International Journal of Geomechanics

Abstract

The stability of the retaining system under seismic conditions is an important aspect of safe design in earthquake-prone areas. In addition, this stability is highly dependent on soil uncertainty and failure mode contribution. On the other hand, imaging the borehole data directly into the analysis section and ignoring the known data by using unconditional simulation can lead to unrealistic results. Against this background, the current study presents a reliability analysis by incorporating geostatistical conditional simulations and a pseudostatic approach into the Finite-Element Method (FEM) MATLAB code to address the aforementioned issues. Then, the Sequential Compounding Method (SCM) is implemented to calculate the overall system reliability from a combination of the individual subsystem. Reliability analysis of a real case study reveals that compared with the Unconditional Random Finite-Element Method (URFEM), utilizing the Conditional Random Finite-Element Method (CRFEM) helps improve the mean value of the Factor of Safety (FS) against all failure modes by 7%–30%, while reducing the related standard deviation by 12%–43%. The results of system reliability show that bending moment and lateral displacement are the fundamental mechanisms in the static and seismic states. Moreover, implementing conditional simulation in seismic stability analysis offers a 16% and 43% reduction in the mean value and standard deviation of an unsafe distance from the excavation edge, accounting for less uncertainty in the slip surface location. Besides, according to the Coefficient of Variation (COV) of the failure modes, it is concluded that the FS against lateral displacement is chiefly affected by the soil heterogeneity compared with others, while shear force failure mode is less affected.

Practical Applications

Soldier piles are widely used in urban and industrial areas as a temporary or permanent retaining system for constructing underground structures. The stability of the retaining system under seismic conditions is an important aspect of safe design in earthquake-prone areas. In addition, the inherent variability of the soil properties dictates that stability problems are probabilistic rather than deterministic. In the current study, a real case with three boreholes of 22.5 m depth was considered and the soil parameters were estimated via field and laboratory tests. Then, the FS distribution and reliability indices of different failure modes were obtained for both static and seismic states by considering the seismic coefficient and efficient soil properties as stochastic parameters. These curves provided the essential data for structural design based on the target performance level. Next, the variation of the slip surface was determined, which could be used for determining the unsafe zone adjacent to the excavation. The responses of soldier piles indicated that by taking the seismic coefficient into account, the mean value of lateral displacement, maximum shear force, and maximum bending moment increased by 80%, 16%, and 37%, respectively. Moreover, considering different failure modes separately led to an overestimation of the reliability indices by three times.

To reduce the negative influence of groundwater on foundation pit excavation and the surrounding environment, an analysis of seepage fields has become very important in deep excavation projects. However, the current studies on the seepage fields of foundation pits lack in-depth theoretical research, partly because the theoretical solution is complex and obscure, and the solution is limited to single-layer soil, which is difficult to apply to engineering practice. By using orthogonality and boundary conditions to construct nonhomogeneous equations, this study deals with the development of an explicit analytical solution for predicting stable seepage around a foundation pit in layered soil underlain by an impervious barrier and a constant water head maintained inside and outside the foundation pit. The validity of the analytical solution is checked by first reducing the proposed multilayered solution to that of a single-layered solution by treating the conductivity of the layers as the same and then comparing this solution with the hydraulic seepage situations predicted by the reduced model with corresponding values obtained from other analytical works. A numerical model is established using FLAC^2D software to verify the solution proposed in this study and to obtain strong consistency. The solution is of a general nature and can account for the foundation pit width, the distance of the retaining wall from the impervious layer, the head difference, and the permeability variation in the layers of the soil. The study shows that flow to a multilayered foundation pit is sensitive to the width of the foundation pit, the embedded depth of the waterproof curtain, the thickness of the completely saturated soil up to the impervious barrier, and the total head difference. Furthermore, this study proves that the distribution of the conductivity in the layers plays an important role in determining the water head and the distribution of the streamlines. The results of this research could be considered in foundation pit design and water conservancy engineering practice.

This paper examines the accuracy of a new elastic–thermoviscoplastic (E-TVP) constitutive model developed based on critical state soil mechanics. The model can be used for simulating the temperature-dependent and strain-rate-dependent behavior of clay soils. The study compares the E-TVP behavior of a single soil element with previously published thermo-mechanical experimental results performed on saturated clay specimens at different temperatures. Suggestions regarding unloading and reloading at constant temperatures as well as thermal consolidation under constant loads are presented. A modification for unloading–reloading adds a new criterion to the volumetric thermoviscoplastic strain rate formulation. A physics-based term is added to the current specific volume of the soil to include the viscous effect induced by temperature change. These modifications improve the convergence of laboratory data and simulated model responses. Comparisons of results from an earlier E-TVP model and the newly improved model provide evidence of improved predictive capabilities.

The performance of batter-piled raft systems during seismic events continues to be a major concern. In response, a series of shaking table tests, including vertical and nonvertical configurations, were conducted, and the effects of superstructure frequency and pile angle on the seismic performance of the models were examined under a wide range of accelerations (0.2–0.7 g). Smaller bending moments, horizontal displacements, and rotations were captured for the nonvertical models, so the application of batter piles is reliable under seismic conditions. The maximum bending moment in the vertical models was recorded to be 8 times greater than in the batter piles at the lowest level of ground motion. Thus, the performance of the system was more sensitive to the frequency of the superstructure for vertical piles.

Geogrids used in roads can not only stabilize granular bases on weak subgrade but also have the potential to reduce excess pore-water pressures and deformations in road layers under traffic loading. In this paper, the solution for the geogrid-stabilized two-layered saturated soil system was derived according to the layered elastic theory and the Biot consolidation theory, and considering the benefits of geogrids. In the derivation, the lateral confinement and tensioned membrane effects of the geogrid were expressed as external stresses applied at the interface as continuity conditions. The effect of the geogrid on suppressing excess pore-water pressures in roads was characterized along the depth. Due to the generation of pore-water pressure, the instant total vertical and radial stresses were higher than those calculated by the Burmister solution without considering pore-water pressure, while the instant vertical strains/displacements were lower than those calculated by the Burmister solution due to the reduction of the effective stresses. The inclusion of the geogrid reduced the pore-water pressure so that the deterioration of the road could be mitigated. The calculations using the proposed solution also showed that the reduction of the pore-water pressure was significant near the location of the geogrid.

In this paper, the theoretical radii of the crushed and cracked zones for underwater rock drilling and blasting with coupling charge under different water depths were computed, and the dynamic finite-element software LS-DYNA was employed to simulate the failure zone of underwater rock drilling and blasting. The results show that the ranges of the crushed and cracked zones in the shallow water condition are slightly larger than those in the waterless condition. This is because the strength of the underwater saturated rock mass is lower than that of the rock mass under the waterless condition, which causes a slight increase in the range of the crushed and cracked zones after blasting. With increasing water depth, the effect of water pressure becomes increasingly obvious; in particular, the water pressure inhibits circumferential tensile stress induced by blasting, resulting in a rapid decrease in the range of the cracked zone. According to the simulation results, the peak value of the blasting vibration increases with the water depth because the generation of the cracked zone is inhibited by the action of water pressure; thus, more blasting energy is dissipated in the form of elastic vibration.

Loose zones and voids often exist behind the crown and the spandrel of a tunnel, and the interface between a tunnel lining and its surrounding medium is therefore partially debonded. To elucidate the partially imperfect interface effect on the dynamic response of tunnel, an analytical solution is derived for the scattering of plane shear horizontal (SH) waves by a circular lined tunnel with such an interface in a half space using wave function expansion and a piecewise integration method. A systemic parametric analysis based on the Xianglu Mountain Tunnel is conducted in a frequency domain. It is found that the effect of the spring model and the noncontact boundary model in simulating the partially imperfect interface is identical when the interface spring coefficient in spring model is small enough. The increment in the degree of interface imperfection (i.e., decreasing the interface spring coefficient or increasing the range of partially imperfect interface) tends to weaken the dynamic stress concentration factor (DSCF) but often intensifies displacements at the crown and spandrel of tunnel under SH waves at relatively high frequencies. The wave-trapping effect of the interface illustrated in the time domain is found to be the major mechanism for the partially imperfect interface modifying the stress and displacement fields in tunnel lining.

The relationship between flow speed and pore pressure gradient does not follow the classical Darcy’s law for seepage within high-permeability and low-permeability media. Thus, considering the non-Darcian flow described by exponential relation in soft clay and Forchheimer equation in granular column, the governing equation for the axisymmetric model of composite ground is established. A finite-difference scheme with central and phantom nodes is used to obtain the numerical solution. Then, the effects of two kinds of non-Darcian flow and geometrical parameters on the consolidation behaviors are drawn from the parametric study. The consolidation rate of surrounding soil by considering the exponential flow is less than that of Darcian flow in the same case. The consolidation rate of the granular column calculated by the Forchheimer equation is less than that of Darcian flow. Moreover, increasing the area replacement ratio is recommended to reduce these effects of non-Darcian flow.

Abstract

The loading stress path affects the soil’s dynamic response, but there are few previous studies on bidirectional shearing, let alone considering the influence of phase difference and bidirectional shear frequencies. This study investigates the undrained responses of reconstituted saturated soft clay under four typical shear stress paths using a multidirectional cyclic simple test system. All the soil samples are consolidated under normal vertical stress sheared in undrained conditions by applying two horizontal shear stresses acting along different directions from the consolidation stress. Test results indicate that soft clay’s dynamic strain, softening index, and dynamic strength depend significantly on the value of phase difference and the bidirectional shear frequencies: dynamic strength and softening index decrease while dynamic strain accumulates with increasing phase difference and decreasing bidirectional shear frequencies. An empirical formula is proposed to predict the development pattern of softening index versus load cycles under various shear paths based on test results.

Practical Applications

In this study, a series of simple shear tests was carried out under multidirectional shear paths, which may be helpful for field pile testing under cyclic loading. The simple shear tests all showed an increase in shear strain accumulation, owing to the change in shear stress path. This increase is undoubtedly smaller than the accumulation of lateral displacements in the pile tests because of the different boundary conditions and stress levels between the field and laboratory tests. Since soil behavior partly defines pile drifts, some models can also be validated at a small scale (element level) before investigating the pile–soil system. It is proposed that the simple shear test results can be used to calibrate numerical models for various stress paths.

This study explores surface-wave propagation through periodic arrangements of multilayered piles in a single-layer soil medium from the viewpoint of bandgaps. The influence of the geometrical parameters of the model on the bandgaps is discussed. The periodic theory of solid-state physics is imposed to derive the dispersion equation. The finite-element method is implemented to calculate the dispersion relation and attenuation zones for surface waves in a periodic pile and soil system. The results show that the bandgaps are sensitive to the size and arrangement of the piles. The practicability of ground vibration-isolation by periodic pile barriers are verified in the time domain. The location and width of bandgaps are further authenticated through finite unit cell–based frequency response analyses. It is found that the frequency range of the Rayleigh wave reduction agrees well with the theoretical attenuation zone. This work provides new insights into the design of periodic piles as wave barriers. This approach has scope for protecting infrastructures, such as nuclear power plants, which pose high environmental risks. It is found that the dispersion analysis gives essential information for Rayleigh wave isolation using piles, including the frequency range and the form of decline.

The existence of soil anisotropy makes the strength and deformation of the ground dependent on the loading direction, which should be considered in some geotechnical engineering designs. This paper introduces the anisotropic transformed stress method that generalizes the isotropic failure criterion and constitutive model for anisotropic cases through modifying the stress. This method brings much convenience for the solution of practical problems in the anisotropic ground. The anisotropic Mohr–Coulomb failure criterion is still a linear function of stress since the internal friction angle and cohesion remain constant along different directions. A simple and explicit formula for the passive earth pressure, which adds only an influence coefficient of soil anisotropy to Rankine’s formula, is derived. The elastoplastic stiffness matrix of the anisotropic modified Cam-Clay constitutive model does not increase any extra item compared with its general expression, so that finite-element simulation can be easily conducted to predict the surface settlement induced by tunnel excavation. Based on the aforementioned formula and simulation, the degree of anisotropy and the depositional direction of the ground on the effects of the passive earth pressure and the surface settlement trough are systematically analyzed.

Deep-buried structures are frequently and inevitably subjected to aperiodic perturbation during their life circle, resulting in damage to the rock mass surrounding the structures under the coupled action of excavation-induced local stress and dynamic perturbation. The investigation presented in this paper concentrates on the analytical and numerical dynamic responses around an unsupported deep-buried tunnel subjected to blasting disturbance with different wavelength-to-excavation span ratios (λ/D). Based on the complex function theory, the integral transform and its inversion, the elastic responses around the tunnel are obtained theoretically. Then the corresponding elastoplastic counterparts are explored using a self-developed code: elastoplastic cellular automaton. The analytical results indicate that Poisson’s ratio, the ratio of total time for blasting load to rising time, and λ/D have a significant influence on the distributions of dynamic stress concentration and velocity vibrations. Moreover, the numerical results reveal that tensile failure and the compression–shear counterpart are major damage mechanisms for the rock mass when the wavelength is less than the excavation span, while the compression–shear failure is major damage mechanism when the wavelength exceeds the excavation span. The analytical and numerical results can provide guidance for the support of deep-buried rock tunnels.

Constitutive coupled modeling has developed rapidly in recent decades, with numerous new models published. However, few models consider dynamic porosity, and experimental validation of such a model remains a challenge due to multiple variables. In this study, a new constitutive model for unsaturated soil with dynamic porosity was developed based on mixture theory and nonequilibrium thermodynamics, then the model was validated using test data from two experimental studies that yielded good results (relative average error AVRE = 0.8631–1.3046, R² = 0.9028–0.9981). The sensitivity of the model to the four primary parameters was analyzed to investigate the influence of model properties on the hydraulic and mechanical behavior. Results show that the calculation of volumetric strain is most sensitive to Young’s modulus (E), while the calculation of specific water volume is most sensitive to permeability (k). In addition, the sensitivity of the parameters changes with their value. Modeled results show that the porosity change significantly affects both hydraulic and mechanical behavior, even when soil undergoes relatively low deformation. Relative calculation error decreases notably after porosity change is considered (44.9% and 35.2% improvement in two different calculations). This study also finds that dynamic porosity affects the deformation energy of solids.

Dry shrinkage cracking of soil is a common phenomenon in nature. The shrinking and cracking of soil have been linked to several geological disasters. To simulate dry shrinkage cracking in soil, we present a continuous 2D moisture diffusion model, which is implemented in a GPU parallel multiphysics finite-discrete element software, namely MultiFracS. In this model, the moisture distribution of the system is analyzed initially, then the shrinkage stress caused by the change of moisture is calculated. Finally, the shrinkage stress is applied to the governing equation of FDEM to calculate the mechanical fracture. By repeating the preceding procedures, the soil shrinkage cracking problem can be simulated and investigated. We first verify the correctness of the model in dealing with the moisture diffusion problem in a continuous medium. Then we study the soil dry shrinkage and cracking, and compare the simulation results with the experimental results. The simulation results are in good agreement with the analytical solution or the existing literature results, which verifies the effectiveness of the 2D moisture diffusion continuous model to simulate the dry shrinkage cracking of soil.

Stability analysis of slopes subjected to steady infiltration is a hot topic in geotechnical engineering. However, the existing three-dimensional (3D) upper-bound limit analyses of unsaturated rotational slopes failed to take variable strength parameters and hydraulic parameters in space into account. To fill this gap, a semianalytical model is developed to capture the factor of safety (FS) and the critical failure region of unsaturated slopes based on the kinematical approach of limit analysis (KALA). A 3D rotational failure mechanism of unsaturated slopes subjected to steady vertical infiltrations is generated by a “point-by-point” technique, which can readily incorporate spatially variable strength parameters and hydraulic parameters. The work rates are calculated to formulate the objective function of FS, and the critical FS are optimized. The proposed model is validated through comparisons with the existing solutions and numerical solutions in terms of both the FSs and the failure patterns. The combined effects of hydraulic parameters and the size of slopes are investigated. An application to the stability analyses of unsaturated slopes with spatially variable physical parameters demonstrates that the proposed model has the potential to serve as a benchmark for the KALA of unsaturated slopes under complex geological conditions. Generally, the described framework can help geotechnical designers quickly evaluate the stability of unsaturated slopes in the preliminary design phase if the water table elevation is available and the hydraulic and strength parameters have been calibrated.

This paper pertains to the finite-element lower-bound bearing capacity analysis of inverted triangular-based strip footings (ITBFs). The solutions are obtained by the construction of a linear stress field that satisfies all the equations of equilibrium, which is the same as that developed by Lysmer in 1970; however, they were modified in conjunction with a nonlinear programming technique (active set algorithm) to isolate the optimal solution. Studies have been conducted on the convergence of the solutions (by varying the number of triangular elements), and the extensibility of the chosen stress field was confirmed by extending the mesh and comparing the solutions that were obtained. Parametric studies were carried out by varying the cone apex angle (β), for relevant soil properties and different values of the coefficients of earthquake acceleration [horizontal (α_h) and vertical (α_v)]. A close examination of the obtained results shows that they were as expected and were similar to those of conical footings.

Abstract

This article presents a model describing the phenomenon of vibration propagation in the subsoil. Stroke-based technologies are extremely effective in geotechnical practice; however, accompanying vibrations are harmful to the neighborhood. Impulses from impacts and vibrations resulting from ground improvement (dynamic compaction or dynamic replacement), installation of piles, sheet piles, and so on, are numerically analyzed. The article focuses on the damping mechanism and description of the significant variability of the deformation characteristics for small strains. In numerical analyses, an advanced multimechanism constitutive hardening soil model is used. The Rayleigh model is used to describe the phenomenon of damping of the soil massif. The finite-element method is used to solve a defined initial–boundary–value problem. The results of the analyses form the runs of displacement after the impulse. On this basis, the acceleration amplitude can be determined and the range of impact on the environment is estimated. For the analyzed drop of a heavy hammer, good compliance of the acceleration amplitudes obtained from simulations with results from field tests is achieved, both in qualitative and in quantitative terms. The presented model can be used to analyze the predictability of the harmful effects of shocks during design work.

Practical Applications

The results presented in the field of numerical modeling of vibration propagation in the soil medium may be of great practical importance. In situ experimental verification of the results obtained from the calculations allowed us to state that the proposed model is realistic and gives reliable results. It must be remembered that shock and vibration technologies are extremely effective in geotechnics. At the design stage, the performance of appropriate numerical analyses may allow for a proper assessment of which technologies of work are applicable in a specific case. This will allow for a significant reduction in the implementation of experimental plots, which impacts the time and price of construction works. On the other hand, in the realization stage, performed numerical analyses will be an excellent supplement to the monitoring results.

This paper describes the findings of a study of the soil plugging progressive formation process during pipe pile penetration using a transparent soil model test. The objective of this study is to visually investigate the factors affecting the plugging effect such as the pile diameter, penetration speed, relative density, and wall thickness. To measure the plugging development, an image measurement system was utilized. It found that pile diameter, relative density, and wall thickness were more sensitively influencing factors and that changing penetration speed had a minor influence on the degree of soil plug. The visualization analysis results show that the formation of plugging is not continuous, but intermittent and progressive. The soil plug was an alternate process from formation to destruction repeatedly. In addition, it revealed that the mobilization of internal frictional resistance depends on the height of the formed plugging and that the degree of soil plug only affects the magnitude of unit internal friction resistance. The underlying dynamic evolutionary mechanism of plugging formation was further discussed. In addition, a linear empirical formula between the incremental filling ratio and plug length ratio value was proposed.

In addition to seismic waves, coseismic displacement is also generated during earthquake events, which decreases gradually away from the seismogenic fault and may bring damages to tunnels in the area. This study aims to investigate the nonlinear response of tunnels under coseismic displacement induced by strike-slip fault. First, a method for applying coseismic displacement on the finite-element model (FEM) is developed by converting the displacement into equivalent nodal forces applied on the element nodes. Then, the nonlinear response of the tunnel under coseismic displacement is numerically investigated, considering the influence of the angle of the tunnel axis with respect to the fault trace, the epicentral distance, and the earthquake magnitude. The numerical results show that the tunnel might suffers tensile damages under coseismic displacement induced by the strike-slip fault, which indicates the coseismic displacement, as one kind of earthquake loads, should also be considered in seismic analysis for tunnels. Moreover, some other conclusions can be drawn: (1) The tensile deformation of the tunnel increases first and then decreases, as the tunnel axis changes from being perpendicular to the fault trace to being parallel to the fault trace, which is converse for the shear deformation; (2) the damage degree on the tunnel lining increases first and then decreases while the epicentral distance increases; (3) with an increasing earthquake magnitude, the tunnel damage increases dramatically. This study offers an insight into further research on tunnel response under coseismic displacement.

Brittleness has a significant influence on rock failure under compression; however, the mechanism is rarely comprehensively discussed. This study numerically investigates the brittleness effect on microcracking behavior of crystalline rock using a grain-based model implemented into a two-dimensional particle flow code, with a focus on the discussion of how rock brittleness affects the failure mechanism. The simulated failure mode changes from tension to shear with decreasing rock brittleness, which is consistent with previous laboratory test results. As the brittleness gradually decreases in the model, the grain boundary (GB) tensile crack to shear crack ratio increases, and the corresponding fractures change from vertical or subvertical to an angle about 45° along the vertical direction. The propagation and coalescence of generated microcracks result in a transition of failure pattern from splitting to shear under uniaxial compression with a decreasing brittleness level in the rock. A transition from GB tensile crack to shear crack is also observed under direct tension when the brittleness index gradually decreases. The tension to shear transition mechanism is closely related to the relative strength of the mineral grain and mineral bonding. The relative strength of mineral and mineral bonding could be used as a parameter to characterize rock brittleness from a microscale viewpoint.

Most studies try to establish a stress field and a compatible velocity field simultaneously to evaluate the seismic bearing capacity of strip footings placed adjacent to homogeneous soil slopes. However, the coupling of stress and velocity fields has not been addressed yet. In this study, the method of rigorous characteristics and the pseudo-dynamic approach are incorporated to resolve the issue. The failure mechanism is represented by the statically and kinematically admissible slip line field, and then the rigorous solution of the seismic bearing capacity can be achieved automatically without assuming any predefined slip surface. The results indicate that the seismic excitation leads to a remarkable decrease in the bearing capacity, especially for the effects of the initial phase difference and the soil amplification factor. Besides, the variation of the seismic failure mode is notably different from that under the static state. The seismic inertial force increases the possibility of the sliding failure, and consequently, the restraint effect of strip footings on the seismic failure mechanism diminishes.

Based on disturbed state concept (DSC) theory, this paper reports an analysis of the progressive failure mechanism of a pile–soil system from a new perspective. Assuming that the strengths of the pile–soil interface elements and the soil elements at the pile end follow an exponential distribution, the load transfer models of skin friction and end resistance based on DSC theory are established, and the significance and value method of the parameters in the models are clarified. The analysis of the relevant parameters shows that the proposed DSC load transfer models can simulate the nonlinear hardening or softening behavior of skin friction and end resistance. Based on the proposed DSC load transfer models, a simple and efficient iterative calculation method for the analysis of the bearing behavior of a single pile is established. It is demonstrated from case studies that, compared with calculated results using other methods, the load–settlement curves at the pile head obtained from the method proposed in this paper are in better agreement with the measured values, and could reflect the skin friction and end resistance softening characteristics of the tested piles in a more realistic manner. Furthermore, a parametric study is carried out to analyze the influence of the relevant model parameters on the response of a single pile.

The paper presents an efficient numerical integration scheme for coupled elastoplastic–viscoplastic constitutive behavior with internal-state variables standing for irreversible processes. In most quasi-static structural analyses, the solution to boundary value problems involving materials that exhibit time-dependent constitutive behavior proceeds from the equation integration, handled at two distinct levels. On the one hand, the first, or local, level refers to the numerical integration at each Gaussian point of the rate constitutive stress–strain relationships. For a given strain increment, the procedure of local integration is iterated for stresses and associated internal variables until convergence of the algorithm is achieved. On the other hand, the second, or global, level is related to structure equilibrium between internal and external forces achieved by the Newton–Raphson iterative scheme. A review of the elastoplastic and viscoplastic model is given, followed by the coupling between these models. Particular emphasis is given in this contribution to address the first level integration procedure, also referred to as the algorithm for stress and internal variable update, considering a general elastoplastic–viscoplastic constitutive behavior. The formulation is described for semi-implicit Euler schemes. The efficacy of the numerical formulation is assessed by comparison with analytical and numerical solutions derived for deep tunnels in coupled elastoplasticity–viscoplasticity. Finally, a parametric analysis is performed to show the importance that this model can have, in the long-term convergence profile, against other models. For the considered flow surfaces, potential functions, and properties, differences on the order of 23% to 52% are found in the long-term convergence profile.

With the rapid development of transmission-line engineering in western China and the frequent occurrence of extreme natural disasters, a great deal of attention has been paid to the bearing capacity of foundation systems. The uplift capacity is still the controlling factor in the design, but neglecting the horizontal load component will induce great potential risks to the stability of the foundation. This paper describes the model test of rock-socketed piles (with soil overlying rock) that were subjected to axial and oblique tension impacts. Furthermore, the load displacement response, failure mode, and load transfer mechanism of the model piles were compared and discussed. The research indicates that the uplift capacity of the model pile under the oblique load can be remarkably reduced by up to 27.3% in comparison with the vertical uplift. Moreover, the load–displacement curve of the model pile under axial and oblique loads present abrupt failure. Notably, the failure mode under the axial tension is an inverted cone-shaped axisymmetric failure, and the failure mode under the oblique tension shows the wedge failure on the compression side and the interface separation on the tension side. The compression side and tension side show the opposite load transfer mechanism, thus inducing the presence of a bending moment in oblique tension pile. The position of the maximum bending moment occurs at the depth of 2.3–2.8d below ground surface. In summary, the research results of this paper have important guiding significance for design of transmission tower foundation in similar geological settings.

Large-diameter piles (commonly called monopiles) are extensively used to support offshore wind turbines (OWTs) for withstanding large lateral and overturning moments. Results from monotonic tests suggested that the design using the current p–y methodology in clay significantly underestimates the pile stiffness. To determine a rational formulation of the undrained clay ultimate resistance on a theoretical sound basis, a plethora of published papers on the ultimate resistance of piles in undrained clays p_u were examined first. It has been found that all proposed methods for p_u were constructed on the assumption of twofold soil failure mechanisms, which are a shallow passive wedge failure and a deep full flow failure. Study of the transition depth separating the two mechanisms revealed the existence of a third pattern of failure, where the soil deforms three-dimensionally. Taking profit of the axisymmetric geometry of the pile, which is subjected to non-axisymmetric loading, an embedded rigid disk was taken to represent the behavior of the soil around a short segment of the pile in the region where the soil is expected to behave in three-dimensional (3D) mode. An expression for the soil reaction was established first by using an analytical approach. Then, p_u resulting from the third pattern was rigorously quantified by extending the obtained formula to failure using some fundamental notions of basic soil mechanics. By joining the obtained p_u to two other expressions for modeling the shallow passive wedge and the deep full flow, the variation of the undrained clay bearing capacity factor resulting from the threefold collapse mechanism was examined as a function of the pile normalized depth and for a variety of undrained clay strength parameters. Comparisons with other rigorous methods show the rationality of the proposed approach.

Negative temperature has an important influence on rock deformation and failure process. In a negative temperature environment, the pore water in rock partially turns into ice lenses. These changes in rock microstructure and components cause the frozen rock to exhibit temperature-related mechanical behavior. To disclose the mechanical damage process and failure mechanism of rock at different negative temperatures, we carried out acoustic emission (AE) tests on frozen sandstone. Results reveal that the cumulative AE count increases exponentially with increasing load, and the AE count mainly occurs in the yield and failure stages. According to the number and density of the AE count rate, the deformation process of frozen sandstone can be divided into four stages: compaction stage, elastic stage, yield stage, and failure stage. A sharp increase in the AE count rate implies that the rock deformation enters an unstable crack propagation section and macroscopic failure will occur. In addition, assuming that the microelement strength of rock obeys the Weibull distribution and the microelement failure conforms to the Drucker–Prager criterion, a constitutive model considering the negative temperature is proposed. A comparison between the experimental curve and the model curve shows that the model can accurately reflect the deformation process of frozen sandstone. This study is expected to improve the understanding of the damage mechanism and failure progress of frozen rock, and the constitutive model can provide a basis for calculating the deformation of frozen rock.

Brittleness has an important effect on the deformation and failure behavior of rocks. In this study, a brittleness evaluation index (B_p) based on the prepeak stress–strain curves of rock was proposed, and its effectiveness was verified by triaxial and uniaxial compression tests on different types of rocks. Based on the newly proposed index, the brittleness effect on the acoustic emission (AE) characteristics, such as the AE b-value, AE energy, average frequency (AF), and the ratio of the rise time to the peak amplitude (RA) of rocks under uniaxial loading was analyzed. The results show that the B_p has a linear negative correlation with the AE b-value. The stronger the brittleness of the rock, the smaller the AE b-value and the higher the ratio of macro to microcracks generated during rock failure. The brittleness effect on the variation law of the AE b-value is reflected during unstable crack propagation. In addition, rock brittleness affects the AF value but had no obvious influence on the RA value. The more brittle the rock is, the higher the proportion of tensile cracks in the fracture process. The research results could further enrich the evaluation system for rock brittleness and contribute to a better understanding of rock damage.

A cantilever retaining wall incorporating a long relief shelf is a specific form of retaining wall. However, currently, there are no reports investigating this retaining wall rotating about the bottom. Herein, the failure mode of semi-infinite noncohesive soils is studied using the finite-element limit analysis method (FELA) when the wall rotates about the bottom. The results show that the backfilled soil initiates the development of first and second failure surfaces at the end of the wall heel, and the third failure surface propagates at the shelf’s end. In the failing soil, there are numerous subfailure surfaces parallel to the first, second, and third failure surfaces. By considering both the effect of the relief shelf and the equilibrium limit analysis of the differential soil slice, this study derived a formula for calculating the active earth pressure of cantilever retaining walls with the long relief shelf. The effect of three different parameters, i.e., relief shelf length and location, and wall heel length, on the distribution of active earth pressure, the total active earth pressure, and its application point was studied. The longer the relief shelf and the shorter the wall heel, the lesser the active earth pressure. Consequently, when the relief shelf is set at the height of 0.3 times the wall height from the top of the wall, the active earth pressure is the smallest.

This work attempts to apply belief rule-based (BRB) model in information fusion method to landslides, to improve the accuracy and efficiency for early warning of landslides. Taking a typical rainfall-type landslide as the experimental area, the monitoring results find that the surface displacement is the most sensitive monitoring data. It is determined that the monitoring data of surface displacement change rate and rainfall intensity could be used as the input parameter of the BRB model. An initial BRB model is established by setting up the rule base for discriminating warning levels. The data from three monitoring points are collected for the optimization of the initial BRB model, and verification of the optimized BRB models. Results shows the optimized BRB model can accurately describe the nonlinear relationship between the selected monitoring data and the warning level, which provides an intelligent method for landslide prevention and has a strong application prospect.

This paper reports the effects of soil–water interaction on the mechanical behaviors of shear-zone soils taken from a bedding landslide in the Three Gorges Reservoir area of China. Two types of wetting treatment, namely cyclic wetting–drying and soaking in fluid, are adopted to mimic the enduring effect on landslide materials caused by reservoir operation. The effect induced by rainfall infiltration is also mimicked by varying water contents in the soils. The degree of soil–water interaction is indicated by the shear strength obtained from reversal direct shear and ring-shear tests. The experimental results indicate that the enduring soil–water interaction gives rise to significant disintegration of the soil particles, whereas the increasing water content greatly decreases the friction between particles at the shear surface. All this interplay between water and shear-zone soils leads to dramatic reduction in the shear strength. Moreover, it is found that the friction angle is more sensitive to cyclic wetting–drying pretreatment, while soaking pretreatment has a larger influence on the stiffness and cohesion of the soils.

Many published studies on seismic conditions have focused on a pseudostatic method with a linear Mohr–Coulomb failure criterion. However, the pseudostatic method ignores the influence of time and spatial variables on seismic accelerations, and almost all soils have nonlinear strength properties rather than linear properties. Herein, a new approach was established for calculating the seismic bearing capacity that considers a linear distribution of the seismic coefficients. A nonsymmetrical failure mechanism and the nonlinear Mohr–Coulomb failure criterion were used to describe the collapse process and soil properties. A layerwise summation method was developed to calculate the work rates because the pseudodynamic method depicts the variation in seismic acceleration as well as the time and spatial variables. In this work, a first application for calculating the seismic bearing capacity of soil foundations with nonlinear strength properties was conducted using the kinematic approach of limit analysis. Based on the numerical results and discussions, the key conclusions were as follows: (1) the reliability of this approach was verified by making exact comparisons with theoretical results and lab data; (2) in general, nonlinear solutions were more conservative than linear solutions; and (3) a high value of initial cohesion c₀ resulted in an increase in the seismic bearing capacity q_lim, and q_lim decreased when the ratio of tensile strength σ_t to initial cohesion c₀ or the value of nonlinear parameter m increased for a given value of initial cohesion c₀.

This paper presents an experimental investigation of the thermal and mechanical behaviors of an energy pile–raft foundation under intermittent heating operation with forced heat recharge, with 16 h of pile cooling and 8 h of forced heat recharge (referred to as 16F, where F indicates forced). The forced heat recharge was found to increase the daily heat exchange rate to 180 W/m, which was 50% higher than the value under general intermittent heating operation without forced heat recharge. The raft and building load at the pile head imposed a significant restraint on the upper part of the energy pile, leading to a minimum degrees of freedom (0.27) near the pile head. The mechanical behaviors of the pile, including strains, stresses, and pile end displacements and stresses, followed reversible paths when plotted against the daily temperature cycles. A slight residual pressure stress (10 kPa) was observed at the bottom of the raft during the initial thermal cycles.