International Journal of Geomechanics

In order to understand the influence of sand content on the secondary consolidation behavior of sand–fine mixtures, a series of one-dimensional creep tests were conducted. These tests used mixtures with sand contents of 0%, 16.67%, 28.57%, 50%, and 60% and were run for 3,000 min. As the sand content increases, the structure of the mixtures transitions from being fine-supported to sand-supported. This results in changes in the time at the end of primary consolidation (TEOP), the proportion of secondary consolidation deformation in the total deformation (PCT), and the coefficient of secondary consolidation. These parameters decrease before the sand content reaches 28.57% and increases after this point. The sand–fine mixtures with a sand content of 28.57% exhibit the minimum TEOP, PCT, and coefficient of secondary consolidation. When the sand content is less than 28.57%, bound water (especially weakly bound water) significantly impacts the secondary consolidation behavior of the sand–fine mixtures. However, when the sand content exceeds 28.57%, the secondary consolidation deformation of the mixtures is primarily governed by particle crushing in the sand grains.

Slurry wall protection is the key to the success of the design and construction of underground diaphragm walls; however, in the analysis of its grooving mechanism, the original slurry in the surrounding environment was usually equivalated to the slurry pressure, while the slurry penetration characteristics and the formation of a filter cake were often neglected, leading to obvious defects in the existing literature. In this paper, by combining computational fluid dynamics (CFD) and the discrete element method (DEM), a model based on the strain softening constitutive equation was proposed to investigate the formation of a filter cake by the effects of slurry penetration and cementation and to calculate the stability of grooving. In this model, material parameters were used to describe the mechanical properties of the filter cake, and the microscopic parameters that were calibrated through experiments were used to explore the optimal particle radius ratio of the filter cake. Then, the feasibility and rationality of the model in describing the slurry penetration and failure trends were verified through comparative analysis. In the stability analysis, the safety factor was introduced to evaluate the impact of the slurry and other influencing factors on the grooving process. The results show that the properties of slurry and the environmental factors such as groundwater level have significant effects on the formation of the filter cake and stress distribution, thereby affecting the grooving effect. The findings of this study can provide useful guidance and reference for theoretical research and practical engineering.

A series of shaking table tests were performed on reduced-scale models of helical soil-nailed walls (HSNWs) to evaluate the effect of the nail arrangement and nail inclination on the failure mechanisms and dynamic characteristics of this type of retaining structures under seismic conditions. The results of particle image velocimetry (PIV) showed that the potential failure surfaces in the helical soil-nailed walls were parabolic ones with an inflection point and the dimensions of failure wedge increased as the length and inclination of the nails increased. A combination of overturning and base sliding was identified as the predominant deformation mode in the HSNWs and that base sliding faded with an increase in the nail inclination. It was found that horizontal helical nails located in the lower half of the wall played a more effective role in reducing lateral displacement, but the opposite was true for HSNWs with inclined nails. The use of inclined nails instead of horizontal ones was found to be an efficient solution for increasing the shear modulus in HSNWs. The efficiency of this solution decreased with the use of shorter nails in the upper half of the walls and was eventually minimized by increasing the length of the nails across the wall height. It was found that, although the use of helical nails instead of grouted ones reduced wall damping, it could be a good solution for increasing the stiffness of the soil-nailed walls.

Although extensive investigations have been performed on soil anisotropy, little information is available regarding its quantification. The quantification of anisotropy reflects the extent to which the inherent anisotropy of soil controls its mechanical behavior and so it is crucial for connecting comprehensive experimental research with soil constitutive models and engineering practices. The present study evaluates the level of shear strength anisotropy in various types of soil. A database is compiled of the variations of shear strength with the direction of major principal stress (α) as established via hollow-cylinder torsional shear tests, covering more than 20 types of soil. This study reviews critically the existing methods for strength anisotropy, finding none of them quantifies anisotropy satisfactorily. The present study proposes using the bracketed area by the S(α)/S(0)–α curve and the line S(α)/S(0) = 1 to measure the level of strength anisotropy, where S(α) is the soil strength as a function of α. The proposed method in this study can measure the strength anisotropy levels of sands, silts, clays, residual soil, calcareous sand, mudstone, and glacial till, among others. Additionally, the anisotropy degree measured using the proposed method appears to be consistent with the results of microstructural anisotropy evaluations. This study enhances the understanding of soil anisotropy by providing a comprehensive database of soil strength anisotropy and proposing a general method for its quantification.

This study evaluated the stability of circular tunnels constructed in anisotropic granular soil in the presence of surcharges on the ground surface and seismic loads. The stability problem was solved using the lower bound limit analysis method in conjunction with the finite-element technique. In addition, the modified pseudodynamic technique was employed, which permits seismic accelerations to vary with depth and time, including the impact of amplitude and phase differences between shear and primary waves. The forces exerted by the soil on the tunnel lining vary over the perimeter. Therefore, the ultimate support pressure should at least be equal to the maximum normal stress from the earth surrounding the tunnel. It was discovered that parameters such as the tunnel cover depth, tunnel diameter, magnitude of surcharge, soil friction angle and its degree of anisotropy, seismic acceleration coefficients, period, and frequency of seismic waves determine the support pressure’s magnitude and location. The influence of surcharge diminished beyond a certain cover depth and diameter ratio for given soil and seismic wave parameter magnitudes. This study showed that the maximum normal stress was 8.5 times greater than the uniform stress distribution. Furthermore, the support pressure was found to be a maximum of about 45.5% higher for a tunnel cover depth-to-diameter ratio of 3 than for 1%, 34% higher for anisotropy than for isotropic case, 25% higher in the presence of ground surcharge than its absence, and 60% higher for the horizontal acceleration coefficient of 0.3 compared to the static case.

Water–rock interaction is an important factor affecting rock mass strength; water weakening of the coal pillar will affect the stability of underground storage. In this work, the Brazilian splitting strength weakening, splitting fracture characteristics, and infrared radiation characteristics of coal samples (CSs) with different moisture contents were studied. With increasing moisture content, the tensile strength of CSs decreases linearly, while the peak strain increases first and then decreases. The flatness of the splitting fractures on the sample surface after tensile failure decreases with the increase in moisture content, and the fractal dimension of the splitting fractures increases from 1.066 to 1.298 from the dry state to the saturated state. The temperature slowly increases during the loading process of CSs with low moisture content, and a sudden decrease in temperature is observed at the moment of fracture. However, the surface temperature of CSs with high moisture content decreases gradually during the splitting test, and the temperature changes are small. It can be concluded that the temperature change in the CS surface at the moment of failure is linearly related to the moisture content. After splitting failure, the stress on the CS is released and the surface temperature decreases gradually. The infrared radiation released by the CS during splitting failure decreases gradually with increasing moisture content. With the help of computed tomography, it is found that the primary fracture of a CS expands after water immersion, and the porosity increase after water immersion is 0.0255. The porosity increase accelerates damage development in the CS, leading to easier formation of penetrating fractures in the splitting process. The existence of water weakens the cementation strength of the primary fracture, so that it takes less strength for the splitting fracture to expand along the joint fracture surface. The reduction in new fractures also reduces the intensity of infrared radiation.

Microbially induced carbonate precipitation (MICP) is an effective method for stabilizing sandy soil. However, this method is not effective for coarse sands. A kaolin-nucleating method was proposed in this study to improve the biotreatment of coarse sands. We comprehensively studied the effect of the kaolin concentration, the volume ratio of the bacterial solution to the cementation solution, the grouting interval between two slurry injections, and the bacterial density on the compressive strength of biotreated coarse sands. We found that the kaolin concentration and the bacterial density are positive factors for enhancing the compressive strength and there are also suitable values for the volume ratio of the bacterial solution to the cementation solution and the grouting interval to improve the biotreatment when other factors are specified. Interestingly, the biotreated condition for the specimen with the maximum strength was identical to that with the maximum ratio of the precipitate volume to the specimen void but different from that with the maximum calcium carbonate content.

The construction of deep foundation pits that are adjacent to an operating subway tunnel can cause significant disturbance to the surrounding soil and tunnel structure. Assessing the stability of the soil in the security area of the tunnel is key to controlling the displacement of the tunnel structure. Assuming that the soil behind the wall is in the elastic stage of small deformation, the unloading stress distribution law of the soil on the excavation surface of the side wall is inversely calculated using the horizontal displacement curve of the retaining structure. Based on the analytical solutions for the horizontal displacement and surface settlement of the soil behind the wall proposed in this paper, the spatial distribution characteristics of the deformation transfer of the soil in the security area are obtained. Considering the interaction between the soil in the security area and the tunnel structure, by simplifying the soil in the security area to a Pasternak foundation model, the tunnel displacement that is caused by deformation transfer can be obtained. The correctness of the theoretical model is verified by comparing it with the measured data for the soil displacement behind the wall and the tunnel structure in project cases of foundation pit excavation.

Grouting reinforcement technology is a vital component of geotechnical engineering, which plays a crucial role in repairing surrounding rock that is damaged and improving its strength. To analyze the impact of grouting on the mechanical properties of rock fractures, specimens of mudstone fractures were selected before and after grouting reinforcement for direct shear tests. The purpose was to investigate the changes in mechanical properties under normal and tangential loading conditions. Furthermore, the microscopic–mesoscopic and macroscopic aspects of grouting reinforcement were discussed to explore its influence on the interface structure, deformation resistance, and strength of the fractured rock mass. By analyzing the test results of the fracture’s mechanical properties before and after grouting, a constitutive model and strength criterion were proposed to accurately describe the mechanical behavior of the fracture surface. Building on a numerical software platform, the custom model was compiled with the VC++ integral programming environment and embedded in UDEC software. Finally, these findings were successfully applied to a typical deep roadway surrounding rock grouting reinforcement project, which showcased the practical implications of this paper. The results demonstrate that grouting reinforcement significantly impacts the normal and tangential mechanical properties of the fracture surface and the shrinkage and dilatation mechanical behaviors. The grout filling and cementation process enhances the rock mass fracture’s resistance to deformation, effectively preventing the gradual weakening and slip in the fracture field. This improves the overall integrity and stability of the rock mass. The proposed mechanical model effectively captures the compression, shear, shrinkage, and dilatation mechanical behaviors before and after grouting. Similarly, the custom fracture grouting mechanical model could be a useful tool to simulate the behavior of grouting reinforcement in engineering rock masses.

A simplified mechanical model for investigating pile–pile horizontal vibration is developed by combining the Pasternak model and the Timoshenko beam theory, with the consideration of the influence of axial load at the head of the source pile. The expressions for horizontal displacements and internal forces of the source pile are obtained with respect to the differential transform method and pile–soil boundary continuity conditions. Additionally, considering that the vibration of the source pile affects the dynamic displacements of the receiver pile, the dynamic equilibrium equation of the receiver pile is established. Then, a closed-formed solution for the response of the receiver pile is derived from the obtained expressions. Further, the pile–pile horizontal dynamic interaction factor is derived based on its definition and validated by comparison with existing related analytical solutions. Finally, the effects of the shear deformations of soil and pile, pile slenderness ratio, and axial load on the pile–pile horizontal dynamic interaction factors are examined. It is indicated that a smaller pile-to-soil modulus ratio of the near-surface layer results in a more significant effect of shear deformation of the soil. In particular, when L/d is small (i.e., L/d < 5) or the pile cross section is annular, the effect of shear deformation of the pile is not ignorable.

Many instances of severe damage to pile foundations and pile-supported infrastructures have been caused by liquefaction-induced lateral spreading during major earthquakes, particularly in coastal areas. The current study conducted a series of shaking table experiments to determine the differences between the responses of a free- and a fixed-head group pile under lateral spreading in the presence of finned and circular protection piles. The results indicated that the maximum bending moment tolerated by nonprotected free-head piles was more than that by fixed-head piles. Also, reductions in bending moments were more significant in free-head piles in the presence of protection piles than in fixed-head piles. The bending moments of front and rear piles under restricted pile head conditions were reduced by about 31% and 21%, respectively, when finned piles were used as protection piles, while they were 34% and 42%, respectively, under free-head conditions. Furthermore, modification factors of recommended lateral pressure distribution along a pile per the current design code were determined for the protected and nonprotected free- and fixed-head pile groups of the current study and it was observed that this modification factor (C_L) was highly dependent on the location of piles in a group, pile head conditions, and the presence of protection piles in the lateral spreading analysis.

Abstract

Understanding the moisture migration of unsaturated soil in response to temperature changes is essential in soil science and geosystems applications. The coupling of thermohydro (TH) processes is a result of changes in fluid density and viscosity; however, gravity can disrupt the moisture migration of unsaturated sand initiated by a thermal gradient when the sand is considerably porous. Moreover, the moisture redistribution caused by the gravity effect is influenced by the imposed boundary temperature and initial moisture content of the unsaturated sand. Therefore, this paper presents heating tests performed on sand specimens of different gradations and subjected to various thermal gradients in a modified and well-controlled soil testing cell to evaluate the coupling behavior of TH processes in unsaturated sand. Two sands were tested in the soil testing cell, which was equipped with thermocouples (TCs) to measure the temperature and time-domain reflectometry (TDR) sensors to measure the apparent dielectric constant (K_a); three temperature boundary conditions were imposed on the soil testing cell to create two thermal gradients. This study shows that gravity, thermal boundary conditions, initial moisture content, and matric suction influence the migration of moisture: the silty sand, as compared with pure sand, more properly displayed the phenomenon of coupled TH processes in unsaturated soil when tested at a temperature gradient of 200°C/m and initial moisture content of 6%. The study provides an advanced understanding of the paired migration of heat and moisture in porous media under various conditions, including thermal gradient, initial moisture content, and gradation.

Practical Applications

When unsaturated soils are under a temperature gradient, the pore water tends to move from the heat source to a cooler end in search of moisture equilibrium. Temperature-driven moisture flow is commonly investigated in soil science, agriculture, and geosystems. For example, the soil surrounding a geosystem (electrical cables and ground heat exchangers) experiences heating and cooling cycles when heat energy is exchanged from buildings to the soil via the geosystem. This heat exchange can effectively cool the buildings in the summer and heat the buildings in the winter. To maintain effective heat transfer in the soil, it is necessary to investigate the temperature-driven moisture flow, as it has been established that redistributed moisture also significantly impacts heat transport. At the same time, the moisture flow is also influenced by gravity, particularly for coarse sands. Moisture flow in coarse sands is more prone to the effect of gravity than that in fine sands. This paper evaluates how the physical and hydraulic properties of the soil, such as gradation and suction, can affect the coupled thermal and hydraulic processes. The gravitational effect can dominate the moisture redistribution depending on the direction of the temperature gradient.

Biotreatment is an emerging reinforcement technology. Avalanche dynamics has recently been used to analyze the fracture behavior of biotreated specimens under unconfined conditions. However, the avalanche dynamics along with fractures in biotreated specimens under confined conditions have not yet been investigated. In this study, we aimed to determine the basic laws of the avalanche dynamics for biotreated calcareous sand specimens through a series of triaxial compression tests under various confining pressures. We found that the probability density distributions of acoustic emission signal (AES) energy, the AES amplitude, and the AES duration of the biotreated specimens under confined conditions obeyed the damped power law, and the AES waiting-time distribution followed the prediction by the gamma function. However, the confining pressure had no significant influence on the relative magnitude, the aftershock-sequence distribution, the AES energy-versus-amplitude distribution, or the AES amplitude-versus-duration distribution. More importantly, the maximum-likelihood estimation of the AES energy could be used to predict the occurrence of catastrophic damage in the biotreated soils.

Abstract

Engineering practices indicate that stratum hydraulic conductivity (SHC) has a significant influence on deep excavations. However, this influence has been ignored in previous studies with undrained analyses. In this study, a numerical model, combined with the verified hydromechanical coupled method, is established to investigate the effect of SHCs on the performances of deep excavations. Excavation deformation, pore-water pressure, lateral pressure, and the stress evolution process are presented, respectively, to illustrate these influences. In addition, the model of a beam on an elastic foundation is employed to interpret the influential mechanism of SHCs on excavation deformations. Analysis results indicate that excavation deformations increase significantly with the increase in SHCs from 1 × 10⁻⁷ to 1 × 10⁻⁵ cm/s (i.e., the range of SHCs of soil containing silt). The influence of SHCs on excavation deformations is mainly attributed to the variation of effective stress levels on the excavated side. As SHC increases, the change in the resultant force of the total stress acting on the retained side of the wall, as loads, can be ignored, while the resultant force of the effective stress acting on the excavated side of the wall, as resistances, decreases dramatically. These findings emphasize the importance of accurate determination of the SHC of strata containing silt.

Practical Applications

Engineering practices indicate that stratum hydraulic conductivity (SHC) significantly affects the performances of deep excavations in Shanghai soft deposits. Constructions in the first aquitard (AdI) have been involved in the many deep excavations in Shanghai, China, and therefore, identifying the effects of the SHC of AdI on deep excavations can further ensure the safety of constructions. In this study, it is found that excavation deformations increase significantly as the SHC of AdI increases from 1 × 10⁻⁷ to 1 × 10⁻⁵ cm/s (i.e., the SHCs in soil containing silt). This finding indicates that valuing the SHC of AdI containing silt requires utmost caution, and adopting appropriate methods such as dewatering can significantly decrease excavation deformations.

The ultimate bearing capacity of a shallow footing decreases when it is subjected to a moment in addition to a centric vertical load. A centric vertical load with a moment on a footing is equivalent to an eccentric load on the footing. The result of this is a net reduction of the ultimate and allowable bearing capacity of the footing. In a situation like this, the bearing capacity of the footing can be improved by providing a skirt around the footing. The present study provides the results of a laboratory test program of a skirted square (B × B) model footing in dense and medium-dense sand as it relates to the ultimate bearing capacity. For the tests, the length of the skirt (L) was varied as L/B = 0, 0.25, 0.5, 0.75, and 1.0. Based on the model test results, relationships have been developed to estimate the ultimate bearing capacity of a skirted footing with eccentric vertical loading from the ultimate bearing capacity of a footing without a skirt subjected to vertical centric loading.

Understanding the rainfall-triggering mechanisms influencing loess landslides and developing targeted prevention and control strategies are critical challenges in engineering. This study focused on a representative landslide-prone area in Huxian County, Xi’an, China, and field experiments involving artificial rainfall simulations were conducted. Utilizing the annual rainfall statistics for Huxian County, three distinct rainfall scenarios—light, moderate, and heavy—were established. The aim was to explore the correlation between internal pore water pressure and temporal and depth-related changes during the postrainfall stage. At the same time, reflective patches were placed on the slope and total stations were used to monitor the impact of different rainfall intensities on slope displacement. Based on the field data, a three-dimensional simulation validation was executed using Surfer software. Our findings suggest that increasing rainfall intensity directly correlates with higher internal pore water pressure. As the rainfall persisted, the daily amplitude of pore water pressure initially surged before moderating, ultimately exhibiting a logarithmic trend with depth. The effective influence depths of the daily amplitude of pore water pressure during light, moderate, and heavy rainfall stages were found to be 1.6, 2.2, and 5.0 m, respectively. Following cessation of the rainfall, the surface pore water pressure underwent substantial change, and the daily amplitude rapidly declined before stabilizing. Slope displacement consistently increased from the summit to the base throughout the rainfall stages, with the base being most susceptible to sliding instability. The maximum displacement at the foot of the slope was in Columns 3–5, with a maximum displacement value of 1,158 mm. Proximity to the slope’s base correlated with greater gravitational and downward forces. Specific maximum displacement values were recorded at different locations along the slope, revealing the most significant changes along the slope’s centerline. This work will contribute to the effective management and landslide prevention of loess slopes.

The consolidation behavior of a foundation with vertical drains under vacuum preloading is affected by the lateral deformation and well resistance. In this study, a nonlinear consolidation model is developed based on the assumptions of equal volumetric strain and time-dependent well resistance. The model considers the relationships between various factors, such as well resistance, linear attenuation of vacuum pressure, lateral deformation, and simultaneous vertical–radial seepage. An analytical solution of the model is provided, and its universality is verified. Additionally, the effects of different consolidation factors on the average consolidation degree ($\overline{U}$) are analyzed, and the error in calculating $\overline{U}$ without considering a single factor is evaluated. The results indicate that well resistance significantly affects the consolidation rate of soil without vertical seepage, particularly at the later stage of consolidation when the constant parameter A, which represents time-dependent well resistance, exceeds 1.0 × 10⁻⁷ (s⁻¹). Not considering the lateral deformation can result in an overestimated soil consolidation rate. For thin layer soils with low liquid limits, the effects of the consolidation factors on $\overline{U}$ are ranked as follows: c_c/c_k (ratio of compression index to permeation index) > k_v (vertical permeability coefficient) > v (Poisson’s ratio) > k₁ (attenuation residual coefficient of vacuum pressure) > q_w (discharge capacity of prefabricated vertical drains).

During the tunneling process of earth pressure balance (EPB) shield machines, the undrained compressibility of foam-conditioned soils in the excavation chamber is essential for reducing the fluctuation of chamber pressure and guaranteeing effective tunnel face support. As conditioned soil is simplified to be radially constrained by the shield shell and in a quasi-one-dimensional compression state under the face pressure along the tunneling direction, a mechanism-inspired analytical model was developed to estimate the void ratio and pore pressure of foam-conditioned coarse-grained soils (FCS) in one-dimensional compression based on effective stress analysis. In the model, an expansion coefficient was proposed to characterize the filling state of foam bubbles in pores and a void ratio threshold (e_th) was defined as the transition point of the FCS with and without effective stress. The variation of void ratio and pore pressure with total stress of FCS in two distinct stages of the void ratio (e), either greater or smaller than its threshold, were calculated based on Boyle’s law and the hyperbolic assumption of the effective stress–strain relation of soil. A good agreement between the analytical and experimental results verified the reliability of the proposed analytical method. Furthermore, a parametric study indicated that the compressibility increases with an increase in the expansion coefficient and foam injection ratio (FIR). Increasing additional water content leads to a decrease in compressibility under low pressure (σ_v ≤ 20 kPa), but an increase in compressibility under high pressure (σ_v > 20 kPa). Meanwhile, the pore pressure in FCS in the stage of e < e_th also positively correlates with the expansion coefficient, FIR, and additional water content. The research findings would provide a convenient method to estimate the undrained compressibility behavior of FCS and theoretically guide the soil conditioning optimization in EPB tunneling.

Batch tests are extensively used in a wide range of fields, including environmental engineering, to forecast the impact of sorption on contaminant transportation in soil and wastewater treatment effectiveness. Recently, batch tests have been utilized to assess sorption kinetics, which was previously considered an instantaneous process. In this study, an analytical solution is proposed to the pseudosecond-order equation for sorption kinetics in batch tests, which considers the initial concentration in both the solution and sorbent material, such as soil. First, a parametric study was conducted to comprehend the effect of model fitting parameters and the initial conditions of the test on the results. Following this, experimental validation was carried out by applying the kinetic adsorption–desorption model to existing literature results. The calibration process involved three fitting parameters that were physically significant and independent of the initial concentration conditions. The main advantage of this model is that it uses the same fitting parameters to predict sorption equilibrium and sorption kinetics under different initial conditions. The calibrated model enabled the estimation of the adsorbed solute for any initial concentrations and provided a physical interpretation of the results for different contact times and initial concentrations.

A series of model tests were conducted to simulate the active failure of narrow cohesionless backfills behind retaining walls rotating about the base (RB mode). The tests aimed to investigate the effect of wall displacement magnitude, backfill widths, and the inclinations of retaining walls and existing structures on the failure mechanism and earth pressure. The test results revealed that the rupture propagation follows a progressive top-down failure pattern and does not extend to the base of the wall under RB mode, contrasting with the assumptions of the existing theoretical solution. Notably, a narrower backfill exhibited multiple parallel shear bands in contrast to the semi-infinite backfill, highlighting the significant impact of backfill geometry on the orientation of these shear bands. Furthermore, the active earth pressure distribution under RB mode displayed an approximately linear trend, slightly reducing earth pressure near the base. The development of earth pressure suggested that the backfill reached the active limit state after the wall had experienced a displacement equal to 0.35% of its height (H). It was observed that the active earth pressure for a backfill width-to-height ratio (B/H) of 0.5 closely corresponded to values obtained through the Coulomb method. Moreover, the results indicated that the active earth pressure increased proportionally with an increase in the B/H ratio and a decrease in the inclinations of both the retaining structures and existing structures.

The freeze–thaw (F-T) cycle is one of the weathering factors that can cause rapid deterioration of the mechanical properties of rocks and threaten the stability and durability of rock engineering in cold regions. To study the influence of F-T action on the mechanical and deformation characteristics of sandstone, triaxial compression tests were performed under four confining pressures (0, 1, 3, and 5 MPa) and five F-T cycles (0, 40, 80, 120, and 160). The experimental results show that the stress–strain curves of the sandstone after F-T cycles can be divided into four phases: compaction, elasticity, strain-hardening, and postpeak failure. According to the deformation behaviors of the sandstone with various F-T cycles, an elastoplastic damage constitutive equation was established considering the compaction effect and F-T action. The model parameters were determined, and the theoretical curves were calculated. The comparisons with theoretical and experimental stress–strain curves demonstrate that the formulated constitutive equation can reflect the key deformation stages and mechanical behaviors of sandstone with different F-T cycles. Because the damage variable is introduced in establishing the model, the proposed model can also provide a quantitative description of the macrodamage, which agrees well with the microdamage of the sandstone after many F-T cycles measured by acoustic emission (AE) technology. The formulated constitutive equation in this paper can well describe the experimental deformation curves of sandstone with various F-T cycles and is easy to embed into numerical analysis software. The results can provide a certain theoretical reference for the evaluation of the durability and stability of rock engineering structures impacted by F-T-induced damage in cold regions.

Ground heat exchangers (GHEs) are commonly modeled using the finite-element (FE) method for the design and evaluation of the GHE performance. However, one of the disadvantages of these FE models is the huge computational time involved due to the complex transient three-dimensional (3D) transport phenomena of GHEs. Thus, it is essential to develop an FE model that can provide the inlet and outlet fluid temperature and 3D temperature field with high accuracy and yet with minimal computational time. The primary objective of this study was to create a streamlined numerical model that could serve as an effective and practical design tool for simulating vertical GHEs, emphasizing a high degree of numerical accuracy while minimizing computational time. A computationally efficient 3D transient FE model was developed in COMSOL Multiphysics, which uses an equivalent 1D pipe flow instead of fully modeling the borehole grout. The proposed model prioritizes the simulation of fluid and borehole wall temperatures with an accuracy comparable to the conventional model, but it sacrifices the simulation accuracy of the borehole grout to reduce computational time and offer more convenient meshing. The proposed model was compared with a conventional model and verified against field measurements of outlet fluid temperature and spatial subsurface soil temperature at different depths and radial distances from a 132.5-m GHE operated in a full-scale geothermal bridge de-icing system. Two FE mesh cases––optimum and extrafine––were designed in order to compare the models. The results indicated that the computational time was greatly reduced, by 95% and 81% for the two mesh cases, respectively, while the same level of accuracy in the temperature evaluation was maintained. Also, the required number of model elements was decreased by 90% and 67% for the optimum and extrafine-mesh cases.

The soil–water characteristic curve (SWCC) model considering the temperature effect is significant in precisely predicting the relationship between the matric suction and degree of saturation in unsaturated soils in geotechnical and geoenvironmental engineering. In this work, we derived a new temperature-dependent wetting coefficient, incorporating a nonlinear temperature-dependent enthalpy of immersion per unit area. We introduce a simplified expression that successfully approximates the wetting coefficient for temperatures between 273.15 and 373.15 K. In addition, we propose a temperature-dependent matric suction equation and a temperature-dependent SWCC model. The new model comprehensively considers the temperature sensitivities of the water–air interface tension and wetting coefficient, which shows that an increase in temperature for a given matric suction leads to a decrease in the degree of saturation. The results illustrate that the new model is suitable for predicting the nonisothermal SWCC of unsaturated soils.

The physicochemical combination method (PCCM), improving upon the conventional pure cement solidification method (PCSM), has been developed as an integrated and sustainable approach to treat and recycle slurry-like mud (MS). To facilitate the practical design of the PCCM, it is essential to establish the relationship between the strength of PCCM-treated MS and the governing factors. In this study, a comparison is made between PCCM-treated MS and PCSM-treated MS to clarify the differences in the microstructures and strength behaviors, and the influence of some key parameters (i.e., preloading pressure p, equivalent initial water content w_ei, and cementitious binder content w_c) on the strength behavior of PCCM-treated MS is investigated via unconfined compression tests. The results indicate that flocculants play a crucial role in increasing the ductility of PCCM-treated MS, and the preloading process further enhances the toughness of PCCM-treated MS. Moreover, empirical equations of deformation modulus (E₅₀) and failure strain (ɛ_f) are formulated based on the results of unconfined compression tests. Additionally, an attempt is made to predict the unconfined compressive strength (UCS) using a simple empirical equation based on the modified water/cement ratio. The main findings are of practical significance for the optimal design and application of PCCM in treatment of MS.

The interaction mechanisms of the underground tunnel passing through the surface structure for a short distance are complex, and there are hidden dangers, with the interaction between the two tunnels having a nonnegligible impact on the seismic performance of the structural system. To explore the interaction law of seismic response between the double tunnel and the surface structure, this study conducted a shake-table test on a surface frame structure–soil–double-tunnel interaction system with a basement, using an actual tunnel project in Zhengzhou, China, as the background. A three-dimensional (3D) numerical model of the system was established using the finite-element analysis software ABAQUS (2021) with the equivalent linear method, and the numerical model's reliability was verified by comparing with the test results. The verified numerical simulation was used to study the interaction between the structures in the system under six different prototype model cases. The research findings revealed that the tunnel's presence reduced the dynamic response of the structural system while amplifying the far-field dynamic response, and the interaction between the two tunnels increased the degree of this reduction and amplification. The frame structure reduced the soil dynamic response while amplifying the acceleration response and shear force of the tunnel. Additionally, the location of weak layers of the frame structure was influenced by the type of seismic wave inputted, while the diameter and crossing location of the tunnel had nonnegligible influences on the dynamic response of the structural system. The research results can serve as a reference to preliminarily determine the interaction laws of the seismic responses of a double-tunnel and adjacent surface frame structures.

The brittleness of rocks is an important factor in the design of rock engineering projects, such as hydraulic fracturing, rockburst prediction, wellbore stability, and drillability. Therefore, an accurate assessment of rock brittleness is of high practical importance. However, the definition and the measurement of rock brittleness are not yet standardized. The present study proposes a new index for describing rock brittleness using crack initiation and crack damage stress thresholds for rocks with Class I stress‒strain curves. Uniaxial compressive strength (UCS) tests were conducted on fine-grained, medium-grained, and coarse-grained dolomite rock specimens in order to evaluate the performance of this index on describing brittleness. Based on the results, first, the effect of grain size on the crack initiation and crack damage stress was evaluated. Subsequently, the effect of grain size on common brittleness indexes was examined and compared to the proposed index. The results indicate that an increase in the grain size in the studied rocks increases the crack initiation, crack damage, and peak stress. It was determined that the ratio between the axial strains corresponding to the peak and crack damage stresses during the uniaxial compressive test is almost constant for all three rock types. Additionally, it was concluded, using the conventional and proposed brittleness indexes, that the brittleness index increases with an increase in grain size.

This study presents a new solution algorithm to calculate the bearing capacity coefficient N_γ for a fully rough strip footing located on an infinite slope considering different soil friction angles φ and ground slopes β° using the stress characteristics method. The results showed that N_γ coefficients decreased with an increase in slope inclination, and roughness contribution prevented further reduction, particularly for higher φ values. The higher contribution of the upside-sloping ground for footing laid on the infinite slope led to a lower reduction of the N_γ coefficients compared with the footing placed at the slope vicinity in terms of a larger area affected by the stress field, and a larger plastic region of the downface slope. The reduction value was more eminent for steeper slopes β ≥ 20° due to the tendency for nonsymmetrical failure pattern, especially for higher φ values. The findings of the current research and those described in the literature were in good agreement, so much so that the lower-bound limit analysis and the current solution technique virtually reflect the same trend. The load inclination values for footings located adjacent to the slope with β ≤ 30° were not meaningful, whereas for footing resting on an infinite slope with β ≥ 25° it exceeds 15°, which reflects the fact that its effect should not be neglected, especially for ground slopes greater than 20°. By increasing β°, the maximum values of plastic length and plastic depth on the left and right sides of the footing decrease and increase, respectively. The maximum depth of the plastic region for β ≥ 20° from around the right side of the footing shifts toward the downward-sloping face. The maximum width of the elastic wedge gradually reduces, and the intersection point of the left and right plastic regions slowly shifts to the left and upside of the footing.

Precipitation is one of the most important factors inducing shallow slope failures, and the shallow slope covering bedrocks is prone to instability after heavy rainfall. In one-dimensional (1D) seepage–deformation coupling issues, permeability coefficient and moisture vary with matric suction in unsaturated soil. Combining mass conservation, Darcy’s law, and elastic theory, an analytical solution for coupled seepage–deformation in unsaturated soil slopes during rainfall infiltration is derived using the Fourier integral transformation method. The analytical solution can be applied to a 1D seepage problem in a soil slope with flux at the top and impervious bedrock in the base under heavy precipitation, and is conducive to study infiltration into the slope under rainfall conditions. To validate the accuracy of the proposed analytical solution in this study, it is compared with monitored pore-water pressure data from the Gufenping Landslide in the red-bed region located in Nanjiang, Sichuan, China. The compared result shows a good consistency between the analytical solution and the measured results, with a minor relative error. Investigation of the parameters demonstrates that the water-level rise is closely related to the coupling, which is influenced by precipitation duration, precipitation intensity, soil properties, and slope angle. The bottom boundary of the slope is considered to be impermeable in this study, which leads to rainfall accumulation at the base over time, and the coupled effect becomes more pronounced at the bottom boundary.

Plate anchors have great advantages that are useful in deep or ultradeep water mooring systems. The keying behaviors have a deep effect on the embedment loss and pullout capacity of strip plate anchors. In this paper, the effect of soil remolding on the keying behaviors of strip plate anchors is studied by large deformation finite-element (LDFE) analysis. First, the LDFE results are compared with centrifugal test results, theoretical solutions, and LDFE data from previous literature, showing good agreement. Then, a series of LDFE cases is studied to investigate the effects of the padeye offset, load eccentricity, soil sensitivity, and initial embedment depth on the embedment loss and pullout capacity of plate anchors during the keying process. The LDFE results show that different load eccentricity corresponds to different soil failure mechanisms, and both padeye offset and soil remolding will reduce the pullout capacity of plate anchors. Finally, an equivalent soil strength is introduced considering rate effect and soil remolding of clay. A combined factor and an equivalent ultimate pullout capacity are used to estimate the ultimate embedment loss and pullout capacity of strip plate anchors in uniform clay, respectively.

Multilayered cover systems (MLCSs) of waste containment facilities are generally prone to translational instabilities, largely governed by their interfacial shear strength parameters. For reliability assessment of a MLCS, it is necessary to characterize the interfacial shear strength parameters probabilistically. Owing to the uncertainties involved with the sample preparation and subsequent laboratory experimentation, estimation of shear strength parameters based on deterministic linear regression becomes an oversimplifying paradigm. Conducting a very large number of repeated experimental trials to estimate shear strength parameters is practically infeasible; thus, geotechnical engineers often resort to best possible inferences from limited data. This necessitates a Bayesian regression–based approach catering to limited data for layerwise estimates of interfacial shear strength parameters of the MLCS. Informative (normal) and noninformative (uniform) priors are utilized to obtain updated probability distributions of shear strength parameters of the interfaces. These estimates are subsequently adopted in reliability assessment of a MLCS. A novel conceptual paradigm of a probabilistic vulnerable interface diagram (PVID) is introduced to identify the most probable vulnerable interfaces of the MLCS when subjected to several factors leading to instabilities.

Stratum cavity collapse induced by water and sand leakage in a subway tunnel is a sudden urban geological disaster, which can cause serious casualties and economic losses. In response to the hazards of stratum cavity collapse induced by water and sand leakage around subway tunnels, a set of visual test devices with variable hole diameters were designed to simulate the stratum cavity collapse induced by water and sand leakage under comprehensive consideration of the size of the cavity diameter, clay thickness, clay strength, and so on. Based on pressure arch theory and unified strength theory, a critical calculation formula was established for stratum cavity collapse under two modes, of tensile shear and shear failure. Furthermore, the accuracy of the theoretical calculation formula was verified by experiment. The results show that the critical radius increases with the increase of clay strength and decreases with the increase of buried depth and friction angle. Clay soil is more prone to shear failure at the arch foot under the same conditions. The larger the soil sand mix ratio and the cavity diameter, the smaller the critical water pressure of soil collapse. The thicker the soil layer, the greater the critical water pressure. The theoretical analysis method has a clear physical meaning and the theoretical results agree well with the test results. The research results are of great significance for the warning of and prevention of such urban geological disasters.

As coalmines extend more deeply, strong mining-induced earthquakes occur more frequently; these seriously threaten the safety of underground miners and aboveground residents, as well as the productivity and effectiveness of mining activities. The distribution of mining-induced earthquake characteristics and hard roof breaking mechanisms are analyzed and revealed using the methods of field monitoring and theoretical analysis, and prevention and control technology were proposed and applied in a field application, for a typical dynamic disaster problem at Dongtan Coalmine. As indicated by the results, strong mining-induced earthquakes (E ≥ 10⁵ J) were mostly related to the coordinated failure of several strata, and the migration and fracture of the overlying strata led to significant subsidence of the surface. As mining activities advance, the abutment stress within the coal seam in front of the coalface will dynamically change and be transferred more deeply into the coal seam under the influence of a mining-induced earthquake. Based on the mechanical behavior, the fracture structures of the overlying multiplicity of key strata are divided into main and subordinate “O-X” types. As the coal is exploited, the O-X scope gradually increases from the near field to the far field. As indicated by the field application, the implementation of deep-hole blasting could effectively weaken the integrity of the thick and hard rock strata and change the length of the overhang roof, so as to reduce the risk of strong mining-induced earthquakes, i.e., the incidence of strong mining-induced earthquakes above 5 × 10⁵ J would be significantly reduced. Meanwhile, the frequency of rock strata collapse increases, and the average distance from the epicenter centrum to the coal seam is reduced to 47 m. The governing effect is good. We expect that the results of this study could provide references for dynamic disaster governance in similar mine areas.

The strength anisotropy and strain softening of natural soil can significantly impact the bearing capacity of shallow foundations on clay. In this article, we present a nonlocal numerical method to study the coupled rotation of the maximum normal stress axis and strain softening on the bearing capacity of shallow foundations on clay through a Cosserat strain softening constitutive model. The strength anisotropy and strain softening characteristics were numerically implemented into a finite-element (FE) program by dynamically updating the anisotropic cohesion in global Newton–Raphson iterations. Due to its nonlocal feature, the proposed nonlocal numerical method can overcome the mesh dependence in simulating the progressive failure of clay through the classical FE method. We first validated the efficacy of this method against the results of the plane strain test and numerical results in the literature. We then study the bearing capacity of a strip footing over anisotropic and strain-softening clay through the implemented numerical method. The results indicated that the deposition angle has an important effect on the bearing capacity and failure mode. The effects of the degree of anisotropy and strain softening on the ultimate bearing capacity are quantified through the numerical method. It is found that (1) the proposed method can effectively reflect the characteristics of the maximum normal stress axis rotation on the failure surface of the footing; (2) the ultimate bearing capacity of a footing (P_u) on anisotropic clay could increase linearly with an increase in the anisotropy ratio k (i.e., k is the ratio between C₁ and C₂) and decreases with an increase in the softening modulus; and (3) the strength anisotropy and strain softening are strongly coupling factors impacting the bearing capacity of anisotropic clay.

This paper studies the design of foundations built on thick compressible soft soil layers that are reinforced by floating columns. Based on a recent methodology, the suggested design combines the bearing capacity and settlement verifications to provide an optimized improvement area ratio (IAR). Then, an optimized length for the floating columns is obtained by introducing the admissible long-term settlement of the unreinforced compressible sublayers and assuming that the total short-term settlement vanishes at the end of project construction. This paper focuses on the variation in the consolidation settlement of the unreinforced compressible sublayer versus the length of the floating columns. The discussion of this design methodology highlights the feasibility of a potential reinforcement solution when producing a cost-effective design, which assures an optimized IAR within the reinforced upper layer and an optimized length for the floating columns. Using typical case history data, a parametric study showed that reinforcement with end-bearing columns is not required to control the admissible long-term settlement. Instead, the suggested design method enables the determination of the optimized length of the floating columns, which satisfies the admissible residual settlement and consolidation time. The comparison between the proposed results and numerical predictions by Plaxis 2D shows good agreement, which confirms the feasibility of an optimized length for floating columns and avoids the systematic adoption of end-bearing reinforcement in columns.

The distribution of lateral earth pressure acting on underwater rock-socketed circular diaphragm walls was investigated using theoretical analyses. Emphasis was placed on the relationship between the motion modes associated with the magnitude of the radial deflection of the wall and the lateral earth pressure. A framework for determining the distribution of radial displacement–dependent earth pressure based on the horizontal differential element method was introduced. The applicability of the proposed theoretical method was then verified by comparison with results that considered earth pressure in limit state, and radial deflection of the wall and water level. The predicted earth pressure and its distribution were found to be in good agreement with the analytical solutions and observed data. Detailed parametric analyses were further performed to study the impact of soil properties, excavation radius, and water level on the distribution of radial displacement–dependent earth pressure under different radial wall movement modes of a circular retaining structure.

Biocementation has broad application prospects for reinforcing granular materials in geotechnical engineering. However, only few studies have been conducted on the size effect in biocemented granular materials, despite the recognition of the size effect in the uncemented ones. In this study, a series of tests on Brazilian tensile strengths were carried out for biocemented sand, focusing on the size effect. Glass bead sand (GBS) and calcareous sand (CCS) of five different particle sizes were adopted at two different biocementation levels. Under otherwise identical conditions, the tensile strengths of biocemented CCS specimens were higher than that of the biocemented GBS specimens. The tensile strengths of the biocemented specimens decreased with an increase in particle size, which can be captured by a power function, inspired by the size–effect relation. The novel findings of this study can provide the size–effect function for the establishment of constitutive models and the data basis for the validation of numerical models when theoretical models are necessary in predictions of deformation and failure for field-scale biotreated soils.

Landslides are frequent and devastating geological hazards that cause significant economic and human losses annually. The selection of appropriate shear strength parameters is crucial for evaluating and preventing landslide failure. Considering the nonlinear characteristics of rock-mass material, a rock slope stability analysis model was built using the nonlinear Hoek‒Brown failure criterion. A Geological Strength Index–material constant (GSI–m_i) curve, based on a deterministic method, was proposed to back analyzed the Geological Strength Index (GSI), which is consistent with a trial-and-error method, but simpler to implement. The back analysis can be extended to other parameters in addition to the GSI. Furthermore, considering the randomness and uncertainty, a reliability-based back analysis method for nonlinear strength parameters of the sliding surface was proposed. The optimal parameter combination that corresponded to the minimum reliability index was determined, which could serve as reasonable values of the nonlinear strength parameters for landslides. A comparison of different failure criteria also suggested that the stress level at the sliding surface should be accounted for in landslides using the significant nonlinear characteristics of strength parameters.

Water decoupling blasting is an efficient method that can significantly improve blasting effects. A three-dimensional (3D) numerical investigation is conducted using the multimaterial Arbitrary Lagrangian Eulerian (ALE) method to deepen the understanding of the method. The blasting effects and pressure attenuation regularities for coupling, air and water decoupling blasting are compared to reveal the fracture mechanism for water decoupling blasting. The simulated results indicate that water is desirable to transmit blasting pressure, because it slows the blasting pressure attenuation and improves the blasting effect. Quantitative analysis of the radial, axial, and radial–axial decoupling charges is performed to optimize the charge structure. The radial decoupling charge is a better charge structure, which results in a more uniform blasting energy distribution. With the increase in the radial decoupled coefficients, the blasting pressure attenuation index first decreases and then increases. The analysis results indicate that 1.5 is the optimal radial decoupling coefficient, which can achieve the highest energy utilization efficiency. The simulated results for radial–axial decoupling blasting show that the rock failure regularities of radial or axial decoupling blasting exist in radial–axial decoupling blasting. By comparing the blasting effect of four commonly used explosives, trinitrotoluene (TNT), which has high blasting pressure, detonation velocity, and initial internal energy density, is the optimal explosive in water decoupling blasting, which is different from coupling blasting.