International Journal of Geomechanics

An experimental study was performed to investigate the effects of suction history on the hydraulic and stress-strain behavior of unsaturated soils. Test results show that, even if the same path of net stress and suction was followed during triaxial shearing, the stress-strain and strength behavior are different between specimens experiencing different suction histories. When the maximum suction experienced in the past was less than the residual suction, the specimen that experienced higher past suction produced higher shear strength. This is because the specimen was subjected to a higher suction, i.e., a higher average skeleton stress, and thus became overconsolidated. In contrast, when the maximum suction experienced in the past was higher than the residual suction, the specimen that experienced higher past suction produced lower shear strength. This is because, in this particular case, the high suction induced structural damage in the specimen, which impacts the stress-strain behavior during subsequent shearing. High suction greater than the residual suction was applied using the vapor equilibrium method by putting the soil sample in a glass desiccator with saturated salt solution. The wide suction history effects should be taken into account in constitutive modeling of unsaturated soils.

Recent laboratory tests and field observations have revealed that unsaturated sands are susceptible to liquefaction. Systematic investigation of liquefaction potential of unsaturated sands is, however, lacking. In this paper, a coupled hydromechanical elastoplastic constitutive model for unsaturated sands is calibrated using available laboratory test results. A parametric study is then conducted using the calibrated constitutive model to investigate the effects of initial degree of saturation, relative density, and effective confining pressure on the liquefaction resistance of unsaturated sands. The results suggest that the liquefaction resistance of unsaturated sands increases with decreasing degree of saturation and increasing relative density and effective confining pressure. The results also reveal that the effect of degree of saturation on liquefaction resistance is more pronounced near 100% degree of saturation. The results of the parametric study are then condensed to create a design chart that can be used for liquefaction potential evaluation of unsaturated sands. The degree of saturation, relative density, and effective confining pressure are taken into account in this design chart.

A common underlying assumption in the development of soil-water characteristic curves (SWCCs) is that the soil is sufficiently stiff such that no changes occur in the volume of the soil associated with soil-suction change. A number of researchers recently recognized the importance of considering soil-volume changes in SWCCs; however, few researchers have evaluated the effect of volume change on the computed rate and degree of wetting/drying of unsaturated soils and the associated impact on computed soil-volume change response. This paper focuses on the impacts of considering soil-volume change in the determination of SWCCs for high-volume-change soils, with emphasis on the estimated unsaturated hydraulic conductivity function and response to wetting. Numerical simulations of unsaturated flow and suction-induced volume change were used to study the effect of consideration of volume change in the determination of SWCCs. Numerical analyses used laboratory-determined SWCCs with and without the inclusion of volume change measurements. The study results demonstrate that the impact of volume change consideration on SWCCs and the estimated unsaturated hydraulic conductivity function can be quite substantial for high-volume-change soils such as expansive clays.

Pitfalls in the common approaches to obtaining material parameters from soil-water characteristic curves (SWCCs) are discussed, and the typical mistakes made in the literature are highlighted. Particular attention is given to the evaluation of the air-entry value (AEV) from the gravimetric water content–based SWCCs. A consistent graphical approach for the determination of AEV based on an understanding of the effects of stress history and volume change on gravimetric water retention behavior is presented. The robustness and application of the approach are demonstrated using an extensive set of experimental data from the literature.

Expansive soils are suitable as backfill and buffer materials in engineered barrier systems to isolate heat-generating nuclear waste in deep geological formations. The canisters containing nuclear waste would be placed in tunnels excavated at a depth of several hundred meters. The expansive soil should provide enough swelling capacity to support the tunnel walls, thereby reducing the impact of the excavation-damaged zone on the long-term mechanical and flow-barrier performance. In addition to their swelling capacity, expansive soils are characterized by accumulating irreversible strain on suction cycles and by effects of microstructural swelling on water permeability that for backfill or buffer materials can significantly delay the time it takes to reach full saturation. To simulate these characteristics of expansive soils, a dual-structure constitutive model that includes two porosity levels is necessary. The authors present the formulation of a dual-structure model and describe its implementation into a coupled fluid flow and geomechanical numerical simulator. The authors use the Barcelona Basic Model (BBM), which is an elastoplastic constitutive model for unsaturated soils, to model the macrostructure, and it is assumed that the strains of the microstructure, which are volumetric and elastic, induce plastic strain to the macrostructure. The authors tested and demonstrated the capabilities of the implemented dual-structure model by modeling and reproducing observed behavior in two laboratory tests of expansive clay. As observed in the experiments, the simulations yielded nonreversible strain accumulation with suction cycles and a decreasing swelling capacity with increasing confining stress. Finally, the authors modeled, for the first time using a dual-structure model, the long-term (100,000 years) performance of a generic heat-generating nuclear waste repository with waste emplacement in horizontal tunnels backfilled with expansive clay and hosted in a clay rock formation. The thermo-hydro-mechanical results of the dual-structure model were compared with those of the standard single-structure BBM. The main difference between the simulation results from the two models is that the dual-structure model predicted a time to fully saturate the expansive clay barrier on the order of thousands of years, whereas the standard single-structure BBM yielded a time on the order of tens of years. These examples show that a dual-structure model, such as the one presented here, is necessary to properly model the thermo-hydro-mechanical behavior of expansive soils.

The principle of effective stress is the most fundamental and important principle in soil mechanics. It serves as the foundation of modern soil mechanics. This paper starts with a discussion of effective stress expressions for unsaturated soils. The relationship between the total stress and stress of each phase in unsaturated soils is developed based on three-phase equilibrium equations of a representative element volume (REV). The expression of average soil skeleton stress, defined as effective stress, for unsaturated soils is then derived. This expression is consistent with the effective stress equation in unsaturated soils derived based on deformation work in the energy conservation equation. The general philosophy for the definition of effective stress in unsaturated soils is pointed out, followed by the discussion of some fundamental problems of unsaturated soils, including effective stress, choice of stress state, capillary phenomenon, and so on. The limitations and application scope of the effective stress in unsaturated soils are also addressed.

A series of experiments were performed to investigate the hydraulic and $${\kappa }_k(S_r)=b_k{\left(\frac{1-S_r}{S_r-S_r^{\text{irr}}}\right)}^{1/d_k},\hspace{0.17em}R=\text{DR},\hspace{0.17em}\text{WT}$$mechanical behavior of an unsaturated silt obtained from the Yellow River Delta. To identify the key factors that influence the soil-water characteristics (SWC), an experimental program was designed to study the SWC of the soil at different void ratios and vertical pressures. It was shown that an that that apparent hysteresis phenomenon occurred on the SWC curves when the soil experienced drying/wetting cycles. It was also shown that the influence of void ratio on the SWC was significant, and the stress state influenced the SWC only through changing the void ratio. Isotropic compression tests were conducted at different constant matric suctions, using a suction-controlled double cell triaxial apparatus. The soil under shearing showed apparent dilatant and softening behavior, in a way similar to medium to dense sand. In addition, the hardening effect of matric suction was significant, and both the stiffness and peak strength of the soil increased with matric suction. Based on the experimental observations, an elastoplastic constitutive model coupling capillary hysteresis and plastic deformation was developed, in which a hysteretic SWC relationship was introduced to characterize the influence of hydraulic history on the skeletal deformation. To better simulate the volumetric change of the soil, a nonassociated flow rule was adopted. The effect of the plastic volumetric strain on water-retention behavior was also taken into consideration. The proposed model was used to simulate the behavior of unsaturated silt under constant-suction, isotropic compression and constant-suction, triaxial shearing conditions, showing the capability of the new model in describing the behavior of unsaturated silt.

Soil compaction is a process used in different engineering works; from the most complex to the simplest, the quality of soil compaction indiscriminately affects the final condition of the compacted soil in terms of engineering projects. Moreover, aspects such as time of construction and cost are extremely important in works that require compacted soils, particularly because of the climate in tropical regions. In these regions, the abundance of residual soils makes this material a preferential candidate for use in engineering projects. Considering that most compacted soils will remain in an unsaturated condition, it is extremely important to study and to characterize these materials, not only in the saturated condition, but also in an unsaturated state. Within this context, this study analyzes the shear strength behavior of a compacted residual soil of gneiss, collected in two sampling campaigns from an area located at the experimental site of the University of São Paulo in São Paulo, Brazil. The focus lies in determining the surface failure envelope for this soil by conducting several triaxial compression tests under saturated and unsaturated conditions. The interpretation of the results is discussed based on the use of the data obtained with the specimen in a saturated state. Thirty-six triaxial tests were performed, 18 of them with direct suction measurement using a high-capacity tensiometer (HCT). Results demonstrated the advantages of the constant water content tests (CWs) with the use of a HCT, such as their simplicity and reduced testing time for obtaining the surface failure envelope.

This paper describes the construction and testing of six 1-m-high model embankments constructed at three different gravimetric water content (GWC) values to study their performance and to validate a set of moisture reduction factors (MRFs) introduced by the authors in their recent studies. The earlier MRF values were obtained from a series of pullout and interface shear tests on the same soil and reinforcement materials. The MRF in this study is defined as the ratio of soil-reinforcement interface shear strength at an increased GWC value [e.g., optimum moisture content (OMC) + 2%] to the shear strength at OMC − 2% representing construction conditions. Therefore, MRF values can be used to account for an anticipated reduction in the shear strength of the soil-geotextile reinforcement interface caused by wetting in the stability analysis and design of reinforced soil structures constructed with marginal soils. The embankment models were built using a lean clay (CL) at the GWC values ranging between OMC − 2% and OMC + 2%, which included a single-reinforcement layer near the top of the embankment. This provided a horizontal soil-reinforcement interface subjected to shear sliding of an overriding block of soil caused by surcharge loading of the embankment. Two different woven polypropylene geotextile products were used to build the six model embankments. Each model was instrumented with a total of 67 sensors to measure the soil GWC, matric suction and excess pore pressure, reinforcement strains, earth pressure, and deformations of the embankment model and the test box during the test. Results from the embankment tests in this study indicate that the change in the matric suction and GWC could have a significant influence on the soil-geotextile reinforcement interface strength. Wetting of the soil and the soil-geotextile interface during construction or service life of reinforced soil slopes could considerably reduce their shear strength, resulting in lower factors of safety for their stability. The results of the study showed that within the range of GWC values examined (i.e., OMC ± 2%), the embankment model constructed at OMC − 2% yielded the greatest shear strength and stability when subjected to a strip footing load. The MRF values for the model embankments constructed at OMC + 2% were found to be as low as 0.74–0.79 for models that were reinforced with different woven geotextiles of comparable apparent opening size (AOS) but different ultimate strength values. The MRF results presented in this study, although obtained from soils with different as-compacted GWC values, indicate that the loss of soil-reinforcement interface shear capacity as a result of wetting in reinforced soil structures involving marginal fills could be significant and deserve proper attention in the design of these systems.

Geomaterials with aggregated structure or containing fissures often exhibit a bimodal pore size distribution that can be viewed as two coexisting pore regions of different scales. The double-porosity concept enables continuum modeling of such materials by considering two interacting pore scales satisfying relevant conservation laws. This paper develops a thermodynamically consistent framework for hydromechanical modeling of unsaturated flow in double-porosity media. With an explicit treatment of the two pore scales, conservation laws are formulated incorporating an effective stress tensor that is energy-conjugate to the rate of deformation tensor of the solid matrix. A constitutive framework is developed on the basis of energy-conjugate pairs identified in the first law of thermodynamics, which is then incorporated into a three-field mixed finite-element formulation for double-porosity media. Numerical simulations of laboratory- and field-scale problems are presented to demonstrate the impact of double porosity on the resulting hydromechanical responses.

With a suction stress–based effective stress representation, stability analysis of unsaturated engineered and natural slopes can be performed effectively in the same manner as the classical limit-equilibrium (LE) methodologies. This paper presents an analytical framework for effective stress LE analysis of unsaturated homogeneous slopes under steady one-directional (vertical) flow. The proposed log spiral failure surface–based LE method involves only two additional hydromechanical parameters for unsaturated soil, approximating the inverse of the air-entry pressure and pore-size distribution. Both parameters are used to describe seepage and effective stress variations in unsaturated soils. Unlike most other LE formulations, the method is statically determinate. A parametric study was performed, and stability charts for general use are presented. The impact of infiltration and evaporation on the stability of slopes for four hypothetical soil types was studied. It is shown that the apparent cohesion due to suction stress may contribute substantially to the stability of slopes. Specifically, different seepage rates can significantly impact the stability of clayey slopes. This impact progressively decreases in silty slopes and further diminishes in loess and sand. Because the proposed method is statically free of assumptions, it can serve as a benchmark for rigorous slope stability methods that can deal with more complex problems.

This study presents the results of one of the first attempts to characterize the pore water pressure response of soils subjected to dynamic loading under saturated and unsaturated conditions. The resilient modulus, which captures the soil stiffness under dynamic loading, is a critical parameter for pavement design. It has been recognized that the development of pore water pressure contributes to modulus degradation. Several efforts have been directed to model the effect of air and water pore pressures upon the modulus. However, none of them considered dynamic changes in pressures but rather were based on equilibrium values corresponding to either initial or final conditions. A testing program was conducted to characterize the pore water pressure response of a clayey sand subjected to dynamic loading. Using the results, models capable of predicting the cumulative excess pore pressure under both saturated and unsaturated conditions were proposed. Findings regarding the influence of the controlled variables challenge common beliefs. Upon further research, the proposed models may become a powerful tool not only to overcome unsaturated soil testing limitations, but also to prevent soil failure as a result of excessive pore water pressure development.

The mechanical behavior of a sandy clay soil was investigated by a series of constant water content triaxial tests on unsaturated samples with suction measurements. The tests were carried out in double-cell triaxial cells on compacted samples and also on samples wetted and dried from the as-compacted conditions. A series of tests on saturated samples was also performed to provide a reference state for the unsaturated tests. Because the specimens were at high degrees of saturation (generally >80%), calculations based on effective stress showed a reasonable interpretation of the data for the critical state parameters M and λ. However, the intercept of the critical state line in the ν-axis ($\Gamma$) differed and increased with an increase in water content (at compaction). The data were also analyzed using the Bishop stress ($p*$) approach, and a better fitting was achieved in the stress plane, where it was possible to define a unique critical state line, where M was 0.91. However, in the $\nu \text{-}p*$ plane, different critical state lines were still obtained for different compaction water contents. The mechanical behavior of the sandy clay soil was found to be governed by the initial conditions, the as-compacted conditions. Although the critical state stress ratio, M, itself was not affected by the initial water content, the differences in volumetric behavior led to differences for samples subjected to wetting and drying after compaction. Samples that were dried back to a particular water content had a higher strength than samples compacted at that water content; in contrast, a sample wetted to achieve that water content had a lower strength.

The principle of effective stress states that the strength and volume change behaviors of soil are governed by intergranular forces expressed in terms of a continuum quantity called effective stress. Although the principle of effective stress is regarded as one of the most fundamental concepts in soil mechanics, its applicability to unsaturated soil has been questioned. The central issue is whether a measure can be developed for three-phase soils that plays an equivalent role as the effective stress does for two-phase soils. Combining the techniques of microstructural analysis and image processing, this study formulated the effective stress for unsaturated granular soils. A novel suction-controlled experimental setup was integrated with an X-ray computed tomography (CT) scanning system and used to image and model microstructural features. A tensorial quantity, called the fabric tensor of the liquid phase, that characterized the complex fabric resulting from saturated pockets and networks of liquid bridges was identified and introduced in the proposed formulation. The trend in the variation of the fabric tensor of the liquid phase as a function of suction (or saturation) was captured for both the wetting and drying paths of the partial saturation. It was observed that the fabric tensor of the liquid phase had an intrinsic association with the evolution of the effective stress tensor. It is concluded that, for unsaturated granular soils, consideration of the fabric tensor of the liquid phase is imperative in effective stress formulations.

The small-strain shear modulus G_max is a key material parameter in modeling the behavior of soils subjected to dynamic loading. Recent experimental results indicate that seasonal weather interaction with near-surface soils causes G_max to change by up to an order of magnitude in some climates, with a hysteretic response upon drying and wetting. The increase in G_max during drying and the stiffer response during subsequent wetting have been postulated to be due to plastic hardening during drying. To further understand this behavior, a series of isotropic compression tests were performed on compacted silt specimens at different values of matric suction to evaluate changes in the preconsolidation stress with suction. The G_max values obtained previously on this silt matched well with a model using a hardening parameter independently derived from the isotropic compression tests, as well as the parameters of the soil water retention curve (SWRC). The model showed an increase in G_max during drying from an initially saturated condition that was directly related to the increase in preconsolidation stress with suction, and the trends in G_max followed transitions in the shape of the SWRC. The hardening parameter from these tests was also suitable for modeling the greater values of G_max encountered during rewetting of the soil. The role of the preconsolidation stress in the model confirmed that changes in G_max correspond to elastoplastic hardening mechanisms during drying rather than solely to changes in matric suction.

A soil-structure interface is defined as the contact surface between a soil and a structure through which stresses are transferred from the soil to the structure or vice versa. The ultimate shear strength at the interface is one of the key parameters required for the design and safety assessment of a structure in the soil, such as pile foundations, retaining walls, buried pipelines, and soil nails. In this paper, the shearing behavior of completely decomposed granite soil and steel interfaces is examined using a modified suction-controlled direct shear apparatus. A series of direct shear tests was performed on two different types of soil-steel interfaces under different stress state variables. The experimental results were used to investigate the influence of counterface roughness on the failure envelopes of soil-steel interfaces. Test results show that matric suction has a significant influence on the shear behavior and shear strength of the interfaces. It has been observed that the critical interface shear strength for a specific counterface roughness and net normal stress (NNS) depends on the applied matric suction. Also, both the peak and the postpeak shear stresses are greatly influenced by variation in NNS. Furthermore, the experimental shear strength data are compared with an analytical model that considers the influence of suction and dilation on an apparent interface friction angle. It is noted that, for the applied NNS and matric suction, the analytical model works well for both rough interfaces.

Experimental and numerical modeling studies related to the behavior of pile foundations are conventionally undertaken based on the assumption that the surrounding soils are in a state of saturated condition. Such an assumption may contribute to erroneous estimations of the stability and settlement behavior of pile foundations installed in unsaturated soils due to neglecting the influence of soil suction. In this paper, the behavior of a single friction pile loaded in drained and undrained conditions in a compacted glacial till is modeled using finite-element analyses (FEAs). The influence of the soil suction on (1) the shear strength and the modulus of elasticity of the soil and (2) the shear strength of the pile-soil interface derived from the experimental studies is discussed and considered in the FEA. There is reasonable agreement between the load-settlement behavior and the bearing capacity of the friction pile modeled using the FEA and the measured results from experimental studies. This study highlights the significant influence of the soil suction on the behavior of single friction pile and suggests a relatively simple approach to reasonably model the pile behavior using the FEA.

The critical-state behavior of an unsaturated dilative specimen under low confining pressure from 0 to 50 kPa was examined by conducting a constant water content–compression (CWCC) test on unsaturated compacted silty soil. Trends in the compressive strength and deformation of specimens were measured from each testing condition. The experimental results were analyzed by assuming that the effective confining stress can be calculated through the use of suction stress, which is defined as the product of the effective degree of saturation and the matric suction. It was found that the postpeak shear-strength states are arranged on the critical-state line for saturated conditions by considering the suction stress as a stress component in the (p_net + p_s, q) plane. The state boundary surface was observed in the relationship between the stress ratio [q/(p_net + p_s)], considering the suction stress, and referential specific volume (${\nu }_{\lambda }$). It can be concluded, therefore, that the existence of a critical state for an unsaturated dilative specimen under low confining pressure is verified through these results.

Desiccation of soil is the gradual process of moisture loss from a fully or partially saturated condition to a dry state. If the soil is constrained against shrinkage during desiccation, it will begin to crack when tensile stresses in the soil exceed the tensile strength. Fundamental to understanding desiccation crack development in clayey soils is the accurate determination of the tensile strength during desiccation. Although numerous published studies have focused on soil desiccation and soil tensile strength, very little has been focused on experimental determination of tensile strength during desiccation. This paper presents the first generation of a novel apparatus designed to determine tensile strength during desiccation. During drying the tensile forces in a thin compacted soil layer are measured while simultaneously monitoring moisture content changes and crack formation via time-lapse photography. Results are presented from desiccation tests performed on two clayey compacted soils of medium to high plasticity. Soil water characteristic curves (SWCCs) were determined to relate the tensile strength to suction. The results demonstrate that the tensile strength of compacted soil is influenced by initial water content, suction, dry unit weight, soil pore structure, and soil type. Measured tensile strengths compare favorably with results of a theoretical model that considers microstructural and macrostructural aspects of unsaturated compacted clayey soil.

Experimental results from a comprehensive series of suction-controlled, consolidated drained (CD) triaxial tests, conducted on statically compacted specimens of unsaturated silty sand, are presented. The experimental program was accomplished in a newly implemented, fully automated double-walled triaxial test system via the axis-translation technique. Results were thoroughly analyzed to gain critical insight into some of the essential elastoplastic features of compacted intermediate geomaterials under controlled suction states, including the effect of suction on yield stress, apparent cohesion, tensile strength, and critical state line, as well as postpeak softening and strain-induced dilatancy under suction-controlled monotonic shearing. Constitutive parameters postulated by the Barcelona basic model (BBM) were then experimentally calibrated and used for prediction of compacted silty sand response at matric suction states that varied from 50 to 750 kPa. Predicted values of deviatoric stress at critical state are reasonably close to those experimentally assessed from suction-controlled conventional triaxial compression tests; however, given the distinct brittle and dilatant nature of the test soil, its postpeak softening behavior was not adequately captured by the BBM framework. The results therefore are primarily valuable to unsaturated soil constitutive modelers in validating more suitable frameworks for compacted intermediate geomaterials, including bounding surface plasticity models, when subjected to suction-controlled monotonic shearing.

Measuring wave velocities of soils is a common methodology of determining the small-strain stiffness of soils. Both confining pressure and degree of saturation affect the magnitude of the wave velocities and hence the stiffness of the soil. However, confining pressure and degree of saturation affect P- and S-wave velocities of the soil differently. At full saturation, increases in effective confining pressure (σ′₃) increase S-wave velocity, but P-wave velocity remains fairly constant. As the soil desaturates, the effects of net confining pressure (σ₃ – u_a) and matric suction (u_a – u_w) were observed to be different from the effect of effective confining pressure. This difference in response was investigated, and the results are reported here. Degree of saturation has been commonly associated with the Skempton’s pore-water pressure parameter B under an isotropic state of stress. However, some soils have a B-value less than 0.9 even at full saturation. In such cases, the P-wave velocity may be a better indication of full saturation because P-wave velocity increases rapidly from 90 to 100% degree of saturation. The objectives of this study were to investigate (1) the effect of matric suction on P- and S-wave velocities of soil and (2) the relationship between degree of saturation, B-value, and P-wave velocity. Experiments were conducted on sand using a triaxial cell modified to include bender elements and a high-air-entry disk for the testing of unsaturated soils. The P- and S-wave velocities and B-values at various net confining pressures and matric suctions were measured. The relationship between P-wave velocity and degree of saturation was found to be dependent on the saturation path (drying or wetting). The intensities of the high-frequency components (more than 20 kHz) greatly increased in the P-wave signals when the specimen approached full saturation. This observation shows that P-wave velocity and the intensity of its frequency components could be a better indicator of full saturation compared to Skempton’s pore-water pressure parameter B. The P-wave velocity decreased rapidly when the matric suction exceeded the air-entry value. Test results show that P-wave velocity was not affected by changes in effective confining pressure or net confining pressure. The changes in S-wave velocity resulting from an increase in matric suction were not proportional to the changes resulting from an equal increase in net confining pressure. Changes in S-wave velocity resulting from changes in matric suction were generally less consistent and varied from soil to soil.

The prediction of actual evaporation (AE) is required when calculating the net moisture flux from the ground surface to the atmosphere. The proposed Wilson-Penman equation appeared to yield reasonable predictions of AE from saturated clayey soils but overpredicted AE from coarse-grained soils in arid regions. In recent years, two distinct approaches have emerged for the prediction of AE from unsaturated soil surfaces. Both approaches are based on the realization that evaporation tends to “shut off” as the natural water content approaches residual water content conditions. The first approach to calculate AE from an unsaturated soil involves the adjustment of the total suction at the ground surface. The second approach to calculate AE involves the determination of the “evaporation-rate reduction point” from the drying soil-water characteristic curve. A vapor pressure reduction factor is then applied to calculate AE. Both approaches are attempts to take the effects of “surface resistance” into consideration. The paper presents the results of a comparative study in which both approaches are used to calculate AE from drying sand column tests. These results provide the geotechnical engineer with improved computational procedures for the calculation of AE from a wide range of soil types.

This work presents a fully coupled formulation developed to handle engineering problems in unsaturated (and saturated) soils that present two dominant void levels. The proposed framework assumes the presence of two porous media linked through a mass-transfer term between them. In its more general form, the proposed approach allows the consideration of nonisothermal multiphase flow coupled with the mechanical problem. The double-porosity formulation was implemented in a finite-element code and has been used to analyze a variety of engineering problems. The approach is especially suitable for cases in which the material exhibits a strong coupling between the mechanical and the hydraulic problems in both media, such as with swelling clays. For those types of problems, the proposed formulation is used in conjunction with the mechanical double-structure model already proposed by the authors. This paper presents the coupled formulation and the application of the proposed approach to problems involving expansive unsaturated clays. Very satisfactory results were obtained in these analyses.

The combined finite–discrete-element method (FDEM) is an advanced and relatively new numerical modeling technique that combines the features of the FEM with those of the discrete-element method. It simulates the transition of brittle geomaterials from continua to discontinua through fracture growth, coalescence, and propagation. With FDEM, it is possible to simulate landslides from triggering to runout and carry out landslide scenario analyses, the results of which can be successively adopted for cost-effective early warning systems. The purpose of this paper is to describe the results of the FDEM simulations of the triggering mechanism and the evolution scenarios of the Torgiovannetto di Assisi rockslide (central Italy), a depleted limestone quarry face where a rock wedge with an approximate volume of 182,000 m³ lies in limit equilibrium conditions, posing relevant issues in terms of civil protection. The results obtained demonstrate that the FDEM is able to realistically simulate the different phases of such a complex slope’s failure as well as to estimate both its runout distances and velocity, key features for landslide risk assessment, and management.

In this study, numerical simulation of rock blocks with nonpersistent open joints under uniaxial compression was undertaken using the particle flow modeling method. First, the micromechanical parameter values of intact material were calibrated through a trial-and-error process using macromechanical laboratory test results. Then, a back-analysis procedure was used to calibrate the joint gap and joint micromechanical parameter values using laboratory test results conducted on jointed rock blocks. Afterward, the effects of joint dip angle, joint persistency, and joint gap on the mechanical behavior of block models having nonpersistent open joints was investigated using the calibrated micromechanical parameter values. The joint dip angle and joint persistency were found to play significant roles in the failure mode, strength, and stress–strain relationship of jointed blocks. The joint gap played a significant to negligible role in the mechanical behavior of jointed block models gradually when the joint dip angle was increased from 0 to 90°. The contact and interaction of joint surfaces were found to have a significant influence on the mechanical behavior of jointed blocks.

The simplified shear-wave velocity (V_s)–based procedure of liquefaction potential assessment was basically developed for terrigenous deposits, whereas its applicability for calcareous soils is not fully recognized. The present study used the seismological and geotechnical data of Kawaihae Harbor, the most strategic port of Hawaii, to evaluate conservatism of the currently used simplified procedure for this case history. During the Kiholo Bay 2006 earthquake, the port experienced extensive liquefaction and subsequent ground failure in the dredged fill and natural calcareous deposits. Using the V_s profiles of the subsoil in Kawaihae Harbor, the simplified procedure and the Monte Carlo simulation (MCS) technique were used to evaluate liquefaction potential of the site through deterministic and probabilistic frameworks. The results obtained from the deterministic and the site-specific probabilistic approaches indicate extents of liquefaction occurrence in the shallow depths between 3.5 and 6.5 m. In contrast, probabilistic analysis with the available liquefaction probability--factor of safety (P_L-FS) correlations resulted in an unconservative prediction, with the liquefied depth ranging between 5.6 and 6.1 m. Results of this study confirm that the current simplified procedure with either deterministic or site-specific probabilistic frameworks obtained reliable estimation of liquefaction occurrence in the studied site. However, further case histories of liquefaction occurrence in calcareous deposits are required to clarify applicability of the simplified procedure for such materials. Based on the results of the current study, there is still potential for liquefaction occurrence in the studied site during future earthquakes.

Rotational hardening is the constitutive ingredient of clay plasticity models that allows rotation of the yield surface in stress space to simulate, more realistically than isotropic models, the stress-strain response under different loading conditions. Based on well-known rotational hardening rules and extensive experimental results, a new unified expression of rotational hardening is proposed in this work, in which the parameters of the unified expression can be determined directly. The proposed rotational hardening expression was imported into a clay model and adopted to simulate the stress-strain behavior of different clays. The simulated results and the experimental results were compared to analyze the influence of the equilibrium values on the stress-strain behaviors. The comparisons show that the constitutive model with the proposed rotational hardening rule had good predictive capability for triaxial tests under different loading paths.

Unlike that adopted in most existing compression models, the complete compression curve of reconstituted clays in the e − lnp′ space is S shaped. In this paper, an accurate S-shaped equation is proposed that is suitable for describing the complete compression behavior of reconstituted clays with p′ ≥ 0.01 kPa. The proposed equation is an elementary function and is ready for implementation into general stress and strain models. The proposed compression equation is validated by simulating the compression behavior of a variety of reconstituted clays.

Structural support in soft rock can be very difficult in deep mining. Shaft sinking is typically a critical phase of the project. An analytical method called the convergence-confinement method (CCM), often applied in tunnels, can be used to calculate both the radial displacements associated with the construction of the shafts and the equivalent loads that the planned shaft support must guarantee. Also, the CCM can be used to calculate the plastic zone. A relationship between the stress acting on a shaft lining and the most important parameters governing the behavior of the rock (cohesion, friction angle, and elastic modulus) and the geometric parameters of the shaft (depth, radius, and lining thickness) has been obtained. The Mohr-Coulomb model was used to represent shear failure in weak rocks, considering ductile behavior (ideal strength criterion). The equations found in this paper allow for the quick estimation of the stress acting on the lining extrados.