International Journal of Geomechanics

The aim of this study was to investigate the optimization of cut-blasting methods for deep rock masses under high in situ stress. Several plane fluid–structure interaction (FSI) models were established, and the blasting effects using common cut-blasting methods were analyzed. Considering the damage range of the rock mass and the blast-induced vibration after blasting, the cut-blasting method was selected as suitable for deep rock masses under high in situ stress. Subsequently, the cut-blasting parameters, including blasthole spacing, blasthole diameter, and the distance between the empty hole and the first cut-blasting hole, were optimized through the crack connectedness between the blastholes and the fractal dimension of the damaged rock mass. The results showed that the pentagonal cut-blasting method is more suitable for deep rock masses compared with other methods and the blasthole spacing should be reduced to resist any inhibitory effects from the increasing in situ stress. For in situ nonhydrostatic stress conditions, it is reasonable to choose a wider blasthole spacing in the direction of the major principal stress and a narrower one in the direction of the minor principal stress. Under high in situ stress, the joint optimization of blasthole spacing and blasthole diameter is recommended in order to avoid the poor cutting effect caused by too-narrow spacing. In addition, the formula for calculating the location of empty holes in shallow rock-mass blasting is also applicable to deep rock masses. The partially optimized results were preliminarily verified through comparison with existing field tests. These findings offer a new approach for enhancing the blasting effect on deep rock masses and may provide valuable guidance for the design and construction of cut blasting in deep rock masses.

Rock mass subjected to acidic groundwater corrosion may cause great property alteration. In this work, the effects of microstructure on change of the pore structure and mechanical property under acid corrosion were investigated. Two types of limestone, which are microstructurally different but have almost same mineral compositions, were corroded in HCl and Na₂SO₄ mixed solutions with different pH values (pH = 3, 4, 5, 6, and 7). A series of approaches including uniaxial compression, Brazilian splitting, and nuclear magnetic resonance (NMR) tests were carried out to examine the strength, brittle index, porosity, and pore distribution. The mechanical properties (uniaxial compressive strength, elastic modulus, tensile strength, and brittleness index) decreased as the pH value decreased. In addition, the larger the initial microstructure, the faster the degradation rate of mechanical parameters except for the brittleness index. Moreover, NMR results revealed that the porosity increment of Group 2 (large initial microstructure) was larger than that of Group 1 (small initial microstructure). Under acid corrosion, the reason for the increasing porosity in Group 1 was the increased proportion of the internanopore, while it was transition from the supernanopore to the submicropore for Group 2. Furthermore, the brittleness index decreased as porosity increased and the proportion of the internanopore decreased. Finally, the degradation mechanisms of pore and mechanical properties were discussed.

In rock masses, there might be structural nonstationarity in the joint morphology that influences the shear behavior of rock joints. However, research into this effect is seldom reported. In this study, shear tests on artificial rock joints that contained stationary morphology and different nonstationary features were conducted. The experimental results showed that nonstationarity has a significant effect on the shear properties of rock joints. Under the action of lower normal stress levels, the peak shear strength of joints increased with the increase in the nonstationary angle, and it was easy for the slip behavior along the nonstationary trend to occur. Under higher normal stress levels, the damage to big areas in the upper and lower joint blocks, especially on the left and right ends of the joint surfaces, readily appeared. In this case, the nonstationary characteristics tended to be the main factor that controlled the damage to joints. The analysis revealed that after subtracting the nonstationary angle, the peak friction angles of the joints with nonstationarity were close to the peak friction angles of the joints with stationary morphology and provided the same normal stress. Therefore, the nonstationary angle and stationary joint morphology were separately but fully considered to describe the peak dilatancy angle. Using the proposed model for the peak dilatancy angle, a new criterion for the peak shear strength of joints that contained nonstationary features was established. Comparisons of the new criterion with the published criteria when estimating the peak shear strength of rough rock joints showed that the new criterion has a good prediction accuracy for rock joints with nonstationarity.

Abstract

The Bayesian method is a versatile data-driven machine learning method that performs well in predicting seismic-induced soil liquefaction, but it does not consider physical mechanisms and its performance is easily affected by class imbalance and attribute weights. In addition, simplified methods consider the mechanism, while simplified methods based on different in situ tests often produce conflicting results for the same site, leaving engineers unable to decide which result to choose. To overcome the aforementioned problems, this paper proposes a framework for combining multiple simplified methods based on the double-weighted Bayesian combination (DWBC) approach, considering the effects of combination mode, class imbalance, and contribution weights of the simplified methods on the performance of the DWBC model. Compared with the three simplified methods based on different in situ tests, the proposed DWBC model significantly improves the liquefaction prediction accuracy and converts the deterministic prediction result to probabilistic. Furthermore, when comparing different ensemble strategies (e.g., majority voting, simple average, and weighted average approaches), different Bayesian combination modes, and the random forest (RF) model based on 250 liquefaction multidatabases using various performance measures, the DWBC model performs the best, followed by the Bayesian combination model without weighting and the majority voting method, while the RF model performs the worst. The performance of the DWBC model depends on the number and mode of the basic classifiers and the performance of the basic classifiers. The sensitivity of the DWBC method with respect to the class imbalance is also discussed.

Practical Applications

Seismic liquefaction is a form of earthquake-induced disaster phenomenon. This study constructs an ensemble model for predicting earthquake-induced liquefaction based on the double-weighted Bayesian method to improve the prediction accuracy. The ensemble model takes the prediction results of the widely used simplified methods in various in situ test databases such as standard penetration test, cone penetration test, and shear wave velocity as inputs and liquefaction or nonliquefaction as outputs, while considering the effects of combination mode, class imbalance, and contribution weights of the simplified methods on the performance of the ensemble model. Thus, the ensemble model can avoid the situation where simplified models predict conflicting results in different in situ test databases for the same site and convert the deterministic prediction results of simplified methods into a probabilistic result. In this study, the proposed ensemble model performs much better than the simplified models and other ensemble models such as the random forest.

The consolidation of Hong Kong marine deposits (HKMDs), a typical soft clayey soil in Hong Kong, is a serious concern in engineering practices, such as coastal embankment construction and marine reclamations. Previous research works illustrate that high temperatures could accelerate the rate of consolidation of soft clayey soils, which has a great potential in future applications. Therefore, studies on the consolidation and stress–strain behaviors of clayey soils under various thermal conditions are necessary. In this paper, a modified temperature-controlled oedometer has been developed and employed to investigate the effects of vertical stress and temperature on the consolidation and creep behavior of remolded HKMD with a temperature range of 20°C–60°C. Scanning electrical microscope (SEM) tests were performed to observe the microstructure of HKMD specimens after oedometer tests under different temperatures. The results show that compression index C_c is nearly independent of temperature, while swelling index C_s is slightly affected by the thermal and stress paths. As temperature increases, both permeability and coefficient of consolidation increase, and the duration to the end of primary consolidation is shortened. It has also been found that with an increase of temperature, the preconsolidation pressure decreases, and there is a reduction in linear creep rate and creep strain limit. Both linear and nonlinear creep functions are adopted to analyze the creep behavior.

The key considerations in the design of a high-pressure tunnel are ensuring stability and limiting water losses. In this paper, a triple-layer, thick-walled cylinder model considering the impact of the loose rock zone was built to investigate the inner water exosmosis and conditional cooperation mechanisms in high-pressure tunnels. An analytical calculation method for the design-related parameters, such as the steel bar stress, maximum crack width, and water losses of the high-pressure tunnel, was proposed. A comparison of the results obtained by the proposed solution with those obtained by other numerical and analytical solutions was presented to validate the proposed model. Then, the research for a hydropower diversion tunnel was conducted, and the impact of the loose rock zone on the design-related parameters was analyzed. The steel bar stress is generally lower than the design expectations due to the conditional cooperation between the concrete lining and surrounding rock during the high-pressure tunnel operation period. The consistency of measured field data in tight rock and calculation outputs further verified the presented analytical model. Finally, the proposed model was applied to investigate various parameters related to the loose rock zone, and the results could be considered general recommendations for developing pervious linings with high internal water pressure (IWP).

Rock bursts are aggressive dynamic failure processes that involve the rapid release of strain energy stored in a rock under unloading conditions. The dynamic fracture and strain energy transformation characteristics of rock unloading failure must be investigated to predict and control rock bursts. This study adopts the discretized virtual internal bond (DVIB) method to investigate this problem. The element partition method is performed in the DVIB method to investigate the effect of cracks on rock unloading failure. Three indicators, i.e., fracture area, the fractal dimension of the failure pattern, and energy release ratio (kinetic energy over strain energy), are adopted to evaluate the failure intensity. Simulation results show that a critical strain energy density (SED) for rock unloading failure exists. The unloading failure occurs only when the SED exceeds the critical value. Subsequently, under the same SED conditions, the effect of the lateral pressure coefficient (LPC), heterogeneity, and size on rock unloading failure is investigated. As the LPC increases, the failure intensity increases slowly and then decreases significantly. The critical LPC is approximately 0.5, indicating that the unloading failure is the most severe. The simulation results suggest that the crack can reduce the energy release capacity of the rock and then restrain rock unloading failure. When the precrack angle is 0° or 90°, the precrack barely affects the rock unloading failure, and the failure intensity is similar to that of the intact rock. When the precrack length or the density of random precracks is larger, the rock unloading failure is weaker.

Extensive research has been carried out to understand the behavior of pile-supported embankments; however, pavement crack, which could appear early on the pavement of low embankments during the service life, has not yet been incorporated in previous numerical models. This study aims to investigate the effect of pavement crack on the response of pile-supported low embankments under cyclic traffic loading. A finite-element model for pile-supported low embankments that considers the pavement crack was developed, and a cyclic traffic loading was simulated using a half-sinusoidal function. The numerical model with a crack under cyclic loading was verified using an existing analytical solution. The effect of pavement crack, including crack type, horizontal distance, and depth, on the response of pile-supported low embankments under cyclic traffic loading were investigated. Results indicate that the vertical stress and settlement in pile-supported low embankments increase with consideration of the effect of pavement crack, which leads to a quicker degradation of the arching effect compared with a case with no crack. Results from a parametric study show that the settlement of soft soil decreases with increasing elastic modulus of the AC layer and wheel velocity and decreasing peak amplitude of cyclic loading.

Different features, such as rotational hardening and nonassociated flow, have been added to the classic modified cam-clay (MCC) model. However, there is little knowledge about their role and importance in simulating in situ soils. This study examined the effects of rotational hardening and associated/nonassociated flow on modeling the undrained shear strength of K₀-consolidated clays. For this purpose, three types of rate-independent models were chosen: MCC, MCC with rotational hardening and associated flow (RAMCC), and MCC with rotational hardening and nonassociated flow (RNMCC). The capabilities of the three models in reproducing the K₀ state were first discussed. Then, by proposing a dummy yield surface to account for the effect of rotational hardening, an analytical solution to predict soil undrained shear strength s_u directly from the K₀ state was established. The predicted s_u values were examined against available T-bar data. Results showed that only RNMCC is able to produce a reasonable match no matter the over stress ratio (OCR) profile, while both MCC and RAMCC show overestimation, which increases with increasing OCR.

The mechanical and hydraulic properties of rock discontinuity are anisotropic, and the main reason resides in the anisotropy of surface morphology. This study delved systematically into the anisotropic characteristics of surface morphology and its evaluation method. Among hundreds of morphology parameters, the most representative one was selected utilizing mathematical statistics and correlation analysis. Through morphology analysis of eight discontinuity specimens, the maximum deviation of roughness in each direction was proposed as an anisotropy evaluation index, serving as a bridge to establish the relationship between the anisotropic characteristics of surface morphology and shear strength. In-depth research was conducted to discuss the distribution range of controlling factors of shear strength and explore the influence of anisotropy degree and controlling factors on the prediction deviation of shear strength. Based on the aforementioned results, an anisotropy evaluation method was put forth to divide the anisotropy degree of rock discontinuity into four levels, and the prediction deviation of shear strength at each level was described in a quantitative manner. The novelty of this study is listed as follows. The existing literature lacks research on quantitative evaluation methods of anisotropic characteristics, and this study would compensate for this deficiency; this method has a valid theoretical foundation and is capable of simultaneously determining the anisotropic characteristics of morphology and shear strength; the methods concerning how to simplify surface morphology as isotropy and embed discontinuity roughness into a numerical algorithm have been proposed, respectively. These findings would provide theoretical support for the deformation control and stability analysis of rock mass in engineering.

Abstract

In this work, an analysis of the propagation of horizontally polarized magnetoelastic shear waves at a loosely bonded interface between two fiber-reinforced (FRC) media is performed. The assumption is that the upper layer is a heterogeneous FRC medium with initial stress, while the lower layer is an FRC half-space subject to gravity. A closed-form expression of the dispersion equation has been derived using Whittaker’s function and its asymptotic expansion for both exponential and linear types of heterogeneous cases. The obtained dispersion equation matches well with previously existing results and the classical Love wave equation. In both cases, it was found that the magnetoelastic coupling parameters, horizontal compressive initial stresses, loosely bound, and Biot’s gravity parameter of the layered structure all have a favoring effect on the phase velocity. It was also observed that in the linear heterogeneous case, the magnetoelastic coupling parameter has a detrimental influence on the speed of shear wave propagation, while in the exponential heterogeneous situation, it has a beneficial impact. The findings of this study can be used to improve analysis in the fields of geotechnical engineering and civil engineering.

Practical Applications

This study examines the characteristic behavior of horizontally polarized magnetoelastic shear wave propagation in an inhomogeneous fiber reinforced layer overlaying a fiber-reinforced half-space in the presence of initial stress and gravity. Reinforced materials are now one of the fundamental necessities of building projects of any significant magnitude. In addition, it is crucial to consider the impact of loose bonding at the common interface between the layer and the half-space while building the sensors to improve their efficacy and ultimately achieve high performance. This work is relevant to geotechnical and civil engineering applications and is innovative. Examining the effect of various nondimensional parameters’ responses to wave motion is of great interest to researchers due to the immense practical and economic potential of composite structures made from such materials. The present article may have numerous applications in the disciplines of space exploration, aviation, construction, geophysics, geomechanics, and so on.

Wave propagation in a layered rock mass is a common problem in geotechnical engineering. The bedding planes in a layered rock mass are generally in situ stressed and adhesively bonded. This study extended the time-domain recursive method to analyze the wave propagation in a layered rock mass with adhesive bedding planes. The maximum stress criterion was used to indicate the adhesive failure of bedding planes. The Bandis–Barton and Coulomb slip models were used to characterize the normal and tangential behaviors of bedding planes after the adhesive bond fails. Based on the backward differentiation formula, an analytical solution reflecting four possible states of the bedding plane and the in situ stresses in rock mass was established. Subsequently, the solution was verified for various conditions. Besides, parametric studies were carried out to assess the influences of adhesive properties of bedding planes and in situ stresses on wave transmission. The transmission coefficient of seismic waves increases linearly as the adhesive strength of the bedding plane increases. The in situ normal stress could facilitate wave transmission across the bedding plane, while the in situ shear stress causes the direction-dependency of transmitted waves. Furthermore, the impacts of bedding plane adhesion and in situ stresses on wave propagation were influenced by the amplitude, frequency, and impinging angle of incident waves. The welded model that ignores the adhesion failure of the bedding plane and the unbonded models that neglect the interface adhesion could overestimate or underestimate the transmitted wave across a bedding plane.

Particle breakage, which is affected by the stress path, is a key factor influencing the mechanical properties of granular geomaterials. According to the results of triaxial tests conducted on granular geomaterials under different stress paths, a particle breakage model considering the effects of the stress path was established in this study, and a mathematical expression of the model and a method to determine the model parameters were established. The results indicated that the integral function of the plastic strain increment can be used to describe the variation in the particle breakage of granular geomaterials under different stress paths; however, the influence of the stress path on the plastic strain increment should be eliminated by introducing a stress-path-related parameter. Because it was difficult to obtain such a parameter directly, particle breakage models under a proportional loading path and a triaxial compression test path were established, and functional expressions of the particle breakage model of granular geomaterials under different stress paths were derived by combining the concepts of constant-breakage surface and stress path decomposition. A comparison of the calculated results with the experimental results showed that the proposed model can not only reasonably predict the particle breakage under different shear strains applied in the loading process but can also describe the variation in the particle breakage under different stress paths, thus validating the proposed model.

With the advancement of water conservancy projects around the world, several concrete-face rockfill dams (CFRDs) are being built in earthquake-prone areas. Among the many factors affecting the seismic safety of a CFRD, the dam–reservoir interaction is the most important one. Dam–reservoir interaction impacts the dynamic response and deformation of the dam and further influences the behavior of the face slab. This study conducted two centrifuge experiments to analyze the influence of dam–reservoir interaction on the behavior of a CFRD. Experimental models of concrete-face slab rockfill dams with and without an impoundment in four earthquake cases were established. In particular, a bidirectional earthquake motion was considered. The acceleration response and the settlement of the dam crest, bending moment and axial force of the facing slab, and the hydrodynamic pressure on the upstream slope of the dam were analyzed. The results showed that the dam–reservoir interaction increases the acceleration amplitude but decreases the progression of the dam crest settlement, enhances the dynamic axial force near the base, and reduces the bending moment near the dam crest of the face slab. Furthermore, the hydrodynamic pressure had a positive correlation with the dynamic axial force of the face slab.

Shield tunnels that cross soft and hard mutation strata will experience severe longitudinal uneven settlement, which results in local damage to the shield tunnel. Previous studies on the longitudinal mechanical properties of shield tunnels generally assumed that the strata were homogeneous or level-layered and that the lining segment ring was uniform and ignored the shield tunnel’s discontinuity and the inhomogeneity in the strata adjacent to the shield tunnel. Therefore, a three-dimensional (3D) longitudinal refined numerical calculation model of a shield tunnel is developed under complex geological conditions, which realistically considers the effects of a staggered assembly of a shield tunnel, longitudinal and circumferential bolts between segments, and the interface between the strata and tunnel structure. An improved Timoshenko beam theory method that has been validated by a model test in the literature is adopted to verify the numerical calculation model’s reliability and applicability and to highlight its advantages. Then, a study is conducted to analyze the longitudinal mechanical properties of shield tunnels that cross soft and hard mutation strata through this numerical calculation model. The influence law for strata on the longitudinal mechanical properties of the shield tunnel is highlighted by comparisons with another numerical calculation model with simplified strata, which includes the longitudinal uneven settlement and local deformation of the shield tunnel, the opening and dislocation of segment rings, deformation, and yield state of the longitudinal and circumferential bolts. Furthermore, a parametric study is further presented to analyze the influence of the elastic modulus difference between soft and hard strata on the longitudinal mechanical properties of the shield tunnel. An empirical formula is introduced to calculate the maximum opening and dislocation of the segment rings. The longitudinal uneven settlement of the shield tunnel becomes more significant and concentrated as the elastic modulus difference increases, which increases the local deformation and longitudinal internal force in the shield tunnel. Similarly, the deformation and internal force of bolts and the interface increase in the longitudinal direction. Significant differences in the elastic modulus between the soft and hard strata will likely induce severe deformation damage and bolt failure into the shield tunnel.

Generally, prevention and control methods are adopted to reduce the possibility of regional stress-field-induced impact bursts in pressure relief engineering. However, such methods lack theoretical support and may inadvertently induce rock bursts owing to their improper implementation during the drilling process. Therefore, this paper proposes a method for calculating the critical softening radius of a development heading causing rock bursts under static load based on the theory of mutation, which is used to guide construction in local unloading engineering. According to the total potential energy principle, a cusp catastrophe model is established to determine the key-bearing ring instability of the surrounding rock; subsequently, a relationship between the softening radius and the stability coefficient of the key-bearing ring is deduced. Furthermore, a prediction model to determine the bearing ring stability is established. The stability criterion for the key-bearing ring of the surrounding rock is obtained, verified, and analyzed using calculation examples and actual engineering cases. The results demonstrate that the stability of the surrounding rock can be improved to a certain extent by degrading the strength of the coal rock mass. When the softening range exceeds a certain limit, the key-bearing ring becomes unstable owing to a nonlinear increase in the external load, thereby inducing rock bursts. Simultaneously, a surrounding rock with a higher hardness value exhibits a higher sensitivity to the pressure discharge; therefore, the softening radius of the area with a higher surrounding rock hardness value should be chosen more carefully. For the engineering cases, the upper limit of the critical softening radius calculated theoretically differed from existing theoretical calculation results by less than 15%. Similarly, the lower limit of the critical softening radius calculated theoretically differed from the stress peak position of the surrounding rock by less than 8%. These results verify the reliability and engineering application of the proposed method.

Installing geofoam inclusions between the rigid retaining wall and backfill can reduce the earth pressure against the retaining wall. However, there is currently a lack of research on the earth-pressure reduction effect of geofoam inclusions on rigid retaining walls with narrow backfill width. In this study, the compression from geofoam inclusions was equated to the displacement of the narrow backfill. An iterative method was introduced based on the displacement-dependent earth-pressure model. A calculation method was obtained to determine the earth pressure for rigid retaining walls with narrow backfill width using geofoam inclusions. Moreover, simplified formulae for at-rest, active, and passive earth-pressure coefficients of retaining walls with narrow backfill width were achieved based on the soil arching effect and horizontal differential element method. A series of laboratory model tests were performed to verify the calculated formulae, demonstrating a high level of formula accuracy. In addition, the parameter analysis results showed that the earth-pressure reduction effect of geofoam inclusions was directly proportional to the interface friction angle between the backfill and geofoam inclusions.

Abstract

The present paper deals with the analytical study of shear horizontal (SH)-wave propagation consisting of a microstructural coupled stress layer over a dry sandy half-space beneath the orthotropic viscoelastic layer with imperfect interfaces. The rigidity and density of the sandy medium are assumed to be exponential distribution functions. Dispersion equations for SH-wave propagation have been derived using suitable boundary conditions in the absence and presence of imperfection parameters. In a particular case, the dispersion equation is reduced to the classical Love wave equation, which validates the present mathematical model. The effect of various parameters in the current model on the phase velocity and damped velocity are discussed in the presence and absence of imperfect interfaces. Numerical computations were carried out for involved parameters and illustrated with the help of graphs.

Practical Applications

In regions near dams, the presence of sandy soil can lead to increased pore pressure during an earthquake, which can cause soil liquefaction. The event of the earthquake can cause the propagation of a shear horizontal (SH)-wave, which is destructive. Therefore, the area near the reservoir is prone to seismic activities, especially SH-wave propagation. The outcomes of the present analysis may have significant applications in reservoir engineering. The rocks in the dam structures are generally composed of an unsaturated sands medium. In these structures, the sand medium is subjected to a high liquid loading. During an earthquake, the SH-wave may propagate through these structures. Due to its destructive nature, the propagation of an SH-wave may cause damage to these structures. The damage to the reservoir may result in huge economic or human life loss. Therefore, examining the propagation of an SH-wave in these structures is crucial. The present investigation identifies the physical factors that cause the elevation and degradation of SH-wave propagation in the studied sandwiched structure. Therefore, the obtained results may find significant advances in analyzing and developing earthquake-resistant designs used in reservoir engineering.

To accurately predict ground settlement caused by shield tunnel construction, a prediction method of ground settlement considering the support effect of the tunnel lining structure is studied in this research. First, based on the Maxwell–Betti power interchange theorem and considering the lining supporting effect of a circular shield tunnel, an analytical formula for ground loss caused by tunnel construction is derived by constructing two groups of elastic mechanical model calculation models for different stress states. The calculation method of ground loss with the influence of the lining support is optimized and improved. Second, considering the tunnel construction method and the lining support effect, the Loganathan formula is improved, a theoretical formula for a vertical displacement field for shield tunnel construction is deduced, and the ground settlement prediction model of a circular shield tunnel construction is established. Finally, the method is compared with other calculation methods, such as the Loganathan method, and three tunnel engineering cases are predicted and analyzed. The results show that the prediction results are closer to the actual monitoring settlement value, verifying that this method has good adaptability and reliability in actual tunnel engineering.

A mathematical model was developed to investigate the consolidation behavior of soft soil deposits improved by prefabricated vertical drains. The smear effect caused by drain installation was incorporated into the model by assuming a parabolic variation of permeability and compressibility with radius. The non-Darcian flow of pore water in the soil and the well resistance effect caused by the limited discharge capacity of drain were also incorporated in the model. The void ratio dependence of permeability and compressibility was taken into consideration to account for their variation with time. The proposed model was validated by comparing the predicted results with experimental data and with existing analytical models. A parametric study was performed to evaluate the influence of various parameters such as non-Darcian flow, permeability ratio, and discharge capacity on the consolidation of the soil deposit. The average effective stress decreased by approximately 20% when the ratio of permeability in the undisturbed zone to the smear zone was increased from 1.5 to 5. The average excess pore-water pressure at the soil–drain interface reduced by approximately 80% when the discharge capacity was increased from 20 to 100 m³/year. The well resistance effect was more significant for non-Darcian flow as compared to Darcian flow. The rate of dissipation of average excess pore-water pressure increased by approximately 75% when the non-Darcian parameter n was increased from 1 to 2. However, the average excess pore-water pressure became independent of the non-Darcian parameter (n) for n greater than 2.5.

Excavation damage induced by the drill-and-blast method (DBM) of the surrounding rock zone in tunneling intensifies the loss of groundwater and causes serious hydroecological imbalance. Traditional theoretical analysis concerning tunnel seepage fields leads to an underestimation of groundwater inflow due to the ignoring of the factor of increased permeability in the DBM damage zone. Meanwhile, the composite liner widely used in DBM tunnels with the waterproofing and drainage system is difficult to simulate numerically. Taking into account the damaged zone, this work presents an analytical solution based on the axisymmetric modeling method suitable for deep tunnels to determine the groundwater inflow, permeability coefficient, and seepage force. The proposed solution combining the equivalent perimeter method is extended to noncircular tunnels. Comparisons of the numerical results with those of a previous study indicate that the proposed approach provides realistic predictions for the groundwater inflow and external water pressure. Introducing the concept of an equivalent liner, a series of numerical simulations for the center-diaphragm (CD) method are performed, in which 14 steps are divided for the tunnel construction and operation. The results indicate that the external water pressures significantly decrease after an upper-section excavation of the left drift and increase after support closure. The seepage velocity of the primary support and second liner reaches the maximum near the arch skewback. The maximum seepage volume Q occurs after a left-drift upper-section excavation and the maximum groundwater table drawdown h occurs before right-drift support closure. The impact of rainfall on h is far greater than that on Q. For damaged and grouting zones, the effects of permeability on Q and h are more significant than those of thickness. Furthermore, a significant advantage of the CD method compared with the full-face and bench methods is deduced for tunnels crossing unfavorable strata.

Red-layer mudstone is a typical expandable rock, that is, it easily expands and deforms in water. This study focused on the dynamic quantitative analysis of the mudstone hygroscopic process and development of strain caused by the hydration expansion of clay, by combining a self-designed simple self-imbibition device with the digital image correlation method. The mudstone samples were self-imbibed in deionized water and salt solutions of different concentrations under the same atmospheric conditions (25°C and 50% humidity). The effects of the salt type and salt concentration on the water absorption quality, expansion rate, crack initiation and expansion, matrix deformation, and water migration of mudstone over time were analyzed. The change in the water absorption capacity of mudstone with time was determined from the water absorption characteristic curve. The location and strain development of the local high-strain area during the water–rock interaction was captured from the full-field strain cloud image. The migration of water on the rock surface at different times was observed using camera photographs. Finally, water absorption was combined with strain, water migration, and crack propagation. The effect of saltwater on the hygroscopic expansion of mudstone was evaluated.

To study the stress distribution characteristics of the surrounding rock of the gob-side coal–rock roadway in a gently inclined coal seam under the influence of excavation and mining disturbance, a physically similar simulation experiment was carried out. With an infrared thermal imager and professional infrared thermal analysis software (SmartView 4.3), the 2D and 3D temperature fields of the detection object were obtained, the numerical simulations were conducted, and the stress state of the surrounding rock was indirectly analyzed. The results indicated that during the excavation disturbance stage, the stress mainly occurred at the coal pillar side. When the coal pillar widths gradually decreased from 10 to 3 m, the stress monitoring value of the surrounding rock showed that the change process was “rising, decreasing, then rising again,” and the increase of the stress level of the surrounding rock was the greatest when the width was 8 m. With the increase of mining disturbance intensity, the coal pillar yielded instability gradually, and the stress concentration area of the surrounding rock gradually shifted from the initial coal pillar side to the lower solid coal side. Under the influence of excavation and mining disturbance, the range of relatively high or low temperatures of the surrounding rock was basically consistent with the large and small area distribution of the stress monitoring value during the surrounding rock stress concentration and transfer. This showed that the method of indirect analysis of the surrounding rock stress state based on infrared temperature detection was highly feasible. The numerical simulation results showed that under the influence of excavation and mining disturbance, the stress distribution of the surrounding rock was basically consistent with the infrared temperature field detection results during the surrounding rock stress concentration and transfer. Our research conclusions provide a scientific basis and theoretical guidance for the deformation mechanism and control technology of the surrounding rock of gob-side coal–rock roadways in a gently inclined coal seam.

The main purpose of this study was to derive analytical solutions for soil structure interaction in single energy piles that exhibit irreversible interface behavior. The solutions were derived for a pile embedded in a homogeneous soil layer subjected to thermal, mechanical, and thermomechanical loads. Furthermore, the solutions were subsequently validated against the experimental data obtained from the full-scale tests. Load transfer diagrams depicting evolutions of displacement, interface shear stress, and axial stress versus depth for semifloating, fully floating, and end-bearing piles were obtained from the analytical solutions and subsequently presented. The effects of a progression of thermally induced interface yielding on the displacement, interface shear stress, and axial stress were illustrated in case of heating and cooling for different end restraints. In addition, the analytical solutions show that the location of the null point changes after the initiation of the interface yielding. The analytical solutions indicate that residual displacement, strain, and stress are generated in the pile upon the initiation of the interface yielding. This finding was also confirmed through a comparison of analytical predictions with experimental data. Finally, analytical solutions show that evolutions of displacement, strain, and interface shear stress are hyperbolic trigonometric functions within the depth of the nonyielded interface. In contrast, within a depth corresponding to the yielded interface, axial stress and strain are linear functions, displacement is a quadratic function, while the interface shear stress is constant with depth.

Determining vertical earth pressure (VEP) is crucial in designing high-filled cut-and-cover tunnel (CCT) structures. This parameter directly influences the safety and economy of the structure. However, the current pressure formulations do not adequately account for the numerous influencing factors that affect VEP for CCTs, including filling height, slope rate, and tunnel span. In this study, the effects of these factors on VEP were investigated through a combination of field tests and discrete element method (DEM) simulations. An empirical formula for VEP suitable for high-filled CCTs was obtained through mathematical regression. The findings indicated that the soil arching effect is present in high-filled CCTs once the backfill reaches a certain height. The final VEP on the vault was only 0.74 times the total overburden weight. The pressure reduction coefficient decreased with increasing filling height and slope rate but increased with rising tunnel span. The proposed empirical formula for VEP took into account the discount of earth pressure under various factors. It is consistent with the field test results, providing a better reflection of the actual VEP for high-filled CCTs.

Field load tests are carried out on a single pile and piled-raft foundation (PRF) consisting of a 2 × 2 pile group with consideration of the time effect. The piles along with the raft in the PRF have been instrumented with load cells and strain gauges. Gradual compressive loading has been applied to the PRF with an increment of 10% up to the estimated safe load capacity. Settlement corresponding to the safe load is monitored for 4 months. The settlement of the PRF, axial load carried by piles, shaft friction along the pile length, moments in the raft, and load sharing ratio between piles and raft for each increment of loading are observed with respect to time. A nonlinear analysis is suggested to scrutinize the behavior of vertically loaded rigid PRFs in layered soil medium (present approach). Considering the theory of the interaction factor, an approximate procedure is implemented to analyze the nonlinearity of pile groups with a rigid raft. Additionally, the nonlinear response of piles using hyperbolic functions is presented (alternative hyperbolic function approach). A simplified method for the calculation of the flexibility matrix considering the time effect is also suggested (present time-based approach). The analyses are validated with the field results and available literature. Parametric studies have been performed to calculate the immediate and time-dependent settlements of the PRF by varying the length to diameter ratio of the pile, spacing to diameter ratio of the pile, and pile group configuration using the present approach and present time-based approach. Immediate settlements corresponding to the safe load by the present approach and alternative hyperbolic function approach are approximately 8.18% and 6.48% less than the measured settlement.

Shallow landslides often occur in unsaturated soil slopes under seepage conditions. The shear strength of unsaturated soils is one of the key factors in evaluating the stability of these slopes. Due to the high nonlinearity in the strength envelope of unsaturated soils, the common criteria cannot fully capture the strength characteristics of all unsaturated soils. Based on effective stress with a matric suction, a power-type strength criterion was proposed for various unsaturated soils from literature studies. In addition, performance of the power-type strength criterion was better than that of two commonly used strength criteria for modeling test data on various unsaturated soils. Furthermore, the proposed strength criterion was applied to analytically assess the factor of safety of the infinite slope under the steady seepage condition by considering the effect of grain size and porosity.

The engineering properties of cemented silt with rubber fines and rubber buffings mixtures are investigated using compaction, unconfined compression, direct shear, and freeze–thaw (FT) cycle tests. The rubber fines (20-mesh size, 80-mesh size), rubber buffings, and cement content in these specimens are equal to 2.5%, 5%, 7.5%, 10%, 12.5%, 15% and 3%, and 5% of dry weights, respectively. The maximum dry density of the modified soil is significantly reduced after adding the waste tire rubber. Furthermore, the addition of rubber fines is more evident in the decrease of maximum dry density compared with the inclusion of rubber buffings. The addition of rubber fines and rubber buffings improved shear strength, including cohesion and friction angles. The unconfined compressive strength of most specimens decreased after the tire rubber is added. However, cement hydration in the early curing stages is inhibited when rubber is added. As a result, the optimal dosage of the rubber buffings is 5%. The FT cycle tests indicated that the strength of the soil blended with the rubber buffings decreased after FT cycles, and the lowest value is found after the sixth cycle, and the specimen porosity increases with rubber buffings, and this effectively reduced the influence of water frost. In general, the modified soil had good FT resistance.

As a novel type of supporting system, servo steel struts have been employed frequently in deep excavations adjacent to important infrastructures. However, the studies concerning the effect of servo steel struts on restraining deformation have not been consummated, and further detailed explorations are required. This study presents the performance of a deep excavation with servo struts based on on-site measurements, including wall deflections, ground settlements, and axial force of struts. To analyze in-depth the supporting effect of servo struts on restraining deformations, the wall deflections and ground settlements obtained from field observation are compared with those in existing studies. Furthermore, the behaviors of conventional struts and servo steel are numerically analyzed and compared. The results indicate that compared with conventional struts, servo steel struts can effectively bring the wall deflections caused by excavation under control. Installation of servo steel struts is an effective measure to reduce the rate of ground settlements but has little effect on the overall settlement trend. Different from the conventional struts, the upper part of the wall is pushed back by servo steel struts, resulting in a wall deformation in an S-shape and increasing the maximum deformation depth. The negative bending moments against the upper part of the wall are significantly greater than those supported by conventional struts.

Energy piles, as an environmentally friendly means to exploit renewable energy, have attracted the attention of global researchers over the past years. Traditional heat exchanger configurations (1-U-shape, 1-W-shape, and multi-U-shape in series or parallel) have been utilized. Traditional 1-U-shape is limited by pile length, short heat transfer path, and low total heat transfer rate. Traditional 1-W-shape heat exchange tubes will cause thermal interference. Moreover, the heat exchange rate per unit tube length is not high for multi-U-shape in series or parallel. Therefore, this paper presents an efficient pile foundation heat exchanger configuration, i.e., deep penetration 1-U-shape configuration. Through a numerical study, energy pile groups with deep penetration 1-U-shape heat exchangers are investigated under continuous operation mode and intermittent operation mode. The temperature change of the piles and soil under intermittent operation mode is analyzed. Thermal performances (e.g., outlet water temperature and heat transfer efficiency) are compared under the two operation modes. Four typical monitoring points under the two operation modes are compared, and the difference in temperature variation is obtained to study the influence on the temperature field of the piles and soil. Results show that in summer mode, the temperature of the pile under intermittent operation mode presents restorability while the temperature of the soil increases gradually. Intermittent operation mode yields a lower temperature of outlet water temperature than continuous operation mode does, and therefore intermittent operation mode is recommended.