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Pore ice content is crucial in evaluating the mechanical properties of frozen soils. Existing strength criterion models are usually empirical and ignore the influence of pore ice content. By assuming that the critical state shear stress ratio of soil is a function of the stress level, a critical state line of frozen soil is proposed to consider pore ice content. By combining the Mohr-Coulomb (M-C) and Drucker-Prager strength criteria to describe the failure shape characteristics on the deviatoric plane, a new strength criterion is established for complex stress conditions. The proposed model is validated against existing models and measured data in the literature. In addition, the proposed model can uniformly describe the CSL of different types of geotechnical materials and has a clear physical meaning, which may provide a theoretical basis for constitutive models.

A series of unconfined compressive strength tests and flexural strength tests are carried out to evaluate the improved effect of polypropylene fiber on the defects of cement mortar soil. The following factors, including the fiber content, cement content, sand content and curing age, are studied to investigate the influences on the mechanical properties and microstructure of the samples. The results show that the unconfined compressive strength (UCS), residual strength and flexural strength of the fiber reinforced cement mortar soil (FRCMS) substantially increase with increasing fiber content. The peak strain and ratio of the flexural-compression strength (Rfcs) of the FRCMS first increase and then decrease with an increase in fiber content, and the optimal fiber content is 3.5%. The brittleness index of the FRCMS is found to be inversely proportional to fiber content. The results suggest that the addition of an appropriate amount of fibers can substantially improve the plasticity and lateral stress capacity of the FRCMS. The strength of the FRCMS improves with the increase in cement content, sand content and curing age within a certain range. The microstructure of the FRCMS are analyzed by scanning electron microscopy (SEM) tests.

The landslide signs were discovered in a high filling embankment slope, which was located on an express highway construction site in Guizhou, China. According to the in-situ monitoring results, the landslide mechanism and the stabilization effect of the portal anti-slide pile were preliminarily analyzed. The sliding shear zone of the landslide was obtained by the in-situ monitoring. Tw o numerical models with imposed sliding shear zone were established to analyze the evolution of the landslide instability and the stabilizing effect of the portal anti-slide pile. The comparative analysis of in-situ monitoring data and numerical simulation result shows that the two numerical model are reliable. Furthermore, the numerical model of embankment slope that reinforced by portal anti-slide pile was implemented to analyze the structural behavior of pile under the different pile parameters, and the pile-soil interaction was considered in the numerical model. The influence of the pile parameters (pile spacing, pile row spacing, and linked beam size) on the stabilization effect, structural deformation, and economic benefit were studied. The numerical results provide a guide for determining the optimum parameters of the portal anti-slide pile.

Coarse-grained soils were considered not susceptible to frost heave. However, substantial frost heave has been observed in unsaturated coarse fills in high-speed railway embankments. Recent experimental results in the literature show that vapour transfer has a considerable influence on the frost heaving of coarse-grained soil. However, vapour transfer has rarely been considered in modelling frost heave. This study presents a new frost heave model that considers vapour transfer and its contribution to ice formation. An updated computer program (PCHeave) is developed to account for the vapour transfer in unsaturated coarse-grained soils, where the rigid ice theory is applied to initiate ice lens formation in the frozen fringe. The results of the proposed model are compared with laboratory test results, which show reasonable agreement. The frost heave data monitored in 2013–2014 along the embankment of the Harbin–Dalian Passenger Dedicated Railway are also used to validate the proposed model. The prediction of the model agrees well with the measured results of frost heave and frost depth. This indicates that the proposed model can reasonably reflect the process of frost heave caused by vapour transfer in unsaturated coarse-grained soils.

Evaporation from unsaturated soil is characterized by vapor transfer in the upper part and liquid water transfer in the lower part of the soil. This study develops an analytical model for identifying the vaporization plane where the evaporation occurs, and the model consists of three partial differential equations that respectively govern the vapor flow, liquid water flow and heat transfer. These equations are solved simultaneously for the transient water content profile, evaporation rate, transient temperature profile and location of the vaporization plane. A series of experiments are used to validate the proposed analytical model, which indicates that this model can reasonably well predict the temporal water content profile and evaporation rate during the evaporation process. The result shows that the evaporation rate during falling rate stage is proportional to the inverse of the square root of elapsed time, and the proportionality is affected by the vapor diffusion coefficient, heat diffusion coefficient, and critical water content. The depth of vaporization plane is found to be independent of soil hydraulic properties, but only dependent on the heat diffusion coefficient of the soil. It is also revealed that heat diffusion coefficient has a pronounced influence on the evaporation process, which has not been observed in previous studies. A larger thermal diffusion coefficient leads to a faster advancing and a deeper vaporization plane, as well as a faster decreasing evaporation rate. The analytical model provides a useful tool for investigating the mechanism of the evaporation process.

Dynamic compaction (DC) is commonly used to strengthen the coarse grained soil foundation, where particle breakage of coarse soils is unavoidable under high-energy impacts. In this paper, a novel method of modeling DC progress was developed, which can realize particle breakage by impact stress. A particle failure criterion of critical stress is first employed. The “population balance” between particles before and after crushing is guaranteed by the overlapping method. The performance of the DC model is successfully validated against literature data. A series of DC tests were then carried out. The effect of particle breakage on key parameters of DC including crater depth and impact stress was discussed. Besides, it is observed that the relationship between breakage amount and tamping times can be expressed by a logarithmic curve. The present method will contribute to a better understanding of DC and benefit further research on the macro-micro mechanism of DC.

Because of ignoring the vapor migration in freezing soils, coarse-grained soils have long been deemed not susceptible to frost heave. However, recent studies reveal that vapor migration can increase the total water content and lead to remarkable frost heave hazards in coarse-grained soils. In this paper, a new numerical model is developed based on the coupled thermal and hydrological processes. The soil water characteristic curve and the soil freezing characteristic curve are taken into account in this model. The model is established by using COMSOL Multiphysics which contains 5 equations and 5 variables. In order to validate the numerical model, laboratory experiments were performed in coarse-grained soils. The result shows that there are sharp increases in water content at the top of samples and the freezing front. A good match between measured and computed results indicates that the new model can make a good explanation for the coupled movement of heat and moisture in coarse-grained soils.

The tamping energy or tamping momentum usually is adopted to evaluate the efficiency of dynamic compaction (DC), meaning that the same tamping energy or tamping momentum leads to the same s...

A series of triaxial compression tests were conducted to investigate the influence of the fiber content and confining pressure on the shearing characteristics of cement-stabilized clay reinforced with glass fibers. The glass fiber contents were 0, 1‰, 2‰, 3‰, and 4‰ by weight of the dry soil. The stress strain and volume change behavior, shear strength, and energy absorption of the test specimen were obtained. The results indicate that the inclusion of glass fibers can increase the shear strength, inhibit the volumetric dilation of the test specimen, and improve its brittle behavior. The cohesion of the cement-stabilized clay reinforced with 4‰ glass fiber content is 2.8 times greater than that of the cement-stabilized clay. The effect of the fiber content on the friction angle is not obvious. It is found that the glass fiber reinforcement is more substantial under a low confining pressure. The scanning electron microscopy test results show that the surface of the glass fiber is wrapped with cement hydrate crystals, which increases the bite force and friction between the fiber and the soil particles. A single fiber is similar to an anchor in the soil, which enhances the mechanical properties of the cement-stabilized clay reinforced with fibers.

Tortuosity is an important parameter for studying the permeability of soil. Existing studies of soil tortuosity are usually of empirical nature and attempt to relate tortuosity to soil porosity alone. By assuming a laminar flow through the pores of two‐dimensional square solid particles, we present a mathematical model for calculating soil tortuosity under different particle arrangements. The effect of the randomness of the particle arrangement on the tortuosity is evaluated, which generates the variation range of the tortuosity. The proposed model provides the upper and lower bounds of the tortuosity, while existing empirical models tend to fall within these bounds. The consistency between the proposed model and the numerical calculation provides a validity for the proposed model.

Long-term cyclic loads with a stress level lower than the critical cyclic stress applied on soft soil can lead to soil deformation but not to failure. The Monismith model is known for its simplicity and capacity to describe the cumulative plastic strain of soil under cyclic loads. However, it is unsuccessfully applied in these cases because the plastic strain in this model would increase endlessly till to failure with increasing number of load cycles. To solve this problem, a novel empirical model with three parameters is proposed based on analogy analysis of the Hardin-Drnevich model and Monismith model. The proposed model is verified by experimental data from existing literature and is shown to have better capability and performance than the Monismith model in predicting the cumulative plastic strain of soft soil subjected to long-term low cyclic loads. The value of parameter b is recommended to be 0.5, and relationships of parameters a and c with the cyclic stress ratio are also proposed for soft clay. Applications of the proposed model are elaborated in detail, and in situ test results for settlement of soft subgrade are used to evaluate the performance of this model. The prediction results are consistent with the test results. The research results present a promising method for investigating the development of deformation and the settlement of soft foundation in the near-shore and off-shore areas caused by wave and/or traffic loads.

Long-term low cyclic loads are often encountered in marine environment, but the cyclic behavior of soil under this loading condition is rarely studied. Undrained pore pressure behavior of soft marine clay subjected to long-term low cyclic loading is of considerable importance for the proper design and maintenance planning of foundations of near- and off-shore structures. In this paper, a new hyperbolic model is proposed to predict the development of undrained pore pressure. This model is verified by experimental data from literature. Compared with the existing models, the proposed model has better capability and performance. With use of the proposed model, a hyperbolic relationship between cumulative plastic strain and pore pressure was derived and verified by experimental data. Finally, the effects of cyclic stress ratio, confining pressure and loading frequency on pore pressure are investigated. In summary, this work provides a novel model and some innovative observations to better understanding undrained pore pressure behavior of soft marine clay under long-term low cyclic loads.

In the fields of nuclear waste geological deposit, geothermy and deep mining, the effects of temperature on the mechanical behaviors of soft rocks cannot be neglected. Experimental data in the literature also showed that the structure of soft rocks cannot be ignored. Based on the superloading yield surface and the concept of temperature-deduced equivalent stress, a thermo-elastoplastic model for soft rocks is proposed considering the structure. Compared to the superloading yield surface, only one parameter is added, i.e. the linear thermal expansion coefficient. The predicted results and the comparisons with experimental data in the literature show that the proposed model is capable of simultaneously describing heat increase and heat decrease of soft rocks. A stronger initial structure leads to a greater strength of the soft rocks. Heat increase and heat decrease can be converted between each other due to the change of the initial structure of soft rocks. Furthermore, regardless of the heat increase or heat decrease, a larger linear thermal expansion coefficient or a greater temperature always leads to a much rapider degradation of the structure. The degradation trend will be more obvious for the coupled greater values of linear thermal expansion coefficient and temperature. Lastly, compared to heat decrease, the structure will degrade more easily in the case of heat increase.

© 2019 The Author(s). A series of laboratory tests were performed to investigate the influences of specimen preparation on pore size distribution of soil and saturated hydraulic conductivity (Ks). Nuclear magnetic resonance technology was used to measure the pore size distribution of the saturated samples of silty soil, which were prepared by three different kinds of methods: Proctor compaction, static compaction, and the consolidation method. The Ks of the samples was measured by the falling head permeability test. The results show that the difference in Ks caused by different specimen preparations can be large as one order of magnitude, as the measured Ks varied from 3.09 ´ 10−3 to 3.36 ´ 10−4 cm s−1. The consolidated specimen tended to have the greatest Ks value, followed by those prepared by Proctor compaction and static compaction. The observed difference highlights the importance of pore structure in determining Ks. This study also presents a pore-information-based theoretical approach for predicting Ks. A comparison of measured data shows that the proposed model performs better than the traditional void-ratio-based models.

Coupled migration of water and heat is one of the core problems in studying the frost-heave and thaw-weakening problems in cold regions. Determination of the hydraulic conductivity of frozen soils is the key to understanding this process. The hydraulic conductivity of a frozen soil is related to the liquid water flow in pores among soil solid and pore ice, which differs from the hydraulic conductivity of an unfrozen soil. This study develops a new hydraulic conductivity model for frozen soils based on the Kozeny-Carman equation, which is consistent in form with the hydraulic conductivity model of unfrozen soils. The proposed model is validated against existing models and measured data in the literature. Parametric analysis of the model shows that the unfrozen water saturation and shape coefficient ratio are important parameters that affect the hydraulic conductivity. In addition, the proposed model can be simplified to a power function, which is very easy to use. The new model only requires one fitting parameter and has a clear physical basis.

A theoretical study of the behavior of structured soils is presented herein. By introducing the effect of soil structure and loading history into the Cam Clay model, a new model was formulated. The concept of differing void ratios was modified to combine structural parameters and the over consolidation ratio, and an evolution law was proposed. Upon introducing the concept of the subloading yield surface, a new two-yield surface model was obtained. The predicted results were compared to the experimental data, demonstrating that the new model provided satisfactory qualitative modeling of many important features of structured soils.

In many geotechnical engineering applications, such as nuclear waste disposal and geothermal extraction and storage, it is necessary to consider the long-term mechanical properties. The effect of temperature could have a complicated influence on the creep damage behavior of soft rock. As a consequence, it is meaningful, both in theory and in practice, to establish a constitutive model that can describe the creep damage behavior. Within the framework of continuum mechanics, a thermo-visco-elastoplastic model is proposed on the basis of a sub-loading Cam-clay model and the concept of equivalent stress. Triaxial creep tests under different confining pressures for Tage stone were conducted to validate the proposed model. The experimental results show that an optimum temperature exists for a certain stress state, and this temperature significantly slows down the creep damage rate. In addition, both the retarding and accelerating effects on creep rupture due to limited warming are observed for the same material, and this phenomenon can be predicted well by the proposed model. Finally, a parametric analysis is performed, and the influence of the material parameter on creep regularity is discussed in detail.

An analytical model based on Richards equation is presented to describe water content redistribution during evaporation. Exponential functions are utilized to describe the relation of hydraulic conductivity and water content on pressure head. The water content at any given depth z and time t, together with the evaporation rate at the soil surface are outputs of this model. The proposed is capable of modelling the transformation of the constant rate stage into a falling rate stage of evaporation, moreover it extends the use of analytical model to arbitrary initial conditions. Detailed parametric analysis was carried out to investigate the effect of six governing factors. The main findings are as follows: hydraulic conductivity ( K s ) and desaturation coefficient (α) affect the water content profile more than the storage capacity ( θ s - θ r ) does; the relation between the duration of the constant rate stage and the dimensionless evaporation rate γ can be expressed by a negative power function; the initial conditions are the most influential factor for the soil water profile among all factors examined. Finally, two evaporation tests conducted on K-7 sand and Fontainebleau sand were introduced to validate the proposed analytical model. Results showed that this model could reasonably predict the temporal water content profile during evaporation process, but some discrepancies still existed in some cases. Nevertheless, the analytical model provides a useful tool for predicting the vertical distribution of water content during evaporation.

The soil freezing characteristic curve (SFCC) describes the relationship between the temperature and unfrozen water content in a soil. The SFCC is indispensable in modelling the hydro-mechanical behaviour of frozen soils, but is less understood for the unsaturated soils. A series of SFCC tests of unsaturated silica sand, silt and red clay are preformed based on a newly developed nuclear magnetic resonance (NMR) apparatus, which can precisely control the sample temperature in the magnetic field. The experimental results show that the measured SFCC varies significantly for different initial water contents, and that a lower initial water content leads to a slower increase in unfrozen water content, proving that the SFCC is closely related to the initial unsaturated state. It is found that the thawing curve is better to represent the SFCC, in contrast the freezing curve is significantly affected by the supercooling phenomenon. A new parameterization of the SFCC is presented for unsaturated soils by combining the Clapeyron equation and the model for Soil Water Characteristic Curve (SWCC). A number of test results from the literature and this study are used to validate the new SFCC model. By inputting the parameters for the SWCC and initial state into the proposed model, the predicted SFCC can agree well with the measured results. The new model has a theoretical basis and simple form and is applicable to both saturated and unsaturated soils.

The effects of vapour on water content in different unsaturated frozen soils have not been systematically analyzed in the literature. Based on the thermodynamic equilibrium theory and coupled water-heat theory, a new method for calculating unfrozen water content and ice content is obtained. A new model is then built by importing this method to the coupled heat and mass transfer theory. Unfrozen water content and ice content in this new model are only related to hydraulic parameters and temperature, which means specific physical meaning. The comparisons between simulations and test results of sandy loam validate the new model. Simulated results also show that temperature is the major factor to vapour transfer instead of suction. And vapour transfer in silt and sand cannot be neglected with freezing except clay. Initial water content, freezing temperature, freezing time and ground water table can all influence vapour transfer in freezing soils. In a word, even though the water content increment is low, the total mass of the increased amount and the average increase of the total water content in the frozen area are about 40 kg and 0.033 within the unit area in susceptible frost heaving soils such as silt, respectively. Remarkable frost heave could then occur due to vapour. Therefore, the vapour in unsaturated frozen soils must be paid more attention to in practical engineering. This paper strengthens the understanding of canopy effect and also validates that canopy effect usually occurs in covered freezing silt instead of sand or clay.

© The Authors, published by EDP Sciences 2020. Substantial frost heave has been observed in coarse fills in high-speed railway embankments. These coarse fills have low fine contents and very low water content. The groundwater table is located below the coarse fills. The coarse fills were considered not susceptible to frost heave. Recent experimental results in the literature showed that vapour transfer has a considerable influence on the frost heaving of unsaturated coarse-grained soil. But vapour transfer has been rarely considered in the modelling of frost heave. This study presents a new frost heave model with considering vapour transfer and its contribution to ice formation. The rigid ice theory is applied to initiate an ice lens formation in the frozen fringe. An updated computer programme PCHeave is developed by considering the vapour transfer. The results of the proposed model are compared with laboratory test results, which show reasonable agreement. The prediction of the model agrees well with the measured frost heave and frost depth, which indicates that the proposed model can reasonably reflects the process of frost heave in unsaturated coarse soil.

© Springer Nature Singapore Pte Ltd. 2019. Recent studies reveal that ice formation via vapour-ice desublimation in unsaturated freezing soils can lead to damage to infrastructures. Actually, the role of vapor flow in a freezing soils is unclear, and it is usually ignored when analyzing water migration process. In this study, a theoretical framework is established to formulate the coupled thermal and hydrological process, where the vapour diffusion governs the mass transfer process. The new model is designed to avoid using the local equilibrium assumption and the hydraulic relations that accounts for liquid water flow. This model contains 6 undetermined variables that are interacted in the 6 governing equations. In order to validate the numerical formulations/codes, a series of laboratory experiments are performed on a coarse sand which is not considered as frost susceptibility soil. The computed results show that the proposed model can indeed reproduce the unusual moisture accumulation observed in relatively dry soils, while the result agree well with the experimental date. This model provides an explanation for coupled movement of heat and moisture in cold and arid regions.

Based on the seepage theory in unsaturated soil mechanics, a coupled model for liquid water-vapor-heat migration is established in this paper, which considers the phase changes of vapor–liquid and water-ice. The results of numerical analysis on layered unsaturated soils show that vapor migration can lead to a significant increase in the total volumetric water content. The depth of the maximum value of the total volumetric water content coincides with the depth of the freezing front (273.15K temperature line). Ground water table has a small effect on the total volumetric water content in silt. However, unfrozen water in the upper sand flows downward from the sand to the silt soil, due to gravitational and matric potentials. A lower temperature of the upper boundary can also lead to an apparent increase in the total volumetric water content. If the temperature of the upper boundary is above 273.15K, the effect of vapor migration on the soil column is small, producing only a 2% increase in the total volumetric water content. Considering actual engineering applications in the northwestern part of China, the water content of the embankments of high-speed railways and airports can also be increased significantly due to vapor migration. Therefore, both liquid water and vapor insulation countermeasures should be considered in practical engineering in frigid and arid regions.

The lateral force on stabilizing piles due to the movement of the landslide has been studied by many researchers. One of the most widely used methods was proposed by Ito and Matsui in 1975 based on the plastic deformation theory. This paper aims to extend the approach of Ito and Matsui by considering the soil arching effects along the height of the sliding layer between two neighboring piles. The analysis is carried out in two stages. First stage involves the plastic deformation of soil adjacent to piles. In this stage, considering the arching effects along the height of the sliding layer, a typical cross section of the soil is employed to analyze the soil stress in the rear of piles. In the second stage, the plastic deformation theory proposed by Ito and Matsui is adopted to analyze the squeezing effects between two neighboring piles. Moreover, the parametric analysis is performed to investigate the susceptibility of the governing factors, which include the geometric and mechanical parameters. The results show that both the geometric and mechanical parameters impart the significant influence on the lateral force. Finally, both the numerical simulation results and the field experiment data from the literatures are introduced to validate the proposed approach. The comparison charts illustrate that the predictions by the proposed approach are consistent with the experimental results.

Surface evaporation is one of the main processes in the soil-atmosphere interaction. Since it is highly related to meteorological factors and soil properties, deter- mination of evaporation rate from soil surface remains a challenge. To investigate the evaporation from unsaturated soil, a climate control apparatus has been newly developed, which has a feature of completely controlling air temperature, relative humidity and wind speed. Twelve climatic conditions are applied to three kinds of soil specimens to carry out the evaporation tests. The results show that only water content cannot allow an accurate estimation, additional variables accounting for soil texture and wind speed must be included as well. Moreover, a simple approach to parameterize evaporation is presented by the soil moisture h of top 1-cm layer with considering the effect of soil texture and wind speed. It is found that the new approach is able to accurately estimate the evaporation from unsaturated soil.

Canopy effect in this paper refers to the phenomenon whereby moisture accumulates underneath an impervious cover. Field observations reveal that the canopy effect can occur in relatively dry soils where the groundwater table is deep and can lead to full saturation of the soil immediately underneath the impervious cover. However, numerical analysis based on existing theories of heat and mass transfer in unsaturated soils can only reproduce a minor amount of moisture accumulation caused by an impervious cover, particularly when the groundwater table is relatively deep. In an attempt to explain the observed canopy effect in the field, this paper proposes a new mechanism of moisture accumulation in unsaturated freezing soils: vapour transfer in such a soil is accelerated by the process of vapour–ice desublimation. A new approach for modelling moisture and heat movements is proposed in which phase changes during the evaporation, condensation and desublimation of vapour flow are considered. A laboratory device is designed specifically to study vapour transfer in unsaturated freezing soils. The test results reveal that vapour transfer can lead to significant moisture and ice accumulation near the freezing end of a soil specimen. The computed results show that the proposed model can indeed reproduce the unusual moisture accumulation observed in relatively dry soils. The results also demonstrate that soil freezing fed by vapour transfer can result in a water content that is close to full saturation. Because vapour transfer is seldom considered in geotechnical design, the canopy effect deserves greater attention during construction and earth works in cold and arid regions.

The role of vapor flow in unsaturated freezing soils is unclear, and usually ignored when analyzing water migration. Indeed, vapor flow is seldom considered in geotechnical design. On the other hand, frost heave damages were recently observed in a cold and arid region in China, where the groundwater table is about 20 m deep, and cannot be explained using the classical frost heave theory which focuses on the coupled flow of heat and liquid water. This paper presents a new approach for modeling moisture and heat movement in unsaturated freezing soils, in which the phase change of evaporation, condensation of vapor flow are taken into account. The method enables numerically stable solutions with energy and mass conservation. The performance of the proposed model was evaluated by a series of laboratory freezing experiments, which involve a 60 cm long soil column subjected to different initial conditions and boundary temperatures. It is shown that the proposed model is capable of effectively simulating the freezing process of an unsaturated soil. The vapor flux is shown to be significant, especially at the end stage where the freezing process is stabilized. Parametric analysis was carried out to clarify the role of vapor in moisture migration. The results show that vapor flow apparently contributes to ice formation and generally accounts for more than 10% of total water flux. The percentage of vapor flux in total flux (vapor flux ratio) positively relates to temperature gradient and freezing depth, but negatively relates to initial water content. Relations between vapor flux ratio and hydraulic parameters are less clear.

Simulating the dynamics of soil water content and modeling soil water evaporation are critical for many environmental and agricultural strategies. The present study aims to develop an analytical solution to simulate soil water redistribution during the evaporation process. This analytical solution was derived utilizing an exponential function to describe the relation of hydraulic conductivity and water content on pressure head. The solution was obtained based on the initial condition of saturation and an exponential function to model the change of surface water content. Also, the evaporation experiments were conducted under a climate control apparatus to validate the theoretical development. Comparisons between the proposed analytical solution and experimental result are presented from the aspects of soil water redistribution, evaporative rate and cumulative evaporation. Their good agreement indicates that this analytical solution provides a reliable way to investigate the interaction of evaporation and soil water profile.