International Journal of Geomechanics

Microbially induced calcium carbonate precipitation (MICP) has attracted great attention recently for its ability to improve the mechanical properties of soils. Calcium carbonate (CaCO₃) precipitates that formed at the contact points and on the surface of particles or in the pore space of soil matrixes could increase the bonding strength, friction, and interlocking resistances due to the enhancement of the interparticle bonds, particle roughness, and packing density, and therefore, greatly improve the macroscopic performances of biocemented soils that were subjected to external loading. Strength is one of the key factors when determining the application of biotreatments in geotechnical engineering during the construction and operation periods. This study presented a systematic, objective, and extensive review of the strength of biocemented soils that was based on previous research. The improvement characteristics were comprehensively investigated under compression, tension, and static and cyclic shear conditions, for unconfined compressive (UCS), splitting tensile (STS), yielding, shear, and cyclic resistance strengths. Particle scale regimes were elaborated to interpret the improvement mechanism in the biotreatment and failure modes in biocemented specimens under external loading. Furthermore, the challenges of biocementation were discussed, and future investigations were envisioned.

Vertical stone columns have been employed to improve the bearing capacity of the foundations for circular oil storage tanks placed on weak clayey strata. A solid stone column was placed along the axis of the foundation along with (1) two annular rings of stone columns for a 10-m-diameter tank, and (2) four annular rings of stone columns for a 20-m-diameter tank. The tank was first placed on a thin granular pad before transferring the load to the underlying weak clayey stratum reinforced with stone columns. The bearing capacity, with and without vertical stone columns, has been determined by employing an axisymmetric finite-element limit analysis. The Mohr–Coulomb yield criterion was used for the granular pad as well as stone column materials, and the Tresca yield criterion was employed for the purely cohesive clayey stratum. The results from the analysis were compared with that reported in the literature. The employment of stone columns leads to a significant increase in the bearing capacity of the foundations on soft clay.

An h-type prestressed anchor cable antislide pile is suggested for dealing with large-scale landslide disasters. At present, the internal force calculation of h-type antislide piles includes a great deal of cumbersome and complex calculus and graph multiplication processes, and the research on the action mechanism of prestressed anchor cables is insufficient. To simplify the calculation process, this study proposes an improved calculation method for the internal force and displacement of the h-type prestressed anchor cable antislide pile. A method to simplify the h-type antislide pile into a plane rigid frame calculation model is proposed, and the action of the anchor cable is added to the pile structure in the form of an unchanged tension. Then, the pile is divided into a loaded section and an anchorage section with the sliding surface as the boundary. Based on the engineering case, the results of internal force and displacement obtained through an improved calculation method, numerical simulation method, and graph multiplication method are compared and analyzed to verify the accuracy and applicability of the improved method. Finally, based on the improved calculation method, the internal force and displacement characteristics of piles are analyzed and compared under different support modes, including h-type pile, h-type with single-row anchor cable, and h-type with double-row anchor cables, and the support characteristics of the h-type prestressed anchor cable antislide pile are investigated. The results show that the tension of the anchor cable can effectively reduce the bending moment and displacement of piles. Compared with the h-type antislide pile, adding two prestressed anchor cables can reduce the maximum positive and negative bending moments of the front and rear piles by 14.8%, 14.5%, 9.4%, and 8.7%, respectively, and reduce the horizontal displacement of the top of the rear pile by 21.7%.

Surcharge preloading is a suitable foundation treatment for high-speed railways in soft soil regions. As a temporary preload on the foundation, the surcharge load must be removed before track construction. In this process, rebound deformation of the foundation and variation in the pore-water pressure have been widely observed. These phenomena significantly influence the further evolution process of foundation consolidation. Although Biot’s consolidation theory is suitable for unloading-induced soil consolidation, the conventional Laplace transform method for solving Biot’s equations entails a time-consuming procedure and cannot reflect the time-dependent characteristics of the preloading and unloading process. To address these issues, a time difference method is proposed in this work. The ordinary differential equation in the transformation domain is obtained using the backward two-step difference method, and a physical analytical solution of the plane strain problem of overloaded subgrade is obtained via the Fourier inverse transform method. The proposed solution is validated through a comparison with existing literature data and actual engineering practices. Finally, based on this calculation method, the influence of the surcharge preloading amount, loading time, and soil properties on pore-water pressure dissipation and distribution after surcharge preloading removal is investigated.

In this paper, we present a three-dimensional (3D) grouting model based on the combined finite-discrete element method (FDEM). The 3D grouting model discretizes the problem domain into tetrahedral elements and joint elements, and the grout flows only in the broken joint elements, which satisfies the planar Poiseuille flow. By combining grout migration, FDEM mechanical cracking computation, and stress-induced fracture aperture variation in a graphics processing unit (GPU) parallel multiphysics FDEM software, called MultiFracS, the 3D grouting model can model rock cracking and the effect of hydromechanical (HM) coupling. First, a grouting example with analytical solutions is presented to validate the 3D grouting model. Then, we investigate the influence of several key parameters on grout penetration in fractured rock masses. The results reveal that the 3D grouting model can model grout migration, pressure distribution, grout–rock mass interaction, rock deformation, and crack initiation and propagation. Finally, the evolution of fracture geometry induced by grouting under different in situ stresses is studied. The numerical results present high coincidence with the in situ experimental results, demonstrating that the 3D grouting model is effective in dealing with fracture grouting.

Pseudodynamic (PD) method is a novel method that has the merit of considering the temporal and spatial effects of earthquake input in seismic stability analysis. Currently, most PD analyses adopted the two-dimensional (2D) plane-strain assumption, which is inconsistent with the fact that many slope collapses have distinct three-dimensional (3D) features. To address that, a 3D PD method was proposed in this paper for rock slopes yielding Hoek–Brown criterion. The present method was established on the one-block mechanism in the kinematic analysis, since this mechanism has considerable efficiency in 3D safety factor computation. The details of the 3D PD method are elaborated herein, including failure mechanism, energy balance equation, and strategy of fining solutions. The effects of temporal–spatial variation of seismic input on slope stability are discussed using the proposed approach. The study reveals that phase change and acceleration amplification have contrary effects on rock slope stability, and which factor dominates determines whether PD analyses result in overestimated or underestimated safety factors than classical PS analyses. Finally, a parametric study is performed to investigate the influences of rock strength, slope geometry, and earthquake parameters in PD analysis.

A controlled uniaxial swelling device is used to saturate sodium-montmorillonite (Na-MMT) clay samples and allow them to swell to various swelling levels. Nanomechanical experiments are conducted on the saturated samples at 0%, 10%, and 20% swelling levels to evaluate the force–displacement response, modulus of elasticity, and hardness and compare those values with those obtained for undisturbed dry clay. Unconfined compressive strength experiments are conducted to evaluate the undrained response for the swelling levels used in the nanomechanical experiments. The modulus of elasticity and hardness decreases with an increase in swelling but is higher than the dry clay. The clay particles also break down into smaller sizes with an increase in swelling. Swelling significantly impacts the unconfined compressive strength, nanomechanical properties, and microstructure of swelling clay. The mechanical properties of swelling clay at various length scales from macroscale to nanoscale and at different swelling levels are essential for the development of models to accurately predict the shear strength of swelling clay, critical for the economical and safe design of civil infrastructures.

Slope stability analysis is an important research hotspot in geotechnical engineering. For a slope under general conditions, the tension stress zone (TSZ) is located at the rear edge and the shear stress elevated zone (SSEZ) is near the slope toe. The aforementioned phenomena influence the stresses of the slip surface (SOSS), which in turn affect the slope stability and make the slope instability present a progressive failure (PF) process. However, traditional limit-equilibrium (LE) methods constructed their calculation models based on slice division, which makes the tension–shear and PF mechanisms less or more difficult to be revealed. Thus, a novel global stress method for slope stability is here established in the framework of the LE theory. In the present method, the slope sliding body is regarded as a whole and the calculation uncertainty is placed on SOSS, the distribution of which is described by functions with some dimensionless variables. From these functions on SOSS, the slope PF pattern can be deduced. Meanwhile, stress constraint conditions (SCCs) at both ends of the sliding body are applied to intuitively demonstrate TSZ and SSEZ. Then, the slope LE state is solved with additional mechanical equilibrium conditions of the sliding body, and the global slope factor of safety is further obtained. After comparison and analysis of homogeneous and heterogeneous slope examples, the rationality and feasibility of the proposed method are verified. Furthermore, the influence on SOSS from TSZ and SSEZ is studied, and the slope PF characteristics are analyzed.

During the hydraulic jacking process, the preexisting joints in a rock mass under grout pressure that exceeds the in-situ normal stress become unstable. This process thus causes the tensile opening and crack growth of joints. In this paper, we describe an analytical approach to evaluating the hydraulic jacking mechanism based on the strain energy release rate method (SERRM). By employing the first law of thermodynamics, it is shown that the amount of energy stored in a grout mixture is equal to the amount of energy released during crack growth. This concept helped us to develop the SERRM. Accordingly, the paper presents development of new analytical equations to determine the allowable grout pressure and length of the resulting crack growth. These equations are fracture-toughness dependent, so as to avoid causing unwanted deformations due to jacking during grouting. The proposed allowable grout pressure equation accorded very well with the existing empirical rules, field data obtained from the Sardasht Dam project, and with the results of a numerical method.

In this paper, the compressive and tensile ultimate bearing capacity of helical piles, in the load range required for designing 63-kV transmission towers, are studied by conducting analytical and numerical investigations. In this light, an explicit easy-to-use analytical framework was developed by considering the unsaturated soil condition that was validated against experimental records. Also, finite-element models were constructed for fully saturated and fully dry soil conditions. Then, to validate the analytical and numerical solutions in fully saturated and fully dry soil conditions, three compressive and one tensile field tests were carried out, and the results were compared quantitatively with analytical and numerical calculations. Comparative studies showed that the analytical, numerical, and experimental results have a high level of conformity. In accordance with the load ranges of transmission towers, analytical parametric studies were conducted for different geometrical aspects of the helical piles in different soils. Also, for two typical unsaturated sand and clay soils, the ultimate load of helical piles was calculated versus matric suction. Moreover, a vast numerical parametric study was performed to investigate the role of the geometrical aspects of helical piles and soil characteristics on the load-transfer mechanism and ultimate bearing-capacity values for helical piles driven in sandy and undrained saturated clayey soils. Results showed that the maximum load capacity of helical piles occurred in a matric suction less than that of a fully dry soil. In addition, the soil type and the geometrical aspects of the helical pile were shown to have significant effects on the load–displacement behavior and ultimate bearing-capacity values.

The bearing capacity of foundations constructed on unsaturated soils depends on the soil saturation degree and thus the soil suction. This paper presents a simple limit equilibrium approach to compute the foundation bearing capacity on unsaturated soil using lateral earth pressure theory. An imaginary retaining wall is assumed to pass the edge of the foundation and active and passive lateral pressures on both sides of the wall are computed using the distribution introduced in an earlier study. Equating total active and passive thrusts on two sides of the wall gives the footing bearing capacity. The soil–water characteristic curve is used to obtain soil suction corresponding to different moisture contents and drained shear–strength parameters are used to determine the foundation bearing capacity. The developed method is applicable to sands and c-φ unsaturated soils with varying saturation degrees. The predicted results have been compared with data from seven case studies reported in the literature and found a satisfactory agreement. Parametric studies have been conducted to investigate effects of foundation embedded depths, two-layer soils, various suction stresses, and ground slope changes on the footing ultimate bearing capacity. The results show that with increasing the soil suction, the footing bearing capacity increases significantly.

Describing the time-dependent free swelling behavior of bentonite in saline solution is challenging as it is determined by the coupling effect of the chemical field and the swelling stress field in soil. The swelling pressure that determines the swelling strain of bentonite is affected by the ion concentration of pore water in soil, which in turn is affected by swelling strain. In this paper, a constitutive model estimating the 1D free swelling behavior of bentonite under chemomechanical coupling action is developed by incorporating the fractal swelling theory into the framework of the existing one-dimensional chemomechanical coupling consolidation model. A negative pore-water pressure is applied to substitute swelling pressure in the calculation model as it can produce the same effects on soil as the swelling pressure that drives the soil to adsorb water and swell in volume. The adsorbed water and swelling strain of bentonite increase with the dissipation of the negative pore-water pressure, or the release of swelling pressure. The model was verified by a one-dimension-free swelling test of bentonite in salt solutions. Furtherly, the influences of permeability coefficient and volume change coefficient of soil, and ion diffusion coefficient on 1D free swelling behavior were analyzed. The results suggest that the rates of the swelling pressure dissipation and the ion diffusion increase with the permeability coefficient, accelerating swelling to stabilize accordingly, whereas the effect of the volume change coefficient on the swelling rate is the opposite. The ion diffusion coefficient has a relatively small effect on the swelling pressure, while the final swelling strain is controlled by the additional pressure stemming from the osmotic suction of the ambient solution.

Cyclic triaxial tests are commonly used to evaluate the mechanical characteristics of subgrade soil under cyclic loads. Most cyclic triaxial tests were conducted on normally consolidated clays, however, some of the subgrade soils are overconsolidated clays. Moreover, both confining pressure and deviator stress are cyclically varying in the stress field induced by traffic loading. Recognizing that, the mechanical behaviors of overconsolidated clays under cyclic triaxial tests with cyclic confining pressure, are the main focus of the investigation. The impacts of both cyclic confining pressure and overconsolidation ratio (OCR) were investigated. Results show that as both OCR and cyclic confining pressure are increased, the accumulated axial strain decreases to a greater extent. Furthermore, the minimum excess pore water pressure decreases with an increase of OCR, while maximum excess pore water pressure remains approximately constant when the OCR exceeds 2.0. As the cyclic confining pressure is increased, so are the maximum and minimum excess pore water pressures. The variations in hysteresis loops with cyclic confining pressures are negligible, while the influence of OCR is greater. Nevertheless, as both OCR and cyclic confining pressure increase, the damping ratio decreases. Based on that, the variations in normalized damping ratio versus accumulated axial strain can be represented by an empirical formula. The proposed formula is not only suitable for normally consolidated clays, but also for overconsolidated clays in cyclic triaxial tests with cyclic confining pressure.

A semianalytical approach has been developed to investigate the nonlinear load–settlement behavior of bored single piles and pile groups embedded in sands. A more rigorous load-transfer function for the pile shaft, adopted to describe the pile–soil interface behavior, is derived from a damage constitutive model of the soil–structure interface. The interface model employed is capable of capturing the strain-hardening/softening and bulk dilatancy properties of the pile–soil interface and reflecting the degradation of the pile shaft skin friction. Meanwhile, an existing analytical solution has been applied to approximately describe the elastic stress–displacement relationship of soils outside the pile–soil interface during shearing. Moreover, the nonlinear stress–displacement relationship of soils at the pile base is simulated by a hyperbolic model considering the particle-crushing behavior of soils. Model parameters can easily be calibrated from laboratory interface shear tests and the physical properties of soils. Based on the matrix displacement method, the governing equation of the load–settlement response for bored piles is computed via an efficient iterative algorithm developed in terms of the midpoint incremental method. The pile-to-pile elastic interaction and the reinforcement effect of neighboring piles are incorporated into the investigation of pile groups. The present approach is verified by comparison with the existing theoretical approach, centrifuge tests, and model pile tests. Extensive parameter investigations are performed to systematically explore the load–settlement response of the single pile and pile groups.

The accelerating pace of development due to groundwater overwithdrawal throughout the world places increasing demands on the unsaturated zone. Estimating evaporation from unsaturated soil has been important for many geotechnical and geoenvironmental applications. As an example, the long-term performance of soil covers, which are widely used in mining and landfill applications to protect the environment, depends on evaporation from their surfaces. Evaporation, in turn, depends on moisture flow within an unsaturated soil mass, which is generally coupled with heat flow. Evaporation also depends on the void ratio and hydraulic and air conductivities of soil, which are, in turn, affected by stress and strain and the resulting soil settlement. As a result, a thermohydromechanical (THM) analysis for predicting evaporation is necessary. A two-dimensional (2D) finite-element program, θ-Stock, can perform THM analysis of unsaturated soil but works only within the soil, not in the atmosphere above the soil. In this study, a 2D model of soil–atmosphere interaction employing atmospheric coupling and using a modified Penman equation was implanted in θ-Stock to develop program EVAP1, which numerically estimates potential and actual evaporation from unsaturated soil using THM analysis. Because of the coupled character of the phenomena, the boundary conditions were determined by the soil state and the environmental data. The program EVAP1 was verified with published experimental and numerical studies on evaporation. The results of analyses using the verified program showed that neglecting THM behavior, and hence soil settlement, leads to an overestimation of evaporation from unsaturated soil surfaces.

Tunnel engineering in the cold region often experiences the coupling of the stress field and seepage field, which has complex mechanical behavior and permeability characteristics. This study takes sandstone as the research object and uses the multifunctional RLW-2000 rock triaxial instrument to perform triaxial compression tests on sandstone with different freeze–thaw cycles under seepage pressure and confining pressure. The development law of rock mass cracks under different load combinations is analyzed, and the correlation characteristics between permeability and crack state of freeze–thaw sandstone in the process of seepage–stress–damage are studied. The results show that the permeability decreases gradually due to the compaction of pores and microcracks in the rock at the beginning of loading. As the crack radial strain increases, the internal cracks in the rock begin to grow steadily, and the permeability increases slowly. As the load continues to increase, the accelerated crack propagation leads to a rapid increase in permeability. In addition, under certain freeze–thaw cycles, the initial permeability of sandstone decreases with the increase of confining pressure. Under a certain confining pressure, the initial permeability of sandstone increases with the number of freeze–thaw cycles. Finally, based on the test results, theoretical methods are used to study the characteristics of rock damage under different freeze–thaw cycles, the correlation between the damage variable and, the crack radial deformation is established. The relationship between the permeability and the damage variable is deduced, which reveals the permeability evolution mechanism of freeze–thaw sandstone. These test results can provide a reference for rock stability monitoring under the coupled action of permeability and stress in geological engineering.

Geomechanical behavior of methane hydrate-bearing sediment (MHBS) plays a major role in evaluation of the stability of a hydrate reservoir. A series of triaxial compression tests were conducted on MHBS to study the influence of temperature and pore pressure conditions on its mechanical behaviors. The experimental results show that temperature and pore pressure have a significant effect on the stress–strain curve, stiffness, and strength of MHBS. As temperature decreases and/or pore pressure increases, the stress–strain curve manifests an enhanced strain-softening characteristic, stiffness, and strength. Furthermore, MHBS cohesion also tends to exhibit a significant increase, but its internal friction angle almost remains constant with decreasing temperature and/or increasing pore pressure. These findings imply that the change in temperature and pore pressure affects the strength of MHBS, which occurs predominately due to change in its cohesiveness. To describe these impacts, a phase state parameter is introduced to characterize the temperature and pore pressure conditions. Meanwhile, three empirical formulas for relating the secant modulus, strength and cohesiveness to phase state parameter are presented. Good agreement between simulation and measured data indicates that the phase state parameter can effectively describe temperature and pore pressure conditions. The proposed empirical formulas are able to address the influences of temperature and pore pressure conditions on geomechanical characteristics of MHBS.

In underground mining, sudden fault reactivation is the root cause of many types of mine disasters, including mine seismicity, water inrush, roof collapse, and gas outburst. The accurate assessment of the risk of mining-induced fault reactivation is important in disaster prevention in near-fault mining. In this study, based on the stress ratios of the three principal stresses under the Andersonian stress state, we introduce a new mode for defining the stress regimes and a new 3D stress-ratio-based approach for the tendency analysis of fault reactivation by extending the original Morris's theory of fault slip-tendency. Our analyses showed that the reactivation tendency of a fault in a stress field is correlated with the stress ratios, whether the correlation is positive or negative depends on the stress regime of the stress field. Considering the abutment stress effects in front of the working face, an approach to the tendency analysis of mining-induced fault reactivation is also proposed using the stress-ratio-based algorithm. Taking the No. 8101 mining face of the Wangzhuang mine as the engineering background, a case study is presented to demonstrate the application of our proposed method in actual mining practice for predicting the risk of fault reactivation. The proposed method is a practical technique and can be applied widely for any mining methods, stress regimes, and fault orientations.

Thermal–mechanical damage is an important feature of natural rock containing internal defects (microcracks and microvoids). However, this damage has not been studied thoroughly. This study improved a statistical damage constitutive model for heat-treated rock subject to external load by assuming the strengths of micro-elements following a Weibull distribution. First, the statistical damage constitutive model at room temperature was developed based on continuum damage mechanics. Then, a modified coefficient for thermal damage was introduced. The damage evolution equation of rock samples was derived at different temperatures. Third, the model parameters were determined with the feature points on the stress–strain curve. Finally, the model was verified against measured data available in literature and parameter analysis was conducted. It is found that the prediction results of the improved model are in good agreement with the measured data, whose parameters are few and have definite physical meanings. The thermal damage of rock increases with the increase of temperature. The curve of total damage evolution is in the “S” shape under the thermal–mechanical combining action. At a constant confining pressure, the slope of the ascending segment in the middle of the damage evolution curve increases with the decrease of temperature. At the same temperature, confining pressure considerably affects the slope of middle segment of the damage evolution curve and weakens the thermal damage effect.

Dikes made up of erodible geotechnical materials are easily broken by overtopping flow, which poses a serious threat to human lives and properties in protected areas. In this study, the plane breach of cohesionless dikes induced by overtopping was simulated via the discrete-element method coupled with computational fluid dynamics. A method of dynamically setting the permeabilities of fluid computation cells was proposed to implement the variation of the free surface of overtopping flow. The numerical model was validated using published experimental results, and the sidewall effect was also analyzed. The influence of three important factors on the dike breach process was investigated, namely, the inflow discharge per unit width, convergence area length, and particle size. The results suggest that the inflow discharge per unit width has little influence on the breach process within a range, outside which it has a promoting effect. The normalized peak breach discharge increases linearly with the increase in convergence area length. When the relative convergence area length increases to 4, the descent speeds of the convergence water level and the dike height reach a balance for a long time during the peak stage of the breach hydrograph. For the dikes consisting of uniform cohesionless particles, the breach process is linearly related to the particle size without regard to the seepage inside the dike. The findings of this study provide new insights into the mechanism of dike breach.

This study aims to predict the effect of liquefaction on an embankment resting on liquefiable foundation soil. A numerical model has been simulated in PLAXIS 2D with plane strain idealization. An effective stress–based elastoplastic UBC3D-PLM model has been used to represent the constitutive behavior of foundation sandy soil. The embankment soil has been modeled using the Mohr–Coulomb material model. Initially, the pore pressure and settlement response have been derived for the model without a stone column. The top surface of the loose foundation soil experiences excessive heaving near the embankment toe toward the free surface beside the embankment on either side. Subsequently, a parametric study has been conducted on the mitigation of liquefaction beneath the embankment and liquefaction-induced settlement considering stone columns as a mitigation measure. Stone columns have been modeled assuming equivalent plane strips by considering the equivalent permeability and bulk modulus of stone columns. The efficacy of stone columns in controlling the heaving has also been revealed from this study in addition to the reduction in excess pore pressure beneath the embankment toe and the settlement of the embankment. The parametric study has also investigated the effect of diameter and spacing of the stone column. It has been observed in the case of cyclic loading input that with increasing the amplitude of loading, the effectiveness of stone columns reduces, and this leads to an increase in the crest settlement. Moreover, a seismic study of the embankment model has been carried out for 10 different ground motions to examine the effect of the stone column. The study reveals that for moderate-intensity ground motions, the stone column shows an effective mitigation of excess pore pressure near the embankment toe along with a reduction of embankment crest settlement.

Frictional energy piles have been emerging as a proenvironmental means in the industry to exploit shallow geothermal energy. A growing concern for energy piles is their bearing capacity typically subjected to temperature variations. To better understand the temperature-dependent behavior involving bearing capacity, herein a series of direct shear tests were carried out to examine the effects of temperature and thermal cycles on the frictional behavior of the pile–soil interface for energy piles. The pile–soil interface consisting of fine-aggregate concrete and kaolin clay was tested under four normal stress levels, i.e., 50, 100, 200, and 300 kPa. The results suggest that: (1) a positive correlation may exist between temperature and the shear strength of the pile–soil interface; (2) the adhesion of the interface may vary with temperature in terms of a nonmonotonic function; and (3) the shear strength of the interface appears to decrease with an increasing thermal cycle and/or an increasing fluctuation amplitude of temperature within a temperature cycle. The experimental data obtained here may help enrich the understanding of the complex behavior of the shear strength of the pile–soil interface for energy piles and related soil–structure interaction.

The goal of full-waveform inversion (FWI) is to extract quantitative information pertaining to the material and geometrical properties from measured wave fields with their full contents considered. As an inverse problem, FWI itself is associated with ill-posedness, which means instability and nonuniqueness of the solution, because the fields are measured only at some locations. Owing to these unfavorable conditions, several regularization techniques have been utilized for stable estimations, but it is difficult when using a regularization technique to select a regularization factor, which has no physical meaning. In this paper, the FWI approach is applied to estimate the material properties of a layered half-space. The thin-layered method, an efficient analysis method for wave propagation in a layered medium, is employed for this purpose. It is formulated in the maximum a posteriori (MAP) form, and Tikhonov regularization is expressed as a prior distribution, whose standard deviation replaces the role of the regularization factor to ensure an intuitive meaning. Additionally, a technique to remove outliers is newly introduced for the regularization technique; it captures discontinuities accurately in the material properties of a layered half-space. Through this additional technique, the limitation of the smoothness effect in existing regularization techniques is alleviated. The proposed MAP approach including the regularization-based prior and outlier-removal technique is applied to several numerical examples to estimate the profiles of the shear velocities of a layered half-space. The numerical investigations conducted here confirm the validity of the proposed approach with satisfactory accuracy.

Shale is often encountered during rock engineering. The inherent anisotropy of shale and the loading and unloading path affect the failure characteristics of this material. In this study, shale specimens with seven different bedding orientations were used to carry out cyclic loading and unloading experiments to explore the anisotropy of the mechanical properties of shale and the energy evolution of its failure. The experimental results indicate that with an increasing number of cycles, the secant modulus of shale with bedding orientations of 0°, 15°, 45°, and 90° decreases; however, for bedding orientations of 0°, 30°, and 75°, the secant modulus increases or becomes constant. During cyclic loading, hysteresis and irrecoverable strain are clearly observed. The irrecoverable deformation with a bedding orientation of 45° is the largest. The energy evolution during cyclic loading clearly presents anisotropic characteristics. Under the same axial stress, the elastic energy storage capacity, which nonlinearly increases with the axial stress, is the largest for the bedding orientation of 15° and the smallest for the bedding orientations of 60° and 90°. The dissipated energy is much larger for bedding orientations of 45° and 75° than for other bedding orientations. A comparison of the damage evolutions defined by the damage energy release rate suggests that the damage evolution trends are the same for all bedding orientations, but damage is more easily generated with bedding orientations of 60° and 75°. To theoretically describe the energy evolution, an elastic energy evolution model that considers the external incentive effect, self-promotion effect, and self-inhibition effect of energy was established. An energy release dispersion coefficient and fabric tensor were defined to consider the effect of confining pressure and inherent anisotropy. Then, a modified energy-based strength criterion for anisotropic sedimentary rocks was proposed. The results show that both the energy evolution model and the strength criterion have good correlations with experimental data.

The undrained shear strength (s_u) and overconsolidation ratio (OCR) of clayey soils are two key parameters that are frequently used in geotechnical engineering practice. In comparison to laboratory tests that are expensive and time-consuming, the fast evaluation of these parameters using the field piezocone penetration test (CPTu) is favorable. The available literature contains a number of correlations that have been suggested by several researchers to estimate the s_u and OCR from CPTu; however, these correlations were mostly empirical and were constants multiplied by CPTu measurements. In addition, these correlations were site-specific and provided rough estimations of these important parameters. In this paper, the process of a CPTu in clayey soils was modeled via finite-element (FE) formulations, and the predictions for excess pore water pressures (EPWPs) that were generated around the penetrating piezocone were elaborated on and used to develop two new relationships for the estimation of s_u and OCR from CPTu data. A major advantage of the proposed relationships is that they could be employed using CPTu measurements and no other information from laboratory experiments or calibrations with field benchmarks or reference values may be needed. The utilized simulation procedure and the proposed relationships were compared and validated with the laboratory and field measurements and the existing relationships in the literature.

Granular base material (GBM) is widely used as the base/subbase course of pavement structure. In the mechanic–empirical design of flexible pavement, both the resilient modulus and permanent deformation are the major deformation properties of base materials, related to early-stage distresses of the surface layer under traffic loading. However, since the microscopic interaction between aggregates of the GBM is quite complex, the deformation behavior was not to be understood merely empirically. This study aims to evaluate the macroscopic and microscopic behavior of the GBM under repeated load triaxial (RLT) testing by the discrete-element method. Both the size gradation and the aggregate shape were considered in numerical simulations. The modeling technology of a heterogeneous structure was developed and verified by laboratory results. The results showed that the resilient modulus measured by the developed simulation was in good agreement with that of laboratory tests, within errors of 5.0%. The deformation behavior of the GBM presents the stress-hardening characteristic that the resilient modulus of the GBM increases from 94.03 to 337.71 MPa with the growth of the volume stress and deviator stress. The microstructure of the GBM maintain a relatively stabilization in dynamic response and anisotropy changes during the cyclic loading and voids within aggregates play a role in buffering the change in internal stress. The principal contact normal trends to the direction of maximum bulk stress through small motions, and rotations of aggregates during the loading. It provides a robust mechanism for the resistance to deformation, which results in dispersing more stresses into the skeleton.

Accurate measurement of the thermal properties (viz., thermal conductivity, thermal resistivity, volumetric heat capacity, and thermal diffusivity) of soils in cold regions necessitates the development of techniques that are robust and efficient and that can incorporate different heat migration mechanisms under the influence of complex initial and boundary conditions. However, devices or the numerical procedures employed to determine them are scanty. In such a scenario, here, a methodology that facilitates the determination of thermal properties of soils in cold regions has been developed based on their heat-pulse migration characteristics (HPMC). To control the temperature of the soil specimen, a temperature-controlled environment chamber has been employed and HPMC was established by using the dual-probe heat-pulse sensor. Furthermore, a technique to estimate the thermal properties of the soil specimen by employing the measured HPMC, which facilitates solving an inverse transient heat conduction problem by using the conjugate gradient method, has been developed. Subsequently, the thermal properties of fine sands corresponding to different initial moisture contents and low temperatures have been determined and the results were compared with those predicted from the HPMC by utilizing interpretation techniques such as the single-point method and nonlinear fitting.

This paper explores how energy piles interact under imbalanced and balanced daily temperature cycles and a range of monotonic thermal loads, combining field experiments and numerical simulations on two bored energy piles with a spacing of 3.5 m. Monotonic heating and cooling loads were simulated for temperature changes of |ΔT| = 5°C, 10°C, 15°C, and 20°C. Balanced, cooling-oriented imbalanced, and heating-oriented imbalanced thermal cycles were simulated between 0°C and 40°C with heating-to-cooling time ratios of 12:12, 16:8, and 8:16, respectively. One of the two energy piles’ axial and radial thermomechanical responses was investigated during single- and dual-pile operations. Soil temperature changes between the piles were greater for dual-pile operation, leading to increased thermal interaction, particularly for higher magnitudes of monotonic thermal loads. However, dual-pile operation did not alter the ground temperatures near the edge of the piles for the pile spacing considered. They remained similar for single- and dual-pile operations for the setting investigated in this paper. As a result, the pile temperatures, axial and radial thermal stresses, and thermal stress rates were similar for all single- and dual-pile operations simulations. Cyclic temperatures, particularly balanced cyclic loads, induced lower thermal effects in the piles and soil than in other cases. Overall, the results from this study provide validated insights into the situations where thermal interaction and different temperatures typical of heat pumps should be considered in designing groups of energy piles.

Abstract

Seismic shear waves that propagate along the axis of underground linear structures (e.g., tunnels, pipes, and piles) generally impose deformations that need to be accounted for in structural design or verification. Preliminary analyses are typically carried out following a free-field deformation approach based on conventional Euler–Bernoulli beam theory for bending behavior and a pure-shear beam model for the evaluation of distortions. This simplified approach, widely used in practice, may lead to inconsistent and overly conservative results. Solutions accounting for soil–structure interaction have also been proposed in the literature, considering an Euler–Bernoulli beam model supported on an elastic foundation subjected to simple harmonic shear waves. This approach, however, may not adequately represent cases where shear behavior dominates over bending, particularly in very stiff ground conditions. This paper presents a simplified analytical solution to evaluate kinematic demands in underground linear structures subjected to axially propagating harmonic S-waves by means of a Timoshenko beam model supported on a Winkler foundation, including transverse and rotational springs, which are in turn derived following a modified Novak approach. The proposed analytical solution can be construed as a generalization of the free-field and soil–structure interaction solutions currently available in the literature, which is also able to represent situations where both shear and bending mechanisms are present, overcoming the mechanical inconsistencies of the current solutions commonly used in practice. Based on the proposed model, simple analytical expressions are proposed, considering both a complete and a simplified solution, which allow the evaluation of peak kinematic demands in an expedited manner. The analytical formulation can thus be used to evaluate displacements, rotations, bending, and shearing demands in tunnels, piles, pipes, shafts, among other buried linear structures when subjected to harmonic S-waves. Results obtained by means of the proposed approach are validated against a full 3D finite-element model.

Practical Applications

The present paper presents a simplified analytical solution to evaluate kinematic demands in underground linear structures subjected to axially propagating S-waves by means of a Timoshenko beam model supported on a Winkler foundation, including transverse and rotational springs, which are in turn derived following a modified Novak approach. Based on the proposed model, simple closed-form solutions can be used to calculate displacements, rotations, bending, and shearing demands in tunnels, piles, pipes, shafts, among other buried linear structures subjected to harmonic S-waves. The analytical expressions proposed in this paper are validated against a full 3D finite-element model (FEM) and allow the evaluation of peak kinematic bending moments and shear forces in an expedited manner.

The statistical law on mechanical parameters of rock mass with size is the key to the study of the size effect. Since the existing statistical methods of the size effect only consider the continuity of the size but not the difference between the samples of each size, a new statistical method that considers single size and multisize is proposed. Based on the proposed method, the true representative elementary volume (TREV) value is used to determine the size effect stability threshold. Combined with the analysis of the three major size effect theories, the unified size effect law model and variation index k are proposed. The results are validated by statistical test data on the uniaxial compressive strength (UCS) obtained in realistic failure process analysis (RFPA) numerical test and from other works, which proves that the proposed method can reflect the variation law of UCS value with size and provide a basis for theoretical research on the size effect in mechanical behavior.