Abstract Road and railway embankments are earth structures that lose stability under rainfall, and accumulation of rainfall causes an elevation of the phreatic surface within an embankment. For these reasons, drainage systems are needed when constructing an earth structure. Drain pipes are one type of drainage system applicable even for an existing earth structure. However, it is difficult to estimate the effects of the drain pipe quantitatively, and design and construction of drain pipes proceed according to past experience. In this study, the authors succeeded in expressing the drainage effects of drain pipes using an existing soil/water/air coupled analysis framework. This study specifically focused on the cross-sectional shape of drain pipes. Five kinds of cross-sectional drain pipe shapes were created, and rainfall infiltration series was simulated using the same procedure for each case. Consequently, the simulations determined that seepage behavior is dependent on the cross-sectional shape of the drain pipe. Furthermore, this analysis found that infiltrated rainwater does not drain when the phreatic surface is located below the drain pipe.

Embankment structures are important to protect against flooding damage. Suffusion, in which fine particles within the soil are transported and washed away following the seepage flow, intensifies the instability of embankment structures. Therefore, it is possible that some embankment structures that repeatedly experienced flooding and rainfall penetration have been deteriorated. However, there is little research investigating the relation between seepage flow histories and deterioration within the embankments. In this study, small-scale modeling tests duplicating a river levee were conducted under different seepage flow histories: (i) short term-critical ground water level, (ii) continuous-high ground water level and (iii) repeated-high ground water level. The work in this paper investigates changes in “drainage flow rate”, “height of ground water level” and “particle size distribution” during the seepage tests, and evaluates the effects of seepage flow histories on them. Soils gradually showed lower permeability under the first seepage experience in each cases. In the case of relatively longer flooding duration, the drainage flow rate is gradually increased. Fine particles were eroded, regardless of the seepage flow histories; “the number of fluctuations” and “height” of ground water level could particularly be a trigger of suffusion.

Recently, mixtures of low-quality soil together with solidification materials, such as cement or steel slag, have been used for earthmoving construction. Solidification materials can improve consistency, shear strength, stiffness, and other parameters of low-quality soil by generating bonding forces between soil particles and changing grain size gradation. However, these solidification materials also contain chemical agents. In this study, simulations of rainfall infiltration into embankment constructed with the soil-solidification material mixture are conducted using the soil/water/air/soluble material coupled finite element analysis code, DACSAR-MP_ad. This analysis code can express not only deformation and seepage for an unsaturated earth structure but can also concurrently model the dispersing behaviour of soluble material. Herein, permeability and rainfall intensity conditions are provided and their effects investigated. Consequently, this study succeeds in expressing different distributions of soluble materials within embankment under different rainfall conditions.

Geophysical exploration, which can explore the distribution of material properties underground, has, for less than the last half a century, been applied for prospecting groundwater and bedrock. Though simulation techniques have improved with greater sophistication of the constitutive model for soil material, comprehension of current soil conditions is important for accurately predicting the behavior of earth structures. Therefore, the importance of geophysical exploration is growing. Soil parameters are indirectly identified from physical parameters, such as wave velocity, electric conductivity and so on. In geophysical exploration, calibrating physical parameters with necessary soil parameters is required for individual soil material and has thus prevented the application of geophysical exploration at the site level. In this study, surface wave and electric prospecting were conducted at a site first investigated circumstantially by borings and other soundings. Then, the applicability of surface wave and electric prospecting were validated through their comparison. Next, geophysical explorations were conducted on a large-size embankment. Consequently, the applicable scope of this type of exploration was demonstrated, proving its applicability for geotechnical engineering sites.

Recently, slope failure due to rainfall occurs frequently and inflicts serious damage. However, slope characteristics that reflect stability, such as gradient, length, thickness of weathered layer, and groundwater condition, differ from one slope to another. Because of this, it is difficult to estimate the risk of slope failure using a single uniform standard. A simple way to model a slope and estimate risk according to rainfall pattern is needed. In this study, a way to estimate slope stability in the framework of unsaturated soil mechanics is proposed. Here, the surface failure of a long slope covered with weathered soil is the target. Various slope gradients and rainfall intensities are considered as influential factors on slope stability. First, rainfall infiltration is simulated with soil/water/air coupled finite element analysis code, DACSARMP. Next, the factor of safety is calculated using the distributions of pore-water pressure and soil moisture obtained from seepage analysis.

In this study, based on field measurements conducted during the period from the start of embankment launch to dismantling, based on the results of the indoor tests on the sampled samples, the deformation and strength characteristics of the embankment receiving the traffic load and rainfall Etc., the performance of the steel slag mixed soil as an embankment material was evaluated by paying attention to the hydraulic characteristics of the embankment. As a result, by mixing and stirring the steelmaking slag and the earth at an appropriate ratio and properly compacting, it is possible to withstand deformation even under traffic load, and it is possible to suppress leaching of high alkaline water from the embankment by rainfall to some extent It could be confirmed. Therefore, it was found that there was no practical problem concerning the concern factor when slag was used as the embankment material.

The migration of contaminant through soil is usually modeled using the advection-dispersion equation and assumes that the porous media is stationary without introducing a constitutive equation to represent soil structure. Consequently, time-dependent deformation induced by soil consolidation or physical remediation is not considered, despite the need to consider these variables during planning for the remediation of contaminated ground, the prediction of contaminated groundwater movement, and the design of engineered landfills. This study focuses on the numerical modeling of solute transfer during consolidation as a first step to resolve some of these issues. We combine a coupling theory-based mass conservation law for soil-fluid-solute phases with finite element modeling to simulate solute transfer during deformation and groundwater convection. We also assessed the sensitivity of solute transfer to the initial boundary conditions. The modeling shows the migration of solute toward the ground surface as a result of ground settlement and the dissipation of excess pore water pressure. The form of solute transport is dependent on the ground conditions, including factors such as the loading schedule, contamination depth, and water content. The results indicate that an understanding of the interaction between coupling phases is essential in predicting solute transfer in ground deformation and could provide an appropriate approach to ground management for soil remediation.

In this study, air pressure behavior within an earth structure was investigated through a full-scale embankment test. The road embankment (2 m height) was constructed on low-permeability soil and measurement devices (tensiometers, air pressure meters, and soil moisture meters) were installed. The embankment was exposed to natural conditions, such as rainfall and evaporation, and vehicle weight was applied. Characteristic behaviors of water and air pressure were observed throughout the 1-year monitoring period. Water pressure increased under rainfall and kept decreasing due to evaporation without rainfall. The infiltrated rainwater flowed toward the slope toe. Consequently, water pressure at top of the slope increased due to rainfall and decreased soon after rainfall stopped; while pressure at the slope toe started decreasing after a period of time. Conversely, air pressure increased under only heavy rain. Moreover, it decreased to a point lower than atmospheric pressure following the heavy rain and recovered after a brief interval.

Bentonite materials have been considered as a candidate material for engineered barriers in transuranium (TRU) waste disposal facilities due to their physical and chemical characteristics. Bentonite materials will be initially compacted and unsaturated. After closing the cavern, the bentonite material will become saturated through exposure to a percolating groundwater. It is therefore important to understand the behaviour of bentonite during saturation, which provides an initial condition of the disposal facilities. This paper explains a mathematical model which can express the saturation process. Subsequently, a series of numerical simulations were carried out. First, the swelling pressure of buffer and backfill was examined to verify the numerical model. It was confirmed that the simulated swelling pressure rises with water absorption, and swelling pressure test results from the literature are shown to be satisfactorily predicted by the numerical model, although these were slightly overestimated. Next, the mechanical behaviour of bentonite materials in a TRU waste disposal facility during the saturation process was examined using soil/ water/ air coupled finite-element method. Although it is difficult to examine the validity of analysis results because of the difficulty of an extremely long-term measurement, the qualitative behaviour of the saturation process could be inferred.

Recently, the frequency of torrential rainfall has increased due to global climate change, and these events cause sediment potential failure. It is difficult to predict when and where a slope failure will occur because of the concentration of heavy rain. Knowing precursory phenomena, however, is effective for disaster reduction. Nonetheless, some of these phenomena have not been explained in the framework of geotechnical engineering. Organic smells and strange sounds, known as precursory signs of slope failure, propagate through the atmosphere. Therefore, it is important to monitor air movement within earth structures. This study focuses on pore air behavior within the ground due to rainfall infiltration. Here, the infiltration column test combined with monitoring smell, as conducted by Tsuchida et al., was first simulated using the soil/ water/air coupled finite element code, DACSAR-MP. Next, a sloping earth structure exposed to rainfall was simulated. Consequently, it was found that distribution of pore air pressure was dependent on drainage conditions of air, and that pore air behavior influenced rainfall infiltration behavior.

Bentonite has remarkable swelling characteristics and low permeability that enhance the stability of the buffer materials in repositories for the geological disposal of radioactive waste. It is necessary to apply reliable numerical simulation techniques to assess the safety and mechanical stability of repositories over a long period of time. Having a constitutive model that can describe the mechanical behavior of bentonite is key to such numerical simulations. This paper proposes an elasto-plastic constitutive model to describe the changes in the mechanical properties of bentonite due to saturation in the progress of a repository becoming submerged under groundwater. In the proposed model, the swelling index is formulated as a function of the degree-of-saturation to express not only the swelling behavior, but also the dependency of the degree-of-saturation on the dilatancy characteristics. The montmorillonite content is used as a material parameter to determine the normal consolidation line. The experimental results of swelling volume and swelling pressure tests in previous literature are shown to have been satisfactorily predicted by the proposed model. (C) 2017 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society.

The B-value, measured after setting up a specimen for triaxial testing, is used for evaluating the degree of saturation of a specimen. However, the stress conditions used when measuring the B-value have not been standardized. Although some experimental approaches have been pursued, no detailed analyses have evaluated the effects of the measurement conditions on the B-value results. In this study, the B-values of nearly saturated specimens under various stress conditions were investigated, using a smart triaxial test apparatus capable of elaborate stress control, and comparisons among measurement results were conducted. Moreover, by applying Henry's law, which governs the dissolution of the gas phase into the liquid phase, to an existing constitutive model for unsaturated soil, a new soil model was proposed. This new model accurately represents the behaviors of pore air even under nearly saturated conditions. In addition, the effects of the stress conditions on the B-values were investigated through numerical simulations of B-value measurements. (C) 2016 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V.

Most onshore earth structures, such as earthen dams, embankment, and river levees, are constructed by compaction. Transportation geotechnics also includes construction of compacted earth structures, such as road and railway embankment. Optimum compaction can increase shear strength, while decreasing compressibility and permeability of earth structures. For this reason, compaction has been used for earthworks since the dawn of times. Generally, a series of lab compaction tests is conducted to obtain a compaction curve before constructing these structures. The shape of the compaction curve, which determines the maximum dry density at the optimum water content, is very important in the design and construction of structures. However, it is difficult to control compaction quality on the basis of lab tests alone, as soil materials are inhomogeneous. Furthermore, there are differences in the compaction methods used in lab tests and at construction sites. Therefore, it is necessary to explain the mechanisms of compaction in the framework of soil mechanics. In this study, compaction of earthworks is simulated in a similar way. The effect of compaction layer thickness and the number of compaction layers on the distribution of dry densities in an earth structure was investigated through soil/water/air coupled simulation. Consequently, it was found that multi-layered compaction can create a gap in the dry density between two layers and that this gap can be reduced by thinner layer compaction. On the other hand, though the average dry density in a compacted earth structure can be increased by increasing the number of compacted layers, some gap between compaction layers was inevitable. Through these findings, this study contributes to the performance design of compacted earth structures.

Undrained shear strength is used for estimating the bearing resistance of foundations and the safety factor of a slope. For this test, the pore-pressure coefficients, namely A and B as proposed by Skempton, are available. These coefficients can be obtained from the undrained triaxial test. According to Terzaghi's effective stress theory, the B-value must be 1.0 in a saturated soil. Therefore, a B-value of 1.0 is used as the target for saturating a specimen. However, it is difficult to achieve a B-value of 1.0 in the triaxial test. Because of this, a specimen with a B-value greater than 0.95 is regarded as saturated. The relationship between saturation and the B-value is still not clear. In this study, the factors influencing the B-value were numerically investigated with a soil/water/air coupled model that considers the solvability of pore-air to pore-water. Consequently, the pore-water pressure behavior, which depends on the initial degree of saturation and initial stress conditions, could be expressed.

Due to its low permeability and excellent expansion characteristics, bentonite materials are considered to be the engineered barrier in Trans-Uranium (TRU) disposal facility. It is necessity to predict the mechanical behavior of bentonite using numerical simulation to evaluate the long-term performance of TRU disposal facility. In this paper, we simulated the saturation process of bentonite materials in TRU disposal facility from an initially unsaturated state. And we examined the mechanical behavior of bentonite buffer during the saturation process. This simulation result shows that Disposal waste is moved upward due to the difference of swelling pressure between buffer and backfill. And the facility existed in unsaturated state even under steady state conditions due to the entrapped air.

In this study, the generation process of the phreatic surface within a river levee is investigated through soil/water/air coupled simulation. Here, the effects of river level fluctuation and rainfall on changes in soil moisture distribution within a river levee are considered. The constitutive model proposed by Ohno et al.1) is formulated to the initial and boundary value problems in accordance with Borja's multi phases' concept and is used for simulation. Consequently, it is first found that high groundwater level is maintained for ground consisting of low permeability and high soil water retentivity. Moreover, it is found that the fluctuation of river level directly influences the phreatic surface, and that, in contrast, the effect of rainfall appears after a time lag.

近年，自然災害における被害は甚大であり，災害医療におけるDMAT (Disaster Medical Assistance Team)の役割が，人的被害最小化に大きく貢献する．しかし，情報が錯綜する災害時に医療活動を必要とする場所・規模等を掌握し，適切なDMAT派遣を行うことは難しい．そこで本研究では，過去の地震災害の経過時間に伴う累積報告死者数から導いた被災者推定式を用いて，死者数を最小にする最適化問題を考える．
その結果，早期派遣が有効であり，条件(DMAT数，被災地の状況)によって累積死亡者数を最小にするDMAT派遣が求められた．また，被災地状況の設定により，妥当なDMAT派遣のあり方を考察することができた．よって，チーム数に限りがあるDMATの有効的派遣のあり方を提案できることで意思決定の一助となり得ると考える．

The present work explains the statics of self-weight transmission restricted to a long prismatic heap inclined at an angle of repose and symmetrically formed on a rigid base. The closure of polarized principal axes with the mobilized state of stress along the slope surface is employed by imposing the orientation of principal stresses on the equilibrium equations. Comparisons were made with calculations based on the finite element method using an elastic model. Moreover, experiments on sand heaps deposited on a rectangular rigid base were conducted to validate the theoretical study. The measured pressure profile generally agreed well with theoretical results. © 2014 The Chinese Society of Theoretical and Applied Mechanics.

Rainfall is one among the most common contributing factor and trigger for landslides. In the majority of the cases, slopes are at partially saturated condition when they are subjected to rainfall. While analysing stability of those slopes, deformation analysis is performed in a conservative way assuming the slope to be in a fully saturated condition. In this research, a fully coupled hydro-mechanical finite element model is described based on the constitutive model developed for partially saturated soil condition. A 1.2 m long and 0.6 m high sandy slope was modelled in laboratory and was subjected to 30 mm/h of rainfall for 3 h. Values of suction measured after 3 h were very close to the numerically calculated values based on the finite element method developed by the authors. This model was used to calculate deformation of slope for different intensities of rainfall and at different angles of slopes in order to predict the amount of deformation or failure condition when a slope is subjected to a continuous rainfall of different intensities and durations.

With the remarkable increase in amounts of waste being generated recently, waste disposal has become a serious issue. There are various types of waste materials, some of which include substances that are harmful to humans and require proper handling for safe disposal. The infiltration of rainwater into a waste repository site can cause possible leakage of these harmful substances. The system for covering any repository site is therefore extremely important and now the use of a capillary barrier system is one of the more promising candidates for a suitable cover system. The capillary barrier system consists of two soil layers: a fine sandy upper soil layer and a coarse lower soil layer. The different water retention capabilities between the upper and lower layers are key to the performance of the capillary barrier system. Also by tilting these soil layers, the capillary barrier system can be made more effective because it prevents vertical infiltration and drain in the direction of the slope. In this paper, a series of parametric numerical computations were conducted using the soil/water/air coupling F.E. technique. The slope angle and thickness of the upper soil layer were changed in order to examine the performance of the capillary barrier system. The mechanism for the capillary barrier was then discussed. Throughout numerical computations, it was repeatedly shown that vertical water infiltration and retention in the soil layers decrease with an increase in the slope angle. The paper also reveals how the thickness of the upper soil layer influences the performance of the capillary barrier.

In this paper, a multiple unsaturated soil barrier system consisting of multiple layers of gravel, sand, decomposed granite soil, and bentonite mixture soil is considered as a hardly permeable covering to prevent rainwater from infiltrating into waste deposits. Water infiltration is prevented due to both the low permeability of the bentonite mixture soil layer and a capillary barrier with different water-retention capabilities. A series of numerical simulations was carried out to evaluate the performance of the barrier system using a saturated/unsaturated soil/water coupled FE computation technique. Impermeability of the barrier system is shown as a graphical chart with rainfall duration on the x-axis and rainfall intensity on the y-axis. The simulation results show that the capillary barrier is a key parameter in evaluating the long-term performance of the barrier system. Results also confirm that the barrier system can work well against the maximum intensity of the rainfall recorded in Nigyo-toge.

In this study, in order to clarify the mechanism of compaction, the static compaction simulations are conducted by using soil/water/air coupled finite element code, which consists of the constitutive model for unsaturated soil, the soil water retention characteristic curve model and the gas state equation. Here, the compaction is assumed as an initial and boundary value problem, namely loading and unloading under drained air and undrained water conditions. Consequently, the shape of compaction curve could be successfully expressed. Moreover, parametric study is carried out to investigate the dependency of compaction curve on material properties. Here, compressibility, permeability and the soil water retentivity are considered as an influential factor. Consequently, the effects of material parameters on compaction quality can be theoretically explained.

Rainfall is considered one of the major triggering factors for shallow landslides. The effect of rainfall in causing landslides depends on the intensity and duration of rainfall, the type of soil, the inclination of the slope, and ground water conditions. The majority of slope stability problems in shallow slides involve partially saturated soils. Although experimental modelling of slopes subjected to various intensities and durations of rainfall are ideal to evaluate the effect of rainfall on slope stability, it is time consuming and expensive. Numerical simulation of such experimental modelling can save a great deal of time and cost. In this study, slope models were prepared at angles of inclination of 30º and 45º with double washed construction sand, at a void ratio of 0.7. The slopes were subjected to 30 mm/h of rainfall for 3 h. Spatial variation of suction during the rainfall and depth of water front with time were measured for the entire rainfall period. The depth of water front and spatial variation of suction were also calculated through the finite element model (FEM) that was developed based on a hydro-mechanical model developed for the partially saturated soil. The numerical and experimental results provided identical results. The numerical result was extended to predict the spatial variation of suction, depth of water front and deformation of slope subjected to higher intensity of rainfall.

The East Japan Earthquake and Tsunami caused serious damages in the coastal area of eastern Japan. Many houses and cars on the road were swept away by the tsunami. Also, industrial facilities such as chemical plants in the coastal area were completely destroyed. Damage from saline seawater was not limited only to the rice field areas, and there were also serious anxieties regarding the possibility of ground contamination as a result of harmful heavy metals that leaked from destroyed chemical plants. In light of this scenario, we carried out a quantitative survey to examine these areas. This paper reports on the results of our survey. It was found that high salt concentrations were detected on the ground surface but predictions state that these concentrations can be diluted with rainfall. It was also revealed that serious ground contamination due to the harmful heavy metals was not detected.

In this study, we use conservation laws to construct a method for describing the movement of dissolved material. This is then applied to a mathematical model. Recently, soil pollution, induced by toxic materials in the ground water, is spreading. The mobility modes for this dissolved material can be divided into advection, induced by distribution of fluid head, and dispersion, induced by distribution of concentration content. First, Darcy's law is derived from the momentum conservation law using Bear's theory. Secondly, the concept of total fluid head is extended for application to various fluids. Additionally, an infiltration equation and an advection-dispersion equation are derived from mass conservation laws. Coupling the two equations, we construct a mass transfer model for unsaturated/saturated ground. Using the model, the effect of density flow is considered assuming basic one-dimensional areas. The results show that mobility of the dissolved material depends on its density. We concluded that density flow dominates along the vertical rather than the horizontal direction and mobility of the fluid is dulled in the unsaturated area.

In order to study the triggering factors for shallow landslides during rainfall, sandy soil slopes were prepared in laboratory angles of 30 and 45 degrees and those slopes were poured with rainfall intensities of 30 and 60 mm/hours through a specially developed rain simulator. Moreover, the rainfall on slope was simulated with using unsaturated soil/water/air coupled F.E. code, and the numerically calculated depth of water front and values of suction at different location in the slopes at various angles of inclinations matched well with the experimentally observed values. The combined results obtained with the numerical and experimental studies were utilized to predict the variation in the depth of water and values of suction at different intensities of rainfall as well as deformation of slopes during rainfall.

三軸試験を行う場合に，供試体設置後に計測されるB値は，供試体の飽和化の度合いを知るために用いられる．しかしながら，このB値に及ぼす要因については，飽和度以外には詳細な力学的説明は加えられていない．本論文では，極めて飽和に近い不飽和状態でも，間隙空気の挙動を精緻に表現できるように，まず既存の不飽和土構成モデルの枠組みに，空気相の液相への溶解を規定するヘンリーの法則を適用し定式化した．次に，得られたモデルを用いて，供試体の飽和度や拘束圧，背圧がB値計測に及ぼす影響を数値シミュレーションによって検討した．その結果，同じ飽和状態であっても，応力条件によって計測されるB値が異なることが分かった．

Results obtained in a lab compaction test are difficult to apply to the design and compaction control at an actual geotechnical engineering site. This is attributed to the fact that the mechanism for compaction has not been explained using the principles of soil mechanics. The main theme of this study is interpretation of the compaction mechanism with unsaturated soil mechanics. Here, static compaction tests were simulated with soil/water/air coupled finite element analysis code DACSAR-MP. Consequently, the shape of the compaction curve was successfully expressed. Moreover, the effects of compaction on compressibility and permeability of compacted soil could be reasonably explained. Additionally, shear deformation was applied to the specimen obtained from static compaction simulations in soil/water/air coupled analysis. The relationships between shear strength and compaction curve showed good agreement with the actual behavior.

© Springer Science+Business Media Dordrecht 2013. An elasto-plastic constitutive model for unsaturated soils is improved to realize numerical stability of computations at the singular point on the yield surface and an accurate prediction of the mechanical behavior of overconsolidated (or elastic state) soils in this chapter. The authors introduce the exponential contractancy model (EC model) by Ohno et al. (J Appl Mech JSCE 9:407–414, 2006) and the subloading surface model by Hashiguchi and Chen (Int J Numer Anal Method Geomech 22:197–227, 1998) to the elasto-plastic constitutive model for unsaturated soils by Ohno et al. (J JSCE 63(4):1132–1141, 2007). The applicability of the constitutive model is verified by simulating triaxial shear tests under constant net stress undrained conditions.

Thermal power plants burn oil and coal to generate electricity. Coal fly-ash is a product of the coal-burning process. Coal fly-ash has a self-hardening property and becomes extremely stiff over time. For this reason, it is being reused as a concrete aggregate in the production of concrete. Recently, coal-fly ash is being mixed with soil from construction waste for reclamation projects. To be able to reuse coal fly-ash in such a way, in the field of geotechnical engineering, the associated self-hardening properties must be incorporated in the framework of the constitutive model. It is generally known that cemented soil, such as fly-ash, behaves similar to unsaturated soil. In the constitutive model for unsaturated soil, hardening due to desaturation is expressed as the increase in yield stress. Here, changes in parameters used in the Cam-Clay model, generated by this self-hardening property, are studied by comparing the simulation results obtained from a soil/water coupled analysis with triaxial test results on two kinds of coal fly-ash. Consequently, the self-hardening property is expressed as an increase in the yield stress and an increase in the frictional angle, dependent on time. Differences between the two methods of producing fly-ash are reflected in the parameter set.

Soil contamination caused by industrial activity has become a serious environmental problem causing ground deterioration. Since soil decontamination is expensive and its efficiency is difficult to estimate, the contaminated ground areas are often abandoned without purification. To encourage the reuse of land, the methods for predicting contaminant transfer, induced by changes in external forces and water levels are required. In this study, the mass transport equation was applied to the existing unsaturated soil/water/air coupled F. E. analysis code for expressing the advection and dispersion behavior of dissolved material within pore-water. First, the continuity condition equations and advection-dispersion equations were developed from mass conservation laws of soil, water and dissolved materials. These governing equations, including the constitutive model for unsaturated soil, were formulated as initial and boundary values problems and coded as DACSAR-Mad. Assuming the ground to be polluted, the effect of external forces on the ground surface was simulated. It was found that the external forces contribute to mass transfer. This analysis code is effective in describing the complications of the mass transfer problem including the effects of external force and water level. © 2012 IEEE.

Desertification poses a serious problem to the global environment. A reported 7.2% of the world's land area is affected by desertification, with 35.8% of this figure located in Asia. Major causes of desertification include excessive deforestation, overgrazing of cattle and damage due to salt, all of which are the results of water cycle disorders relating to the geosphere and atmosphere. Through hierarchization (structurization) analysis, this paper discusses the issue of desertification as it pertains to issues threatening the health of the global environment. The key issues to be taken into consideration with regard to desertification have been extracted and examined from a geotechnical viewpoint. The authors focus on the role that geotechnical engineering can play in the prevention of desertification and in its restoration process. The paper highlights a northeastern area of Thailand where salt damage is likely to result in desertification. In order to numerically simulate what is happening there, a set of mathematical models based on unsaturated geomechanics is formulated, taking into account key issues revealed through a hierarchization analysis. The paper also includes a discussion on the applicability of these models for addressing the salt damage problem affecting this northeastern part of Thailand. The importance of unsaturated geomechanics is demonstrated in this paper, particularly as it pertains to prevention and restoration of salt-damaged areas that finally lead to desertification. © 2012 IEEE.

Bentonite is usually modeled as a geo-material with elasto-plastic isotropic compression/expansion and plastic dilatancy characteristics. In this paper, fundamental considerations of elasto-plastic constitutive modeling for fully saturated bentonite are investigated. According to uniaxial compression test data by Sasakura et al. (2003), where lateral earth pressure was measured, it was found that the hysteresis response between loading and unloading processes does not appear. It suggested that bentonite is an elastic material in which the swelling line corresponds to the normally consolidated line in the 'e-logp' relationship. Also, according to triaxial CU test results of bentonite, it was seen the effective mean stress remains almost unchanged during shearing. This implies that bentonite does not have dilatancy characteristics as defined by the critical state theory. Similar interpretation can be derived from the experimental results obtained from a series of triaxial CD tests by Cui et al. (2006). © 2012, International Journal of GEOMATE.

This study presents a new constitutive model for expansive soils. Under any arbitrary state of degree-of-saturation, the mechanical void ratio predicted by the elasto-plastic constitutive models, i.e. EC model and Se-hardening model are combined with the additional void ratio in order to characterize the typical swelling behavior of expansive soil. Herein, the fully saturation curve which derived from compaction and consolidation experimental tests are taken into consideration. The proposed model is examined by simulating the typical experimental test on expansive soil, i.e. normally consolidation and swelling pressure tests. © 2012 IEEE.

Compacted soil is widely used for earth structures. However, the mechanism of compaction has not been explained, so it is difficult to grasp distributions of stress, void ration, and soil moisture within compacted earth structure. Therefore, estimation of safety and stability of compacted earth structures exposed to natural disaster is complicated. Compaction is decreasing void ratio by applying stress under certain water content and pushing air out of soil mass. Thus, the mechanics of unsaturated soil, which includes air within void, is needed for understanding of compaction. In this study, we regarded compaction as compression and expansion phenomenon of unsaturated soil under drained air and undrained water conditions and formulated it in initial-boundary-value problem. Here, the influences of permeability and soil water retention characteristics on compaction were considered and static compaction tests were simulated. Moreover, multi-layered compaction was examined.

Compacted soil is widely used to build earth structure. Although construction management of the soil progresses day by day, it is said that mechanism of compaction effect isn't fully made clear. This is due to the complication of compaction mechanism of unsaturated soil. Recently, some constitutive models for unsaturated soil and SWCC models were proposed and advanced the study on unsaturated soil. In this study we regarded compaction as the consecutive cycle of compression and expansion of unsaturated soil under undrained condition, and simulated it with unsaturated soil/water/air coupled finite element analysis. In this study, we expressed the characteristics of the mechanical behavior of compacted soil, which has not been explained for a long period of geotechnical engineering. And we considered the difference of compaction procedure affected the quality of earth structures. The achievement can be managed reasonably the compaction of earth structure.

The coastal area of eastern Japan was hit by Tsunami due to the gigantic earthquake on March 11th 2011. Tsunami gave serious damage to Rikuzen Takada and drowned out famous pine forest, called “Takadanomatsubara”. However, only one of 70,000 pines could survive miraculously without falling down. People decided to preserve this pine as the monumental pine for the symbol of recovery. However, there are some problems, groundwater rise due to land sinking and salt concentration from seawater. These factors can kill root system. In this study, the current situation around the monumental pine was simulated with soil/water/air coupled F. E. code applying the mass transfer equation first. Next, the alternative preservation methods were examined. Consequently, it was found that pumping up from deep inside of sheet pile is effective for inhibiting salt diffusion and flashing is effective for washing salt away from ground.

Coal fly-ash is a product of the coal-burning process in thermal power plants. Coal fly-ash has self-hardening property and increases its stiffness with time. Therefore, it has been reused as a concrete aggregate in the production of concrete up to now. Recently, coal-fly ash is mixed with dredged soil from construction waste and reused for reclamation. In order to reuse coal fly-ash in the geotechnical engineering field, the self-hardening property in the framework of the constitutive model needs to be expressed. In this study, the self-hardening property is assumed as increases of the frictional angle and the yield stress. Our model is formulated for the initial-boundary problems with finite element method. Triaxial tests and the self-weight consolidation test are simulated with soil/water coupled F. E. code.

Shortage of landfill capacity in areas where industrial waste materials are dumped is a serious environmental problem. In this study, the mechanical characteristics of two kinds of soil samples, produced by burning sludge, were examined. In order to grasp some key fundamental mechanical properties of these soil samples, a series of laboratory tests were performed. It was found that the stress-strain characteristics and the permeability of these soil samples were very similar to those of standard sandy materials. In addition, particles in the soil samples were easily crushable and exhibited high water retentivity. Next, the applicability of the unsaturated elasto-plastic constitutive model of Ohno et al. (2007), in reproducing the mechanical behavior of these soil samples, was examined. The results of this study will help in useful utilization of micro-porous ceramic materials, obtained from sludge burning, in the field of geotechnical engineering. © 2011 Taylor & Francis Group, London.

It is difficult to estimate the current stress state of existing embankments because of their inherent sloping geometric shapes. Therefore an elastic analysis is always carried out in advance and the calculated stress state, assumed as the current stress, is used as an input parameter in the deformation analysis of an embankment. However, the stress state of a banking material can be quite complicated since banking materials are elasto-plastic and unsaturated in most cases, and, their behavior strongly depends on the stress history. In this study, the banking process is simulated with an elasto-plastic constitutive model for unsaturated soil. Specifically, the effects of banking speed and initial suction within the banking material are considered. It is found that the post-banking stress state depends on the distribution of the initial suction due to soil-water retention characteristics. © 2011 Taylor & Francis Group, London.

Although compacted soil is widely used for constructing earth structures, the mechanism of compaction has not been explained using principles of soil mechanics. Therefore, designing and constructing such structures depend on empirical methods. In this study, we considered compaction as un-drained compression of unsaturated soil, and have simulated the compaction process using principles of unsaturated soil/water coupling problem. The constitutive model proposed by Ohno et al. (2007) and the soil-water retention characteristic curve model proposed by Kawai et al. (2000) were used for these simulations. When compared with static compaction tests performed by Kawai et al. (2003), the simulation results showed good agreement. Consequently, the shape of the observed compaction curve could be explained. The results achieved in this study can be applied to construction management on geotechnical engineering sites. © 2011 Taylor & Francis Group, London.

An evaluation method for the mechanical behavior of unsaturated soils is studied in this paper. Although the mechanical behavior of unsaturated soils is complicated, a simple modeling is preferable in practice. This is because the soil properties are not homogeneous and ground data is limited when structures are being designed. In addition, in order to evaluate the reliability of the design, the physical meanings of the parameters applied in the prediction model should be clear. Firstly, the authors study the relationship between compaction curves and compression indexes in the unsaturated state that is used in the proposed constitutive model. Based on the constitutive model, the stress paths for constant volume shear tests are formulated under a constant void ratio condition and the stress paths for undrained shear tests are calculated under a constant water content condition. In the case of unsaturated specimens, the volume of these specimens changes with the shear deformation and the stress paths depend on the initial degree of saturation. The results of the calculation qualitatively describe the test results by considering the changes in effective confining pressure in the undrained condition and the water retention curves. © 2010 Springer Science+Business Media B.V.

Desertification due to salt damage has recently become a serious problem throughout the world. Salt damage is a phenomenon where salt in the groundwater gets concentrated at the ground surface and kills vegetation. In this study salt damage due to disequilibrium of water balance was simulated with unsaturated soil/water coupled simulation code, as applied the material transport equation. Evaporation and precipitation cycles were applied to a model of ground that contained salty groundwater in its deep region. This allowed the successful reproduction of the phenomenon of salt accumulation on the ground surface. Additionally, identical climatic conditions were applied to model grounds consisting of two types of soil, different in terms of their soil-water retention characteristics. It was found that two methods of overlay and insertion of a layer of coarse-grade material, known as 'mulching', are effective in the prevention of salt accumulation. © 2011 Taylor & Francis Group, London.

Due to its low permeability and excellent expansion characteristics, bentonite is an excellent candidate with potential use as a buffer in the disposal of nuclear waste. Its expansion characteristics, activated by wetting, can be interpreted based on the full saturation line, depicted as a unique line on the density and the confining pressure relationship as proposed by Kobayashi et al. (2007). In addition, its elasto-plastic constitutive relation can also be formulated by introducing additional irreversible strain component describing the expansion of the montmorillonite present in the bentonite material. A constitutive model can consistently express the mechanical behavior of the compacted bentonite material from the unsaturated to the fully saturated state. This paper describes the density homogenization process that was conducted through a series of soil-water coupled elasto-plastic finite element simulations. Specifically, bentonite specimens, with different initial densities, were permeated with a constant water head. Stresses and strains developing in bentonite, particularly the density change, were carefully examined. A series of numerical simulations, performed on the two specimens, showed that specimens did not homogenize to a unique value of density upon reaching the fully saturated state. To confirm the simulation results, we carried out a series of experiments. The experimental results also support our simulation results. Copyright © 2011 by ASME.

The ground pollution is one of the most serious environmental issues all over the world now. Industrial wastes discharged from various human activities infiltrate to the ground, diffuse and damage to plants and animals indirectly. Therefore, it is strongly requested to know the transfer behavior of contaminant movement in the ground. In this study, continuous equations and advection-dispersion equation are derived from mass conservation laws in soil, water, air and dissolved material phases. These governing equations are applied to the constitutive model for unsaturated soil and formulated in the framework of the initial boundary value problems with the finite element method The soil/water/air coupled analysis program, DACSAR-M_ad, applied mass transfer equation to is coded. Here, the mass within the ground due to loading is simulated with this code.

To predict the long-term elasto-plastic behavior of unsaturated earth structures, a constitutive model, which can express the following typical mechanical behavior of unsaturated soil, is needed. This includes shrinkage and increase of stiffness upon drying (i.e. suction increase), collapse with reduction of stiffness upon wetting (i.e. suction decrease), and the influences of suction history related to the hysteresis of soil-water retention characteristics. In this study, a new constitutive model is proposed for unsaturated soil where the effective degree of saturation is used as a parameter relating to stiffness. The model shows good agreement with experimental results. In addition, a soil/water coupled finite element simulation code (simulator), as applied to this model, is introduced. The appropriateness of the simulator is demonstrated for the case of a virtual fill. © 2010 Taylor & Francis Group, London.

This paper synthesizes the state-of-the art of the various laboratory testing techniques presently available for measuring the water hydraulic constitutive functions of unsaturated soils. Emphasis is on the laboratory testing techniques for measuring the soil-water retention curves and the water hydraulic conductivity functions of unsaturated soils. The significant recent advances in the investigation of the hydraulic behaviour of unsaturated swelling soils, are also presented. Comprehensive recent references on each measurement method are listed and discussed. © 2009 Springer Netherlands.

It is empirical knowledge that vegetation can influence the behavior of earth structure. It prevents surface failure and erosion due to rain and wind, and contributes to the stability of earth structure. Moreover, it encourages water circulation with transpiration, fixes atmospheric nitrogen and carbon via photosynthesis, and improves the environment. Therefore, surface seeding is purposely performed when an earth structure, such as an embankment or an earth dam, is constructed. Typically, vegetation grows on unsaturated soil. Consequently, a constitutive model for unsaturated soil is needed for understanding the effects of vegetation on the ground. In this study, we focus on the effect of vegetation-induced water uptake. The effect of water uptake due to evapo-transpiration can be regarded as reduction of water content within soil and appropriately represented in simulation studies. The constitutive model proposed by Ohno et al. (2007) is used for the simulation. In this model, the effective degree of saturation is treated as a parameter expressing hardening/softening. Moreover, the 'root element,' where the reduction of water content occurs, is applied to the soil/water coupled analysis with unsaturated soil mechanics. To verify the applicability of this model, the accident in Poland where non-uniform settlement and building damage were caused by water uptake of vegetation was simulated. The results show that water uptake increased suction and induced non-uniform settlement. This method is effective for understanding the effects of vegetation on the ground. © 2009 IOS Press.

When troublesome sludge discharged from industries and purification plants are burnt by 1300 degree, they change to innocuous micro-porous ceramic materials. The authors are seeking for practical use of such micro-porous ceramic materials in the geotechnical engineering field, particularly for geohazard mitigation. Then, in order to grasp fundamental mechanical properties of the micro-porous ceramic particles, a series of laboratory tests, that is, triaxial compressive shear tests, permeability tests and water retention tests, were performed. It is found that the stress-strain characteristics and permeability of the micro-porous ceramic particles are very similar to those of standard sandy materials but they have very high water retention capability. Next, applicability of the unsaturated elasto-plastic constitutive model proposed by Ohno et al. (2007) to the mechanical behavior of micro-porous ceramic particles was examined in this paper.

Prediction method for undrained shear behaviour of unsaturated soils is discussed in this paper. Based on Original Cam Clay model, authors have proposed constitutive model for unsaturated soils that the effect of water content is incorporated into superloading surface concept. Firstly, stress path of constant volume shear test is formulated under constant void ratio condition. And relationship between water content, dry density and constant volume shear strength is also derived. Secondary, calculation method of undrained shear tests is studied. In the case of unsaturated specimen, volume of the specimen changes with shear deformation and stress paths depend on initial degree of saturation. The calculation results described the tendency of test results qualitatively by considering the change in effective confining pressure in undrained condition and water retention curve.

Empirically, it is known that the vegetation influences on the earth structure. Kawai et al. focused on the effects of water uptake induced by the vegetation. They regarded it as an effect of decreasing soil moisture and applied the effect to unsaturated soil/water coupled F. E. analysis. In this study, the soil/water coupled F. E. analysis code is rearranged with the constitutive model for unsaturated soil proposed by Ohno et al.. In their model, the effective degree of saturation are applied as a parameter expressing stiffness of unsaturated soil to enable application of unsaturated soil mechanics to actual problem in geotechnical engineering site. To verify the applicability of soil/water coupled analysis, the accident that the vegetation uptake work brought about the non-uniform settlement of the ground and damaged the building in Poland are simulated. Consequently, it was found that the uptake increased suction and encouraged non-uniform settlement of ground surface. Its effects appeared prominently in a dry ground having low groundwater level and much uptake. This method is effective to understand the effects of vegetation.

Many of earth structures on the ground keep stability in unsaturated state. Moreover, these structures are exposed to drying and wetting conditions and changes in soil moisture always occur. Therefore, the constitutive model with unsaturated soil mechanics is needed for predicting the elasto-plastic behavior of the earth structures for a long term. The objective of this study is developing soil/water coupled F. E. analysis with unsaturated soil mechanics. In this study, the constitutive model proposed by Ohno et al. is used. Their model can express typical behavior of unsaturated soil, such as shrinkage on drying process, collapse on wetting process, and the effects of hysteresis on soil-water retention characteristic curve, and have the flexibility for dependencies on soil properties. Moreover, isoparametric element is applied on spatial discretization to preventing the dependency on mesh, which can be seen in the Akai and Tamura's method. This simulation method allows us precise prediction of the behavior of unsaturated earth structures.

This paper synthesizes the state-of-the art of the various laboratory testing techniques presently available for measuring the water hydraulic constitutive functions of unsaturated soils. Emphasis is on the laboratory testing techniques for measuring the soil-water retention curves and the water hydraulic conductivity functions of unsaturated soils. The significant recent advances in the investigation of the hydraulic behaviour of unsaturated swelling soils, are also presented. Comprehensive recent references on each measurement method are listed and discussed. © Springer Science+Business Media B.V. 2008.

In this paper, a series of numerical simulations of conventional laboratory experiments on normally consolidated clays under undrained condition subject to uniaxial compression/extension loading at constant applied rate of strain in axisymmetric and plane strain conditions was performed in rectangular and octagonal modelled specimens in order to investigate failure behaviours of clays. The soil/water coupling finite element technique formulated under finite deformation theory based on the updated Lagrangean scheme were applied for the numerical simulations. Herein, the Cam-clay material with von Mises type failure criterion, which is independent of the Lode angle, is used to describe constitutive behaviour. It can be seen that the stress states at failure of the specimens obtained from the numerical simulations do not show the von Mises shape on the pi-plane but rather more closely resembles the Lade-Duncan model, which is dependent of Lode angle. The result suggests that Lode angle dependence consistently observed in the laboratory at failure is not a constitutive behaviour but is instead a result influenced by applied boundary conditions and material imperfections. Copyright (c) 2006 John Wiley & Sons, Ltd.

The soil/water-coupled analysis for unsaturated soil mechanics with the finite element method is used to express the behavior of compacted earth structures exposed to rainfall. The constitutive model, which is proposed by Karube et al. (1996, 1997) and modified by Karube and Kawai (2001), is formulated for initial and boundary problems and coded as DACSAR-U (lizuka et al., 2000). A deep fill, which consists of compacted, unsaturated soil, was analyzed with DACSAR-U. Different patterns of rainfall were applied to deep fills in finite element simulations. As a result, non-uniform settlement of deep fill can be calculated and the magnitude of settlement of deep fills is dependent on the amount of collapse, namely, the compression due to the decrease in suction. Moreover, delayed settlement due to rainfall and an accumulation of an irreversible settlement due to cyclic rainfall was observed.

不飽和地盤の長期挙動を高精度に予測するためには，不飽和土の特徴である，乾燥時の収縮および剛性増加，湿潤時の剛性減少に伴うコラプス沈下，乾湿履歴の影響を，表現する必要がある．本論文では，実務への適用を見据え，剛性を表す状態量として，簡易に測定可能な有効飽和度を用いた，不飽和土弾塑性構成モデルを提案する．提案モデルは，降伏面の設定に関して軽部らのモデルを参考にし，水分特性曲線モデルを設定すれば，乾湿履歴が変形特性に及ぼす影響を，変形および水収支に関して矛盾なく表現できる．また，有効飽和度の剛性への影響量を2つのフィッティングパラメーターで表すため，従来のモデルよりも柔軟性に富む．本研究では，締固め土のコラプス挙動を提案モデルと比較し，モデルの妥当性を検証している．

It is known that the vegetation is effective in preventing slope failure. In this study, we focus on the vegetation uptake from ground and show the way to estimate its effects on the ground quantitatively. The effect of uptake can be regarded as reduction of water content within soil. The ‘root element’, where the reduction of water content occurs, is applied to the existing code of soil/water coupled finite element analysis with unsaturated soil mechanics. To estimate the effects of uptake, three kinds of conditions, such as the amount of uptake water, the initial degree of saturation of the ground, and groundwater level are provided. Consequently, it was found that the uptake increased suction and encouraged non-uniform settlement of ground surface. Its effects appeared prominently in a dry ground having low groundwater level and much uptake. This method is effective to understand the effects of vegetation.

This paper discusses the volume change characteristics of compacted soil based on oedometer test results. After making specimens with different water contents and under different compaction loads, compression tests are conducted under both saturated and unsaturated conditions. The effects of the compaction conditions on the compression curves are discussed. It is confirmed that the yield stress and the water content are important factors when evaluating a compression curve, while dry density and suction are important factors when evaluating the yield stress. Copyright ASCE 2006.

This paper proposes a new mathematical formulation for the unsaturated soil-water coupled stress-deformation problem in which the advection and dispersion phenomena are taken into consideration. The conventional mathematical formulation for advection and dispersion phenomenon cannot take account of influence arising from the stress change and deformation of the ground. Therefore, if some construction works such as irrigation facilities and wells are planed as measures for some contamination damage, their influence on the advection and dispersion phenomena of the contaminant cannot be quantitatively examined by the conventional mathematical formulation. Then, in this paper, a new mathematical formulation for the advection and dispersion phenomena is rebuilt and a set of governing equations coupled with the soil deformation is presented. This new formulation is capable of introducing any constitutive model for unsaturated and saturated soil. In this paper, an elasto-plastic constitutive model for unsaturated and saturated soil proposed by Kawai et al. is employed together with the water retention model for the unsaturated soil considering the hysteresis response under wetting and drying processes. Finally, the performance of this new formulation for advection and dispersion phenomena is demonstrated through a numerical simulation of salt damage in an imaginary ground.

本論文では締固め土における圧縮特性の評価手法を検討している. 現在の締固め施工では乾燥密度に着目した品質管理が主流であるが, 管理値と力学特性との関連性を明確化する上では検討の余地が残されている. 本論文では締固め土の圧縮挙動に及ぼす影響要因として乾燥密度, 含水比, サクションおよび締固め荷重に着目し, それぞれの組み合わせが異なる供試体の一次元圧縮試験結果から圧縮挙動との関連性を考察した上で, 降伏応力および圧縮曲線の評価方法を提案している.

Changes in the instantaneous shear modulus associated with the non-coaxiality of NC clay materials are presented. A series of hollow cylindrical shear tests was performed to measure the changes in the instantaneous shear modulus with shear history. After each normally consolidated clay specimen was compressively sheared until a prescribed shear level, it was continuously torsionally sheared under a constant volume to measure the instantaneous shear modulus. Coaxial constitutive relations, such as these of the conventional Cam-clay type of models, predict that the instantaneous shear modulus obtained, does not change regardless of the compressive shear history. On the contrary, it is known that non-coaxial constitutive relations theoretically bring about changes in the instantaneous shear modulus in relation to the compressive shear history. The test results supported the predictions made by the non-coaxial constitutive models. Finally, the proper formulation for the non-coaxiality between the stress and the incremental plastic strain is discussed.

in the book of Dislocations, Plasticity, Damage and Metal Forming : Material Response and Multiscale Modeling, Key-note-lecture, Proc. Of PLASTICITY'05 : the 11th International Symposium on Plasticity and its Current Applications, edited by A.S.Khan and A.R.Khoei.

This paper presents the modeling of the composite soil-geosynthetic structure and discusses the effect of the reinforcement arising from the confining of the deformation of the soil by geosynthetics. A series of compressive shear tests for compacted sandy soil specimens, wrapped in geosynthetics, is carried out for the purpose of quantitatively examining the effect of the geosynthetic reinforcement arising from the confining of the deformation of compacted soils during shearing. Furthermore, an elasto-plastic modeling for compacted soil and a rational determination procedure for input parameters, needed in the elasto-plastic modeling, are presented. In this paper, the subloading yielding Surface is introduced to the elasto-plastic modeling in order to describe the irreversible deformation characteristics of compacted soil during shearing. Since compacted soil is essentially unsaturated and its mechanical behavior is influenced by the suction working in the compacted soil media, the suction effect is taken into account in estimating of the degree of compaction. Finally, an elasto-plastic finite element simulation is conducted and the geosynthetic-reinforcement effect is presented. (C) 2004 Elsevier Ltd. All rights reserved.

There are some constitutive models for unsaturated soil. However, their mathematical structures, particularly for expression of collapse phenomenon, are essentially the same. Therefore, it is possible to unify the constitutive models which were proposed in the past. In this paper, a generalized constitutive model for unsaturated soils is presented. First, we outline existing constitutive models for unsaturated soil and, next, we propose a comprehensive constitutive model for unsaturated soils in terms of the effective stress for unsaturated soils. To this new elasto-plastic model, it is easier to introduce sophisticated methods such as a rotational hardening, a subloading surface and so forth. This model is formulated in the form of incremental general stress and strain relationship and is incorporated into a finite element code, DACSAR-U, for unsaturated soils. The performance of the new constitutive model is demonstrated by comparing with the models proposed by Karube et at and by Honda et al

The mechanical behavior of soils is essentially dependent on the stress/deformation history in the past. It implies that the choice of construction sequence influences on the quality of the soil structure. This paper describes the numericalsimulation of a geo-dome excavation for CAES, which is an energy store system originally proposed by Hayashi. Throughout examining the deformation of ground and effective stress change with the construction sequence in representative elements, the crucial points not only in the construction stage but also in the long term use are tried to find. Herein, two dimensional soil/water coupled elasto-viscoplastic finite element technique is employed in the computation. Thefinal target is to develop a new method enabling to positively evaluate the total life-cycle-cost

不飽和供試体の非排水三軸圧縮試験を行い, 不飽和土の非排水変形強度特性および水分特性について調べた. 試験は, まず飽和状態にある供試体を加圧板法で不飽和化し, その後供試体の間隙空気圧を一定に保ち, 非排水状態で軸圧縮を行った. 比較的飽和度が高い供試体では, 間隙水圧は, せん断による体積圧縮とともに増加し, 膨張とともに消散した. しかしながら, せん断による体積膨張量が顕著になってくると, 再び間隙水圧は増加した. 一方, 飽和度が低い供試体では, 体積変化とは無関係に, 間隙水圧が増加するという傾向が現れた. これは, バルク水とメニスカス水の骨格変形に対する作用の違いとして説明できることが分かった. また, サクション応力を用いれば排水試験と同様の破壊基準を用いることができ, 飽和土の限界状態線と一致することがわかった.

The mechanical behavior of unsaturated soils strongly depends on the pore water distribution as well as the suction. The water characteristic curve (W. C. C) specifying the pore water content and the suction value plays a very important role in describing the mechanical modeling for unsaturated soils. However, the W. R. 0 shows the hysteresis loop in the wetting/drying processes. This paper emphasizes the importance of considering the hysteresis of W.C.C in the modeling. The accumulation of irreversible strains in the soil structures caused by rainfalls cannot be explained well without considering the hysteresis of W. C. C. An existing model of W. C. C is modified so as to express the accumulation of irreversible strains as the cyclic suction loading. Finally, it is shown that the modified model well explains the experimental results.

This paper describes the development of soil/water coupled dynamic finite element computation technique considering irreversible deformation characteristics of porous media such as soils. Incremental governing equations taking into account of the effect of acceleration, first, are summarized and discretized in spatial and time domain. Thus obtained discretized equations are formulated based on the finite element technique so that the acceleration and the total pore water head are unknown values that should be solved under imposed boundary and initial conditions. The finite element code newly developed in this paper is verified by comparing some strict solutions for solid/water coupled problems and is examined whether the seismic responses of soil/water coupled media can be explained. Fina ly, the vertical settlement due to the horizontal seismic external force is successfully simulated.

The objective of this study is to apply mechanics of unsaturated soils to prediction of compacted soils behavior. First, we performed static compaction tests with monitoring the change of applied stress and suction of specimen during compaction. Next, we carried out compression tests for the statically compactedsoil specimen and measured consolidation yield stress of them. As a result, it was found that suction of compacted soil depends on the dry density as well as the water content. Moreover, compression lines of compacted soil retaining samesuction converged into on unique compression line. Finally, we proposed the simple method to predict consolidation yield stress of compacted soil using simplified model of unsaturated soils.

一定エネルギーで締固めた, さまざまな飽和度のシルト質土供試体を用いて, サクションおよび体積変化を測定した一軸圧縮試験を行った. 得られた応力～ひずみ関係は初期飽和度に依存した傾向を示した. また, 破壊時のサクション応力～サクション関係の実測値は水分特性曲線より得られる予測値に近い傾向を示した. この結果はサクション～粘着力関係を一軸圧縮試験により予測できる可能性を示している. さらに, 破壊時の応力状態は, 破壊時のサクション応力を拘束応力とした場合, Fredlund, Morgenstern & Widger により提案されている不飽和土の破壊規準に従うことが判明した. このことは, 非排水状態で得られる一軸圧縮試験の強度が, 排水試験に基づいて得られた破壊規準に従うことを意味している.

Suction influences on the mechanical behavior of unsaturated soil. However, suction cannot be regarded as a part of effective stress. ne interpretation of suction effect is of much difference in the formulation of constitutive modeling. The authors have confirmed that we can predict the shear strength of unsaturated soil by adding the suction-induced stress to the net normal stress. In this study, anisotropical consolidation tests are performed under the condition of various net normal stress ratios. As a result, the relationship between the stress ratio and the incremental strain ratio is obtained. And the coefficient of earth pressure at rest is estimated by interpolation. The effects of suction on strains are revealed clearly.

Deformation and failure of soils are governed by the stresses acting on the soil skeleton. The isotropic stress acting on the soil skeleton can be divided into two components. One is the stress component which is transmitted through the soil skeleton. This skeleton stress is influenced by the pore water ("bulk water") in the soil. The other is the internal stress component which does not contribute to equilibrium with a given external force. The internal stress is induced by the capillary tension of meniscus water clinging to the contact point of soil particles and acts so as to connect the soil particles tightly. Therefore, in modeling the stress and strain relations for unsaturated soils, it is of much importance to quantitatively evaluate how the pore water exists in the soil. This paper discusses the role of pore water on the mechanical behaviour of the soil. In particular, the significance of the water retention curve is emphasized from a mechanical viewpoint. Essential features required in modeling of the constitutive relations for unsaturated soils are discussed and presented.

大水深の海域に大規模な埋立地を造成すると, 大きな荷重増加が海底地盤の深所にまで及ぶことになる. このことが造成地の沈下挙動の予測に幾多の問題を引き起こしている. 本論文は, 神戸ポートアイランドおよび六甲アイランドの多くの地点や構造物について続けられている長期沈下測定記録の一部を埋立経歴とともに整理したものである. それによれば, プレローディングは, その撤去後の地表面沈下の軽減に有効であり, このことは, 地震時沈下にも当てはまる. また, 双曲線法の長期沈下予測への適用性も詳しく検討され, その限界が示された.

Deformation behavior of an unsaturated soil in collapse was studied using a modified triaxial test apparatus. Three kinds of wetting test were conducted on compacted clay specimens. (i) wetting tests under isotropic stress state, (ii) wetting tests under constant shear stress, and (iii) repeated wetting during shear test under a constant mean net stress. Collapse occurred later in comparison to isotropic stress state conditions under triaxial stress state when shear stress was kept constant. This phenomenon is due to the decrease of the coefficient of permeability, which relates to the changes associated with bulk water to meniscus water. The relationship between void ratio change and increase in water content observed under the different stress states tested showed similar behavior. In the repeated wetting during shear test, a continuous decrease in void ratio was observed with water absorption and drainage. This phenomenon is also related to the change of the bulk water to meniscus water. The secondary wetting process is observed in the experimental testing program discussed in this paper. The presently available constitutive models do not take into account the secondary wetting process. The research studies presented in this paper provide more insight into the collapse behavior.

Deformation behavior of an unsaturated soil in collapse was studied using a modified triaxial test apparatus. Three kinds of wetting test were conducted on compacted clay specimens, (i) wetting tests under isotropic stress state, (ii) wetting tests under constant shear stress, and (iii) repeated wetting during shear test under a constant mean net stress. Collapse occurred later in comparison to isotropic stress state conditions under triaxial stress state when shear stress was kept constant. This phenomenon is due to the decrease of the coefficient of permeability, which relates to the changes associated with bulk water to meniscus water. The relationship between void ratio change and increase in water content observed under the different stress states tested showed similar behavior. In the repeated wetting during shear test, a continuous decrease in void ratio was observed with water absorption and drainage. This phenomenon is also related to the change of the bulk water to meniscus water. The secondary wetting process is observed in the experimental testing program discussed in this paper. The presently available constitutive models do not take into account the secondary wetting process. The research studies presented in this paper provide more insight into the collapse behavior.

本論文では, 水分特性曲線に与える要因の検討を行うために, 3種類の試験方法でサクションによる脱水曲線と吸水曲線を得た. 一つ目は, 初期状態 (含水比, 間隙比, 飽和度) の異なる水分特性曲線, 二つ目に, サクション履歴の異なる水分特性曲線, そして, 拘束圧条件の異なる水分特性曲線である. 得られた水分特性曲線は, その形状を定量的に評価するために, Brooks and Corey 式で近似し, 算出されたフィッティングパラメーターの値を比較した. その結果, 水分特性曲線は間隙比に大きく依存することが分かった. その効果は空気侵入値, 水侵入値に現れ, それぞれ間隙比の関数で表される. この関係を Toll の提案するサクション～間隙比/等価間隙比面に適用した新しいモデルを提案する. このモデルによって, 任意の初期状態から描く脱水曲線, 吸水曲線を予測することができる.

本論文は不飽和粘性土の応力～ひずみ関係式を提案している. Jennings らが Bishopの有効応力式の適用限界を実験的に明らかにして以来, 不飽和土に対してはサクションの作用を独立に取り扱うことで定式化した構成モデルを用いて力学挙動を表現する試みがおこなわれている. 本稿においては土塊内の間隙水分布状態を反映させた応力成分を用いて力学挙動を表現しているモデルに対して塑性降伏条件と硬化パラメータに新たな概念を適用し, 関連流動則にもとづいた応力～ひずみ関係式を定式化している. 計算結果と三軸試験結果との比較は良い一致を示している.

本論文では, 不飽和状態に置かれている土構造物を対象として, 有限要素法を用いた初期値・境界値問題として取り扱う手法を提示している. 不飽和土の力学特性を特徴づける水分特性曲線のヒステリシスを考慮した弾塑性構成モデルを用い, 土/水連成の有限要素プログラムを開発した. まず, 解くべき初期値・境界値問題を述べ, 用いた数理モデルを説明している. さらに, 有限要素プログラムの検証を行った後, 簡単な例題として仮想堤体の問題を取り上げ, 堤体上流側の水位変化による堤体内部の応力変化と変形を調べている.

盛土や宅地造成などの締固め施工では，効率よく強固な締固め状態が得られる様に，大型重機を用いた転圧が行われる．しかしながら，材料の締固め特性を規定する室内締固め試験とは，サイズも締固め方法も異なるため，締固め後の地盤で現場密度試験やCBR試験を実施し，締固め効果を確認する必要がある．これらの試験では局所的な地盤状態を計測することになるため，誤った締固め管理となることも懸念される．そこで，本研究では，「締固め」を地盤材料内の土粒子～間隙水～間隙空気の相互作用の結果として捉えることで，不飽和土の力学として体系化し，施工時の「締固め」による品質変化や締固め構造物内に発現する不均一性の原因となる要因を整理，設計や施工，維持管理手法を普遍的なモデルで記述することを目的としている． 初年度は，土/水/空気連成解析によって，転圧をシミュレーションし，材料の含水比や締固め層厚が地盤内の締固め度分布に及ぼす影響について検討した．「締固め」は，排気非排水条件の載荷・除荷で表現し，仮想模型土槽を水平方向に「締固め」をしながら移動することで転圧を表現した．その際に，転圧ローラーによる回転滑りや試料の前面への押出しを締固め面でのせん断力として作用させた解析条件も設定した．その結果，転圧は地盤内の締固め度の不均一性を生じさせることが明らかであり，含水比や締固め層厚によって，その効果は異なることも確認できた．層厚が大きい場合，厚さ方向の不均一性は増すものの，繰り返し転圧による改善が見込めることも分かった． また，次年度以降の実物大盛土試験で実施する物理探査のために，機器の動作確認と共にいろいろな現場で計測を行うことで，探査・分析技術を向上させた．

X線コンピュータートモグラフィー装置（以下，X線CT装置）を用い，土壌凍結による凍上過程における土壌の移動量の時間変化の計測を試み，その妥当性を検証することを目的として実験を実施し，以下のような成果を得た． 円筒型のアクリル製カラム内に飽和させた珪砂5号を詰め，上端をラップで密封し側面を断熱材で覆う．次に，X線CT装置を用いてカラム内の土壌の再構成画像の撮影を行い，カラムを冷凍庫内に約24時間設置し，土壌を凍結させ，再構成画像の撮影を行った．その後，自然解凍により土壌を融解させて再構成画像を撮影した．三次元画像相関法（Digital Volume Correlation，DVC）により土壌の凍結前，凍結後，融解後の再構成画像を比較し，土壌内部の体積ひずみの3次元分布を求めた．また凍結に伴う土壌の温度の変化調べるために，別途飽和した珪砂5号の土壌カラムを作成した．カラム内には所定の位置にT型熱電対が挿入されており，土壌を上述の方法で凍結させて，その間の温度の変化を1分毎に計測した． その結果，凍結後と融解後の土壌内部の体積ひずみの鉛直および平面分布が得られ，凍結・融解に伴う膨張および収縮が確認できた．また土壌の中央よりやや上方で膨張が大きい領域が観られたが，この発生の原因は土壌の温度の変化，すなわち凍結の発生過程によるものと推察された． さらにこれらの結果を踏まえて，今後の研究を進めるために，X線CT装置内で土壌の冷却と再構成画像の撮影が可能な土壌冷却装置を設計した．

「締固め」は陸上土工構造物建設の際に用いられる施工法であり，多くの構造物建設に太古の時代より用いられている．近年は，土質力学の知識技術が発達するとともに，施工機械も大型化高度化している．しかし，「締固め」のメカニズムは以前力学体系の中で説明が不十分であり，施工は経験的になされているのが現状である．本研究では，数値シミュレーション，室内模型試験，現地計測を併用することで，「締固め」メカニズムの解明と，施工方法が構造物の品質に及ぼす影響を明らかにすることを目的としている． 初年度は，「締固め」を初期値境界値問題として捉え，精緻な不飽和土構成モデルを用いた土/水/空気連成解析で締固め要素試験を模擬し，「締固め」の力学的意義を明らかにするとともに，実際の土工構造物で表面波探査，電気探査によって，既存構造物の内部状態を把握する手法の検討を行った．その結果，「締固め」方法によって地盤内に締固め度の不均一性が生じることが分かった．実際の「締固め」施工はてな圧で行われることが多く，より不均一な締固め度分布が生じる可能性がある．そこで，模型土槽を転圧によって締固め，得られた模型地盤をX線CTスキャナーにかけることで内部状態を把握することを試みた．模型試験では，内部の締固め度分布が初期の転圧方向に依存することが分かった．また，同時に土/水/空気連成解析による転圧シミュレーションを実施し，模型実験で得られた結果を定性的に表現できた．

降雨の浸透が地盤を不安定化させることは知られているおり，降雨浸透シミュレーションや現地計測で降雨浸透挙動の把握を目的とした研究が多くなされている．しかし，その時の地盤内空気相の挙動に注目したものは少なく，その影響もよく分かっていない．ここでは，地盤内空気相の構造物の品質に与える影響について検討した．まず，土/水/空気連成解析によって，傾斜地盤への降雨浸透挙動を明らかにするとともに，その時に空気圧の局所化が生じることを確認した．また，実物大盛土で詳細な浸透挙動計測とともに空気圧も計測し，解析結果の妥当性を検証した．その結果，降雨強度や総雨量によって，浸透・空気圧発生挙動が異なることが分かった．

本研究は，塩害による沙漠化抑止と修復の技術提案を通して，地盤工学の地球環境問題への積極的な寄与を目的としている．過伐採，過放牧，塩害が沙漠化の三大要因であり，全体の約8 割を占めている．森林などの植生伐採に伴う気圏・地圏間の水循環の狂いが原因である．特に塩害による沙漠化は，地下水中の希薄な塩分が高濃度化して地表に析出することにより生じ，ユーラシア大陸などの大陸の広範囲な地域で発生している．このような塩害による沙漠化メカニズムを表現できるFE シミュレータを開発し，さらに，環境負荷の低減を可能とするPS 灰や浄水場汚泥のリサイクルによる粒状材料などを活用できる塩害抑止工法を開発した．

東日本大震災で発生した膨大な放射能汚染土砂を安全に管理することが求められており，土砂を汚染物質の漏出なく最適に締固めることが重要となってくる．そのためには，これまで経験学的に行われてきた締固めを力学的に説明する必要がある．ここでは，まず締固めを土/水/空気連成問題としてとらえ，解析によって表現することを試みる．また，物質輸送方程式を組み込み，外力変化による土壌内の物質移動も同時に予測できる解析手法を確立する．

ユーラシア大陸地下には,広く岩塩層が堆積していることが知られる.地層褶曲などにより岩塩層が比較的地表近くまで迫出している場合には,表層地下水にまで塩分が含まれていることが多い.典型的な事例をタイ東北部(内陸)に見ることができる.乾期,雨期の乾湿繰返しに伴って地表面への塩の析出と塩害に伴う農業生産の低下を引き起こしている.一方,東南アジアの国々では,製紙業から排出されるPS(ペーパースラッジ)や浄水場発生汚泥の処理は深刻な環境問題となっている.このような汚泥を1300度程度で焼くと,微細な多孔構造を持つ安定した多孔質材とすることができる.本研究課題は,タイ東北部をフィールドに,この多孔質材料を塩害防止・対策に用い,塩害防止と農耕地保全に役立てることを目的とし, 1.水収支の狂いによる塩分析出シミュレータの高度化, 2.タイ東北部で計測された塩害,地盤変状の解析, 3. PS焼成材,浄水場排出焼成材の力学特性の把握, 4.塩害防止,農耕地保全の構造体の提案を行った.

沙漠化の主要因の一つである塩害は,不適切な灌漑などの人為的要因と長期の乾湿繰り返しといった自然要因によって起こるため,地盤に及ぼす複雑な外的要因を考慮した対策が必要となる.本研究では,地盤の変形,地下水流れ,物質移動を同時に表現できるシミュレータの開発を行った.また,解析精度の向上を図るため,ライシメーターを用いた地盤からの蒸発量計測も行い,塩害抑制地盤の提案も行っている.

中越地震や能登半島地震で発生した地盤災害は, 地下水位の高い盛土に集中していた. 一方, 豪雨による盛土崩壊も後を絶たない. 兵庫県で発生した台風による補強土壁の崩壊事例では, 雨水の浸入により盛土本体が弱体化したことに加えて, 盛土背部で水位が急激に上昇し, 補強土壁盛土全体が押し流された. この種の地盤災害軽減のためには, 盛土内および周辺への雨水の浸入を決して許さないことが肝心である. 本論文では, 盛土を囲むようにジオシンセティックス排水材をL型に配置し, 鉛直に設置した排水材で受けた浸透水を盛土底部に水平に設置した排水材に流すことにより盛土外へ速やかに排水させる方法であるジオシンセティックスを用いたL型排水盛土防水工を新たに提案した.

本研究は, 塩害に伴う地盤変状をシミュレートする飽和/不飽和土・水・移流拡散連成有限要素解析手法の開発とそれを用いた塩害軽減・修復技術の開発を目的としている. 多くの「塩害→植生枯死→砂漠化」の地盤環境変状・地盤環境崩壊プロセスは, 「森林の伐採」などによって, 降雨などの供給水量と植生からの蒸散水量と地表からの蒸発水量のバランスが崩れ, 塩害をもたらすと説明されてきた. 一旦, 地表面付近に塩分が析出すると, もはや少種の草木を除いて, 植生は育成することができず, さらなる地盤の乾燥化を招き, 砂漠化に至る. しかしながら, 世界の多くの地で問題視される「塩害」は, このような単純なプロセス(一次的塩害)では収まりきらない. 森林伐採は人類の生活圏の拡大に伴って生じる. 例えば, タイの場合, 新たな水田の確保のために森林が伐採された. 水田への農業用水の供給は, ため池などの地上水からの供給ばかりでなく, 地下水の汲み上げによっても補われている. 降雨の少ない乾燥地ほど地下水への依存度は高い. 地下水には, もともと希薄であったにせよ, 塩分が含まれている. 地下水への塩分の溶解は, その上流部もしくは地中深部に存在する塩岩層に起因していることが多い. 塩分を含んだ地下水を地表に汲み上げることにより, 乾季における蒸発によって塩分濃度が上昇し, さらなる塩害をもたらす. また灌漑水路などの建設は, 塩分含有地中水の濃度上昇をもたらし, これまた塩害を引き起こす(二次的塩害). 一方, 地下水の汲み上げは, 地盤変状をもたらし, 農地の機能損失, 道路の沈下・陥没などとして現われる. すなわち, 塩害の発生と,水路や道路の建設などの人為的力学作用との相互作用が重要となる. この目的を遂行するため,(1) 飽和・不飽和状態にある土の透水・力学特性,(2) 植生を介しての蒸散などの水循環, (3) 降雨による水供給と地表面蒸発などの水循環,(4) 地中水に含有している塩分などの移流拡散,(5) 地盤の変形・応力・浸透を考慮した数理モデルを組み立てた. この数理モデルのキャリブレーションを行うために, タイのカセサート大学の協力を得て, 平成18年11月27日に, バンコクでワークショップを開催した. さらに, タイ東北部のサコナコン, ウドンタニにて, 地表塩分渡度の現地測定を行った.さらに,(6) 本研究で開発した数値シミュレータを用いて, 塩害地盤の代表的な修復法であるフラッシングの効果を定量的に検討できる手法を開発し,(7) 塩害防止策として, 粗粒材料を用いたマルティング法およびパイリング法を考案した.

自然,人工問わず地盤構造物の多くは土粒子間隙に水と空気を含む三相構造で存在している.間隙が水で満たされている場合を飽和状態と呼び,空気が存在する一般的な不飽和状態とは区別する.しかしながら,地盤工学の発展は飽和状態にある土の挙動を表現することで発展してきたため,未だに不飽和土の力学が実問題へ適用されることは少ない.本研究は,申請者らが究明してきた不飽和土の力学体系を初期値境界値問題として定式化し,実用化するために実現象における各種水理境界変動の解析上の表現法を確立し,その影響を明確にすることを目的としている. 前年度,行った土柱試験により地下水位変動と降雨による地盤内含水率変化を実験により求め,解析結果との比較を行った.今年度は,蒸発と外力が地盤内含水率分布に及ぼす影響を検討した.蒸発に関してはモニタリング法という水分特性曲線を求める方法が提案されており,蒸発時の含水率低減とサクション変動が水分保持特性に一致するのは明らかにされている.ここではその影響深度に関して,模型実験と解析の結果を比較した.その結果,地盤表面が乾燥してくると,実蒸発量が低下するため土内部での含水率低下がかなり抑制されることが明らかとなった.また初期の含水率分布によって,地盤のサクション増加挙動が大きく異なることが分かった.外力に関しては,シミュレーションによる検討を行った.非排水条件下で不飽和状態にある地盤に外力を加えると,外力や初期含水状態に依存した,異なる含水率分布を呈することが分かった.この結果は,締固めなどの外部との水収支がない状態で外力が作用する条件で,締固厚さや外力の大きさによって,品質が異なる可能性があることを示唆している. 以上,本研究で得られた知見は,不飽和土の力学を地盤工学上の問題へ適用するための一助となったと思われる.今後は,定量的な表現において解析精度を高めていくことを目的とする.

土構造物に対する補強とは,剛な固定端で反力をとって土構造物を支えようとする機構ではない.土と補強材が一体となって剛性や耐荷力が向上しているメカニズムである.では,その力学的相互作用がどのように土構造物の剛性や耐荷力の向上に結びついているのであろうか.本研究では,土のダイレタンシー変形を補強材が拘束するメカニズムがポイントであると考えた.しかも不飽和状態におかれている土を考えねばならない.土構造物に荷重が作用する.土はせん断変形しようとするが,ダイレタンシー特性により体積膨張変形を生じようとする.この体積膨張変形を補強材が拘束することにより,土全体の剛性と強度が増し,補強効果が発現すると考えている.もしそうだとすると,土の締固め度合い(または地盤の過圧密度合い)と補強材の剛性との間に,最適な組み合わせがありうるはずである.さらに,最適な補強材の配置が見出されるはずである.本研究は,締固め土(不飽和土)を対象に,まず,1)ダイレタンシー拘束による補強効果発現メカニズムを検証し,2)ダイレタンシー特性を決定する最大締固め荷重(過圧密度合い)の推定法を提案した.これらの成果を組み込んだ数理モデル(有限要素解析手法)を開発した.これにより補強効果の定量化が可能となる.そして,3)補強材の最適な剛性,配置,量の算定を可能とし,4)最終的には,杜会ニーズに応えるべく,補強された土構造物の経年的機能変化,品質変化を予測できる手法としてまとめあげられている.

間隙に空気相と液相を含む不飽和土は、土構造物の設計の際に締固め土という形で材料として用いられる。本研究の目的は、従来の飽和土の力学ではなく、不飽和土の力学を用いて締固め土構造物の変形挙動予測を行うことにある。前年の、締固め土の圧密降伏応力算定手法の開発に続き、本年は水理境界条件が土内部の含水状態に及ばす影響を検討するために、模型土槽を作成し、土柱試験を行った。ここでは、特に地下水位以上の領域での、含水状態に焦点を絞っている。模型土槽は、直径20cm、高さ100cmの土柱内の水位が下部ポーラスメタルを介して連続するマリオット管を用いて制御できるもので、負の間隙水圧を測定できるようにテンシオメーターと含水率測定のためのADR水分計を設置した。水位変動履歴の影響を検討するために、3種類の水位変動パターンを与えた。また、既存の不飽和土/水連成解析プログラムDACSAR-Uを用いて、解析を行い試験結果との比較を行った。 一般的に、地下水位以上の間隙水圧を計測することはまれであるため多くの場合、地下水位以上の飯域に対して、静水圧分布に準じた負の間隙水圧を仮定するが、試験結果は静水圧分布ほどの大きな負の水圧は見られなかった。しかし、時間とともに水位変動とは独立に静水圧分布へと接近していく様子が伺えた。解析でも同じ結果が得られたことから、不飽和化によって土の透水係数が劇的に小さくなるため、容易に静水圧分布を呈することができなくなっていると考えられる。実現場では、地表面の乾湿などさらに境界条件が複雑になることから、間隙水圧分布はさらに複雑になっていると考えられ、本研究は、現場計測の必要性を問うている。しかし、測定される負の間隙水圧と含水率の関係は、別途試験によって得た水分特性曲線と一致しており、負の間隙水圧が測定できれば、含水率は算出可能であることを示した。

粒状材料が破壊時に発揮する粘着力は、粒子間付着力を有する粒子の集合体のマクロな挙動より決定されるものである。本研究ではこの粘着力の根本的な原因である粒子レベルでの粒子間付着力に着目して、そのマクロな挙動への影響を明らかにし、さらに、拡張された構成モデルに結びつく現象を個別要素法に基づく数値実験により明らかにすることを目的とした。このため、粒子間付着力を導入した2次元および3次元個別要素法解析(DEM)を行った。その結果、以下のことが明らかとなった。 3次元DEM解析において粒子間付着力を増加すると、ピーク強度に基づく内部摩擦角および粘着力は増加する傾向を示した。これは、従来サクション一定での不飽和土の三軸圧縮試験結果において得られている傾向と一致している。 2次元DEM解析において粒子間付着力を増加させると降伏線は拡大することが分かった。しかし、拡大の傾向がどのような理論に拠るかは明確でなかった。 3次元DEM解析により得られたπ面上におけるピーク強度点は、Lade規準に一致する傾向を示した。このことは、砂のような粒状材料の破壊規準がLade規準に従う可能性を示している。また残留強度点は、SMP規準に一致する傾向を示した。このことは、正規粘土のようなせん断時に圧縮する材料の破壊規準がSMP規準に従う可能性を示している。 3次元DEM解析により得られたπ面上における等せん断ひずみ線は、Lade規準と一致する傾向を示した。このことは、砂のような粒状材料については破壊規準のみならず、変形挙動までもがLade規準に従うことを示している。 以上の結果は、通常、材料特性を調べるために地盤工学において行われている、三軸圧縮試験や3主応力試験結果からは明らかにはされなかった。これらの結果は、理想の粒状材料が備える材料特性と考えられ、土を含む地盤材料の力学特性を考える上で重要である。

基礎地盤もしくは土構造物内に補強材を敷設して,土構造物の剛性や強度を増加せしめようとする補強土工法のアイデアは,古くから土木技術の一つの要であった.多くの土構造物は多種多様な補強土工法の恩恵の上に,機能を持続し続けている.しかし昨今の社会ニーズは,新規構造物の建設から既設構造物の維持・補修に移りつつある.過去に土構造物が受けた履歴と無関係に,その構造物のグローバルな安定に寄与する形にまとめあげられている現行設計法では対処しづらいケースが増えつつある.構造物の部分的なリニューアル,機能更新が求められるからである.本研究課題はこのような社会ニーズに合理的に答えうる技術体系の確立を目的とした.また,層状に敷設されたジオシンセティックス,基礎の底面端部に付けられたスカート,テールアルメの定着帯,盛土底部横断方法に設置された松杭連結の梯子,松杭,砂杭や摩擦杭,…これらが立派に地盤を補強して(地盤の力学特性の改良=地盤改良に寄与して)機能していることは,経験で知ってはいても理屈がついてこない.構造物のグローバルな安定を考える現行設計法の限界である.これらの「経験」に「理屈」を提供しようとしているとも言える.土構造物に対する補強とは,剛な固定端で反力をとって土構造物を支えようとする機構ではない.土と補強材が一体となって剛性や耐荷力が向上しているメカニズムである.では,その力学的相互作用がどのように土構造物の剛性や耐荷力の向上に結びついているのであろうか.本研究では,土のダイレタンシー変形を補強材が拘束するメカニズムがポイントであると考えた.土構造物に荷重が作用する.その荷重によって土はせん断変形を生じようとするが,土はダイレタンシー特性を有するため,同時に体積膨張を生じようとする.この体積膨張を補強材が拘束することにより,土の剛性と強度が増し,補強効果が発現する.これを室内試験,模型実験,数値解析により検証し,その発現メカニズムを明らかにした.このような補強効果は,土自身の材料特性ばかりでなく,その土の締固め度合い,含水状態などによって変化すると考えられる.そこで本研究では,不飽和状態にある土の力学特性,特に締固め度合いや含水状態の影響を,一連の室内三軸試験を実施して議論している.この成果は,新しい水分特性曲線モデルの提案に結びついた.さらに,土構造物の品質を評価する解析手法を開発し,実際の土構造物の品質評価への適用性を検討している.以上の成果を,順次,学会論文集や国際会議などに発表していった.

地盤材料は少なくとも土と間隙水との混合体であって,両者の力学的な相互作用の考慮が重要である.せん断帯の生成のみを追跡していたのでは地盤材料の破壊を説明することはできない.土供試体の破壊形態はせん断速度か異なる.供試体内ひずみの局所化は,土と間隙水との相互作用の発現の仕方に左右されて,せん断が進むにつれて,「はじめほとんど均質場→ひずみが局所化→局所的に体積膨張→吸水軟化→強度低下」というプロセスを経ることが予見される.供試体が正規粘土であれば当然,供試体全体での平均過剰間隙水圧は正であるが,局所化変形領域では,負の過剰間隙水圧が発生する.すなわち「ダイレタンシーの局所化」の発現である.本研究は,まず,土のダイレタンシー特産を考慮できる弾塑性構成モデルを検討し,このようなダイレタンシーの局所化メカニズムに注目しながら,土供試体のせん断破壊現象を土/水連成の有限要素法を用いてシミュレーションしている.さらに,土のダイレタンシー挙動が,実際の土構造物において,どのような力学的相互作用を引き起こしているか,ジオシンセティックスのような異種材で補強された土構造物において,どのような補強効果を担っているのかを,現場実測事例と有限要素シミュレーションによって検討している.多くの人工土構造物は,間隙が水で満たされた飽和土から成らない.間隙に水ばかりでなく空気も存在する「不飽和」状態にある.このような不飽和状態におけるダイレタンシー挙動の発現メカニズムについても検討を行っている.不飽和土内部の間隙水分布の違いによって,その挙動は大きく異なることが分かった.さらには,そのような挙動を考慮できる数理モデルの開発した.