Language：English   Publishing type：Research paper (other academic)  

Global warming has caused many lands to degrade, making them vulnerable to desertification. Therefore, finding innovative solutions is essential to prevent such phenomena from exacerbating. However, this requires a comprehensive understanding of the unsaturated layer formed due to the high-water loss from soil profiles by evaporation. In the present study, a new technique to trace the unsaturated layer from drying soil profiles was developed, and its accuracy and reliability were confirmed. Consequently, the spatial and temporal development of the drying front, vaporization plane, and film region were investigated for two soil profiles of different pore structures. It was found that soil profiles with broader pore distribution lose water from deeper drying fronts during Stage 1, while diffusion during Stage 2 occurs from shallower depths. Moreover, the film region’s thickness increased at early drying stages, followed by a slight drop associated with the onset of Stage 2. During Stage 2, the thickness slightly fluctuated until reaching the same thickness at the end of Stage 1, where a second significant drop in the thickness was observed.

Language：English   Publishing type：Research paper (other academic)  

Soft ground is widely distributed in the coastal areas of Japan, and the cement stabilization method is commonly used as a countermeasure to the associated problems. However, recently, it was reported that cement stabilized soil might deteriorate when exposed to seawater for an extended time in such regions. The deterioration mechanism of cement stabilized soil is still not well understood, and a general method for predicting the deterioration progress is lacking. In this study, the influence of the fine fraction content of the cement stabilized soils’ base material on the seawater resistance was investigated, and the deterioration characteristics when exposed to seawater were discussed. The results of chemical analysis by the μXRF test showed that the leaching of Ca, penetration of Mg, and penetration of sulfate(S) increased with depth for the specimens with higher fine fraction. Finally, the penetration of sulfate (S) in seawater was confirmed as one of the causes of the strength deterioration of cement stabilized soil. Furthermore, the distribution of S concentration through the specimens was expressed using the diffusion equation, assuming that the penetration of S into the specimens proceeds in the same way as the diffusion of material with concentration. The predicted deterioration depths were compared with the results obtained in the laboratory.

Language：Japanese   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

Global warming is one of the most alarming environmental issues worldwide, disrupting the natural water cycle and exacerbating desertification. Proper understanding of the soil-atmosphere fluxes (mainly evaporation) is crucial. Most existing studies focus on the evaporation stages and the governing mechanisms. However, an environmental-friendly simple method to control the actual evaporation flux in arid regions is in great need to efficiently combat desertification. Trough this paper, a simple design concept for a soil cover to maximize water conservation is proposed based on a series of 1-D column tests. It was found that using a coarse cover layer, the head gradient is oriented towards the bottom layer, disrupting the water supply to the surface and limiting the evaporation flux. While a fine cover induces a reversed head gradient oriented towards the cover layer, ejecting the water from the bottom to the top and resulting in a higher water loss. The proposed cover design includes two criteria: a) relative retention potential. b) relative cover thickness. The water storage capability can be maximized by applying a proper cover to minimize the criteria values.

Language：English   Publishing type：Research paper (scientific journal)  

Due to climate change, drylands worldwide have been suffering from extensive droughts and desertification. Finding innova¬tive solutions requires a thorough understanding of the evaporation process dominant in such regions. The process is divided into three stages based on the actual evaporation rate. Previous studies confirmed the significance of Stage 2, the falling rate stage, in drylands. One of the process’s main controlling factors is the drying front, or the region separating the saturated and unsaturated zones. This paper studied the drying front’s spatial and temporal development during Stage 2 in sandy soil profiles that differ in the pore structure. The drying front was determined experimentally using 1-D homogenous drying column tests. Besides, a front depth determination method from the literature was adopted. Both methods showed an acceptable agreement with the front receding rate during Stage 2. Moreover, coarser sandy soils with narrow pore size distribution tend to have shallower front depths. However, during Stage 2, their drying front recedes faster into the soil profile. The is study serves as a fundamental step towards evaluating the drying front during evaporation; It is believed to contribute to designing an environmental-friendly soil cover system used to maximize land water storage.

Language：English   Publishing type：Research paper (scientific journal)  

This research aims at developing a water retention technology utilizing the capillary barrier (CB) concept for irrigat¬ed ground in drylands using local geo-materials. To increase the water retention by CB, where plants can grow pre-planting stage in dryland, clarifying the including the layers’ thicknesses ratio, grain size distributions, and watering method through experimental and numerical approaches is considered. The main findings include 1) The experiment of the CB with drip irrigation revealed that the volumetric water content (VWC) at a depth of 200 mm exceeded the target value of at least 0.1 on the third day when watering twice a week with 1000 mL per irrigation. 2) From the numerical analysis, supplying water twice a week was enough to maintain the VWC within a depth of 200 mm higher than the targeted value of 0.1. 3) To maintain at least a target value extending up to 200 mm depth by supplying 1000 mL water twice a week, an optimum configuration with an effective grain size ratio of 5.2, mean grain size ratio of 3.9, and a thicknesses ratio of 0.1 comprised of coarse and fine sandy soil layers was confirmed

Language：English   Publishing type：Research paper (scientific journal)  

Indonesia’s government has planned a project for a high-speed railway connecting the capital cities, Jakarta and Surabaya, about 700 km. Based on that location, it has been planning construction above the lowland soil region. The lowland soil region comprises cohesive soil with high water content and high compressibility index, which in fact, led to a settlement problem. Among the variety of railway track structures, the adoption of the ballastless track was used effectively to reduce the settlement; it provided a lightweight structure and minimized workspace. Contradictorily, deploying this thin layer structure above the lowland area was compensated with several problems, such as lack of bearing capacity and deflection behavior during traffic loading. It is necessary to combine with ground improvement to assure a settlement behavior on the clayey soil. Reflecting on the assurance of strength increment and working period, those were convinced by adopting methods such as cement-treated soil as the substructure of railway track. Particularly, evaluating mechanical properties in the field has been well known by using the plate load test and cone penetration test. However, observing an increment of mechanical properties has uncertainty, especially for evaluating cement-treated soil on the substructure. The current quality control of cement-treated soils was established by laboratory tests. Moreover, using small strain devices measurement in the laboratory can predict more reliable results that are identical to field measurement tests. Aims of this research are to show an intercorrelation of confining pressure with the initial condition of the Young’s modulus (E0), Poisson ratio ( υ0) and Shear modulus (G0) within small strain ranges. Furthermore, discrepancies between those parameters were also investigated. Experimental result confirmed the intercorrelation between cement content and confining pressure with a power function. In addition, higher cement ratios have discrepancies, conversely with low mixing ratios.

Language：English   Publishing type：Research paper (scientific journal)  

Indonesia is developing high-speed railway lines that are expected to connect the major cities. Along the railway, the lowland area is mainly comprised of clayey soil characterized by a high compressibility index and high water content, which causes soil settlement in the long term. Therefore, to reduce the potential of settlement, choosing a suitable railway structure, such as the ballastless track, is essential. Despite the track structure, the subsoil mechanical properties often require improvement to limit the railways’ settlement. Using cement-treated soil, a combination technique was provided to protect the shallow ground and the ballastless track, effectively reducing the stress distribution during construction periods and maintaining low construction costs for developing countries. To assure longer serviceability, there is a high need for an accurate evaluation of the elastic settlement subjected to train loading. Therefore, this paper proposes an elastic settlement prediction model for cement-treated soils considering the curing period, cement content, and confining pressure within the small-strain ranges. The model optimizes the mixing ratio at a specific curing period, reflecting the wheel-base loading on the cement-treated soil layer. Moreover, a simple power formula to determine the initial mechanical properties of the cement-treated soils was proposed.

Language：English   Publishing type：Research paper (other academic)  

Proper determination of the unsaturated soil hydrological and retention properties, including the Soil Water Characteristics Curve (SWCC) and the Hydraulic Conductivity Function (HCF), is crucial for understanding the behavior of unsaturated soil profiles. The conventional SWCC and HCF determination approaches are characterized by several limitations associated with the testing complexity, discrete measurements, and prolonged testing time. Therefore, a simple, continuous, rapid, and concurrent SWCC and HCF determination technique is in great need. Through this paper, the Continuous Pressurization Method (CPM) was extended, and a novel quasi-state model was proposed to concurrently determine the SWCC and the HCF. It was found that the proposed quasi-state model adopting the extended CPM is an accurate, reliable, and rapid method that allows for a concurrent and continuous determination of the SWCC and the HCF in less than 3% of the time required using the conventional methods. Furthermore, an indisputable hysteresis in the HCF was observed where comparing the drying and wetting phases, the unsaturated coefficient of hydraulic conductivity varies up to one order difference for the same volumetric water content (or matric suction).

Language：English   Publishing type：Research paper (scientific journal)  

Recently, climate change has been causing severe droughts and water scarcity in drylands. A proper understanding of the soil surface-atmosphere boundary fluxes is essential to combatting such environmental problems. In those regions, evaporation is considered to be the dominant flux. It is divided into three stages that follow different mechanisms and are highly dependent on the soil properties. Most of the existing studies focus on the evaporation process from a macroscale perspective and estimate the evaporation rate based on the atmospheric conditions, while only a few of them consider the soil properties. This paper studied the influence of the soil pore structure on the actual evaporation and formation of the unsaturated layer. Homogeneous drying sandy soil column tests were conducted under a unified low atmospheric demand. The pore structure was investigated by varying the texture and relative density. The significance of Stage 2 in the evaporation process was asserted. Additionally, it was affirmed that vapor diffusion is dominant during Stage 2, where the actual evaporation reduction rate depends on the receding rate of the vaporization plane. Finally, a comprehensive, robust, and easily determined index, that correlates well with the duration and evaporated water during Stage 1 and Stage 2, was proposed. The Pore Size Distribution Index (IPSD) was found to reflect the variations in the pore structure and to consider the capillary and diffusion flow mechanisms. It serves as a fundamental step towards evaluating the actual evaporation and drying front depth during the evaporation process.

DOI： https://doi.org/10.1016/j.sandf.2022.101108

Language：English   Publishing type：Research paper (scientific journal)  

1g model test is carried out to evaluate the ultimate lateral capacity of the spiral model pile in dense and medium dense cohesionless soil. The spiral model pile is scaled down using a proper similarity equation considering the equivalent second moment of area. The equivalent second moment of the area was obtained from a four-point bending test on a flat bar and compared with a spiral bar. In order to identify the lateral capacity of the spiral model pile, the conventional pipe and flat bar model piles were conducted as well. Winkler's model was adopted to predict the rigid spiral pile's ultimate lateral capacity in cohesionless soil. A simplified model is proposed by developing ultimate lateral soil pressure. The novel shape factor for spiral was obtained for the evaluation of ultimate lateral soil pressure by considering the projected area of the pile. The projected area of the spiral pile was compared with the pipe pile. The comparison study was conducted to spiral, flat, bar, and pipe pile, respectively, for inspecting accuracy. Among the comparison, the proposed model was indicated as a more accurate model than others. The spiral pile was shown a similar performance with a flat bar in both the empirical and the experimental results.

Language：English   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Evaluation of the Soil Water Characteristics Curve using the Continuous Pressurization Method Linked with the Practical Measurement of the Soil Shear Strength

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1007/978-3-030-60713-5_14

Language：English   Publishing type：Research paper (scientific journal)  

Black volcanic ash soil which is also known as Kuro-boku soil in Japan is a problematic type of soil. Kuro-boku is usually rich with allophane minerals, which are characterized by unique problematic properties. Through this paper, the shear strength and characteristics of the black volcanic ash soil collected at Kumamoto slope failure after earthquake 2016 were studied using three main approaches. The chemical composition of the black volcanic ash soil was investigated using the X-ray fluorescence analysis. Furthermore, the soil structure disturbance effect due to the earthquake shakes on the total shear strength was evaluated using a simple method that considers the pore size distribution that is reflected from the soil-water characteristic curve. In addition, the constant volume direct shear box considering static and cyclic tests were carried out. It was found that the main chemical content of the black volcanic ash soil is allophane which accounts for about 94%. Furthermore, the undisturbed samples exhibit a unimodal pore structure, and the disturbed showed a bimodal pore. Since the pore structure of the disturbed sample is unstable, the static shear strength tends to be lower and the degradation index value is higher than that of the undisturbed sample.

Language：Japanese   Publishing type：Research paper (scientific journal)  

Measurements of Unsaturated Hydraulic Characteristics for Sandy Soil utilizing the Continuous Pressurization Method

Language：English   Publishing type：Research paper (scientific journal)  

Natural disasters like earthquakes and heavy rainfall events induce slope failures and other disasters. Proper determination of the water retention properties of porous mediums is necessary. The conventional Soil Water Characteristics Curve (SWCC) determination techniques are limited due to their complexity and lengthy time required. A highly accurate simple remolded and undisturbed samples SWCC determination method that requires a short time is lacking. A novel automatic system which adopts the continuous pressurization method and allows the direct determination of the SWCC in a short time suitable for use with remolded and undisturbed samples was developed. The accuracy of the newly developed system was validated, and it was shown to have excellent repeatability. It is a reliable and direct method that requires a short time for the SWCC determination, with the drying and wetting SWCCs obtainable in less than 10% of the time required using the conventional multi-step flow method. Consideration of the pore water pressure was shown to be necessary when calculating the matric suction utilizing the axis-translation technique. Finally, because remolded samples do not properly represent the in-situ natural conditions, the significant discrepancies should be carefully considered when conducting analysis and proposing countermeasures against unsaturated soil-related Geo-disasters.

DOI： 10.1016/j.sandf.2020.03.014

Language：English   Publishing type：Research paper (other academic)  

© 2020 The Authors, published by EDP Sciences. The effect of soil disturbance on the shear strength of black volcanic ash soil was investigated using a constant volume direct shear apparatus. Disturbance of soil structure was considered as the pore size distribution which obtained from the soil-water characteristic curve (SWCC). The disturbed sample was used as a representation of soil structure disturbance due to earthquake shakes. A series of cyclic tests were conducted under unsaturated and saturated samples. It was found that the undisturbed samples exhibit a unimodal pore structure, and the disturbed samples indicate to a bimodal pore structure. Since the pore structure of the disturbed sample is unstable, the degradation index value is higher than that of the undisturbed sample and increases with the increasing number of cycles. In other words, the cyclic normalized vertical stress of disturbed samples degrades faster. Furthermore, the degradation index value in the normallyconsolidated samples was found to be larger than the overconsolidated. It might be attributed to increasing of the pore water pressure during shearing. Where in the over-consolidated samples is lower than normally-consolidated. On the other hand, the normalized shear stress of unsaturated samples, it is slightly larger due to the suction forces in the total strength of soils.

DOI： 10.1051/e3sconf/202015602004

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Necessity of Measuring the Pore Water Pressure when Determining the SWCC

Language：Japanese   Publishing type：Research paper (scientific journal)  

Soil Water Characteristics Curves of In-situ Samples with Low Disturbance Obtained from Disaster Slopes

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (other academic)  

The Authors, published by EDP Sciences. The mechanical behaviour of unsaturated undisturbed black volcanic ash soils was investigated using a constant volume direct shear apparatus. A series of static and cyclic tests were conducted under unsaturated and saturated samples. The cyclic test under two patterns were adopted. First type of pattern, cyclic one-sided shearing was applied. For the second type, two-sided shearing was conducted. For further understanding of the chemical content and microstructure, X-Ray Fluorescence analysis (XRF) and Scanning Electron Microscope (SEM) were evaluated. It was found that, under static shearing, the unsaturated sample exhibits a higher apparent cohesion and friction angle in comparison to the saturated sample. The normalized vertical stress under one-sided cyclic shearing in both overconsolidated and normally consolidated samples rapidly reduced at the beginning of shearing. This might be attributed to increase of the pore water pressure during shearing. Furthermore, there is a significant difference between the normalized shear stress under cyclic one-sided and two-sided shearing. For the two-sided cyclic shearing test, the normalized shear stress value is higher than the one-sided cyclic shearing test. In addition, the normalized shear stress under unsaturated condition is significantly larger. This can be related to the suction forces to the total strength of soils. The main chemical content of the black volcanic ash soil is allophane. Further, the microstructure of the black volcanic ash changes due to shearing. For the overconsolidated sample, particles of soil more severe damage than normally consolidated sample.

DOI： 10.1051/e3sconf/20199207004

Language：English   Publishing type：Research paper (other academic)  

The Authors, published by EDP Sciences. Through this paper, a sampling methodology and a novel full automatic system adopting the continuous pressurization method which is capable of determining the Soil Water Characteristics Curve (SWCC) for both remoulded and undisturbed samples in a very short time were developed. The proposed system was validated by comparing the SWCCs of standard testing soils obtained using the developed system to the SWCCs obtained using a conventional method. Remoulded and undisturbed natural soil samples were tested, where the degree of disturbance influence on the obtained SWCC was discussed. In addition, the undisturbed samples containing moulds material influence on the obtained SWCC was investigated. It was found that remoulded samples do not properly represent the in-situ conditions with significant error that should be carefully considered when conducting analysis and proposing countermeasures against unsaturated soils related Geo-disasters. In addition, the material which the containing mould is made from has minor influence on the obtained SWCC which can be neglected. Finally, it can be concluded that the developed undisturbed soil water characteristics curve obtaining system is direct, rapid, reliable and simple. In addition, the proposed undisturbed sampling and testing methodology can be used to accurately evaluate the spatial variations of the SWCC regardless the heterogeneity of the soil profile.

DOI： 10.1051/e3sconf/20199207008

Language：English   Publishing type：Research paper (scientific journal)  

Evaporation from porous media involves a complex pore scale water and vapor transportation that directly affects the liquid phase distribution and fluxes. The presence of textural contrast boundary in multilayered profiles adds to the complexity. This study aims at evaluating the textural contrast boundary depth and individual layer thickness influence on the actual evaporation and water storage through double-layered soil profiles. For coarse overlying fine sand, it was found that the top layer small capillaries contribute to the majority of water lost through the falling rate stage. Considering fine overlying coarse sand profiles, the pumping phenomenon from the bottom coarse layer to the top fine layer occurs before the arrival of the drying front to the textural boundary due to the increasing suction forces within the top fine layer. The water storage capability of double layered soil profiles depends highly on the top to the bottom small capillaries ratio multiplied by the layer thickness ratio. Regardless the atmospheric conditions and layering sequence, it was concluded that the shallower the textural contrast boundary results in decreasing the total duration required to achieve the residual evaporation stage thus leads to higher water storage capabilities through the first and second evaporation stages.

Language：English   Publishing type：Research paper (scientific journal)  

Every year about 20 million tons of Granulated Blast Furnace Slag (GBFS) are produced as a manufacturing byproduct. GBFS is mainly utilized in cement production accounting for 70% of the total utilized weight, while the geotechnical engineering applications accounts for 2%. Therefore, finding innovative utilization methods is a necessity. It was reported that the GBFS can be used as substitutive material in sand compaction pile (SCP) method. This study aims at evaluating the time-dependent mechanical, hydrological and chemical properties of the GBFS and the GBFS-sand mixtures. It was found that for early hydration stage, the hydrological and mechanical properties of the GBFS depends on the microstructure of the material, while the generation of the calcium silicate hydrate can be neglected. On the other hand, for longer curing time the influence of the calcium hydrate silicate generation becomes significant. Finally, it was concluded that mixing the GBFS with sand is a simple efficient way to control the time dependent mechanical, hydrological and chemical properties of the GBFS, however, the combined effect of the hydration reaction rate and the void ratio developments in response to the mixing ratio and the curing time should be properly considered to optimize utilizing the GBFS.

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This study aims to evaluate the effect of the layer thickness on the evaporation rate and the water content redistribution through layered soil system without water table. In order to satisfy the aim, two experimental series were conducted where evaporation rate and water redistribution were continuously observed through the soil profile. It was found that the deeper the horizontal textural contrast boundary has the effect of increasing the amount of water lost by evaporation in addition to increasing the time needed to achieve residual evaporation rate stage (Stage III). Series A results showed that the deeper the horizontal textural contrast boundary has the effect of increasing the thickness of the severely desaturated zone [coarse sand top layer], while the bottom layer remained close to saturation [initial state]. Furthermore, the deeper the horizontal textural contrast boundary has the effect of increasing the thickness of the severely desaturated zone [coarse sand bottom layer], where during the falling evaporation rate stage [stage II], the top layer [fine sand] had higher water content than the bottom layer. The results illustrated the strong influence of the layer thickness on the evaporation rate and water redistribution through the evaporation process.

Language：Japanese   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (other academic)  

Recently, desertification became one of the most global alarming environmental problems. As mentioned by the United Nations Convention to Combat Desertification UNCCD 2009, deserts and drylands form 41.2% of the total earth's land, where due to drought and desertification each year 12 million hectares are lost. In order to efficiently combat desertification, it is important understand the soil atmosphere interaction fluxes considering mainly the evaporation flux. A key element is to minimize the actual evaporation rate and maximize the water storage through soil profiles. Most of the existing studies that consider multilayered soil profiles focus on the evaporation flux from soil profiles without considering the effect of individual layer properties. The primary objective of this study is to identify the soil body properties influence on the actual evaporation flux and water redistribution through sandy soils. An experimental study considering individual layer dimensions, geotechnical properties and layering sequence for double layered soil profiles was carried out. The top to the bottom layer thickness ratio [Horizontal Textural Contrast Boundary], layer tihckness, top layer density and top layer median diameter were studied for coarse overlying fine sand profiles and fine overlying coarse sand profiles. It was found that providing soil cover that has different geotechnical properties from the underlying layer us a simple efficient way of maximizing the water storage through soil profiles. In addition, the results showed that the actual evaporation flux is highly dependent on the top to the bottom layer thickness ratio, individual layer thickness and top layer median diameter. While the top layer density has very weak influence that can be neglected.