International Journal of Geomechanics

This paper proposes an empirical equation to evaluate the shear strength of rock mass with nonpersistent joints. A novel specimen preparation method is proposed and is used to created plaster specimens containing nonpersistent joints. Utilizing the proposed method, it is possible to create specimens with nonpersistent closed joints with different roughness levels along different directions. The normal stress applied to embedded nonpersistent joints is the key factor for estimating the joint friction contribution to the shear strength of rock mass with the joints. An analytical equation and an experimental approach are proposed to calculate the normal stress applied to the nonpersistent joints. Seemingly good agreement was found between the normal stress values obtained using the analytical equation and those measured by the experimental approach. To study the effects of four influential parameters, namely rock bridge ratio, material strength, joint roughness, and normal stress, on the shear strength of specimens with a single nonpersistent joint, an experimental layout was designed based on the Taguchi method. The results of the extensive experimental work were then expressed in terms of an empirical equation to calculate the shear strength of specimens embedding a single nonpersistent joint.

Transversely isotropic rock is a typical anisotropic rock type. The existing creep constitutive models for isotropic rock do not fully reflect the creep mechanical properties of transversely isotropic rock. By considering a set of creep parameters as the internal connection among the rock specimens with different bedding directions, a three-dimensional creep constitutive equation of transversely isotropic rock is derived, which can effectively describe the characteristics of the instantaneous strain, decaying creep, and steady creep of a transversely isotropic rock. A method to determine the creep parameters for the three-dimensional creep constitutive model is proposed. Based on the creep test experimental data of horizontally orientated and vertically orientated phyllite, the transversely isotropic creep properties and creep parameters are successfully identified using the proposed method. The rationality and validity of the new model are certified by comparing the theoretical curves with experimental data. The results of this paper provide a new approach to study the three-dimensional creep mechanisms of rock and provide scientific research support for the design of rock creep tests.

The design and maintenance of embankments is still a challenge in practical geotechnical engineering because of some features of soft sensitive soil behavior that are not considered in conventional methods. These features originate from the soil structure, including soil anisotropy, interparticle bonding, and decay as a result of the loading and deformation process. In recent years, many efforts have been made to incorporate the aforementioned features in various soil constitutive models. However, their application in practical geotechnical engineering is limited, owing to the complexity of the models, a number of parameters, and difficulties in the implementation in a computer code. The aim of this study is to modify a simple anisotropic constitutive model (SANICLAY) in order to take into account destructuration, named SANICLAY-D, and its implementation in computer code with a simple and robust algorithm. The capability of the proposed soil model in simulating the effects of the aforementioned soil features on the behavior of the well-known Test Embankment A constructed at Saint-Alban, Quebec, Canada, is explored. This model predicts, with sufficient accuracy, the effect of anisotropy on embankment failure behavior, especially the height and the failure surface, despite its simplicity.

Research on soil biocementation has gained momentum given its advantages over ordinary Portland cement-based techniques that entail a negative environmental impact. Soil biocementation occurs when bacteria-induced urea hydrolysis precipitates calcite crystals that bind sand grains together, hence increasing both the strength and stiffness of the otherwise uncemented material. This paper presents an experimental and analytical study, simulating the geotechnical behavior of biocemented sand and explaining the precipitation mechanism of the effective calcite crystals. The experimental results of this study showed that the precipitation mechanism of the calcite crystals (calcite–silica bond or the calcite–calcite bond) plays a significant role in the strength improvement of biocemented sand, and the predictions obtained from the analytical model were found to be in good agreement with the experimental results.

Various mechanical responses of rocks under a complex stress state have attracted the attention of engineers. A hollow cylinder torsional apparatus (HCA) was constructed using the discrete element method (DEM). A series of conventional triaxial compression tests under different confining pressures and a complex stress path test with torsion were conducted. The numerical results are consistent with laboratory and theoretical findings, which indicates that the microscopic parameters of the DEM sandstone specimens were correct and reasonable. Based on the HCA DEM specimen, the macro–micromechanical response of sandstone specimens under four typical unloading stress paths were studied, and variations in the strain energy density, strain energy, and dissipated energy of sandstone specimens were obtained. These results could provide a reference for the study of the mechanical properties of unloaded sandstone in geotechnical engineering.

The ideal notion of footings placed in isolation is rarely implemented in practice and footings are often placed adjacent to each other, interfering with one another's performance. In this paper, the lower-bound finite-element limit analysis method is used to investigate the pseudostatic bearing capacity of a strip footing placed in close proximity to an already-existing strip footing, over cohesionless soil. The pseudostatic approach is used to model the seismic loading. Analyses conducted for different accelerations, soil friction angles, and service load magnitudes on the existing footing and spacings showed that while the presence of the existing footing can improve the pseudostatic bearing capacity of the new footing, an amplified rate of reduction with seismicity ultimately causes the new footing to withstand smaller accelerations compared with its isolated case. The increase in spacing generally reduced bearing capacity. An exception was observed for a friction angle of 40° for all service loads and pseudostatic accelerations, where a maximum in both bearing capacity and fluidization acceleration was observed around 0.1 of the footing widths.

Due to the complicated geological conditions and complex loads, the pile–soil interaction is a three-dimensional (3D) and highly nonlinear problem. Conventional numerical models have deficiencies to model the nonlinear soil–structure interaction (SSI) responses. This paper developed a 3D pile element model, which is capable of robustly simulating the pile behaviors under complex loadings in 3D analysis. The dominant feature of the model was the direct integration of the soil properties into the element formulation to consider the nonlinear SSI responses so that the soils were not necessarily modeled explicitly. Element tangent stiffness matrices were computed via the total potential energy equation. A semianalytical method based on the Gauss–Legendre integration method is developed for the summating process. The kinematic description of motion established by the updated Lagrangian approach was developed to allow intermediately large deflection of a pile. Formulation of the 3D pile element was derived, and the numerical implementation of the 3D pile element was provided. Finally, several examples were worked out to validate the efficiency and accuracy of the proposed model.

This paper presents a novel Bayesian machine-learning approach for unsupervised and simultaneous soil stratigraphic interpretation of cone penetration test (CPT) soundings at the site scale. The proposed approach interprets numerous CPT soundings in a joint manner, and it leverages the statistical similarity of the measured sounding data in feature space (i.e., the Robertson chart) and the spatial constraints induced from spatial correlations of the sounding data both vertically along a single CPT sounding and horizontally across multiple soundings in physical space. The mathematical core of the proposed approach consists of the following two parts: (1) a quasi-3D (or 3D axial-symmetric) hidden Markov random field (HMRF) model describing both the statistical and spatial patterns of the CPT soundings; and (2) a model inference process, in which the statistical and spatial patterns are extracted from the dataset using a Bayesian unsupervised learning algorithm. The joint interpretation strategy of the proposed approach facilitates the use of rich statistical information and spatial constraints contained in an ensemble of CPT soundings to enhance the accuracy and consistency of a stratigraphic interpretation at the site scale. The proposed approach has been tested in a real-world case consisting of 44 CPT soundings collected from a geotechnical investigation site. The interpretation results show that the proposed approach can extract the soil spatial and statistical patterns from multiple CPT soundings and significantly increase the accuracy and consistency of the soil stratigraphic interpretation results.

The lining rings of a shield tunnel are connected by steel bolts, which play an important role in longitudinal structural deformation during long-term operation. In recent decades, there have been increasing numbers of tunnel-crossing projects. In order to better understand the impact of undercrossing excavations on existing tunnels and to provide a quick and effective tool for evaluating the behaviors of existing tunnels before construction, a simplified analytical method is proposed. In the proposed model, a tunnel was simplified into a series of short beams connected by shear, tensile, and compressive springs, and the Pasternak two-parameter foundation model was used to describe the tunnel–soil interaction. The tunnel model not only considers the shear effect between the linings but also the rotation effect of the lining ring. The field data from two cases were used to compare with the calculated results, and the predictions were found to be in good agreement with the measured data, thus verifying the effectiveness of the method.

For the displacement-dependent earth pressure on a rigid wall that rotates around its base, an analysis approach will be established based on the Duncan–Chang stress–strain model, log-spiral potential slip surface in the retained soil, a horizontal slice method, and a graphical procedure to solve implicit expressions for the mobilized internal friction angle (φ_m) of the retained soil in the non-limit state. The shear strain on the potential log-spiral slip surface will be derived as a function of φ_m and height from the wall base. The active and passive ultimate wall displacements will be obtained based on the shear strain expression. A complete relationship between the earth pressure and wall displacement from the active to passive limit states of the soil will be quantitatively determined and calibrated by considering the practical wall displacement in the at rest state of the soil. Analysis results from examples indicate that the earth pressures by the proposed method are identical with those obtained via tests with a relative error of approximately 5%–10%. The profile of the earth pressure under the active and passive non-limit states are concave outward and inward to the wall, respectively. The two ultimate displacements decreased as the internal friction angle (φ) increased, and the active one decreased but the passive one remained almost unchanged with an increase in cohesion (c). In addition, the passive one increased slightly with the wall–soil friction angle (δ), but the angle did not influence the active one.

The self-bearing capacity of tunnels possesses a dynamic evolution process. However, there is a limited advanced knowledge to evaluate the dynamic self-bearing capacity of tunnels quantitatively. In this paper, the time-dependent self-bearing factor of the tunnel surrounding rock is proposed, and an analytical approach for the circular excavations is developed. In this paper, the rock mass is regarded as a viscous material with a distinguishable strain-strengthening property. The stress states around circular excavations are determined using the Drucker–Prager criterion and the power-hardening constitutive model. Then, the Burger-creep viscoplastic model is introduced to evaluate the time-dependent deformations. Finally, the formula of a time-dependent self-bearing factor of tunnels is obtained. The sensibilities of time-dependent self-bearing factor and time-dependent deformation of tunnels to the incorporated model parameters are investigated in depth. Effects of incorporated model parameters on time-dependent self-bearing factor and time-dependent deformation of tunnels are consistent with their physical meanings. This paper provides an analytical approach for quantitatively evaluating the dynamic evolution process of the self-bearing capacity of tunnels.

Although much has been discussed on the liquefaction phenomenon and cyclic behavior of saturated sands, relatively little has been clarified on the difference between their cyclic behavior under simple and triaxial shear modes, particularly under strain-controlled conditions. Thus, in this study, comparative cyclic strain-controlled simple (DSS and T_xSS) and triaxial (CTX) shear tests were performed on reconstituted specimens of Baie-Saint-Paul and Ottawa C-109 sands. To indicate further investigation into the cyclic behavior under triaxial and simple shear modes, the CTX and T_xSS tests were numerically simulated using a proposed energy-based pore-water pressure model through the FLAC^3D platform. The outcomes of the numerical simulations were presented in terms of the stress–strain hysteresis loop and the distribution of the dissipated energy and excess pore-water pressure generation within each element of CTX and T_xSS soil specimens. Unlike T_xSS soil models that experience a relatively uniform stress state, the numerical simulation revealed the nonuniformity of the produced stress–strain and pore-water pressure within triaxial specimens. The comparative cyclic strain-controlled test results revealed that the DSS and T_xSS specimens liquefy slower than triaxial specimens, in contrast to cyclic stress-controlled results found in the literature.

Caissons are rigid foundations most commonly used to support bridge piers. In this study, numerical analysis using the finite-element method based computer program ABAQUS was carried out to study the response of caissons under static and pseudostatic conditions. The caisson was embedded in layered soil comprising a saturated clay layer sandwiched between two sand layers. Sand was modeled using an elastic, Mohr-Coulomb plastic model and clay was modeled using a porous elastic and clay plasticity model to account for soil consolidation. The wall friction angle (δ) and seismic acceleration coefficients (k_h and k_v) were varied in this study. Calculations were made by executing a mathematical code in MATLAB to obtain the lateral soil pressure, maximum and minimum base pressures, tilt, shift, and point of rotation of the caisson. The analysis was further extended to develop three-dimensional (3D) interaction diagrams relating the combination of applied vertical load (V), lateral load (Q), and moment (M) in nondimensional form required to cause caisson failure for different wall friction angles and seismic acceleration coefficients. These diagrams can be used for the safe design of caissons under different seismic conditions and ground conditions for a variety of design loads.

Degradation of geomaterials, that is, particle breakage, can be harmful to the full life-cycle stability of practical engineering; for example, rockfill dam, energy-pile foundation, railway embankment, and retaining wall. A key issue is how to precisely quantify grain crushing during the life-cycle operation of the project that suffers high pressure or dynamic loading. This paper reviews the advantages and limitations of existing particle breakage indices and proposes a new simple breakage index for estimating the evolution of grain crushing. The new index without an integral grading area can be easily and directly obtained from the sieving results and independent of the coordinate of particle size axis. It can also adequately capture the grain crushing at all grain sizes. Moreover, it can be used for uniformly graded, well-graded, and gap-graded crushable soils.

In general, the microdefects in rocks obey Weibull distribution. Based on the laws of statistics of microdefects in rocks, the relationship between the damage and the strain is established. Moreover, by considering characteristics of the viscoelastic–plastic and the damage evolution in rocks, a nonlinear creep model for rocks considering damage evolution is proposed to predict the creep behaviors of rocks based on the modified Nishihara model. In the proposed model, a dashpot element and a nonlinear viscoplastic body are added into the classical Nishihara model to simulate the accelerating creep stage of soft rocks. Moreover, the damage of rocks is considered in the process of creep. The effects of the shape parameter, the scale parameter, the peak stress, the peak strain, and the confining stress on the damage are investigated using the proposed method. The novel model is suitable to predict the creep behaviors of hard rocks and soft rocks simultaneously, and the difficulty to simulate the accelerating creep stage using the traditional creep model is overcome. To verify the robustness and precision of the proposed model, the creep behaviors of granite, coal, and red sandstone at different stresses are investigated. The predicted creep behaviors of soft and hard rocks using the proposed method are in good agreement with the experimental data, especially for the nonlinear accelerating creep stage.

Motivated by recent studies showing concave slopes are more stable than planar slopes, this paper presents a feasible approach to build a dry-stone concave gravity segmental soil retaining wall (GSW) using special prefabricated concrete blocks (Porcupine Blocks). Unlike common segmental blocks that can only be assembled in one particular facing configuration, the Porcupine Block can be assembled with three different options, making it possible to build a concave GSW using a mixed block assembly. In this study, results from both centrifuge tests and numerical analyses indicated that a concave GSW has better performance than planar walls because concave facing contributes to reduced active earth pressure acting at the back of the GSW and the presence of porcupine offsets behind the concave wall provides additional downward forces to resist overturning. An additional highlight of this study is the use of 3D printing technique to fabricate 1:10 Porcupine Blocks for centrifuge model testing and to fabricate equipment parts for measuring the interfacial strength of the blocks.

The moisture content of rocks in nature often changes with the natural hydrological environment, and generally natural rock may be classified into three types, that is, dry, natural, and saturated rock. The corresponding responses to dynamic loads may have considerable difference, and therefore, impact tests in this paper were conducted on single cleavage triangle sandstone specimens with three types of conditions, respectively, under various loading rates. The ingredient of sandstone was determined by X-ray diffraction and optical microscopic image. The crack propagation parameters were recorded with the aid of a crack propagation gauge. The dynamic stress intensity factors were calculated using ABAQUS code. The results show that the fracture toughness of all the three types of specimens increase with loading rate, which could be expressed by power functions. Compared with dry and natural sandstone, the crack propagation speed of saturated sandstone specimens is more sensitive to the loading rate. Both the rate effect and the water effect, including water-weakening effect and water-enhancing effect, play a significant part in rock dynamic fracture behavior.

When tunneling with a tunnel boring machine (TBM) in permeable soil, excess pore-water pressure are inevitably generated in the soil surrounding the TBM. Because excess pore-water pressure reduce the effective face support pressure, accurately predicting their magnitude is important for determining the required effective face support pressure. In this study, a long­­­–short-term memory (LSTM)-based deep learning model is employed to predict variations in pore-water pressure generated by TBM tunneling using time-series data derived from field monitoring data and TBM data collected during construction of the Green Hart Tunnel (GHT) in the Netherlands. Four obtainable input variables are selected to quantify pore-water pressure at two monitoring points that have different distances (8.3 and 107 m) along the transverse axis. Three accuracy metrics are introduced to evaluate the performance of two prediction tasks, with input variables' importance on the output ranked according to their corresponding sensitivity values. It demonstrates that the proposed LSTM-based deep learning model can accurately predict the pore-water pressure ahead of the TBM in drilling–standstill cycles, which can further serve as a tool for TBM operators to use in assessing real-time tunnel face stability.

Due to uncertainties in the geological evolution process, engineering geological conditions, and nonuniqueness of the solution for in situ stress regression analysis, stress field regression has always been a difficult issue in geotechnical engineering. In view of this problem, a refined back-analysis method for the stress field is proposed in this study based on in situ stress and disturbed stress. First, the in situ stress and disturbed stress in the unloading zone are measured by field tests. The process of geological evolution and excavation disturbance is numerically simulated. The theoretical values of in situ stress and disturbed stress are obtained. The nonlinear mapping relationship of the boundary condition and the stresses at the measuring points is established by the evolutionary neural network. The measured in situ stress and disturbed stress in the unloading zone are imported into the neural network to obtain the boundary conditions. Finally, the boundary condition obtained by back analysis is assigned to the numerical model for calculating the stress field at the project site. The method proposed in this study was applied to analyze the stress field of Mengku Iron Mine in Xinjiang, China. It was found that the accuracy of back-analysis results has been greatly improved because the contributions of both the in situ stress and the disturbed stress were considered in the proposed method. Meanwhile, according to the engineering analysis, the maximum horizontal principal stress in the open-pit slope was reduced by a certain degree, with a maximum reduction of 30%–40% after mining. However, the major principal stress at 0–350 m below the mine pit increased remarkably, with an increment of above 60% compared to the in situ stress. It indicated that excavation unloading has a great influence on the local stress field.

Three-dimensional scanning technology was used to construct the database of natural block stone shapes with different particle sizes. On the basis of Particle Flow Code 3D, a discrete element random model of soil–rock mixtures with different stone contents and shapes was established. A flexible boundary loading method of multisection wall was adopted to simulate the flexible film constraint mode of indoor triaxial test. Large-scale triaxial numerical simulation tests were carried out on the soil–rock mixture with different stone contents, stone shapes, and loading modes to analyze the macromechanics, microscopic deformation, and failure laws under various working conditions. Results showed that under the flexible loading mode, the stress curve of the samples with low stone content (0%–20%) has no obvious peak value and the deformation is mainly shear shrinkage. The stress curve of the samples with high stone content (40%–60%) showed the obvious peak value, and the dilatancy was prominent. Under the action of vertical load, the specimen bulged and formed multiple fork shear bands. Compared with the flexible loading mode, the rigid loading mode showed that the strength of the specimen increased in the rigid loading mode, and the cohesion and internal friction angle improved overall, but the friction energy was basically the same. During shearing, no obvious bulging was noted at the edge of the sample, and the shear bands were K-shaped and diagonal. The shape of block stone had significant influence on the strength, friction energy, and shear band shape of the soil–rock mixture.

The Ma Lan loess is a typical structural soil due to its water sensitivity, collapsibility, and seismic vulnerability. In this study, Ma Lan loess samples were extracted from 17 sites distributed on the Loess Plateau, and field and laboratory tests were conducted to ascertain the physical and mechanical parameters of the loess. The optical microscopy-based serial sectioning method was adopted to systematically research the characteristics and regional variation in the microstructure of the Ma Lan loess. The results show that the relationships of the equivalent diameter of loess particles, pores, and throats versus the corresponding quantitative percentages satisfy the rational and Gaussian distributions, respectively, and that the channel length of the loess throat versus the quantitative probability can be accurately fitted by adopting the gamma distribution. The distributions of particle size and orientation, pore size, throat radius, and channel length of the Ma Lan loess show obvious regional zonation on the Loess Plateau, which are influenced by the factors of source properties, aeolian power, migration distance, erosional history, and so on. The microstructure of the Ma Lan loess can be classified into the following three categories: particle aerial structure (I), aggregation aerial structure (II), and flocculated structure (III); the loess in the northern Loess Plateau is primarily Category I, and the loesses from other locations are primarily Categories II and III.

Permeability is one of the important parameters to evaluate the long-term sealing performance of Callovo-Oxfordian (CO_x) argillite for high-level radioactive waste repository. In this study, scanning electron microscope images were used to analyze the pore structure of CO_x argillite. The pore size distributions (PSD) obtained by the discrete algorithm and two continuous algorithms (Munch continuous algorithm and Song algorithm) are quite different, the range of pore size obtained by the discrete algorithm is larger than those obtained by continuous algorithms. The results of continuous algorithms are closer to that from mercury intrusion porosimetry. For the permeability prediction, the continuous methods show better results, but there is still a big gap. By further considering the contribution of pores with different sizes to permeability, the results obtained by continuous methods are very close to the measured result. The values of A2 obtained by the Munch continuous algorithm are 2.2 × 10⁻¹⁶, 1.8 × 10⁻¹⁶, and 0.94 × 10⁻¹⁶ m² for magnifications ranging from 2,000 to 8,000 times; the corresponding values obtained by the Song algorithm are 2.42 × 10⁻¹⁶, 2.02 × 10⁻¹⁶, and 1.12 × 10⁻¹⁶ m², respectively, while the laboratory result is 1.67 × 10⁻¹⁶ m². More accurate permeability can be obtained by more representative PSD. Therefore, for soil materials with uniform pore distribution, more accurate permeability can be obtained by considering continuous algorithms and pore contribution rate.

The soil stratum is heterogeneous and may be tilted with significant influence on the footing bearing capacity (BC). In this paper, a combination of influence of the anisotropy orientation and thickness of soil layer and rock stratum inclination on the BC of strip footings was evaluated using a random finite-difference method (RFDM). The Monte Carlo simulation (MCS) approach was used to elucidate the effect of spatial variability, and soil strength characteristics were assumed as log-normal and bounded random fields. The failure mechanism and produced shear strain in probabilistic method were compared to those obtained from deterministic analysis. The results showed that the soil stratum inclination has a significant effect on the footing BC magnitude, which reaches a minimum value when the deposition orientation is 45°−ϕ/2 with the horizontal direction (ϕ = soil friction angle). Parametric studies were performed on the variability level of strength parameters, the correlation coefficient of strength characteristics, correlation length, soil layer thickness, and stratification orientation.

This paper investigates the limiting force profile (LFP) for laterally loaded piles embedded in undrained clay. Based on the three- and two-dimensional finite-element limit analysis (FELA), the failure mechanisms and methods for calculating the limiting soil resistance under both flow-around failure at a certain depth and wedge failure at ground surface are presented, respectively. For the flow-around failure, the limiting soil resistance increases with the adhesion factor α, and an empirical formula is proposed for practical application. Under the wedge failure condition, a curved conical wedge is developed in the front of the laterally loaded pile. Based on the parametric analysis, a generic design model as well as the determination procedures of the model parameters for predicting the limiting soil resistance under wedge failure is proposed. Finally, the proposed design model is validated by a comparison with the centrifuge test results reported in literature.

Cement stabilization is a soil improvement technique widely adopted for soft soils. The extent of improvement to the physical properties varies largely with soil type and often requires laborious laboratory tests to ascertain such extent of improvement when soil samples from a source are obtained. To offer a quick estimate of the improved unconfined compressive strength of the composite, it is crucial to develop relationships of the strength with essential parameters of the soil. Furthermore, existing studies mainly focused on cement-stabilized clays with minimal granular content. The influence of commonly encountered sand impurities in actual field condition is much less discussed. In view of these limitations, the current study explores the use of activity number (A), liquid limit (w_L) and modified apparent void ratio $(e_c^{*})$ as a proxy to unify the strength development of cement-stabilized soft soils used for land reclamation in the modified Abrams's strength predictive model. Incorporation of A and w_L is achieved by introducing a new parameter α. Friction due to geometric proximity between sand particles in the composite is represented by $e_c^{*}$. Results show that the proposed model is able to successfully consider the effect of soil properties in the strength development of soils stabilized with Ordinary Portland cement (CEM I) and Portland blast-furnace cement (CEM III/C) and validated with published literature. The proposed models enable quick check of the design when only mix proportions and index properties are available. They also incorporate the influence of sand content, which is merely considered in existing models.

The large step-tapered hollow (LSTH) pile is an invented foundation solution for critical infrastructures overlying difficult geological profiles. In this paper, the time-dependent load-transfer model and the theoretical solution for calculating the long-term settlement of the new pile were presented. Using FLAC^3D software, the time-dependent bearing characteristics of an LSTH pile were analyzed. A time-dependent load-transfer model (LTM) was employed to describe the time-dependent disturbance characteristics of pile–soil interaction based on the disturbed state concept (DSC). Using this LTM, the relatively intact state was defined by the Kelvin constitutive model, while the fully adjusted state was described by the perfectly viscoplastic constitutive model. Based on the LTM and the governing equations for the pile–soil interaction, an analytical solution for the long-term settlement of the pile was established. The proposed method was verified by means of a case study. The proposed model can be used to describe the time-dependent disturbance characteristics of pile–soil interaction.

The geotechnical materials formed by natural deposition usually have transverse isotropic properties, and the transverse isotropic properties not only have a direct influence on the deformation of geotechnical materials but also have a nonnegligible influence on their strength characteristics. In order to reasonably consider the influence of transversal isotropic properties on strength properties, the soil's failure properties of complete isotropic and transversal isotropic soils were compared. At the same time, a hypothesis was adopted, that is, at the failure moment, the ratios of principal stresses corresponding to completely isotropic soil and transverse anisotropic soil had linear relationships to each other, and the ratio coefficient β was assumed to be a transverse isotropic parameter. The proposed parameter β was utilized to reflect the influence law of the original anisotropy on the shape of the failure curve on the deviatoric plane. The proposed parameters were employed to reflect the influence law of the original anisotropy on the shape of the failure curve on the deviatoric plane. For the relationship between the isotropic criterion and the transversal isotropic criterion, a kind of β transformation method is proposed, which can realize the transformation of isotropic stress space and transversal isotropic stress space. Based on the isotropic generalized nonlinear strength criterion (GNSC), the method of determining the transverse isotropic parameter β is given by making use of the condition that the shape parameters $\overline{\alpha }$ and α of GNSC in the isotropic stress space and the transverse isotropic stress space, respectively, are exactly the same. By comparing the strength test data under different Lode angles with the predicted results of the generalized nonlinear criterion of transverse anisotropy, the results showed that the proposed anisotropy criterion can simply and accurately reflect the failure law of the geotechnical materials under the true triaxial loading condition.

This study is devoted to deriving a semianalytical solution to one-dimensional consolidation of multilayered unsaturated soils subjected to an instantaneous loading. The proposed multilayered consolidation model based on Fredlund and Hasan's consolidation theory for unsaturated soils was analytically studied with a combination of Laplace transform and transfer matrix techniques. For two types of boundary conditions, the analytical solutions in the Laplace domain were acquired, while Crump's technique was utilized to carry out the semianalytical solutions in the physical domain. To verify the accuracy of the proposed solution, three examples for single-layered, two-layered, and three-layered soils were presented. In the case of single-layered and three-layered unsaturated soils, the solutions were in agreement with the existing analytical solutions. For two-layered unsaturated soils, the finite-difference result was adopted to illustrate the validity of the semianalytical solutions.

Electroosmosis often dewaters soil into unsaturated conditions. Due to the shrinkage deformation and decrease of effective voltage that occur during the electroosmotic consolidation as the soil changes from the saturated to unsaturated state, an analytical solution with the consideration of the coupled deformation and time-decreasing effective voltage was developed for one-dimensional (1D) electroosmotic consolidation in unsaturated soils. The effect of nonuniform distribution of the initial water content was also considered. To validate the effectiveness of the proposed analytical solution, a laboratory test was conducted. Thereafter, the proposed solution was used in a parametric study to investigate the effects of the coupled deformation, distribution pattern of the initial water content, and decrease rate of the effective voltage. The results indicated that the coupling effect increases with a decrease in the desaturation coefficient, and the coupling effect is significant for soft soils with high retention capability and compressibility. The nonuniform distribution of initial water content also had a great influence on the consolidation rate. When the initial water content increased from the anode to the cathode, the consolidation rate was fast in that direction but slow in the other direction. Finally, with the consideration of time-decreasing effective voltage, the calculated maximum matric suction and drainage decreased and the completion time of electroosmotic consolidation was shortened. In summary, the analytical solution developed in this study could capture the actual problems for electroosmosis consolidation in field applications to some extent.

This paper presents a model that allows the evaluation of the mobilized response of piles subjected to downdrag and drag forces. The presented technique couples the soil and pile settlement profiles with the pile-mobilized skin friction and end-bearing resistance in an interactive model to determine the downdrag (pile settlement), load distribution along the pile length, and location of the neutral plane or transition zone. The load transfer (t–z and q–z) models employed in the current technique are constructed based on soil and pile properties, soil–pile interaction, and a constitutive soil model. The proposed model detects the variation of the neutral plane location with the increase of pile-head load up to the pile’s geotechnical limit. Additionally, the technique deals with superlong piles under downdrag forces and determines the mobilization of negative (downward) and positive (upward) skin friction with an increase of soil settlement and the effect of the pile’s end-bearing stiffness on developing drag forces. The proposed procedure is described in a detailed flowchart and validated through comparisons with long-term full-scale field tests conducted on piles subjected to negative skin friction.