks a protective layer and shows minimal improvements in its ability to withstand erosion. In contrast, the LS-amended sandy silt remains stripped with individual soil particles with insignificant changes in erosion resistance.DiscussionThis study can provide a conceptual framework for choosing foundation treatment techniques in future urban development projects.

Revealing the mechanisms of water permeability enhancement of urban loess subgrades due to vibration application

Urban loess subgrades are affected by considerable vibrations from traffic, especially when the underground pipelines leak, and seepage under vibrations often causes road damage. However, the influence of vibrations on the water permeability of loess subgrades remains elusive. Here we address this issue by performing vibration-assisted permeability tests and scanning electron microscopy, mercury intrusion porosimetry, and suction–nuclear magnetic resonance measurements. This allowed the evolution of the saturated hydraulic conductivity (Ks), water-air migration, soil microstructure, and pore water forms to be evaluated. The water permeability of the loess subgrade is promoted by vibrations due to the increase in Ks, the acceleration of wet front migration, and the escape of entrapped air. Moreover, the value of Ks under vibration is 3–14 times greater than that without vibration, and the maximum increase occurs at a vibration frequency near the natural frequency of the loess. Furthermore, a theoretical framework of loess vibration permeability is proposed, and the mechanisms by which vibration accelerates the permeability behavior of the loess subgrade are revealed. Vibration promotes the expansion of soil pores, a decrease in the binding capacity of pore water, the mobilization of fine particles, and the formation of local low-permeability layer. Moreover, it accelerates the opening of entrapped air bubbles and the displacement of water-air, the reduction in seepage resistance. Thus, seepage water flows rapidly along infiltration channels. These findings are highly important for the road safety performance and the sustainable development of the traffic environment in loess regions.

Improved stabilization of loess soil using magnesium oxysulfate cement-based ecological composite binder

The technology of loess solidification plays a crucial role in addressing issues such as soil erosion, with the key material in this process being the loess stabilizer. To tackle the high energy consumption problem associated with traditional loess stabilizers primarily composed of Portland cement, this study employed a more ecological sustainable alternative by incorporating solid waste coal gangue and magnesium oxysulfate (MOS) cement as a binding agent for consolidating loess. The alterations in bulk density, porosity, mineral structure, and microstructure of the consolidated soil with different MOS content were systematically investigated and validated. The pore size of MOS-solidified loess decreased significantly to a range of 0.04–3.60 μm compared to 0.80–3.88 μm for pure loess. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and thermogravimetric (TG/DTG) analysis revealed that the addition of MOS binder generated hydrated magnesium silicate (M-S-H), Mg(OH)2, and a small amount of 5Mg(OH)2·MgSO4·7H2O phase which filled the gaps between soil particles and bonded them together effectively. When the proportion of MOS binder added reached 11 %, the compressive strength of stabilized loess after curing for 28 days increased up to 9.4 MPa. After immersion in water for 24 h, the strength only decreased by 5.3 %, with a softening coefficient of 94.7 %. The test results consistently indicate that the enhancement in mechanical properties can be attributed to the binding effect facilitated by MOS. The ecological composite binder based on coal gangue and MOS demonstrates great potential in the field of soil stabilization.

Enhancing Soil Stability through Innovative Microbial-Induced Calcium Carbonate Techniques with Sustainable Ingredient

Expansive soil poses significant challenges for civil engineers, leading to structural damage, particularly in lightly loaded structures. This study employs an innovative and sustainable recipe to stabilize highly expansive soil using the Microbial-Induced Calcium Carbonate Precipitation (MICP) technique by substituting conventional ingredients with olive mill wastewater and hydrated lime. A series of laboratory tests were performed to evaluate the improvement in Atterberg's limits, Free Swell, Unconfined Compressive Strength (UCS), and pH, in addition to a series of qualitative measurements, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Optical Microscopic Images, and bacteria growth rate. Different mellowing periods and different cementation concentrations were used. The proposed recipe results showed a 50% reduction in the soil's free swell value. The UCS of the treated soil using the proposed recipe was eight times that of the untreated soil and twice that of the soil treated with the traditional recipe. The SEM images showed flocculation and aggregation in the soil particles, with the voids becoming smaller and filled with calcium carbonate (CaCO3). The XRD results showed the formation of new CaCO3particles. The optimized recipe demonstrated remarkable enhancement improvement and significant changes in soil physical properties and microstructure. Doi: 10.28991/CEJ-2024-010-08-08 Full Text: PDF

Water retention property and microscopic mechanism of shallow soil in inner dump improved by fly ash and polyacrylamide.

Improving the water retention property of shallow soil in the inner dump is the key step in the sustainable development of mines. In recent years, the use of fly ash to improve the structure of the inner dump and polyacrylamide as an additive to enhance water retention was an effective method. The article used a physical model test, filter paper method, and microstructure analysis method to compare and analyze the water retention property and microstructure of slope-improved soil with different fly ash and polyacrylamide content. The results show that the combined use of fly ash and polyacrylamide improved the water retention property of the amended soil. Fly ash and polyacrylamide had a greater effect on the low suction stage of the amended soil. Polyacrylamide reacted with water and bound soil particles to form aggregates, and the structural unit bodies were a block structure. Fly ash was non-sticky and was a matrix of fine particles, which weakened the bonding effect of polyacrylamide, and reduced the aggregates of soil particles, and the structural unit bodies were a flocculated structure of aggregates mixed with matrix. This, in turn, enhanced the capillary action and improved the water retention performance of the improved soil. In addition, polyacrylamide could connect water molecules, further enhancing the water retention property of the improved soil. The combined use of fly ash and polyacrylamide improved the available water content of improved soil, providing a viable and sustainable solution for improving the comprehensive utilization of fly ash, and laid the foundation for land reclamation at the inner dump.

Interpreting the Initial Growth Process of Surface Peeling: Microstructural Evolutions of Soil Deterioration on Archaeological Sites

ABSTRACT Few previous studies have investigated the mechanism of surface peeling from the perspective of soil microstructure. This study investigated surface peeling patterns and their growth feature in a large-size archaeological site, and SEM-EDS observed microstructure characteristics towards soil samples collected at different stages. Muddy Peeling (MP) irregular crusts with curling edges and Peeling with Salt Efflorescence (PSE) triggered by salt accumulation and formation of flakes in different shapes and thicknesses were the two main surface peeling patterns on the site. The average particle size of MP and PSE decreased from 6.0 μm to about 3.1 μm and 2.5 μm, respectively. Average pore size (4.5 μm) in unweathered soil decreased to 2.21 μm (MP) and 2.36 μm (PSE), and then rose to 4.86 μm (MP) and 5.74 μm (PSE), respectively. Micro-observation showed that the formation of flocculated calcium secondary minerals in MP and CaSO4 in PSE triggered by different water impacts caused different surface peeling patterns. This is the first study to reveal the differences lying in the initial growth process of archaeological site’s surface peeling in depth.

Effects of ionic strength and bentonite ratio on the migration of Cr(VI) in clayey soil-bentonite engineered barrier.

Soil-bentonite (S-B) barriers have been widely used for heavy metal pollution containment. This study conducted batch adsorption tests and diffusion-through tests to evaluate how ionic strength and bentonite ratio influence the migration of Cr(VI) in natural clay-bentonite mixtures. The test results indicated that the adsorption of Cr(VI) exhibited an obvious anion adsorption effect, the pH of the soil mixture increased with the addition of bentonite, resulting in a decrease in the positive surface charge. This change led to a decrease in Cr(VI) adsorption capacity, from 775.19 mg/kg for pure clay to 378 mg/kg for mixture samples with excessive bentonite. Furthermore, as the ionic strength increases from 0 to 0.1 M, the Cr(VI) adsorption capacity increases slightly due to the weakening of electrostatic repulsion on the clay particle surface, but the effective diffusion coefficient (De) increases by 21.97%. The compression of the diffusion double layer (DDL) under high ionic strength conditions enlarges the diffusion path and enhances the migration of Cr(VI) through the pore flow paths. Moreover, hydrated bentonite effectively fills the interaggregate pores of natural clay, thus creating narrower and more tortuous flow paths. However, excessive bentonite increases the pH value and pore volume, resulting in changes to the soil microstructure and disrupting the continuous skeleton of natural clay, which is unfavorable for Cr(VI) containment. Based on the study of the Cr(VI) contaminated site, a bentonite ratio of 2:10 is recommended for optimal natural performance of the natural clay-bentonite barrier.

Long‐Term Performance on Drought Mitigation of Soil Slope Through Bio‐Approach of MICP: Evidence and Insight from Both Field and Laboratory Tests

AbstractDrought is a serious global environmental issue that causes water resource scarcity and threatens agriculture and food supplements. This study aims to investigate the long‐term performance of an eco‐friendly technique‐microbial induced carbonate precipitation (MICP) on drought mitigation at field and laboratory scales. Seven in‐situ slopes treated with different MICP rounds and cementation solution concentrations were subjected to 16‐month weathering. Tests were conducted to evaluate the evaporation characteristics, water retention capacity, and CaCO3 distribution. Laboratory soil samples were further prepared to provide evidence related to underlying weathering mechanisms. The results show that MICP has a time‐dependent performance on drought mitigation. After MICP treatment, soil performs a remarkable evaporation suppression ability and the evaporation rate can decrease by 50%. This is attributed to the soluble salts which increase soil water retention capability and dense hard crust which inhibits water vapor migration into the atmosphere. However, the soluble salts and crust are sensitive to weathering thus leading to degradation of MICP. Suffering 16‐month weathering, the MICP‐induced CaCO3 decreases by more than 60%. The evaporation rate of soil increases with MICP rounds and cementation solution concentrations and can reach nearly two times of untreated soil. MICP‐treated field soil exhibits weaker water retention capacity than untreated soil because MICP alters soil microstructure which expands macropores and decreases volume of micropores. Connected macropores act as favorable evaporation channels and accelerate evaporation. To ensure MICP long‐term effects, periodical treatments are necessary. The most effective MICP treatment scheme is four to six treatment rounds and 1.0 M cementation solution.

Internal erosion in granular soils with different microstructures under cyclically increased hydraulic gradients

Internal erosion is one of the leading causes of failures and accidents of embankment dams, dikes, and slopes. The hydraulic loading acts as the driving force to detach the soil particles, while the initial soil microstructure determines the susceptibility of particle loss. In engineering practices, the soil may be subjected to cyclic hydraulic loadings due to water level fluctuations by extreme weather of intensive rainfall and drought. Under such conditions, the soil internal erosion process will be different from that under the steady unidirectional seepage, which has not been fully studied and needs urgent investigation. Thus, in this study, the internal erosion process and hydraulic characteristics of soils with different microstructures were investigated by both laboratory seepage tests and the discrete element method (DEM) simulation. The results indicate that the soil with a higher fine content was more structurally stable, and required a larger hydraulic gradient for erosion initiation. Once the internal erosion occurred, the particle loss and the soil hydraulic conductivity increased with increasing fine content. Additionally, when the applied hydraulic gradient was essentially the same, the soil experienced a server erosion under the cyclically than monotonically increased hydraulic gradients, and the amount of eroded soils increased with the increasing gradient amplitude. The results of this study will expand our understanding of the physical mechanism and hydraulic behaviors of soils subjected to cyclically increased hydraulic gradients and with different microstrures.

Combined Effect of the Microstructure and Mechanical Behavior of Lateritic Soils in the Instability of a Road Cut Slope in Rwanda

A very common hazard in Rwanda is represented by the instability of steep road cut slopes in lateritic soil. In its natural state, this material appears as a fine-grained weak and altered rock, generally in unsaturated conditions. Steep cut slopes made by this material could remain stable for a long time unless weathering weakens its mechanical behavior and heavy rainfall provokes a rapid landslide. This paper presents the results of an experimental investigation on the microstructural, petrophysical, and geotechnical properties of lateritic soil from a road cut slope located in Kabaya (Ngororero District—Rwanda), which was recently subjected to a landslide. The mechanical properties of the material are strictly related to the geological origin and history of the deposits, their formation environment, and weathering processes. These characteristics were revealed by peculiar microstructural features (micro-texture, porosity, and degree of alteration of original mineral paragenesis). The experimental investigations included identification and classification tests, direct shear tests on saturated samples, and swelling tests. This multidisciplinary approach provided insights into the relationship between geotechnical properties and the microstructural, petrophysical, and chemical characteristics of the altered rocks. This study showed how different levels of chemical alteration operated by weathering processes, in conjunction with brittle deformation related to the tectonic history, formed in the same site two shallow rock layers with similar macro-scale features and mechanical behaviors but markedly different microstructural and chemical properties. The innovative aspect of this research suggests an integrated multidisciplinary approach to considering microstructural aspects in addition to mechanical behavior in the slope stability analyses in lateritic soil. In particular, this study demonstrates the importance of such an approach since the failure mechanism is better explained if it is based on microstructural observations instead of considering the soil shear strength parameters only. This research helped to explain the formation of the landslide failure mechanism in a specific road cut slope, which could be assumed as representative of many other similar slopes subjected to landslides in Rwanda.

Properties and microstructure of soil solidified by titanium slag-flue gas desulfurized gypsum-Portland cement composites as solidifiers

Using Portland cement for soil solidification has sustainability issues due to high energy-consumption and carbon emissions. An innovative approach suggests using titanium slag and flue gas desulfurized gypsum as substitutes for Portland cement for soil solidification. This study systematically evaluates the effects of titanium slag-flue gas desulfurized gypsum-Portland cement composite (TS-FGD-OPC composite) solidifier on the performance of solidified soils. The evaluation includes assessing the unconfined compressive strength (UCS), elastic modulus, moisture content, and leachate pH value. Additionally, the hydration process and microstructure development of the solidified soils are characterized through the XRD, TG-DSC, BET, and SEM tests. The results indicate that the although its compressive strength is much lower, TS-FGD-OPC composite can be used as soil solidifier. With the titanium slag content increase, the TS-FGD-OPC composite solidifier brings the solidified soils to have lower UCS, elastic modulus and leachate pH value, and higher plastic deformation and moisture content. However, to get the same UCS, the utilization of the TS-FGD-OPC composite solidifier can bring the significant reduction of the Portland cement consumption. At the same dosage, the TS-FGD-OPC composite incorporating 50 % titanium slag and 20 % flue gas desulfurized gypsum yields an UCS achieving up to 92.5 % of that in pure Portland cement solidified soil. This is attributed to the filling of pores between soil particles with hydration products and unhydrated particles, resulting in the densification of the solidified soils and the cohesion increase of soil particles. The findings confirm the feasibility of substituting Portland cement with titanium slag and flue gas desulfurized gypsum to prepare an effective and environmentally friendly soil solidifier, to reduce the demand for Portland cement in soil solidification.

Study on the microstructure and strength characteristics of marine soft soil under wet-dry cycle condition

For marine soft soil under the periodic wave loading, the pore water content in soil suffering dry-wet cycle for a long time, which affects its microstructure and macroscopic mechanical strength, resulting in insufficient bearing capacity and excessive deformation of soft soil. To reveal the microstructural characteristics and strength attenuation law of marine soft soil under dry-wet cycle condition, electron microscopy scanning and direct shear tests under different times of dry-wet cycles were carried out, and the mathematical equations of pore structure and strength parameters were established based on fractal theory. The research results showed that: (1) The pore structure changed considerably after the first dry-wet cycle, and then changed gently with the increase of dry-wet cycle times, which was reflected by the fractal dimension D value decreases to a constant value gradually. (2) The shear strength of the soil diminishes with an increase in the number of dry-wet cycle times, and the maximum attenuation occurs after the first dry-wet cycle. (3) The relationship between cohesion (c), internal friction angle (φ), and fractal dimension (D) is exponential, with the curve shapes being concave and convex, respectively.

Monitoring of early curing stage of cemented soil using polymer optical fiber sensors and microscopic observation

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.