International Journal of Geomechanics

In this work, a novel elastoplastic damage model is proposed to capture the mechanical and deformation behaviors of hard rocks subjected to true triaxial compression (TTC). A yield function based on the Mogi–Coulomb strength criterion is constructed in the stress space. Generalized plastic shear strain as a function of a continuous and smooth hardening or softening variable is adopted in the yield function; this guarantees that the yield function at the peak stress level has the same form as the strength criterion. Moreover, a proper damage criterion is derived, considering the development of microcrack-induced damage. The novelty of the proposed model consists in the ability to derive its analytical solutions under a novel TTC loading with a constant load angle; this is helpful for calibrating the model parameters. For application, an efficient and convergent semi-implicit return mapping (SIRM) algorithm involving a plasticity-damage decoupling correction procedure is then developed for the numerical implementation of the proposed model under general loading cases. The robustness of the SIRM algorithm is examined through comparisons between numerical results and the derived analytical solutions. An interesting observation is that, for the SIRM algorithm, plasticity and damage evolution are insensitive to the size of the load step. The verification of the model is finally shown through applications to Westerly and Linghai granite under a typical TTC loading path.

For embankment dams over 150 m in height, there is a strong tensile effect on the core near the bank slope under the action of water storage. The cracking of the core due to tension can threaten the overall safety of the dam. Therefore, it is very crucial to perform a reliability analysis of the tensile crack resistance of a high asphalt core. In this study, the tensile crack of the core is considered the basis of failure. Taking the ultimate tensile strain as the control index, a calculation method is established for the crack resistance reliability of a high embankment dam core based on a mixed-level uniform design (MLUD) and the response surface method (RSM). Considering the Duncan–Chang E-B model parameters, the random variables for the reliability calculation assessment are determined by the single-factor sensitivity analysis method. Based on the combination of the MLUD and the RSM, the explicit expression of the core strain is derived. Further, the checking point (JC) method is used to evaluate the performance of the core. The Quxue dam with a dam height of 171.2 m is used as an engineering example for verification. The results show that the random variables K, n, and φ, and the upstream water level H are highly sensitive parameters. The core crack resistance reliability index β is 4.2695, which is greater than the standard reliability index. The calculated results are in good agreement with the collected actual measurement results.

Traditional analyses for active earth pressures considered soils dry or saturated by the application of a two-dimensional (2D) failure pattern. However, soils are usually unsaturated in nature, and the collapse of backfills presents a three-dimensional (3D) characteristic. The extant studies proved that the existence of cracks and seepage flow encountered in backfills would impact active earth pressures but are still limited to 2D conditions. To this end, this study developed an analytical framework to evaluate the 3D active earth pressure considering the presence of cracks and steady-infiltration effects within unsaturated backfills. Based on the kinematic approach of limit analysis, a suction-induced effective method is introduced into a 3D failure mechanism to characterize the collapse of unsaturated backfills. By means of the work rate balance equation, the most adverse location of cracks and the explicit expression of active thrust under steady seepage conditions can be obtained through the incorporation of the suction stress profile. The presented method is verified by comparison with the exact cases in previous studies and comparison with the results of numerical simulation. A systematic parametric study is conducted to reveal the impacts of width-to-height ratio, air-entry value, pore-size distribution, vertical discharge, and cracks on the active earth pressure variations. The results show that considering 3D effects is significant because it leads to a lower economic cost for the design of retaining walls; the presence of cracks and the effect of steady infiltration encountered in unsaturated backfills would increase the lateral force of earthen structures. This study presented a more realistic understanding of the service state behavior of retaining walls and a useful strategy for evaluating the 3D active earth pressure.

This paper discusses the second-order reliability-based design optimization (SORBDO) of unsaturated finite slopes. An efficient search algorithm is proposed to locate the most probable slip surfaces using the Morgenstern–Price method of slices. The variability of fitting parameters of the soil water characteristic curve (SWCC) and shear strength parameters have been taken into account for evaluating the reliability of unsaturated finite slopes. Six unsaturated shear strength (USS) models are considered for the analysis of unsaturated soils. The most conservative model for the optimum design of finite slopes is recommended. Moreover, the results indicate that the mean and standard deviation of the fitting parameters of SWCC have a significant effect on the critical centers, critical slip surfaces, and reliability index of the unsaturated finite slopes. The results demonstrate a significant change in the critical centers associated with critical slip surfaces due to the change in the mean and coefficient of variation of the fitting parameters of SWCC. Statistical analysis of the experimental data shows that a positive correlation exists between fitting parameters of SWCC related to air entry value (a_f) and residual water content (m_f). Negative correlations are found between the fitting parameters of SWCC related to air entry value (a_f) and slope (n_f). Similarly, the SWCC fitting parameters related to residual water content (m_f) and slope (n_f) have negative correlations for clayey soils. It is observed that the correlated value of the reliability index is overestimated with reference to the uncorrelated value for clayey soil slopes. The proposed design charts are beneficial for engineers and practitioners for the sustainable design of unsaturated finite slopes. Overall, the developed rigorous SORBDO framework offers a more rational approach for assessing critical failure surfaces and critical centers, considering the interdependency of random variables.

Ground improvement adopting stone columns or rigid inclusions has become popular in engineering practice as it can be more economical under certain design criteria. In typical designs of either stone columns or rigid inclusions, the column diameter, column length, and grid spacing are three main parameters that affect the costs and performance of the improved ground. This work is concerned with achieving an optimal design for these two ground improvement methods. The design of the three main design parameters is subject to optimization using a multiobjective optimization algorithm with respect to minimizing the construction cost of the soil improvement system. We explain how the semiautomated design optimization works in connection with the considered calculation method used for the design and how execution constraints, if required, can be incorporated in the design workflow. Through the use of Priebe’s method and (ASIRI) recommendations for the calculation of stone columns and rigid inclusions, respectively, the usefulness of the presented design optimization approach for each of the two ground improvement methods is demonstrated.

The tip shape of penetrometers and piles has an important influence on the soil resistance mobilized during penetration. Blunt or flat tips typically generate greater penetration resistances, which can lead to refusal during in-situ testing and pile driving in the field. Results are presented from numerical and experimental investigations on probes with conical tips of varying apex angles to quantify the effect of the apex angle on the mobilized penetration resistance and associated failure mechanisms. Discrete element modeling (DEM) simulations were performed in unconfined and confined (i.e., stress-controlled) specimens to model shallow and deep penetration conditions, respectively. Centrifuge penetration tests were performed by quasi-statically advancing an instrumented probe to a depth-to-probe-diameter ratio of 16.7. The numerical and experimental results indicate that at shallow depths, the sharper tips mobilize smaller penetration resistances. In deep penetration conditions, the changes in penetration resistance with tip apex angle are less pronounced. Based on the results of the two investigations and values reported in the literature, a relationship characterizing the functional form between tip apex angle and normalized penetration resistance is proposed. A mesoscale analysis of the DEM simulation shows differences in the failure mechanisms induced by sharp and blunt tips: the zone where large particle displacements and stress changes occur is large and located below the tip for penetration with blunt tips, whereas the zone is smaller and located both laterally and below the tip for sharp tips.

A modified thin-layer interface model (MTLIM) is established to investigate stress wave propagation across a fracture filled with viscoelastic materials in a rock mass. First, this MTLIM treats the viscoelastic filling material as a composite of elastic thin layers and viscoelastic bonds. The displacement discontinuity at the bond is described by the Zener model, and the wave propagation equation through the fracture is derived in the time domain. Then, this MTLIM is degenerated to the thin-layer interface model (TLIM) for the extreme case and verified by the transmitted wave in a dynamic experiment. Its performance is compared with those of the TLIM and a zero-thickness interface model (ZTIM). Finally, the waveform evolution, transmission and reflection coefficients, and the energy dissipation ratio for stress wave incidence are investigated for viscoelastic filled fractures at different thicknesses. Results indicate that the MTLIM has better performance than the TLIM, Maxwell model, and Kelvin model in accurately reproducing the dynamic response of stress waves through viscoelastic filled fractures. Significant differences are observed between thin and thick filled fractures in the variation of the waveform and the velocity transmission and reflection coefficients with filling thickness. A thin filled fracture can cause more total energy dissipation than a thick one in some cases. The MTLIM can describe the effects of repeated reflections and the viscoelastic effects of filled fractures on the frequency and amplitude of seismic responses.

Abstract

A bounding surface plasticity p − y model is used to examine the internal energy responses of a laterally loaded pile in static and dynamic simulations. The model response is first compared with those observed in physical centrifuge tests, including monotonic and cyclic loading, in a normally consolidated fine-grained soil. Then, the model is used to examine hypothetical static and dynamic situations. The monotonic load capacities determined by the model and an upper-bound limit analysis method are in agreement with that inferred from the physical test. The work done by external loads in static conditions is principally balanced by the plastic work in the p − y springs and the elastic strain energy in the structural pile elements, which are comparable in the cases examined. The numerical model is capable of reproducing accurately the observed test structural responses as well as the characteristics of plastic energy dissipation. In a dynamic free-vibration simulation, the pile is highly damped as a result of the significant plastic energy dissipation. The simple work-hardening elastic–plastic p − y model is theoretically sound, applicable to arbitrary loading histories, and requires the same level of effort to use as traditional p − y methods.

Practical Applications

An easy-to-use p − y model facilitates an efficient analysis of piles exposed to arbitrary lateral loadings. The implementation, use, and interpretation of results are familiar to engineers experienced in traditional p − y methods associated with piles founded in normally consolidated fine-grained soils. Energy balance equations demonstrate its theoretical soundness and provide insight into the accuracy of the numerical solution strategy. The calibration of the model parameters is accomplished with data available from standard site surveys and laboratory mechanical tests. Suggested typical model parameters are provided. The model is useful to those interested in computing the response of piles to loading conditions for which there are specific displacement service condition limitations. In the offshore oil production industry, typical applications would include the following: anchors to prevent pipeline walking as a result of thermal cycles, the design of conductors supporting wellhead control equipment, an evaluation of the dynamic response of riser bases exposed to dynamic environmental loads, and the design of foundation anchor piles for fixed or floating structures.

Crushed waste rocks, generated from mining operations, have been widely used for mining infrastructure constructions such as haul roads because of their low cost, high strength, and availability. Crushed waste rock gradation can, however, vary greatly, depending on blasting, mineralogy, and crushing process, but it is a key factor influencing the mechanical properties of crushed waste rocks (including resilient modulus, permanent deformation, and shear strength). Gradation should therefore be optimized to enhance their performance in the field. A series of repeated load and monotonic triaxial tests were carried out on crushed waste rocks with different gravel-to-sand (GS) ratios and fines contents (FC). Results showed that the optimum GS ratio was between 1 and 1.5 and contributed to provide higher resilient modulus and shear strength, and lower permanent strain. An increase in FC could, to the contrary, result in the decrease of resilient modulus and permanent strain and also a significant increase in shear strength. The structure state of crushed waste rocks was quantified using the c_m model, and the mechanical properties of crushed waste rocks were dominated by sand and fines when the content of sand and fines was higher than 80%, while it was dominated by gravel particles as the content of sand and fines was lower than 60%. Here, the M_R − θ model and the Rahman and Erlingsson model (extended using time-hardening approach) were well adapted to describe resilient modulus and accumulated permanent strain, respectively. Prediction models were also developed based on correlation analyses to predict the resilient modulus and permanent strain of crushed waste rocks based on gradation parameters.

Rainfall infiltration can alter the pore-water pressure and decrease matric suction, which can lead to slope instability and landslides. Most of the previous numerical studies conducted on rain infiltration have assumed a two-dimensional (2D) failure mechanism, which neglects the three-dimensional (3D) characteristics of slopes. An analytical assessment framework was developed using the upper-bound theorem of limit analysis to determine the factor of safety and failure pattern in the case of a 3D vertical cut slope under diverse rainfall situations combined with the unsaturated soil mechanics. The Green–Ampt model was adopted to depict the infiltration process and the progression of the wetting front into the soil. The slope factor of safety was determined using the energy balance equation by adopting the strength reduction approach. The validity of the framework was verified using the numerical simulation method. The effects of duration, intensity, and patterns of rainfall and the 3D traits of slope on the slope failure pattern and stability were determined. A set of design charts was included for the preliminary design. The present study quantitatively determines the stability of slopes susceptible to rainfall infiltration.

Abstract

The stability of earth slopes can be enhanced by introducing an anchoring system. The factor of safety of an anchor-reinforced slope is one of the essential items required to evaluate stability. This parameter can be predicted using limit equilibrium and numerical approaches by relevant software. Taylor’s stability chart has been frequently used to estimate the factor of safety of an unreinforced homogeneous cohesive-frictional soil slope. An analytical expression was developed in this study based on the friction circle method by which the factor of safety of anchor-reinforced slopes can be predicted using Taylor’s chart. The anchor-reinforced slope considered in the analysis consisted of homogeneous cohesive-frictional soil. The analyses were carried out considering different slope inclinations, anchor loads, anchor orientations, and slip circles. An illustrative example explained the procedure for finding the factor of safety and showed how the developed method could be used by practicing engineers. A comparison between the factor of safety estimated by Taylor’s chart and the limit equilibrium method using SLIDE indicates a good agreement.

Practical Applications

An anchoring system can improve the stability of earth slopes. The safety factor of an anchor-reinforced slope is the most critical design parameter as it reflects whether the slope is stable against driving forces. In geotechnical engineering, the factor of safety can be computed using an analytical/numerical approach, based on which relevant commercial software programs have been developed. These software programs might not be available to everyone. More importantly, they often require parameters of soil that need complex tests to be found, making their use unattractive for practicing engineers. The factor of safety of plain slopes can be found using Taylor’s stability chart, which is widely used in practice due to being convenient. This study presents a method through which the factor of safety of each potential slip surface in an anchored reinforced slope can be determined using Taylor’s stability chart. According to the approach, an anchored slope is equalized with a plain slope having a greater value of internal soil friction angle. Then, the factor of safety of equalized plain slope is determined using Taylor’s stability chart.

Owing to the uncertainty in the rock formation process, there are different forms of fissure combinations that significantly influence the stability of engineering. In this paper, the peak strength and failure characteristics of rock-like materials with four types of double prefabricated fissure combinations was investigated by combining similar material tests of the digital image correlation (DIC) techniques and discrete-element numerical method (PFC2D). With reference to the experimental observation of crack initiation and propagation, the prefabricated fissure combination effect was analyzed by varying the fissure angle and its combination type. The results indicated that the mechanical properties of the specimen with prefabricated fissures were affected by the fissure inclination angle. When the double fissure inclination angles were 45°, the total fracture length was longest and the peak strength and the proportion of dissipated energy were smallest. It can be obtained that when the fissure inclination angle reached 45°, the effect of the prefabricated fissure combination was maximum. Except for the specimens whose fissure inclination angles had 90° cracks that processed along a perpendicular direction, the cracks of other types propagated and coalesced near the lower side of the middle specimen. The research can provide guidance for controlling engineering disasters involving complex fissure combinations under natural geological conditions.

Finite-element limit analysis (FELA) is an effective numerical method to evaluate the stability of reinforced geostructures. Such an analysis has been commonly performed in the literature by assuming the earthen material to follow the well-defined associated plastic flow rule. In this study, the effect of adopting the nonassociated plastic flow rule on the ultimate bearing capacity of eccentrically-obliquely loaded shallow footings placed over geosynthetic-reinforced granular soil is rigorously examined through a comprehensive set of lower-bound FELA simulations along with second-order cone programming. The nonassociativity of the plastic flow rule is incorporated into the formulation of the Mohr–Coulomb yield criterion by considering a wide range of dilation angles (ψ) varying between 0 and the soil internal friction angle (φ). Unlike the previous FELA studies, both pull-out (sliding) and tensile (structural) modes of geosynthetic failure are taken into account. Accordingly, the impact of considering the nonassociated flow rule for the sand deposit on the bearing capacity ratio, failure envelopes, and the failure mechanism of overlying shallow foundation is investigated and discussed. The results show that failing to consider the significant influence of nonassociativity in the FELA simulations leads to overestimations of the tensile forces mobilized in the reinforcement layer as well as the ultimate bearing capacity of the overlying shallow foundation, thus yielding nonconservative and insecure designs.

Abstract

The behavior of annulus stone columns in soft clays is significantly influenced by the outer-to-inner diameter ratio. For this reason, in the present study, a comprehensive experimental investigation program was undertaken in the laboratory on a soft clay from Warangal, India, by varying its water content for achieving different undrained shear strength values and to determine the load-carrying capacity of conventional and annulus stone columns with different outer-to-inner diameter ratios that were double-encapsulated with geotextile. Investigations were also extended to determine the optimum L/D ratio and spacing between the groups of annulus stone columns. Based on these studies, a theoretical framework is developed for interpreting and determining the load-carrying capacity of the stone columns. The studies presented in this paper offer a novel ground improvement technique to enhance the load-carrying capacity of soft soils.

Practical Applications

Conventional in situ pile foundations and stone columns have been extensively used in geotechnical engineering to support widespread loads arising from infrastructure, such as oil storage tanks and embankments on soft soils. However, stone columns typically fail, due to bulging action. Therefore, the geotechnical engineering community uses pile foundations to alleviate failures and support widespread loads on soft soils. However, a significant decrease in the cost of the project and carbon footprint is realized when stone columns replace conventional pile foundations. Therefore, the proposed geosynthetic double-encapsulated annulus stone columns with enhanced confining resistance could be a suitable replacement for conventional stone columns and pile foundations to support widespread loads. The results presented in this paper show a significant reduction in bulging when the conventional stone columns are replaced with annulus stone columns. However, the installation technique adopted in the model tests differs from those in the field. Full-scale field testing of the proposed technique is required to understand the strengths and limitations of the proposed design approach.

A rigorous analytical continuum subgrade model translated into an equivalent two-parameter mechanical model of the Pasternak type is used to study the static response of piles to lateral loads. The model fully accounts for the soil shear missing in the conventional Winkler representation. The two parameters of the model are derived in advance. After conducting static analyses of a wide range of cases of the pile–soil system using both the proposed analytical model and finite-element models, closed-form relations are obtained for the adjustment factor left open in the model parameters that are found to mainly depend on the soil’s Poisson’s ratio. Back substitution of this factor showed that the model parameters take simple forms that depend only on a few factors such as the pile–soil stiffness ratio and the pile-end conditions. The model is validated by means of results of finite-element models. Closed-form pile head stiffness coefficients for various pile-end conditions are provided for both infinite- and finite-length piles. Expressions for a newly defined pile critical length are proposed for several combinations of pile-end conditions. It is demonstrated that the analytical approach employed is convenient and avoids the high degree of empiricity inherent in the conventional Winkler-based backward approach. The model has also the unique advantage of being convenient to conduct parametric studies, including the influence of soil shear resistance.

This paper investigates the failure mechanism of nonuniform large geotextile-reinforced cofferdam under seepage and excavation effects on soft sediments. A numerical model is established and validated with available testing results. Then, parametric studies are carried out to investigate the potential influence factors. This study found that the difference between the upstream and downstream water levels and the excavation depth both have significant influences on the stability of cofferdams, where excavation is the key influence factor affecting the stability of the cofferdam. Numerical results revealed that the safety factor could reduce by about 20% with excavation of about 1.5 m. An empirical equation is proposed for quantitative prediction of the stability of geotextile-reinforced cofferdams. A thorough understanding about the failure mechanisms of cofferdams as well as an empirical formula for predicting the stability is concluded in this study, which could provide engineering guide for flexible foundations reinforced by geotextiles.

Subgrades that are constructed from fine-grained cohesive soils undergo large settlements; therefore, the study of their deformation behavior is important to avoid early deterioration in the traffic infrastructure. In this study, the deformation behavior of two different types of cohesive subgrade soils at different compaction states has been addressed that considered the effect of influencing factors, such as water content, deviatoric stress, and confining pressure (σ₃). The results from the unconsolidated undrained cyclic triaxial tests show that the deformation behavior of soil is highly influenced by the level of applied deviatoric stresses and moisture content on the wet side of optimum (WS) and is slightly affected by σ₃ and moisture content on the dry side of optimum (DS). The elastic strain (ɛ_e) component showed a decreasing trend with an increase in the number of load cycles (N) and then attained a steady value toward a higher N; however, the plastic strain (ɛ_p) component continuously increased for a given magnitude of applied cyclic deviatoric stresses (σ_d,c). From the test results, logarithmic strain models were proposed to predict the long-term total (ɛ_t) strain and ɛ_p that developed in cohesive subgrade soils, which were subjected to various combinations of variations in moisture content and stresses. The proposed model has been compared with the existing model and shows better prediction ability with a coefficient of correlation (R²) of >95% in most cases.

Traffic-load-induced principal stress rotation has been widely studied. Most of these tests were conducted using a hollow cylinder apparatus to simulate ground-level traffic conditions, and only one shear direction was considered. However, fewer studies focused on the stress conditions of subsoil below slopes or embankments, which involved bidirectional shear. In this study, a series of bidirectional cyclic simple shear tests were performed using the variable-direction dynamic cyclic simple shear apparatus to investigate the effects of multidirectional principal stress rotation on sand induced by traffic loads. The specimens were first $K_{\alpha }$-consolidated with various static shear stresses and then subjected to traffic-induced cyclic shearing in different directions. The experimental results showed that both the magnitude and orientation of the initial static shear stress had significant effects on sand strain development and stress–strain behavior. A larger angle led to a higher axial strain, while larger initial shear stresses led to stiffer sand responses.

The usage of the Haar–von Kármán hypothesis for circumferential stress in axisymmetric problems is still questionable. This study aims to reveal statically admissible stress fields in conical sand valleys and heaps by applying the Haar–von Kármán hypothesis to rigid-plastic material obeying the Mohr–Coulomb criterion. The original boundary-value problem reduces to a pair of ordinary differential equations by employing the self-similarity assumption in conjunction with the condition of incipient failure everywhere. The pair of governing equations are numerically integrated with the fifth-order adaptive Runge–Kutta method. The shooting method is employed to numerically convert the boundary-value problem to the initial-value problem. Moreover, the singularities that occurred in the integrations are coped with by numerical perturbation of the initial boundary conditions. A line of stress discontinuity together with the stress jump condition is imposed to link the stress solution between the rigid and plastic regions. Admissible stress fields in various axisymmetric geometries are successfully achieved whereby the load transfer mechanisms in the conical sand heaps and valleys are elucidated. The arch action that occurred in bulk solid is observed. The effect of the circumferential stress hypotheses, that is, Haar–von Kármán hypothesis and Lévy’s flow rule, on the results of rigid-plastic solution is demonstrated; therefore, the advantages and disadvantages of both the hypotheses are elucidated. This study rigorously justifies the validity of the Haar–von Kármán hypothesis, thus a guideline on determining the value of hoop stress using the Haar–von Kármán hypothesis is proposed.

In this study, the effect of an eccentric load on the ultimate bearing capacity (UBC) of a strip footing of width B resting above a circular cavity in the rock mass is investigated using upper -and lower-bound finite-element limit analysis incorporating an adaptive meshing technique. The effect of governing independent variables, such as the diameter of the circular cavity, d_c, load eccentricity, e, distance of the cavity from the footing (horizontal, P, and vertical, Q), and rock mass parameters based on the generalized Hoek–Brown (GHB) failure criterion on the reduction of the UBC, is studied using a reduction coefficient, R_c. This study reveals that the influence of the cavity on the UBC is minimal for a cavity beyond a depth of Q/B ≥ 2.5 when e/B ≥ 0.3; and that Q/B ≥ 3 when 0.1 ≤ e/B ≤ 0.2, irrespective of P/B. Similarly, a cavity situated at −2 ≤ P/B ≥ 2 and Q/B ≥ 2 when e/B = 0.3–0.4, and −3.5 ≤ P/B ≥ 3.5 and Q/B ≥ 2.5 when 0.1 ≤ e/B ≤ 0.2, does not show any significant impact on the reduction of the UBC. Dominant potential failure patterns that could cover at least all the representative cases are presented and discussed to strengthen the insight into the possible mechanism of such a footing failure.

The present study discusses the effect of hydraulic loading in terms of water infiltration caused by rainfall on load-mobilization mechanism of single-pile (SP) and monopile–raft foundation (MPRF) embedded in unsaturated sand by means of the finite element-based computer program Plaxis3D. Soil was modeled using the conventional Mohr–Coulomb model incorporating Bishop’s effective stress, and the hydromechanical behavior was incorporated using the van Genuchten model. A fully coupled flow deformation analysis based on Biot’s theory of consolidation was employed to model the behavior of soil during water infiltration. Water infiltration at different rates ranging from 5 to 864 mm/day was simulated using the time-dependent flow boundary condition at the ground surface. After successful validation of the developed numerical model using the experimental study available in literature, the evolution of suction, effective saturation, and suction stress during the different rates of infiltration was investigated and the responses of SP and MPRF in terms of settlement and axial forces were obtained. The results indicated the contribution of suction stress in increasing the stiffness of soil to an infiltration rate of 240 mm/day, thereby increasing the capacities of both SP and MPRF. The mobilization of shaft resistance was greatly dependent on the suction stress, and a reduction in the suction stress upon infiltration led to a lesser mobilization of shaft resistances (reduced around 6%). This caused a higher pile deformation, leading to further mobilization of pile base resistance. The rate of infiltration and the raft dimension has significant effect on mobilization of raft and pile resistance within MPRF due to raft–soil and pile–raft interactions. A higher rate of infiltration led to a greater mobilization of pile resistance due to positive pile–raft interaction brought by reduction in the contribution of raft base resistance that was associated with reduction in Bishop’s stress. The outcome of the present study would help in better understanding the effect of hydraulic loading on the behavior of SP and MPRF and can be extended to pile group and combined pile–raft foundation.

Elastoplastic constitutive equations for soils often employ the nonlinear rate-type isotropic Hooke’s law, which is based on the additive decomposition of strain rate and considers the pressure dependency in the elastic part. Hooke’s law has independent isotropic and deviatoric components, and therefore, it cannot express elastic dilatancy as confirmed in experiments. In this model, although the elastic volume change is path-independent, the shear strain exhibits a significant residual when subjected to an effective stress cycle. This study proposes a rate-type elastic constitutive equation for soil applicable to elastoplastic constitutive equations based on finite deformation theory using an objective stress rate and additive decomposition of stretching; these equations cover these shortcomings of the rate-type Hooke’s law. The proposed rate-type elasticity constitutive equation is based on the hyperelastic body in the infinitesimal deformation theory proposed by Einav and Puzrin or Houlsby et al. and has confining pressure dependence, path independence of elastic volume change, and elastic dilatancy. Further, the residual strain is considerably smaller than that of the rate-type Hooke’s law. Moreover, this study improves the elasto-plastic constitutive equation, SYS Cam-Clay model, based on the skeleton structure concept by introducing the proposed elastic constitutive equation. The basic behavior of the elastoplastic constitutive equation for clay and sand is demonstrated to show that the newly acquired elastic dilatancy improves the mean effective stress reduction behavior during shear stress unloading under undrained conditions and the stiffness recovery behavior during liquefaction, which is essential for describing cyclic mobility.

Soils above the groundwater table and near the ground surface are often partially saturated, and the changes in the degree of saturation and matric suction caused by infiltration may have substantial effects on the stability of geotechnical systems. This work evaluates the significant effect of transient flow on the ultimate bearing capacity of strip footings founded on unsaturated soils under the simultaneous actions of vertical and horizontal loads and moment using the lower-bound theorems of the finite-element limit analysis and the incorporation of second-order cone programming. The unified effective stress theory is incorporated into the soil yield function to model the partially saturated state, and the closed-form solution for one-dimensional transient flow is adopted so as to evaluate the tempo-spatial variations of suction stress. For both sand and clay underlying soils, it is found that the increase of infiltration time leads to a notable decrease of the size of the normalized failure envelopes for either obliquely or eccentrically loaded shallow foundations. The impact of transient flow on the ultimate bearing capacity of surface footings is also observed to be greater for clay soils as compared with sand deposits due to the significant contribution of higher induced suction stress.

This paper presents an iterative horizontal method of slices (iterative HMS) for the global stability analysis of a slurry trench in layered cohesive-frictional soils. The iterative HMS differs from existing HMS models in terms of the assumptions on interslice forces. Preceding HMS techniques postulate that normal interslice forces can be evaluated from overburden pressures, which can lead to the violation of failure criteria along interslice boundaries. The iterative HMS ensures that a limit equilibrium system is established without violating the failure criterion throughout the entire soil mass. This is achieved by iteratively adjusting interslice forces by means of enforcing the failure criterion for the aforementioned problematic slice boundaries violating the failure conditions. The performance of the iterative HMS is evaluated in example problems of a slurry trench in uniform clayey soils and cohesive-frictional strata. The results are compared against solutions obtained using finite-element limit analysis (FELA) and a shear strength reduction FEM (SSRFEM). This comparative analysis shows that the adjustment in interslice forces is important for reasonably assessing trench stability conditions. A parametric analysis is performed by using the iterative HMS to show under what trench construction parameters the adjustment of interslice forces cannot be neglected in the stability analysis of a slurry trench.

Investigation of granular materials’ geomechanical and geological characteristics could provide invaluable information to researchers working in petroleum and civil engineering, geoscience, and petrophysics. In this study, the effects of normal stress and sand grain size on the petrophysical and geomechanical characteristics of artificial samples (made of a wide range of sand grains and cement) were investigated, while the chemical composition and mineralogy of all the samples were kept identical. The results showed that the rock porosity and permeability, the main criteria for evaluating rock storativity and transmissibility, respectively, were adversely affected by applying normal stress and the increase of grain size. Based on the results, there is a critical range of grain size (i.e., 0.1–0.2 mm) above which rock permeability decreases sharply with an increase in normal stress. The geomechanical outcomes revealed that improving the cementation process by applying compaction force, and thus, increasing the degree of hydration has a greater effect on ameliorating rock strength than reducing rock porosity. Besides, the uniaxial compressive strength (UCS) and Brazilian test results indicated that fine-grained samples fail at lower normal stress (i.e., at 38% and 66% of the coarse samples, respectively) compared with coarse-grained samples because of the large number of grain-to-grain boundaries. The fracture patterns showed a straight line for very fine and fine-grained samples, while an irregular shape appeared for medium and coarse-grained samples. In the end, a comparison of distinct petrophysical and geomechanical rock properties, such as X-ray fluorescence analysis, UCS, porosity, and permeability, between artificial and natural samples has been made to analyze the difference between them.

To capture the influence of temperature variation of pile–soil interface on the response of a single energy pile, numerical simulation and theoretical analysis were adopted in this paper. The temperature variation mechanism of a single energy pile was clarified using numerical simulation, and the temperature variation model of the pile–soil interface was established. Considering the influence of temperature variation on the conventional load transfer model of the pile–soil interface, the improved hyperbolic functions were proposed, and the parameters related to the improved load transfer model were determined. To predict the response of a single energy pile considering the temperature variation of the pile–soil interface, an iterative algorithm was developed using load transfer methods. Comparisons of the load-settlement response of three well-documented cases between the present computation results and the results derived from other methods were made to verify the reliability of the calculation method. Furthermore, a parameter analysis was carried out to assess the influence of soil properties and the parameters related to the load transfer models on the thermomechanical response of a single energy pile.

Soil–rock mixture (S–RM) is a natural geomaterial with multiple grain grades. It has dramatic trans-scale and hierarchical natural characteristics, and its mechanical properties are dramatically influenced by water. Various S–RM samples with multiple grain grades in engineering in situ state were prepared for large-scale and conventional direct shear tests in a native state and an immersion state under water to investigate the shear strength and deformation characteristics of S–RMs. The experimental results show that the S–RM in the natural state has high shear strength; the cohesion c is 44.0 kPa, and the internal friction angle φ is 34.7°. The shear strength of the S–RM after water immersion drops significantly: the cohesion c is 45.7 kPa, and the internal friction angle φ is 7.7°. The research results indicate that the cohesion of S–RM is mainly provided by the shear bond strength of the coarse grains, the development of which is governed by the gradation and surface topography of mineral grain and affected by constraint conditions. The interpretation of the sharp drop in the shear strength of S–RM after water immersion is that the sliding friction resistance between coarse grains and clay membrane and the occlusion friction resistance generated by the rotation transfer of coarse grains through clay membrane decreases sharply as the clay membrane around coarse grains becomes substantially soft. The shear strength of S–RM presents a dramatic scale effect and engineering design may come across major deviation and adventure when it adopts shear strength parameters determined by small-scale testing apparatus.

In the Hong Kong–Zhuhai–Macau Bridge mega project, several ground treatment methods were applied in the transition area between the artificial island and immersed tube tunnels to reduce the potential uneven foundation settlement underlying the tunnel, as the backfilled sand layer is more than 10 m around it. One of the foundation improvement methods involves the combination of preload and high-pressure jet grouting (HPJG) columns. Current field tests, such as core bowling, standard penetration test, and plate loading test, are not suitable for evaluating the strength of this reinforced foundation. This study presents a full-scale load test to examine the construction quality and effects of an HPJG-reinforced foundation. A novel method was designed based on the Boussinesq equation to simulate the additional stress distribution from the immersed tube tunnel. The tangent modulus method considering the impact of modulus nonlinearity was employed to calculate the nonlinear settlement of the treated foundation. Preferable settlement results were obtained using a set of pre-embedded high-precision hydrostatic leveling systems. Both the measured data and calculated settlement demonstrate the reasonableness of the present in situ test.

Clay–sand mixtures are deposited worldwide, such as naturally sedimentary soils and dredged clays in human activities. These mixtures usually have a fine fraction above the transitional fine content, and the compressibility is dominated by clay matrix and affected by sand fraction. In this paper, an explicit equivalent compression curve is proposed for clay–sand mixtures. This is done by directly incorporating the equivalent void ratio into the intrinsic compression model of the clay matrix. The roles of initial and evolving soil structure developed during the compression process are described by a structural variable, which can be directly computed from the experimental data. Experimental data compiled from various literature are used for evaluating the accuracy of the suggested model. They indicate that the proposed relationship of stress versus equivalent void ratio is simple yet effective to evaluate the compressibility of clay–sand mixtures with a wide spectrum of sand fraction. The model is also practically useful for estimating the compressibility of other gap-graded soils, such as clay–gravel mixtures. The proposed stress versus equivalent void-ratio equation is an elementary function and can be readily implemented into general elastoplastic models.

Calcareous sand fractures easily, has poor mechanical properties, and usually needs to be stabilized for engineering applications using additives. In this study, nano-MgO was used to enhance the mechanical properties of cement-stabilized calcareous sand (CCS). Unconfined compressive strength (UCS) and unconsolidated undrained (UU) triaxial shear tests were conducted on nano-MgO-modified CCS (MCCS) specimens, and the microscopic mechanism was investigated using scanning electron microscopy and X-ray diffraction. Finally, models to predict the UCS and shear strength of MCCS were formulated. The results showed that the addition of nano-MgO can enhance the strength and stiffness of CCS, with MCCS reaching its maximum strength of 2.1 MPa at 28 days when the nano-MgO content was 1%. Furthermore, the deviatoric stress first increased and then decreased as the nano-MgO content increased, reaching its maximum value when the nano-MgO content was 1.5%. The optimal nano-MgO content obtained from the UCS tests was different from that obtained from the UU tests. This improvement in CCS strength was due to the nano-MgO filling and cementation of hydrates such as Mg₇Si₈O₂₂(OH)₂, Mg(OH)₂, and CaAl₂Si₃O₁₀(H₂O)₂. However, too much nano-MgO reduces the strength of CCS because the nano-MgO expands during hydration.

In mining industries, the prime concern is to overcome the challenges of using conical cutting bits for excavating hard and abrasive rocks. In this research, a speculative investigation was performed to measure the efficiency of rock cutting and identify the wear behavior of aluminum titanium nitride-coated conical cutting bits. A newly designed and customized shaping machine is used with a triaxial force dynamometer to cut the rock samples linearly and to calculate their associated powers. Coated conical bits have a maximum hardness range of 2,291 to 2,459 HV, and uncoated conical bits possess minimum hardness range of 1,945 to 1,948 HV. Two rock samples of fine-grained sandstone with UCS of 83.77 and 97.00 MPa are used in this study. Various cutting ranges were investigated and the best range of cutting parameters are identified between the variables, such as cutting forces and extracted volume of rock, cutting effectiveness, specific energy produced while cutting, and bit wear. The percentage decrease in wear rate of a coated conical bit compared with an uncoated conical bit is 40.36%, 52.28%, and 53.30% for Rock 1 and 42.67%, 54.76%, and 60.90% for Rock 2 under varying depths of cut. The worn surface has been significantly investigated through scanning electron microscopy and energy dispersive X-ray analysis. The output of this study helps in extending the application of a surface miner for excavating harder rocks in mines.

A two-dimensional (2D) finite-element limit analysis (FELA) was performed under plane strain conditions to investigate the undrained stability of tunnel launch with a rigid wall in anisotropic clays. The anisotropic undrained shear (AUS) failure criteria were applied to identify anisotropic soil behaviors. The average bound solutions were employed to compute the stability load factor. Different sensitivity analyses were carried out to determine the effect of cover–depth ratio (C/D), overburden factor (γD/s_uTC), and anisotropic strength ratio (r_e) on the load factor (N) of the opening in tunnel launching with a rigid wall. The failure patterns that were predicted by certain parameters were explored and investigated. To adopt a practical approach, some new design charts for the undrained stability of tunnel launching with a rigid wall in anisotropic clays were devised.