Unsaturated Conditions Research Articles

Phase Transition in Geomaterials Under Unsaturated Conditions

Phase Transition in Geomaterials Under Unsaturated Conditions

Development of a reactive transport model for microbial induced calcium carbonate precipitation in unsaturated conditions

Microbial induced calcium carbonate precipitation (MICP) offers a sustainable technique to improve geologic properties of soils in engineering structures. The applications encompass improved soil strength, scour mitigation, fracture sealing, and in situ contaminant immobilization. Previous studies have presented fundamental processes and implementation in lab- and field-scale. Most of these studies were examined in saturated conditions despite many MICP applications including those in coastal and riverside areas which will likely take place under unsaturated conditions. The study herein investigated the effect of soil water retention curve (SWRC) parameters and attachment coefficient ( Kat ) on CaCO3 precipitation in sand. Using numerical analyses, a continuum model was developed in which unsaturated flow and transport were coupled with biological and chemical reactions in variably saturated conditions. Predictive modeling results compare mass percentage of calcium carbonate resulting from MICP at degrees of soil water saturations of 20%, 40%, 80%, and 100% in sandy soil media. The results indicate the bacteria attachment coefficient increases by a factor of 3 as the degree of saturation is decreased from 100% to 20%, as the higher suctions at lower saturation levels improve bacteria fixation. The drying branch of SWRC versus wetting front yields higher CaCO3 for identical MICP treatment. Numerical results show the trend in hydraulic conductivity with increasing cementation level.

Analytical solution of electroosmotic-surcharge preloading coupled consolidation for unsaturated soil via Electric Prefabricated Vertical Drains (EVDs)

Electric prefabricated vertical drain made of new geosynthetic materials has the advantages of corrosion resistance, good water filtration, and unobstructed drainage. It has been used in unsaturated soils for embankment and slope stabilization as well as roadbed improvement. A theoretical model of the axisymmetric, free-strain consolidation for unsaturated soil under the coupled electrical-flow-mechanical fields considering radial-vertical flow is formulated, using the homogenization theory, method of separation of variables, and Bessel-Fourier series orthogonality. The relevant cases of saturated and unsaturated conditions are compared with the current analytical solution to examine the validity. The spatial and temporal distributions of excess pore-water and pore-air pressure are accurately reflected in the proposed solution, and its variation under electric fields is effectively displayed. The numerical calculations are also performed to investigate the effects of various important parameters, such as the single-layer unsaturated soil thickness, the effective voltage, and the radial water-to-electrical permeability ratio, on the excess pore-water pressure, excess pore-air pressure, and surface settlement. It is observed that the final negative pore-water pressure and the final settlement increase linearly as the effective voltage increases.

Interdependent factors influencing the carbon yield, structure, and CO_{2} adsorption capacity of lignocellulose-derived carbon fibers using multiple linear regression

Cellulose has experienced a renaissance as a precursor for carbon fibers (CFs). However, cellulose possesses intrinsic challenges as precursor substrate such as typically low carbon yield. This study examines the interplay of strategies to increase the carbonization yield of (ligno-) cellulosic fibers manufactured via a coagulation process. Using Design of Experiments, this article assesses the individual and combined effects of diammonium hydrogen phosphate (DAP), lignin, and CO_{2} activation on the carbonization yield and properties of cellulose-based carbon fibers. Synergistic effects are identified using the response surface methodology. This paper evidences that DAP and lignin could affect cellulose pyrolysis positively in terms of carbonization yield. Nevertheless, DAP and lignin do not have an additive effect on increasing the yield. In fact, combined DAP and lignin can affect negatively the carbonization yield within a certain composition range. Further, the thermogravimetric CO_{2} adsorption of the respective CFs was measured, showing relatively high values (ca. 2 mmol/g) at unsaturated pressure conditions. The CFs were microporous materials with potential applications in gas separation membranes and CO_{2} storage systems.Graphical abstract

The Seepage Evolution Characteristics in Undisturbed Loess under Dynamic Preferential Flow: New Insights from X-ray Computed Tomography

Preferential flow is widely developed in varieties of voids (such as macropores and fissures) in loess areas, affecting slope hydrology and stability and even leading to geological disasters. However, the model of seepage evolution with dynamic preferential flow is not clear, which obstructs the disclosure of the mechanism of landslides induced by the preferential flow. This study aimed to capture the seepage and occurrence status of water in loess voids, explain the variability characteristics of the loess pore structure, and reveal the seepage evolution model of dynamic preferential flow. Preferential infiltration experiments were conducted by combining X-ray computed tomography (X-ray CT) nondestructive detection with contrast techniques under dynamic seepage conditions. Three-dimensional (3D) visualized reconstruction, digital image correlation (DIC), image processing, and quantitative analyses were performed in AVIZO 2019.1, including two-dimensional (2D) and 3D characteristics of preferential flow distribution and macropore changing, dynamic variation of the porosity, pore number, volume, dip angle, and connectivity. Results showed that (1) preferential flow exists under saturated and unsaturated conditions in loess with strong uniformity and anisotropy; (2) preferential flow not only migrates into existing connected macropores, but also connects the original isolated pores into channels and forms larger percolation groups of contrast medium under the gradually increased high pressure; (3) the seepage develops with the evolution model of ‘preferential flow–piston flow–preferential piston mixture flow–piston flow’ in the dynamic process. The new insights into the characteristics of the seepage evolution in undisturbed loess under dynamic preferential flow will enrich the understanding of loess seepage and provided an important reference for future research on the slope instability of the loess induced by preferential flow.

Soil mechanical reinforcement by the fibrous roots of selected rangeland plants using a large soil-root shear apparatus

Soil reinforcement by fibrous roots of rangeland plants is essential for soil conservation. This study was done to: i) determine the effect of two genotypes 75B and 75C of Festuca arundinacea, Bromus inermis, and Bromus tomentellus on soil reinforcement at saturated/unsaturated conditions, and ii) explore the relationships between soil shear strength, and root area ratio (RAR) determined by image analysis and root chemical composition and mechanical properties in a sandy clay loam soil. Two genotypes of F. arundinacea were chosen based on their different morphological/physiological responses to environmental stresses. Rooted soils were sheared at three depths, 10, 25, and 40 cm. Peak shear strength and shear displacement-at-failure in the rooted soils were about four times greater than in the non-planted ones. B. inermis (with highest numbers of stretched roots) showed the highest shear strength (i.e., 35.7 kPa), and the roots of B. tomentellus were as effective as F. arundinacea. However, their effects on shear displacement-at-failure were significantly lower. Highest and lowest shear displacements were observed in the rooted soils of F. arundinacea and B. tomentellus, respectively. Greatest soil reinforcement was observed in the shallow soil (i.e., depth 10 cm). Soil reinforcement and the intercept and slope of shear strength vs. RAR were greater in the unsaturated soil (i.e., matric potential –10 kPa), indicating higher mobilization of root strength in soil reinforcement and lower root slippage. Shear strength differences of rooted soil were better noticeable in unsaturated condition. More than fivefold decrease in shear strength was observed from unsaturated to saturated state in control, but it was in the range of 1.4–1.7 for planted soils. This revealed that the reinforcing effects of roots moderated the role of soil water status in mechanical strength. Little changes in the slopes of shear strength vs. RAR relations for F. arundinacea 75C and B. inermis imply that they are effective in soil reinforcement irrespective of water status. However, the slope of relations for F. arundinacea 75B and B. tomentellus considerably increased from saturated to unsaturated state, showing that the roots of these two plants effectively reinforced unsaturated soils. Highest soil reinforcement by the roots of B. inermis was partly related to their greater lignin and hemicellulose contents and tensile strain-at-failure. Highest and lowest values of shear displacement-at-failure were observed in F. arundinacea 75C and B. tomentellus, respectively; it means that the roots of F. arundinacea 75C with higher cellulose/lignin ratio, tensile strength, and strain-at-failure stretched greater under shear.

Enhancement of a multi-species reactive transport model for cement-based materials under cyclic wetting and drying conditions

To understand the underlying phenomena that drive concrete deterioration under cyclic environmental conditions in the marine environment, a reactive transport model (RTM) for unsaturated cement-based materials has been established in this study, including multi-ionic and moisture transport coupled with a chemical equilibrium computation. The two-phase moisture transport model, which considers pore structure changes, is introduced with capillary pressure as the primary variable parameter. The modified Poisson-Nernst-Planck (PNP) equations were illustrated for multi-ionic transport through pore solution under unsaturated conditions. A modelling approach for moisture conductivity based on the pore structure and moisture storage was presented to account for pore structure changes on the mass transports. The consideration of boundary conditions and moisture flux through the exposed surface is demonstrated for wetting and drying conditions, separately. Numerical results for mortar samples subjected to NaCl solutions under various cyclic wetting and drying conditions were in good agreement with experimentally measured moisture gain and total chloride content. Under more prolonged wetting conditions, the deeper influence depth and a wider range of moisture fluctuation lead to an increase in concrete deterioration. For all cyclic wetting conditions, the precipitation of Friedel's salt is predicted, which subsequently limits the transport of chloride ions to deeper depths from the exposed surface. A peak in the chloride profile is observed near the exposed surface. Meanwhile, the peak region continuously expands and moves deeper into the specimens with increasing wetting time duration and exposure times, consistent with Friedel's salt precipitation. In contrast, the chloride content near the exposure surface shows a significant decrease due to the decomposition of the C–S–H phase caused by ion leaching and carbonation of the exposed surface.

Empirical Equations Expressing the Effects of Measured Suction on the Compaction Curve for Sandy Soils Varying Fines Content

To effectively apply various soil types for embankments, understanding their compaction characteristics is crucial. One crucial factor affecting compaction is suction, which plays a significant role as it is typically performed under unsaturated conditions. Suction varies with soil density, water content, and fines content. This study directly measures suction after soil compaction using the triaxial apparatus, unlike the Soil water characteristic curve (SWCC), assessing its impact on compaction characteristics. Immediate suction measurement after compaction provides apparent suction, resembling on-site conditions with open pore air pressure. Comparing SWCC with apparent suction at each compacted state reveals that suction and air entry value increase with initial density, positively impacting compaction. Notably, apparent suction aligns better with wetting process suction from the SWCC due to added water during specimen preparation. Empirical equations are derived to obtain suction contours across various density and saturation ranges, aiding in understanding suction variations on the compaction curve. Even slight variations in saturation causes noticeable changes in apparent suction during higher compaction efforts, affecting soil compaction characteristics. Therefore, the precise control of saturation control is needed to achieve desired properties of compacted soil, especially at higher compaction efforts and with various soil types. This understanding significantly impacts the mechanical behavior of unsaturated soils.

Comparative study of performance of wicking and conventional railway geotextiles under the synergetic simulation of train loads and flooding

Geotextiles are used within railways and highways to reduce settlement and improve drainage characteristics. However, the drainage performance of conventional geotextiles under unsaturated conditions can be limited due to capillary barrier effects. Therefore, more recently, wicking geotextiles consisting of woven fibers with deep groves have been developed to improve drainage performance. Despite these potential performance benefits and many related highway studies, there has been minimal study into the performance of wicking geotextiles for railways. Therefore, this study performs large-scale laboratory tests on railway ballast-subgrade materials under three conditions: non-stabilized (NSS), conventional geotextile stabilized (CGSS), and wicking geotextile stabilized (WGSS). Each test sample is subject to 600,000 cyclic loading cycles over 3 phases. The first phase is a stationary phase for consolidation, the second is to simulate loading directly after rainfall, and the third is to simulate loading after flooding. The results are analyzed and four conclusions are drawn: 1) both geotextile types prevent rainfall water from infiltrating into subgrade soils, however the wicking shows elevated performance, 2) the wicking geotextile produces capillary suction, which compared to the conventional geotextile, significantly delays infiltration and helps to reduce the moisture content in subgrade soils, 3) both geotextiles are capable of separation and filtration during rainfall and flooding simulation, however the wicking offers additional performance, 4) the deformation of both geotextiles is similar.

Stability of shallow sub-surface cavities under surface loading using granular media through model testing

Buried cavities are one of the commonly occurring Ground related issues. Every year, thousands of cave-in episodes are documented as a result of the collapse of underground cavities, damaging infrastructure and frequently resulting in fatalities. Cavities at shallow depths are critical and can seriously harm the surface infrastructure, which in most cases are the highways and the roads with traffic loadings. The fault or cracks in subsurface structures, such as box girders, pipelines, etc., primarily contribute to the cavity initiation at shallow depths. The cavities remain stable until the soil arching and the capillary forces in the unsaturated media can collectively resist the pressure of overburden soil. The stability of the shallow cavity is of concern when it lies beneath the heavy traffic loads of the highways. In this study, a particular model test equipment was prepared, having a soil chamber, water level indicator, and a base with a slit opening to induce a cavity in the soil. Model tests were performed using granular media of spherical and non-spherical (clumped and deformed) glass particles under unsaturated conditions to form a stable shallow cavity. The resultant cavity was tested with surface loading using surface plates and having variable loading rates. It was found that particle shape has a significant effect when surface loading is applied to the stable cavity. Clumped particles showed approx. Ten times higher peak resistance to surface loading compared to the spherical particles, both having equivalent mean particle size. The loading rate was found to be effective for the cases with unsaturated conditions; however, for dry samples, the loading rate was found to have insignificant effects on surface loading.

Moisture and soil type are primary drivers of Helicoverpa zea (Lepidoptera: Noctuidae) pupation.

Studies in the lab have demonstrated that evaluating the effect of soil moisture and other variables is essential for understanding the importance of environmental factors influencing the Heliothinae pupal stage, but simulated field studies are conducted infrequently. We compared the pupation of Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) under saturated and unsaturated conditions across 3 distinct soil types (coarse sand, high organic muck, and fine-textured clay) and observed adult emergence, as well as pupal depth and weight. The interaction between soil type and moisture had a significant effect on adult emergence. Fewer adults emerged from dry fine-textured clay soil than from dry coarse sand and high organic muck. However, there was no effect of soil type and no interaction between soil and moisture on pupal depth. Soil moisture was the primary driver of pupal depth, suggesting prepupae use moisture to mediate their position within the pupal chamber. In addition, pupal weight was unrelated to soil type, moisture, or their interaction. Our study demonstrates that soil moisture can be a greater driver of H. zea pupation than soil type, but additional observations are necessary to understand the mechanism by which moisture impacts pupation.

Unraveling mechanisms behind reduced nitrate leaching with graphite nanomaterials addition with fertilizers in soil column experiments

Overuse or mistimed application of nitrogen fertilizer can cause nitrate contamination in groundwater and surrounding surface waters. Previous greenhouse studies have explored the use of graphene nanomaterials, including graphite nano additive (GNA), to reduce nitrate leaching in an agricultural soil while growing lettuce crops. To investigate the mechanism of GNA addition in suppressing nitrate leaching, we conducted soil column experiments using native agricultural soils under saturated or unsaturated flow conditions to simulate varied irrigation. We investigated the effects of temperature (4 °C compared with 20 °C) on microbial activity and dose effect of GNA was also explored (165 mg/kg soil and 1650 mg/kg soil) for biotic soil column experiments whereas a single temperature condition (20 °C) and GNA dose (165 mg/kg soil) was employed for abiotic (autoclaved) soil column experiments. Results showed GNA addition had minimal effects on nitrate leaching in saturated flow soil columns due to short hydraulic residence times (∼3.5 h). In comparison, longer residence times (∼3 d) in unsaturated soil columns reduced nitrate leaching by 25–31% relative to control soil columns without GNA addition. Furthermore, nitrate retention in the soil column was found to be suppressed at 4 °C compared with 20 °C, suggesting a bio-mediated mechanism for GNA addition to reduce nitrate leaching. In addition, the soil dissolved organic matter was found to be associated with nitrate leaching, where less nitrate leaching occurring when higher dissolved organic carbon (DOC) was measured in leachate water. Following studies of adding soil-derived organic carbon (SOC) resulted in greater nitrogen retention in the unsaturated soil columns only when GNA was present. Overall, the results suggest that GNA-amended soil reduces nitrate loss through increased N immobilization in the microbial biomass or loss of N in gaseous phase through enhanced nitrification and denitrification process.

A constitutive model for structured soils under saturated and unsaturated conditions

AbstractMany constitutive models for unsaturated soils have been reported in the literature, but only a few of them attempted to incorporate the influence of soil structure, which is a combination of fabric and bonding. Some important aspects of unsaturated soil behaviour, such as the effects of soil structure on the loading collapse (LC) curve, cannot be well captured by the existing models. This study developed a new elastoplastic model for isotropic structured soils under saturated and unsaturated conditions. In particular, several new equations were proposed to model (i) the influence of soil structure on the LC curve; (ii) the evolution of the LC curve during structure degradation. Therefore, the initial soil structure and its evolution under hydro‐mechanical loads can be properly simulated. To validate this new model, it was applied to simulate the behaviour of structured and unsaturated soils along different suction and stress paths, including constant‐stress wetting, constant‐suction isotropic compression, one‐dimensional (1D) compression and triaxial shearing. The measured and computed results are well matched, demonstrating the good capability of the proposed model.

Unsaturated transport of Escherichia coli through disturbed soil column: effect of natural zeolite and cow manure addition

Organic and inorganic amendments are routinely applied to ameliorate soil conditions in semi-arid regions. This study aimed to examine the unsaturated transport of nalidixic acid-resistance Escherichia coli (E. coli NAR) in soil amended by cow manure (CM) and natural zeolite (NZ). Two levels of NZ (5 and 15% w/w) were added to a loam soil containing 5% w/w CM and incubated for 60 days. Then, the soil mixtures were poured into cylinders (3.6 × 15 cm) and a pulse (0.1 pore volume) of bacteria suspension (106 Cell mL−1) was added on top of the soil columns and leaching experiments were conducted at a steady-state, unsaturated flow condition and filtration coefficient (λf ), relative adsorption index (SR ), maximum depth of bacteria transport (Zmax ), average (Cav ) and cumulative cell density (Ccum ) were calculated. CM and NZ application significantly increased the peak density, Z max , C av , and C cum of E. coli NAR. The Cav , and Ccum of E. coli NAR in both 5 and 15% NZ containing mixtures were about 1 and 2-fold higher compared to the control. CM and NZ addition to soil decreased the filtration coefficient (λf ) and relative adsorption index (SR ) compared to the control. According to our results, we should conclude that the presence of NZ and CM, separately or together, can significantly increase the risk of groundwater contamination and it should be used with prudence.

Exploring the vertical transport of microplastics in subsurface environments: Lab-scale experiments and field evidence

Microplastics (MPs) defined as smaller 5 mm plastic particles have received increasing attention due to their global occurrence and potential toxicity. This study investigated the effects of environmental factors (rainfall intensity, 13 and 29 mm/h) and MP characteristics (morphology (fiber, flake, and film), polymer type (polypropylene (PP), polyethylene terephthalate (PET), and polystyrene (PS)) and size (100–300, 300–500, and 500–1000 μm)) on the vertical transport of MP in unsaturated soil conditions using lab-scale column experiments. Additionally, the occurrence and characteristics of MP detected in soil/sediment (total 13 samples) and groundwater samples (total 6 samples) were explored in the field study. Laboratory-scale column experiments revealed that heavy rainfall intensity (29 mm/h) increased the degree of MP vertical transport in unsaturated soil conditions and MP fibers showed the greatest vertical mobility among the various morphologies of MPs assessed. For the polymer type and size, the lighter PP polymer or the larger size of MP (500–1000 μm) showed higher mobility. In the field study, a statistical difference in MP abundance was observed depending on the population density and degree of urban development in both soil and groundwater samples. Comparing to the two different types of environmental media samples obtained from the same site, there was a significant difference in the composition of polymer types present while statistically no difference in MP abundance was observed between the two media samples (i.e., soil or sediment and groundwater). In addition, MP fibers and polyethylene (PE) were predominantly detected in our two study areas. These results suggest that various types of MP can pass through the unsaturated zone by water infiltration, even if it takes a long time to reach groundwater. Overall, we found that the degree of vertical transport of the MPs was highly sensitive to environmental conditions and MP characteristics.

Two-Level Full Factorial Design Approach for the Analysis of Multi-Lane Highway Section under Saturated and Unsaturated Traffic Flow Conditions

Oversaturation of highways occurs due to their inadequate assessment and design. In this paper, we propose both a mathematical queuing model and a Discrete-Event Simulation (DES) framework based on Newell’s triangular flow-density relationship for the performance analysis of a multi-lane highway section. The proposed framework is a finite capacity queuing system, which captures an increase in the flow with the vehicle density up to the capacity of the section in an unsaturated condition and a decrease in the flow in the case of a saturated condition, depicting the actual traffic conditions on the highway section. First, the Birth–Death Process is used to build the mathematical queuing model (BDP), and the average number of vehicles (average queue length) and blocking probability on the highway section are estimated. Then, the accuracy of the mathematical queuing model is verified by the proposed DES framework. The “significance and effects” of different design factors are evaluated using the two-level full factorial design technique. The analysis of the experimental results reveals that the length of the highway section and the number of lanes are the most significant factors affecting the average queue length and blocking probability, while the jam density only has a significant effect on the average queue length and does not affect the blocking probability. In case of a two-way interaction, the combined effect of the “length-lanes” significantly affects the average queue length. In the end, a multiple-factor linear regression model is also developed for the prediction of the average number of vehicles on the highway section based on the design factors.

Swelling and collapse behavior of unsaturated expansive subgrades stabilized with recycled glass

The swelling and collapse behaviors of expansive soils cause significant damage to light infrastructures such as pavements. This study investigates the swell-collapse behavior of expansive clay subgrade improved using recycled glass (RG) under unsaturated conditions. First, the optimum recycled glass content (ORGC) was determined based on the reduction in swelling potential. Next, static compaction tests were carried out on clay specimens stabilized at ORGC to establish a constitutive surface, namely virgin compaction surface (VCS) that exhibited the relationship between the moisture, stress and deformation states. The capability of the VCS in interpreting the swell-collapse responses was evaluated by applying various state paths. One-dimensional compression tests were conducted on specimens to investigate the mechanisms of swelling and collapse under a range of moisture contents and stress levels. Findings showed that the specimens’ behavior at ORGC = 25 % followed the developed VCS during loading, unloading and wetting paths, except those prepared at low moisture contents and wetted under low stresses. Utilizing the volume change data, a prediction model was developed and validated to estimate the swelling and collapse potential at ORGC. The proposed model provides a practical methodology to predict the volume change response of mixtures of fine and granular pavement materials through unsaturated soil theory.

Numerical Modelling for effect of rainfall on unsaturated soil slopes

Expansive soils are predominant in many parts of the world. Expansive soil treated as problematic soils, as economic and design a safe slope on expansive soils is major challenge for civil engineers. Expansive soils were compacted under unsaturated condition, in various construction projects. Major failures reported in many countries around the world are due to swell shrinkage characteristics causing unstable slopes. Fills and compacted soils have an inherent suction when they are first compacted. The suction is the most important factor which affects the shear strength of unsaturated soil. variation of suction in unsaturated soil is an important factor considered for solving issues like slope stability and bearing capacity failure in unsaturated soil. Rainwater infiltration are major triggering factor for failureof expansive soil slopes. The strength of unsaturated soil changes with water evaporation and infiltration. Due to infiltration of rainwater into the soil a significant change in the pore water takes place. Hence, this fluctuation in pore water pressure responsible for the distinct mechanical behavior of unsaturated soil under different Geotechnical problems.A numerical modeling was done with Plaxis LE software, considering parameters of unsaturated soil. As the changes in pore-water pressure and moisture content are a function of the flow of moisture through the soil-atmosphere boundary.The effect of soil type, rainfall intensity, location of ground water table, permeability functionsareconsidered to reproduce the soil-atmosphere interaction. Obtain results illustrates the combine effect of suction and increase of saturation due to rainfall on slopes. It was observed that rainfall increase the induced matric suction and increase the positive pore water pressure finally results in slope failures.

Effect of saturation on liquefaction properties of various volcanic ash coarse-grained soils under unsaturated conditions

日本国内に分布する 6 種類の火山灰質粗粒土を対象に，飽和・不飽和繰返しせん断試験を実施し，飽和度の低下に伴う繰返しせん断変形特性，液状化特性を把握した。試験結果から，降下火砕堆積物であるボラを除き，飽和度の低下に伴う液状化強度比の増加が確認された。しかし，その増加傾向は中密な豊浦砂に対してどれも鈍感であり，飽和度の低下による液状化強度比の増加が中密な豊浦砂ほど見込めないことが示唆された。火砕流堆積物である支笏軽石流堆積物およびしらすでは，飽和度 80%から 70%で液状化強度比の増加傾向は降下火砕堆積物に対して敏感であり，降下火砕堆積物に対して，初期細粒分含有率が大きい火砕流堆積物では，飽和度の低下に伴う液状化強度比の増加が大きい結果を示した。ボラは，飽和度の低下に伴う液状化強度比の変化が微小であり，明確な増加傾向は示さなかった。

Compressibility characteristics of collapsible gypseous soil: A review

Gypseous soil is located in dry and semi-arid areas in unsaturated conditions and this type of soil becomes a serious issue for engineering and geotechnical when it becomes wet. the properties and structure of this soil change, when exposed to soaking and leaching, because gypsum is dissolved in water causing a rupture in the bonds that hold soil particles together and a reduction in the suction power that holds them together. Large settlements and potential collapse will happen which cause problems for the constructions built on it. This paper gives an overview of some of the properties of gypseous soils and previous research on the behavior of this soil. It was found that the collapse potential of gypseous soil increases with increasing the gypsum content and void ratio, and collapse potential decreases when the initial water content and dry density increase.