International Journal of Geomechanics

This study explored the thermal cracking resistance of hot-mix asphalt (HMA) mixes containing recycled asphalt pavement (RAP). One RAP source was used to design two types of Superpave mixes, namely, Oklahoma S3 base and Oklahoma S4 surface course. Four mixes containing different percentages of RAP, namely, 25 and 40% RAP for S3 base courses and 0 and 10% RAP for S4 surface courses, were designed and tested. It was found that at lower temperatures, the mix containing a lower RAP content was stiffer, as indicated by higher creep compliance and indirect tensile strength values. At higher temperatures, however, the mix containing a higher content of RAP was also stiffer. Furthermore, the measured creep compliance values were compared with current predicted compliance values. The influence of RAP content on thermal cracking resistance was also evaluated through thermal stress analysis within the mechanistic framework.

The stress–dilatancy relationship is a key point to capture the evolution of both strains and excess pore pressure during an undrained creep of natural soft clay. This paper focuses on investigating the stress dilatancy of natural soft clay during an undrained creep. Undrained triaxial creep tests are performed on $K_0$-consolidated and isotropically consolidated samples of a typical Chinese soft marine clay with different stress levels. A unique stress–dilatancy curve is obtained from all test results. Several typical stress–dilatancy relations for soils are discussed, comparing them with experimental results. A common modification method for the stress dilatancy of sand is adopted and discussed for clay. All comparisons demonstrate that modified dilatancy equations can describe the stress–dilatancy relationship during an undrained creep. The modified dilatancy equation with the inclination of a potential surface seems to better describe the whole trend, and is suitable for natural soft clay.

Two recently proposed anisotropic rate-dependent models are used to simulate the consolidation behavior of two soft natural clays: Murro clay and Haarajoki clay. The rate-dependent constitutive models include the EVP-SCLAY1 model and the anisotropic creep model (ACM). The two models are identical in the way the initial anisotropy and the evolution of anisotropy are simulated, but differ in the way the rate effects are taken into consideration. The models are compared first at the element level against laboratory data and then at the boundary value level against measured field data from instrumented embankments on Murro and Haarajoki clays. The numerical simulations suggest that at the element level, the EVP-SCLAY1 model is able to give a better representation of the clay response under oedometric loading than ACM, when the input parameters are defined objectively. However, at the boundary value level, the issue is not as straightforward, and the appropriateness of the constitutive model may depend heavily on the in situ overconsolidation ratio (OCR).

The time-dependent settlement of soft soils following the application of surface loading may be modeled using elastic viscoplastic constitutive models to describe the soil behavior. For applied loadings that increase the stresses toward and beyond the in situ yield stress, the predicted behavior is strongly influenced by the associated breakdown of the clay structure and the way in which this is modeled. Four elastic viscoplastic models are compared and it is shown that, despite presentational differences, all calculate creep rate in fundamentally the same manner. This paper describes some predictions for a hypothetical case prediction exercise organized recently by the Norwegian Geotechnical Institute that compared different calculation methods used in settlement analyses of soft soil. The results presented here are from a one-dimensional coupled consolidation analysis implemented in a spreadsheet-based software and using a finite-element program. Parameters were obtained from an oedometer test, and the results were extrapolated over the full soil profile. Various plausible assumptions about the shape of the isotaches around yield were explored, and it is shown that the predicted long-term settlement may vary by a factor of two or more, depending on the assumptions made.

A cyclic elastoviscoplastic constitutive model for clayey soils is proposed based on the nonlinear kinematic hardening rules and considering the structural degradation. The performance of the model is verified through the undrained triaxial test simulation of soft clay samples under cyclic and monotonic loading conditions and the cyclic compression test. The simulated results are compared with the experimental data through stress-strain relations and stress paths. The simulated results have shown a good agreement with the experimental data, which indicates the capability of the proposed model to reproduce the cyclic behavior of soft clayey soils.

A practical use of the isotache concept in creep settlement prediction is newly introduced in this study. The isotache concept introduces a unique relationship between the strain and the consolidation pressure corresponding to the strain rate in association with viscosity. The authors have proposed a method to simply introduce the isotache concept, which uses a compression curve normalized by preconsolidation pressure $\left[\epsilon –\log \left({\sigma }^{\prime }/{\sigma }_p^{\prime }\right)\right]$ and a strain rate dependency relationship between the preconsolidation pressure (${\sigma }_p^{\prime }$) and strain rate ($\dot{\epsilon }=d\epsilon /\mathit{dt}$). The strain rate dependency relationship is modeled as an equation based on power law. According to the authors’ method, the slope of the strain rate dependency relationship ($\log {\sigma }_p^{\prime }–\log \dot{\epsilon }$), which coincides with $C_{\alpha e}/C_c$, can be calculated as a function of strain rate, showing that $C_{\alpha e}/C_c$ is not constant but decreases with decreasing strain rate. In engineering practice, consolidation settlement is generally estimated based on the compression curve obtained from the 24-h incremental loading oedometer test, which corresponds to a strain rate of about $1\times {10}^{-7}\hspace{0.17em}{\text{s}}^{-1}$. Using the compression index $C_c$ at the consolidation pressure and initial void ratio $e_0$, creep settlement can be easily calculated as a function of $C_c/\left(1+e_0\right)$ and in situ strain rate (several orders of magnitude smaller than $1\times {10}^{-7}\hspace{0.17em}{\text{s}}^{-1}$).

In this paper, a number of fundamental concepts are presented and explained. These include (1) differences among an instant compression line, a normal consolidation line, and a true instant compression line; (2) the uniqueness of viscoplastic strain rates with a stress–strain state; (3) whether the creep compression is smaller than the instant compression; (4) the separation of the total strain rates; (5) the relation between elastic–plastic models and elastic viscoplastic (EVP) models, etc. The major conclusions are the following: (1) the elastic compression is the true instant compression; (2) the magnitude of a creep-strain rate at a stress–strain state point is unique, independent of the loading path to reach this point; (3) the true instant (elastic) compression is much smaller than the creep compression; (4) it is more appropriate that strain rates of geomaterials are composed of elastic strain rates and viscoplastic strain rates; (5) the one-dimensional (1D) EVP (1D EVP) is a genuine extension of Maxwell’s linear rheological model for considering the nonlinear behavior of soils; (6) the EVP model is more general than an elastic–plastic model; (7) the nonlinear functions proposed by the author are good for fitting the creep compression and the compression under high stress of most soft soils in 1D straining; and (8) the three-dimensional EVP model is rigorously derived using the 1D EVP model approach and the modified Cam–Clay model, but further improvements of this model are still needed. At the end, a number of areas are presented for further study.

This paper focuses on nonlinear creep behavior with a consecutively decreasing creep coefficient $C_{\alpha e}$ fully related to the soil density. Conventional oedometer tests on reconstituted samples of several natural soft clays are selected to clarify the evolution of creep coefficient throughout testing. On this basis, a simple nonlinear creep formulation is proposed accounting for the effect of volumetric packing of soil assemblies. The formulation is then incorporated into a newly developed elastic-viscoplastic model to take into account the nonlinear creep of natural soft clays. One additional parameter is added that can be determined in a straightforward way from an oedometer test without additional experimental cost. The enhanced nonlinear creep model is examined by simulating a conventional oedometer test on reconstituted Haarajoki clay. The improvement of predictions by the nonlinear creep formulation is highlighted by comparing predictions with constant $C_{\alpha e}$. The enhanced model is further applied to Murro test embankment. The influence of consideration of nonlinear creep on the embankment behavior is discussed.

The soil-water retention curve (SWRC) is the relationship between the suction values and water content of the soil. This curve has one or more branches depending on the suction imposition paths, and represents one of the most important properties of unsaturated soils. In this paper, by using a percolation approach and introducing a trial-and-error process, a randomly distributed pore network model is first calibrated using experimental data corresponding to the main drying branch of the SWRC. The influence of the stress state on the pore-size distribution of the network is further studied. The calibrated network model is used to predict the main wetting and scanning branches of the SWRC. Piston-type and cooperative fillings are used as the two wetting mechanisms. The proposed method facilitates modeling pore networks with large numbers of pores covering a wide range of suction values (full saturation through the residual degree of saturation). The results indicate that with an increase in the applied stress, micropores and macropores are affected. However, it is the change in the macropores that strongly influences the SWRC. Also, it is possible to predict the wetting and scanning branches of the SWRC with reasonable accuracy once the model is calibrated when using the main drying curve.

In this work, the swelling behavior of sodium (Na)-montmorillonite clay with increasing amounts of hydration is studied using molecular dynamics. The molecular models of the dry clay and the hydrated clays, consisting of 2, 4, 6, 8, and 10 monolayers of water in the interlayer, are used in this study. This work captures the evolution of interaction energies in the interlayer of Na-montmorillonite swelling clay with increasing hydration and provides insight into swelling mechanisms. This work shows the important role of bound water and clay-Na interactions during swelling to stabilize clay structure during hydration. Changes to water molecule conformations in the interlayer during swelling are also reported. The results and insight provided by this work will help in modeling and predicting exfoliation and resulting particle breakdown in swelling clays, in addition to expounding the key role of interlayer interactions on swelling in smectite clays.

Geosynthetic reinforced piled embankment systems (GRPESs) have proven to be an effective and economical technique to address the problems posed during the construction of embankments on soft soils. In this paper, the predictions of the performance of GRPESs from three modeling approaches [axisymmetric, three-dimensional (3D) column, and full 3D models] were compared. The numerical models in this study were calibrated against the measured data of GRPESs from a full-scale field test. The load distribution between different components of the GRPES and the tensile force developed in the geosynthetic reinforcement were compared with the results obtained using various design methods and other analytical results. Further, the numerical investigation was extended to examine the tensile force developed among the layers of a multilayer GRPES, and the results were compared with the empirical solutions.

A series of large-scale triaxial compression tests on Tacheng rockfill material (TRM) showed that the dilatancy and stress-strain behaviors were significantly influenced by density and pressure. The critical state friction angle of TRM decreased with an increase in the initial confining pressure. In addition, the critical state line of this material in the $e\text{-}\log p^{\prime }$ plane ascended with an increase in the initial void ratio. On the basis of the specific critical state behaviors of TRM, a state-dependent constitutive model was slightly adapted in the triaxial stress space. The model, with only a set of model parameters, could capture the state-dependent behaviors of the dilatancy, stress-strain, and mobilized friction angle of TRM at various densities and pressures. The peak friction angle of TRM was found to be linear, with a coefficient of 0.21, in relation to the maximum dilatancy angle. The coefficient for rockfill materials was smaller than that for sands, indicating that the influence of dilatancy on the strength for sands was more pronounced than that for rockfill materials.

In this paper, the flow of an incompressible fluid in a deformable porous solid is considered. A mathematical model using the framework offered by the theory of interacting continua is presented. In its most general form, this framework provides a mechanism for capturing multiphase flow, deformation, chemical reactions, and thermal processes, as well as interactions between the various physics, in a conveniently implemented fashion. To simplify the presentation of the framework, the results are presented for a particular model, which can be seen as an extension of Darcy’s equation (which assumes that the porous solid is rigid) and that takes into account the elastic deformation of the porous solid. The model also considers the effect of deformation on porosity. It is shown that by using this model identical results can be recovered as in the framework proposed in the literature. Some salient features of the framework are as follows: (1) it is a consistent mixture theory model, and adheres to the laws and principles of continuum thermodynamics; (2) the model is capable of simulating various important phenomena, such as consolidation and surface subsidence; and (3) the model is amenable to several extensions. Numerical coupling algorithms used to obtain a coupled flow-deformation response are also presented. Several representative numerical examples are presented to illustrate the capability of the mathematical model and the performance of the computational framework.

In a drained underwater cavity, seepage forces and pore-water pressure that develop around the cavity may affect the response of the rock mass. In this paper, a fully analytical solution is proposed for analysis of underwater cavities excavated in elastic–brittle–plastic and Mohr-Coulomb rock material, considering the induced seepage forces under steady-state flow. The initial stress state is assumed to be hydrostatic, and the seepage flow is assumed to be radial; thus, the problem is considered axisymmetric. In the proposed solution, in contrast to the failure processes that are represented as a function of Terzaghi’s effective stresses, the induced deformations are considered as a function of Biot’s effective stresses. The proposed solution is used to explain the behavior of cavities under different hydromechanical conditions. The results show that, in the case of drained cavities, seepage flow causes the induced radial displacements to increase and the stability of the cavity to decrease. From a practical point of view, the simplified analytical solution presented in this study can be used to approximate the design of circular cavities, such as a tunnel excavated below a water table, under seepage forces.

This paper studies the effect of certain parameters closely related to the design of column foundations such as the improvement area ratio, especially at low values, e.g., 1 and 4%, and the grain size of the column material (Hostun sand and Hostun gravel) for both strength and rigidity characteristics such as the undrained Young’s modulus and shear strength. Then, the lateral expansion of a cavity in a hollow specimen made up of preconsolidated kaolin clay followed by the installation of the granular material in the cavity is investigated. The purpose of this work is to study the effect of the installation procedure of the column on the behavior of reinforced clayey soil. A comparison between the experimental results and existing analytical ones is presented and discussed.

This paper presents the results of an experimental study on the effect of suction and compaction pressure on the elastic and plastic parameters of unsaturated silty soil. The experimental tests were performed in a specially designed double-walled Bishop and Wesley triaxial cell on dense and loose samples of an unsaturated silty soil. In the experiments, each soil sample was consolidated isotropically to a virgin state, followed by unloading under constant suction. Furthermore, some experiments were undertaken with constant net stress and varying suction. The results were used to study the effect of suction and soil fabric on the elastic and plastic parameters of soil. It was concluded from the experimental results that the plastic parameters are generally dependent on suction and soil fabric (except for suction change tests). The elastic parameters related to the variation of specific volume are independent of suction and the fabric of the soil. The elastic parameters related to the variation of specific water volume are dependent not only on suction but also on the fabric of the soil.

Geocells are three-dimensional expandable panels with a wide range of applications in geotechnical engineering. A geocell is made up of many internally connected single cells. The current study discusses the joint strength and the wall deformation characteristics of a single cell when it is subjected to uniaxial compression. The study helps to understand the causes for the failure of the single cell in a cellular confinement system. Experimental studies were conducted on single cells with cell pockets filled up with three different infill materials, namely silty clay, sand, and the aggregates. The results of the experimental study revealed that the deformation of the geocell wall decreases with the increase in the friction angle of the infill material. Experimental results were also validated using numerical simulations carried out using Lagrangian analysis software. The experiment and the numerical results were found to be in good agreement with each other. A simple analytical model based on the theory of thin cylinders is also proposed to calculate the accumulated strain of the geocell wall. This model operates under a simple elastic solution framework. The proposed model slightly overestimates the strains as compared with experimental and numerical values.

The dilatancy of a soil is significantly influenced by matric suction, and it affects the apparent friction angle and shear strength of the soil. To examine the influence of dilatancy on interface behavior, a series of direct shear box tests are conducted on a compacted completely decomposed granite (CDG) soil–grout interface in a cast in situ condition under different matric suctions and net normal stresses. The test results indicate that matric suction and net normal stress have significant influence on the hardening-softening and dilatancy of the soil–cement grout interface. The failure envelopes for different matric suctions are observed as linear. The apparent interface friction angle and adhesion intercept increase with matric suction. The suction envelope is found to be nonlinear as the ${\delta }^b$-angle decreases with matric suction. A modified model is proposed to consider the influence of dilatancy on the apparent interface friction angle and hence on the interface shear strength. Experimental shear strength data are compared with the analytical shear strength results obtained from the modified model using effective interface strength parameters and analytical values of dilation angles obtained from dilatancy curves. The experimental shear strength data agrees well with the analytical results for different net normal stresses and matric suctions.

Prediction of pore-water pressure is important for understanding the behavior of soils under both static and cyclic loading and also for estimation of their effective stresses. Undrained cyclic pore pressure models available in the literature are for some typical soils and are hardly applicable for other soils. In this paper, a generalized hyperbolic model for prediction of undrained pore-water pressure has been proposed as a function of cyclic stress ratio, frequency, and plasticity of soils using data reported by a number of researchers. The proposed model has been validated by a chi-square goodness-of-fit test. The correlation between the predicted and measured pore pressure ratio at various confining pressure regimes has also been statistically examined to discern the model. The model output has been found to be correlated to an extent of up to 85% with the literature data.

The uplift failure mechanism of buried pipe and its linked soil resistance are key concerns in pipe design. Although the uplift responses of pipe buried in remolded backfill have been discussed extensively, little effort has been spent on pipes buried in cemented ground, a situation that could emerge in practical engineering. This paper aims to eliminate this deficiency through a comprehensive, two-dimensional distinct element method (DEM) study on the failure mechanisms of uplifting pipe buried in loose cemented sand ground with respect to soil bond strength and pipe cover ratio. Two forms of failure mode are identified, namely the global slide failure mechanism and the local flow failure mechanism. Three stages are identified for the global failure mechanism: (1) full mobilization of uplift resistance, (2) postpeak softening with full development of the crack zone, and (3) continual growth of the trapezoid zone with further softening. The local failure mechanism presents with the opposite flow of soils around the pipe, with soils above and below the pipe flowing upward and soils from the two lateral sides of the pipe to the far field flowing downward. With the soil bond strength decreasing or the pipe cover ratio increasing, the failure mechanism gradually changes from the global failure mode found in relatively strongly cemented cases to the local failure mode commonly found in weakly cemented or uncemented cases. A new dimensionless parameter $r$ incorporating both the effects of bond strength and the cover ratio is proposed to identify the uplifting failure modes.

Active heat injection and temperature monitoring are methods that may have potential for the detection of anomalous seepage at the interface between earth dams and concrete structures. A finite-element modeling investigation was conducted to assess the feasibility of using such a seepage-detection approach. Anomalous seepage at the interface between a clay and concrete structure was simulated by increasing the hydraulic conductivity in a 3-m-thick zone and imposing a range of hydraulic gradients. The results indicate that the heat-injection location would need to be less than 1.0 m from the interface to ensure seepage-related temperature deviations of 1.0°C or greater. Provided the heat-injection location is within 1.0 m of the interface, it is concluded that the interpretation of temperature data collected prior to, during, and following heat injection should be a feasible method for identifying locations of anomalous seepage. A simulation with realistic dam geometry, including seasonally varying reservoir and air-temperature boundary conditions, showed that these factors should not overwhelm the temperature deviations generated by active heating.

Although rammed aggregate piers (RAPs) have attracted much attention as a cost-beneficial ground improvement technique, their construction process and the other affecting parameters on the behavior of these geotechnical structures during the construction and loading phases have not been properly investigated and only some predictions for downward and radial expansion resulting from the construction process have been proposed to be used in numerical simulations. The goal of this paper is to numerically simulate the RAP construction process to investigate the effect of construction sequences on RAP behavior. Keeping this aim in mind, a hybrid distinct element–finite difference algorithm is developed to simulate the placing and ramming of the RAP’s clean crushed stone layers in detail. Introducing several numerical models, a parametric study was then conducted to compare the behavior of RAPs during the construction process for different pier geometries and soil properties. The results of this research not only help to understand the RAP behavior during the ramming process but can also be used as a guide for predicting the amount of downward and lateral expansion of RAPs after the ramming process.

The research presented in this paper is focused on the effect of various parameters on the deformation response of embankment dams and the corresponding performance limit states. The parameters considered include the geometry of the embankment and hydraulic loading in terms of intensity, duration, and cycles of loading and unloading as a result of the rise and fall of the water level in the reservoir. The analysis of a model embankment dam is conducted using the finite-element approach and the results are incorporated into simplified deformation-based probabilistic analyses. The effect of the change in geometry on shear strains and horizontal deformations and the corresponding probabilities of exceeding three predefined limit states are presented. The analyses are also used to demonstrate the importance of taking into account the storm loading history when assessing the stability of the flood protection earth structures under future flood events. In a larger embankment model, the shear zone propagates deeper for failure to occur. The time to exceed Limit States I, II, and III increases as the size of an embankment model becomes longer. For example, failure occurs after 4.6 days in a model with a size factor of 0.1 compared with 12 days for a model with a size factor of 0.2. This is mainly because the advancement of the saturation front to a critical level occurs in less time in the smaller embankment.

A lower-bound limit analysis formulation, by using two-dimensional finite elements, the three-dimensional Mohr-Coulomb yield criterion, and nonlinear optimization, has been given to deal with an axisymmetric geomechanics stability problem. The optimization was performed using an interior point method based on the logarithmic barrier function. The yield surface was smoothened (1) by removing the tip singularity at the apex of the pyramid in the meridian plane and (2) by eliminating the stress discontinuities at the corners of the yield hexagon in the $\pi \text{-plane}$. The circumferential stress (${\sigma }_{\theta }$) need not be assumed. With the proposed methodology, for a circular footing, the bearing-capacity factors $N_c$, $N_q$, and $N_{\gamma }$ for different values of $\varphi$ have been computed. For $\varphi =0$, the variation of $N_c$ with changes in the factor $m$, which accounts for a linear increase of cohesion with depth, has been evaluated. Failure patterns for a few cases have also been drawn. The results from the formulation provide a good match with the solutions available from the literature.

This paper presents a numerical study using three-dimensional (3D) finite-element (FE) analyses for slopes that contain a weak thin layer and are reinforced with piles. The presence of a thin weak layer usually has a negative effect on slope stability. In the FE analysis, a strength reduction technique is employed using FE software. In the numerical model, an elastic-perfectly plastic with Mohr-Coulomb failure criterion is used for the soils. The pile is assumed to be an elastic member, without considering failure. Some of the effective factors, such as the optimal pile location and pile length, were verified beforehand using two-dimensional (2D) FE analysis. The spacing effect of the pile, $S/D=4.0$ ($S$ is on-center spacing; $D$ is diameter), is found to be comparable for the 3D model in relation to the 2D model. The appropriate length of the pile used in the 3D analysis is based on the length of piles typically used in engineering practice. It is concluded that proper stabilization can be provided if approximately half of the pile length extends below the weak layer and piles are installed in the middle portion of the slope. The analysis methods are based on a coupled analysis method; that is, both slope stability and pile response are considered simultaneously. Also, the 3D FEM is able to overcome the limitations of the 2D FE model that lacks proper consideration of the boundary effect, the soil movement between the piles, and the spacing between the piles. The effectiveness of the pile-stabilized slope depends on the strength of the soil contained in the interbedded layer. Slope stability analysis for a slope with piles was also performed, whereby three typical failure mechanisms were observed, from translational to rotational failure for the different $C_{u2}/C_{u1}$ ratios ($C_{u1}$ is the undrained shear strength of the slope soil, and $C_{u2}$ is the undrained shear strength of the soil in a thin layer). The presence of the stabilizing piles in such a slope can change the failure mechanisms and the depth of the slip surface. The restricted conditions applied to the pile head are also found to have similar effects in changing the failure mechanisms in a slope. Fixed-head piles are found to provide substantially more improvement to slope stability than free-head piles. However, fixed-head piles are not always recommended, depending on the $C_{u2}/C_{u1}$ ratio and the required factor of safety after being stabilized with piles. This paper also provides a realistic soil–pile interaction model that is subjected to lateral loading on an inclined slope.

This paper uses limit analysis to develop a two-dimensional (2D) and a three-dimensional (3D) analysis of slurry trench local and overall stability for cohesive soil. Formulas for the slurry trench stability analysis are obtained through theoretical derivation based on limit analysis theory, and rotational mechanisms are then presented for slurry trench stability. For 2D slurry trench local and overall stability, the failure surface has the shape of a circular arc, whereas it has the shape of spherical cap for 3D local stability, and it has the shape of a torus with an outline defined by a circle for 3D overall stability. Examples are provided to illustrate the safety factor influenced by the slurry and soil bulk density ratio, slurry level depth and trench depth ratio, thickness of the weak soil layer, cohesion, and trench width and depth ratio. The safety factor for the 3D solutions is approximately 1.1 times greater than the safety factor for the 2D solutions for local stability but 1.2 times greater ($B/h=1$) for overall stability.