International Journal of Geomechanics

The seepage characteristics of fractured rock mass under compression and shear are one of the important factors affecting the stability of rock mass engineering. In order to understand the effect of shear action on the variation of joint surface aperture and reveal the mechanism of shear action on the seepage behavior of joint surface, in this paper, laboratory tests and numerical simulations were used to study the shear flow in the rough rock joints. Based on the results of shear tests in the laboratory, a numerical seepage model considering the contact mode of joints surface was established by introducing contact mode into the elastic deformation of rock, and the changing trend of the fluid flow characteristics in the shear process was studied. The results show that the numerical model can restore the stress distribution and contact region evolution, and the inhomogeneous distribution and evolution of the apertures are closely related to the distribution and evolution of the fluid flow velocity inside the fracture, with the area of higher flow velocity showing a distribution trend perpendicular to the flow direction. This model can be used to predict the effect of shear on rock seepage in underground projects with fracture surfaces under complex stress conditions, and it is a guide for the study of shear-flow models with rough connection surfaces.

Ground vibrations initiated by the passage of vehicles in public transport infrastructure including railways and highways are likely to produce an adverse influence on adjacent structures. Under extreme conditions, this is likely to introduce disastrous consequences. While mitigation of these vibrations is a challenge to geotechnical engineers, adoption of open trenches besides the transport corridors is one of the widely used techniques followed in last few decades. However, it was reported that such techniques initiated several critical problems mostly relevant to the stability problem of those trenches. In this paper, a new technique is proposed for ground vibration mitigation where the open trench is filled with hollow pipes. A two-dimensional (2D) finite-element model is developed and validated to analyze the efficiency of this new technique in ground vibration isolation. The influence of various critical geometric parameters, including the underground water table and elastic modulus of soils, are studied in detail. In addition, the influences of different frequency harmonic load and measured load on the ground vibration reduction by hollow pipes are investigated. Furthermore, a three-dimensional (3D) finite-element model is developed to carry out a comparative study with the 2D modeling. This 3D modeling was applied analyzing the vibration isolation trench with other configurations including different locations of hollow pipes and moving load on the ground vibration isolation. It is observed that the proposed method is not only potentially viable in mitigation of subsurface vibration but also worthwhile for eliminating stability problems in open trenches. The detailed description of the studies conducted has been presented in this paper.

The microstructure can have an important impact on the hydraulic and mechanical behaviors of unsaturated soil; therefore, it must be considered in constitutive models to enable accurate predictions of soil behavior. This paper focused on the constitutive modeling of soils that exhibited a dual porosity structure. Based on the assumption that macro and micropores contained in the double porosity structure had different influences on the mechanical and hydraulic behaviors, the effective degree of saturation (S_e) was selected as a microstructural index. This microstructural index was implemented within Bishop’s effective stress-based approach and the Glasgow coupled (GCM) and modified Cam-Clay models (MCC) were adopted as the basic framework for the development of a constitutive model. Typical samples of low expansive, nonexpansive, and collapsible soils with dual porosity were selected to validate the model’s performance, and the model performed well when compared with experimental data for isotropic compression, triaxial shear, and wetting tests.

Although belled piles have been widely applied to structures subjected to large horizontal loads, such as coastal structures, high chimneys, and transmission towers, their uplift capacity characteristics under various conditions have not been investigated in detail. In this study, model tests were performed in circular and half-circular chambers to determine the uplift capacity of belled piles in sandy ground under conditions such as relative density, penetration depth, and pile-tip inclination angle. Furthermore, image analysis was conducted by monitoring the model tests in a half-circular chamber to verify the shape of the failure surface. A semitheoretical model to predict the uplift capacity of belled piles in sandy ground was developed using the pile-tip failure angle and failure surface curve in accordance with the relative density, penetration depth, and pile-tip inclination angle based on the limit-equilibrium equation of a previous conventional pile. The values calculated using the proposed model were in good agreement with those obtained from experimental model tests.

The Kunming peaty soil exhibits distinct physical and mechanical properties from the inorganic clay due to the special soil-forming process and material composition. To better understand the viscous behavior of peaty soil, a series of laboratory tests, including four types of oedometer tests (one- and multistage loading creep tests, constant rate of strain tests, and constant rate of stress) and constant rate of strain undrained triaxial compression tests, are conducted on the Kunming peaty soil. The experimental results demonstrate that the Kunming peaty soil shows significant secondary compression during oedometer creep tests. Meanwhile, the variations of the measured preconsolidation pressure and undrained shear strength with the strain rate are essentially linear in log-log plot for the examined range of strain rate. Based on the generalized power law overstress viscoplastic theory, it is confirmed that the rate-sensitivity and time-dependency of the Kunming peaty soil can be uniformly described using the sensitivity parameter involved in the theory, regardless of the applied loading conditions. The average value of 0.06 for the sensitivity parameter is generally greater than those for inorganic clay, indicating that the Kunming peaty soil exhibits more significant viscous behavior. Finally, by using the yield surface of the modified Cam–clay model, an overstress elastic-viscoplastic model is established and numerically implemented. The numerical model with a unique sensitivity parameter can well predict the rate-sensitive and time-dependent response of Kunming peaty soil under different loading conditions.

A force-based limit-equilibrium analysis is presented for the stability of a general two-dimensional, three-wedge sliding mass of soil with vertical or nonvertical interfaces between the wedges. The analysis is conducted using five failure planes and can accommodate variable conditions for wedge geometry, pore pressure, shear strength parameters, reinforcement, applied loads, and pseudostatic seismic coefficients. A constant factor of safety is assumed for each failure plane and reinforcement element, although this assumption can be relaxed through the selection of strength parameters. The factor of safety is obtained analytically and requires solving for the roots of a polynomial equation. A numerical example is provided to demonstrate the method and illustrate the importance of selected parameters, including wedge interface angles, for the stability of an earth slope. The analytical solutions take compact form, provide insight for the three-wedge method, and offer good capability to tailor conditions for applications that can be suitably characterized by wedge failure.

The cyclic stresses in subgrade soil induced by traffic loads are three-dimensional—cyclic major, intermediate, and minor principal stresses. To investigate the permanent deformation of natural undisturbed clay under three-dimensional cyclic stresses, a series of undrained true triaxial tests was carried out, using a true triaxial apparatus that could apply cyclic major, intermediate, and minor principal stresses simultaneously. The emphasis was on the effects of the cyclic stress ratio (CSR), the coefficient of cyclic intermediate principal stress (b_cyc), and the reciprocal slope of the stress path in the p–q plane (ξ) on the permanent deformation characteristics. The test results show that b_cyc reduces the accumulation of permanent major principal strain $({\epsilon }_1^p)$ remarkably. For given values of the number of loading cycles (N), CSR, and ξ, ${\epsilon }_1^p$ decreases approximately linearly with increasing b_cyc. ξ also limits the accumulation of ${\epsilon }_1^p$. Furthermore, the ratio of ${\epsilon }_1^p$ for a given value of ξ to ${\epsilon }_1^p$ for ξ = 1 decreases from 1.095 to 0.887 when ξ increases from 0.67 to 1.5, and the relationship between ${\epsilon }_1^p(\xi )/{\epsilon }_1^p(\xi =1)$ and ξ is described by a linear formula. A critical value of b_cyc is observed at which ${\epsilon }_2^p$ changes from tension to compression, that is, ${\epsilon }_2^p$ is zero at the critical value of b_cyc. The difference among the critical values of b_cyc in all the tests is relatively small, and the mean critical value of b_cyc is 0.328. Moreover, an empirical formula is established for predicting the permanent major principal strain under three-dimensional cyclic stresses.

Interaction of two back-to-back mechanically stabilized earth (MSE) walls in bridges has been the subject of many studies in road engineering. But regarding the other formations of this system with other types of retaining walls in excavation cuts stabilization, structure retrofitting, and other factors, the analysis of the interactive behavior of two back-to-back anchored walls (BBAW) by plate anchors and subjected to the vertical loading of a shallow foundation has not been the subject of comprehensive studies. This study experimentally investigated the effect of compound system architectural parameters [horizontal distance of two walls (W) and breadth of loading plate (B)] on its mechanical behavior. The loading plate yield and shear failure stresses, and also displacements and deformations of BBAW were measured and the results are presented. In order to evaluate the shape and form and how the critical failure surfaces behind the walls and beneath the foundation intersect with one another, the particle image velocimetry (PIV) technique was applied. The experimental tests results showed that in this compound system, the effective distance of walls is about W = 2.5*H (H: height of walls) and foundation effective breadth is about B = H, concerning foundation yield and shear failure stresses, walls displacement, and their deformations. In larger values of W and B, foundation and walls have no interaction that can be considered as an alternative solution to the limitations of the architectural parameters in practical cases. In addition, in this study, the failure modes and their mechanisms of this compound system were studied as well as its mechanical behavior.

Vugs and fractures are the main channels within porous rock aquifers and play a dominant role in the water inrush of the karst tunnel. In this paper, a mathematical model of the coupled free-fluid seepage-fluid with second-order accuracy was established to analyze the flow field characteristics of vuggy and fractured porous rock aquifers. The Navier–Stokes equation was used to govern the free fluid flow in vugs and fractures, while the Darcy–Brinkman equation was employed to describe the seepage fluid motion in the porous rock matrix. The analytical solutions for the flow velocity and water discharge were derived under the requirement of continuous velocity and shear stress at the interface between free and seepage fluids. These solutions can be successfully reduced to those of the classical Poiseuille’s law, assuming that the rock matrix is impervious to water. The numerical, experimental, and analytical results were compared to validate the present analytical model, and the results of the analytical model showed greater accuracy compared with the classical Poiseuille’s law and cubic law. Furthermore, the water inrush of the Xiangpingshan karst tunnel was selected as a real engineering case. Perforated bricks were used to stack a vuggy and fractured porous physical tunnel model (1:100) with the same hydraulic conductivity as the Xiangpingshan tunnel. The relative errors between current theoretical and physical tests obtained for the water inflow discharges are within 18%. The current model can provide a reference for predicting the water inflow of karst tunnels in vuggy and fractured porous rock aquifers.

In this study, the seismic response of submerged slopes is evaluated using a coupled smoothed particle hydrodynamics (SPH)–discrete-element method (DEM) framework. In this technique, DEM particles represent the soil grains and the fluid domain is idealized using SPH. The interaction forces between the two phases are estimated based on well-established semiempirical equations. The submerged slope was created utilizing the coupled scheme and subjected to a variety of base excitations with various amplitudes and frequencies. The results suggest that the stronger input motion generally induces larger displacements and shear strains. In addition, the frequency of the input motion can also have a significant effect on the level of deformation the system experiences. It was observed that the soil strength and stiffness can severely degrade due to pore pressure buildup, leading to excessive lateral deformations at input motion frequencies considerably lower than the initial fundamental frequency of the deposit. In contrast to the level parts of the model near the slope toe and crest, soil dilation close to the slope surface leads to a drop in the excess pore pressure and a temporary regain in soil strength and stiffness reflected by sharp acceleration spikes and asymmetrical shear stress–strain loops.

The spatial variability of soil parameters notably influences the accuracy of numerical analyses of earth–rockfill dams. This research establishes a stochastic finite-element method (FEM) considering the spatial variability of soil parameters. The autocorrelation distance and distribution function of the soil dry density are determined according to the monitoring values in situ. The regression functions between the dry density and Duncan E-B model parameters are developed using the triaxial test results. According to the dry densities distribution function and these regression functions, the cumulative distribution functions of E-B model parameter are determined, and the soil parameters random field are established using the isoprobabilistic transformation method. The Guanyinyan composite dam was taken as an example, and the convergence of the stochastic FEM, the effect of random field element size, and the sensitivity of E-B model parameters were discussed. The stochastic FEM analysis of Guanyinyan composite dam showed that the mean value of maximum settlements considering the spatial variability of soil parameters is close to the calculation of inversion parameters. The mean value of maximum settlements began converging in the region when stochastic FEM analysis calculations exceeded 400 times. The influence of the random field element size of the soil parameters on the stochastic FEM calculation is less than that on the FEM calculation. K_b has the largest impact on the stochastic FEM calculation, and R_f has the least influence.

Baffle structures are effective measures for decelerating granular flows and reducing their destructive power. However, the engineering design of baffle structures, particularly with respect to their height and strength, requires estimation of the run-up height and impact force, respectively, and remains challenging and immature. To describe the debris–baffle interaction, we propose an analytical model that incorporates the Froude number and ratio of the slit size to the particle size. The proposed model was verified based on numerical data. In this paper, we first discuss the determination of the empirical coefficients adopted in the proposed model. Then, using the flow properties of free flow in the proposed model, the calculated run-up height and total impact force on the first baffle array are compared to the results obtained by discrete element modeling. With regard to engineering design, the performance of the proposed model with a correction strategy and the baffle design considering unsteady-state flow dynamics are discussed in detail. The findings of this study suggest that the global maximum flow velocity and flow depth should be adopted in the engineering design of baffle structures.

Huge and critical structures, such as fuel storage tanks and nuclear power plants, are often built on dense sandy grounds, which may cause excessive plastic deformations under multidirectional cyclic shearing conditions caused by earthquakes. The lack of investigation of sand behavior under multidirectional loading may lead to unsafe designs, and thus significantly increase the maintenance cost for infrastructures during their long operational time, which might be longer than 100 years. This study presents a numerical investigation on the liquefaction behavior of dense sand under bidirectional cyclic simple shear using the discrete element method. The bidirectional cyclic simple shear tests with varying stress trajectories on the deviatoric stress plane, including figure-8, circular, and straight lines, were conducted. Additionally, a series of unidirectional loading tests was conducted in the simulation scheme for comparison purposes. The effect of the initial static shear on the cyclic behavior and liquefaction resistance of granular materials was examined. Four loading categories, including full reversal, partial reversal, intermediate reversal, and no reversal, were implemented in the numerical simulations. Although the presence of the initial static shear may enhance the cyclic resistance of granular samples under unidirectional loading, it mitigates the liquefaction resistance and promotes the failure of specimens under bidirectional shearing conditions. The microscopic analysis was performed to reveal the relationship between the fabric evolution and external loading, which can provide profound insights into the underlying mechanism of the cyclic behavior and liquefaction susceptibility of granular material when both the bidirectional shearing and initial static shear effects are considered.

The mechanical response of granular materials has been investigated widely using discontinuous modeling, such as the discrete-element method (DEM). Contact detection and contact resolution have been critical issues when modeling multiple body contacts, especially for arbitrary polyhedral blocks. In this study, the contact overlap calculation algorithms, including polyhedron–polyhedron and polyhedron–boundary contact, were developed to calculate the contact characteristics. For polyhedron–polyhedron contact, the contact overlap volume algorithm is developed based on the geometric dualization theory. The Gilbert–Johnson–Keerthi (GJK) and Quickhull algorithms are used to calculate the overlap polyhedron. The contact characteristics, such as normal direction (n), contact area (a), and penetration depth (u_n) could be extracted from the contact overlap volume. For polyhedron–boundary contact, a novel and effective algorithm is presented, where the polyhedron–boundary contact is transformed into polyhedron–triangle contact. Then, two types of benchmarks are used to verify the previously mentioned algorithms, which demonstrated that the algorithms could handle the complicated contact types and maintained contact continuity even from face to edge contact. As a complex benchmark, the failure process in a masonry structure is simulated and compared with the model test.

Frequently, the Mohr–Coulomb (M-C) yield criterion is used to determine slope stability. It offers an exaggerated, unreliable, and cautious assessment of the tensile strength of bonded materials, which are composed primarily of compressive elements, especially when subjected to seismic excitation. This work modifies the M-C yield criterion to integrate the concept of tensile strength cutoff, which involves restricting or eliminating the tensile strength of bonded materials. Analyses of the seismic stability of heterogeneous slopes use the discrete kinematic approach. Using a pseudostatic method of analysis, vertical and horizontal forces simulating seismic excitation are characterized. The primary objective of this study is to provide an insight into the effect of tensile strength cutoff on critical failure surfaces. For steep slopes, seismic excitation increases the range of base failure and decreases stability by 45%, while tensile strength cutoff exacerbates the decline. On steep slopes, an overturning failure is guided by the tensile strength cutoff; however, on mild slopes, it is indifferent to such a cutoff. Its application to two nonhomogeneous slopes indicates that a face failure may occur when a relatively weak layer exists in the slope and that the introduction of a tension crack yields the most conservative estimates, while its failure surface corresponds to the critical failure surface with tensile strength cutoff under the strong seismic excitation.

Abstract

A set of model tests using a miniature Earth Pressure Balanced Shield (EPBS) machine are carried out to examine the effects of grain-size distribution on the mechanical behavior of granular soil in response to EPBS tunneling. The combined effects of particle size (D₅₀) and tunnel depth on the vertical movement and volume loss of ground are studied. A discussion of the implications of the soil arching effect and volumetric strain associated with D₅₀ to the results is also provided. The results show that the deformation patterns of ground are highly dependent on the grain-size distribution of the soil, especially for relatively deep tunnels. The value of trough width parameter (k) for fine soil exhibits an obvious nonlinear increase with the depth. However, it is linear for the soil with a relative large grain size. The particle size has a significant influence on the variation of soil volume loss at the surface level, especially for relatively deep tunnels.

Practical Applications

Typically, when EPBS tunneling is undertaken in granular soil, a target value of the pressure in the chamber of the EPBS machine and grouting pressure in the tail are required to define to control the soil volume loss within an acceptable range, which is important to keep surface settlement in compliance with maximum specified values. The results in this study highlight the effects of the grain-size distribution of granular soil on the surface settlement trough and volume loss. Potentially, data from testing of model tunnels could provide a useful basis for making this assessment. According to the findings in this study, for fine granular soil, a tunneling engineer with a target volume loss at the surface level will have to target less volume loss at the tunnel level than the desired maximum value for the surface volume loss. In the granular soil with a relatively large grain size, the target values for volume loss at tunnel level can be greater than the desired maximum value for the surface volume loss. The results in this study confirm that the settlement trough in the fine granular soil is steeper than that in the granular soil with a relatively large grain size. This suggests that tunneling in granular soil with a relatively large grain size is likely to induce a wider settlement trough but probably causes less damage to buildings, whereas in fine granular soil, the settlement trough is likely to be narrower but may potentially cause greater building damage.

Artificial ground freezing construction is an effective and widely adopted method for reinforcement in constructing subway tunnels. Regarding sandy clay in artificial frozen walls, changes in its microstructure can affect macroscopic properties during the freezing and thawing processes. An enlargement in the pore space can cause a reduction in compactness due to the frost heave, resulting in a degradation of mechanical characteristics of sandy clay. This study attempted to quantify the effects of freeze–thaw (F–T) damage with different negative temperatures on the shear strength and pore structure of natural soil. Accordingly, four cooling temperatures were applied to the soil samples, which were tested using a triaxial shear instrument and a nuclear magnetic resonance (NMR) imaging scanner. Moreover, by utilizing pore-size distributions and pseudo-color images, changes in pore structures were evaluated both quantitatively and qualitatively, and the mechanism of mechanical properties was thoroughly elucidated according to NMR observations. The results demonstrated that the F–T process affected the cohesive force more than the internal friction angle. Triaxial shear indexes consecutively declined as the cooling temperature decreased, whereas the attenuation amplitude was stale when the temperature was below −20°C. The F–T process was shown to have an expansive effect on pore characteristics (e.g., an increase in porosity, pore diameter, and proportion of macropores). In addition, a strong negative linear correlation was observed between the total porosity and shear strength of sandy clay. This study can improve the understanding of the frost heave mechanism of soil in artificial walls, which may be beneficial for providing insight into designs and protections in the construction of subway tunnels.

Batter piles are often designed as foundation of high-rise structures to resist large lateral loads. The sizeable overturning moment of the superstructure will be transferred to the foundation so that batter piles are subject to the oblique uplift loading with changing directions. Due to the lack of understanding of the working behavior, the design and application of the oblique uplift batter pile are limited. In this study, 11 groups of laboratory tests are carried out in a testing box. The instrumental batter piles are made of polyvinylchloride pipes and loaded via pulley and counterweight. The variation of internal force, pile deformation, and load–displacement curve of the pile head is acquired. The load transfer mechanism and failure mode are summarized. A new type of tactile pressure sensor (TPS) is attached to the pile surface, and the actual pile–soil interaction forces in the normal direction are measured. The results show that the loading angle α controls the overall stability of the pile, the critical angle is 15° (in this study, qualitatively). When the α is within ±15°, the axial component of the oblique uplift load controls the overall stability of the pile; otherwise, the lateral component controls the stability. The increase of the loading angle α will increase both the bending moment of the negative and positive batter pile, but with different increments. The increase of pile inclination β will weaken the bending moment concentration effect. The soil pressure on the batter pile is in the offset state, which can be fitted by elliptic function. The pile–soil interaction below a certain depth is not affected by the pile inclination β and loading angle α. The middle to lower sections of the batter pile can be designed as the axial uplift pile, considering its resistance of axial skin friction only. This study shows the working mechanism of the oblique uplift batter pile in a manner way, which has practical significance for design and engineering application of batter pile.

A semianalytical solution was obtained in the time domain directly for the one-dimensional transient response of a saturated multilayered soil column under typical boundary conditions based on Biot theory, which could take into account the inertial, viscous, and mechanical couplings of saturated porous soil media. First, one-dimensional wave equations were established by using the nondimensionless method. Then, by decomposing the displacement solution into dynamic and static components, the boundary conditions of the soil column were homogenized. The transfer matrix method was used to obtain the eigenvalue and eigenfunction of homogenized boundary conditions. With the help of undetermined coefficients and orthogonality of eigenfunctions methods, the solution to the problem of nonhomogeneous boundary conditions could be converted to solve the initial value problem of a series of ordinary differential equations. The semianalytical solutions were approached by the precise time-integration method. The proposed method can be used for a soil column under various boundary conditions. Several numerical simulations were carried out to validate this method. Finally, the one-dimensional transient responses of hard–soft double-layered saturated soil under step load was analyzed. The results demonstrate that the rigidity of substratum and different rigidity ratio of hard–soft layers mainly affect the responses over a long period of time.

This paper aims to present an integrated analytical model for geosynthetic-reinforced and pile-supported embankments (GRPSEs) by rationally combining the reinforced embankment, the pile-embedded soft soil foundation, the stress adjustment region, and the equal settlement region of the substratum. The embankment geometry boundary is considered for computing the additional stress beneath the adjustment region of the underlying stratum. The geosynthetic reinforcement (GR)-reinforced embankment together with the composite foundation is considered as a whole system by ensuring the consistency of differential settlement between pile and soil on the subsurface. The stress distribution predictions of the proposed model provide reasonable agreements with the previously published results. Parametric studies and quantitative results of this proposed analytical model show that the whole GRPSE is methodically combined. It is demonstrated that increasing the area converge ratio by decreasing the center-to-center spacing is seen to be a more effective way to enlarge pile efficiency, especially when the area converge ratio is less than 10%. Increasing the compression modulus of the embankment or embedment of pile-toe into a deeper underlying stratum will be beneficial to the increment of pile efficiency. The force captured by the pile increases almost linearly with the ratio of GR deflection to the clear pile spacing.

Geosynthetic-reinforced soil (GRS) retaining walls have been widely adopted in engineering practice based on the development of several design methods. However, the temperature effect, which was proved to be an important influencing factor of retaining wall performance, was not considered in the existing design methods. This study investigates the temperature distributions of a (GRS) wall subjected to freeze–thaw (FT) cycles using (1) a lab-scale physical model test within a custom-made temperature-controlled tank; and (2) a commercial finite-element computer program for conducting numerical modeling. The numerical model was first validated using the lab-scale model test data obtained in this study, and then a full-scale numerical model was created for achieving an in-depth understanding of the temperature distribution behaviors of a real GRS wall subjected to FT cycles. Both model test and numerical results demonstrate that (1) the periodic variation of the ambient temperature during the FT process induces a temperature fluctuation in a sinusoidal shape in the soil, and the temperature distributions of the soil are distinctly related to its location inside the GRS wall; (2) the soil temperature in zones with a distance of 2.0 m to the exposed boundaries (i.e., back of facing panels and road pavement) of the GRS wall is more sensitive to the variation of the ambient temperature. Also, the temperature amplitudes in these regions during each FT cycle are greater than those in the zones far away from the exposed boundaries of the GRS wall; and (3) the frost depth in the vertical direction or frost thickness in the horizontal direction increases constantly with a decrease of the ambient temperature lower than 0°C, and vice versa. The maximum frost depth or thickness behind the GRS wall is lagged to the lowest ambient temperature and decreases with the increase of the distance to the exposed boundaries. In addition, a mathematical model was proposed for predicting the soil temperature amplitudes at different locations inside the GRS wall.

Even though extensive research works have been carried out to understand the trapdoor responses in frictional materials, those in cohesive–frictional materials have not yet been well studied due to the complexities involved. This paper focuses on formulating new analytical solutions for cohesive–frictional soils above deep active trapdoors. Finite-element limit analyses (FELA) were conducted to study the failure mechanisms of a deep active trapdoor considering various cover ratios, soil cohesion, and soil friction angles. Three distinct failure modes could be observed, depending on various combinations of cover ratio and soil strength parameters: internal, vertical, or external collapses. The analytical solutions, allowing the failure mechanisms and load-transfer mechanisms to be taken into account, were further proposed to calculate the modified lateral earth-pressure coefficient and vertical stresses in soils. The results from previous works and FELA solutions were compared with validate the proposed solutions. A parametric study was performed to explore the effects of cover ratios and soil-strength parameters on soil-arching ratio. The proposed solutions provide a theoretical guideline available for the initial design of geo-infrastructures spanning voids.

In this study, six shaking table tests were conducted to investigate the effects of two biomaterial solutions on liquefaction and lateral spreading in a sandy layer. The desaturation liquefaction mitigation method, which was induced by biogas bubbles in loose sandy soil, was modeled in a shaking table box that was subjected to sinusoidal motions. The biogas process was based on urea hydrolysis, which was catalyzed by two urease enzymes [e.g., jack bean (Canavalia ensiformis) and soybean], into ammonium (NH₄⁺) and carbonate ions. The strain energy approach, which was based on shear stress–strain hysteresis loops, was implemented and used the recorded accelerations and pore water pressures to evaluate soil liquefaction. In addition, to measure lateral spreading displacements in a block placed on the liquefied soil, direct observation, and grading methods for soil surface displacement, and the particle image velocimetry (PIV) method were utilized. The results showed that accelerations for the treated tests presented less amplification than for the untreated (UT) test, and the pore water pressure ratio decreased by 40% and 47% due to induced biogas bubbles within a soil that used jack bean and soybean solutions, respectively. The soil layer shear wave velocity and the liquefaction energy capacity of the soil significantly increased, by approximately 100%, due to a decrease in the degree of saturation (S_r). In addition, the horizontal displacements, measured by the PIV method, showed a significant decrease in sloped block movement from 0 to 30 to 0 to 7 mm, and the grading line displacement on the soil surface was reduced by approximately 70% based on the direct method. The volumetric strain decreased by 80% when the biomaterial solutions were applied to the sandy layer.

Piles are walls that are installed underneath hydraulic structures to control seepage flow, uplift pressure, and exit hydraulic gradient. In this study, the effect of the ratio of width of the apron to the foundation depth (B/D), the ratio of the width of the apron to the downstream pile depth (B/d₂), and the ratio of the upstream and downstream pile depths (d₁/d₂) on seepage flow characteristics is numerically investigated using the finite-element method. From the numerical simulations, design charts, and explicit formulas for estimating seepage flow characteristics, such as the percentage residual uplift pressure at key points, the discharge flow factor, and the exit hydraulic gradient factor underneath aprons with end double-piles for both states of equal and unequal depths are developed. The simulations are validated with existing analytical solutions for simple cases. To assess the accuracy of the presented formulas, statistical metrics; that is, the determination coefficient, root mean square error, and percent relative error (RE%) were used. The statistical metrics are satisfactory, and their values quantified the reliability of the proposed formulas. The proposed explicit formulas, with RE% less than 5%, could be used by design engineers instead of implicit analytical equations that involve elliptic integrals.

Dredged clay slurry is usually regarded as a waste material due to its high water content, high compressibility, and low strength. Treating dredged clay slurry with carbide sludge (CS)–activated ground granulated blastfurnace slag (GGBS) can efficiently improve its strength. However, the compressibility and permeability behavior of CS-GGBS–treated slurry have not been investigated. In this study, a marine clay slurry with water content of 100% was treated with 60 kg/m³ of CS-GGBS, and the compressibility and permeability were evaluated. The untreated clay was also investigated as a reference. The results showed that although the treated slurries had a significantly higher initial void ratio (∼2.5) than that of the untreated clay (0.96), they yielded similar vertical strains, that is, around 25%–31%, in an oedometer test. The compression curve of the treated slurries consisted of two distinct phases, which can be elucidated by the evolution of the soil-cementation structure. At the pre-yield state, the cemented structure of CS-GGBS–treated slurry sustained the external stress, leading to insignificant strain. When the vertical stress exceeded the yield stress, the soil-cementation structure largely collapsed, and considerable strain occurred due to its high void ratio. In this stage, the compression index (C_c) of the treated slurry was three times higher than that of the untreated clay. Additionally, the treated slurry had a coefficient of consolidation (c_v) 30–100 times greater than that of the untreated clay, which was attributed to its high permeability. During the oedometer test, the permeability of the treated slurry decreased sharply upon initial compression of the specimens, and then decreased at a lower rate as the void ratio decreased, presenting a bilinear correlation between permeability and the void ratio.

Abstract

This work focuses on the development of a three-dimensional shield tunneling model coupling the finite-difference method (FDM) with the discrete-element method (DEM) and evaluates its tunneling performance in boulders. The tunneling process of cutterhead rotation, cutting the formation, soil entering the chamber, and discharging of the screw conveyor is simulated to explain the characteristics of particle movement in front of the tunnel face. The range of the soil failure zone under different shield discharge ratios is determined by the correlation between the discharge ratio and the tunnel surface stability. The evolution process of the soil arching effect in the boulders along with shield tunneling is investigated to understand the mechanisms of the delay settlement in the boulders. Subsequently, the shield discharge ratio is optimized by investigating its influence on the surface deformation. Finally, the average stress distribution on the shield cutterhead in the tunneling process is analyzed to provide the scheme of the cutterhead structure and arrangement. This work can be referred for evaluating the shield tunneling performance and optimizing the excavation design scheme of shield machines during tunneling construction under similar geological conditions.

Practical Applications

The coupled finite-difference method (FDM)–discrete-element method (DEM) calculation method proposed in this study was successfully applied for boring tunnel equipment performance analysis in Beijing Metro Line 16. This shield tunnel was excavated in the strata with boulders rich in large size and high strength, and the previous tunneling experience shows that the shield is prone to encountering accidents such as tool damage and cutterhead jamming by large boulders when tunneling in such strata. Based on the present parametric analysis and calculation results, the suitable engineering suggestions have been proposed to enhance the shield equipment specifically, such as strengthening the central and peripheral cutters and the wear resistance of the cutterhead sides. In addition, the cutterhead opening and band-type screw conveyor were also adjusted to allow large size stones to pass through the cutterhead and discharge from the soil chamber as much as possible instead of being broken by the cutters. The adoption of these techniques has made it possible for the earth pressure balance shield (EPBS) machine to continuously excavate 1,300 m in boulders without cutter exchanges.

This study aims to propose a seismic performance analysis framework based on the oblique incidence theory, estimate a normalized damage response (RDVR) through seismic parameters and incident angles, and explore the variation in dynamic responses of concrete dams with arbitrary incident angles under near-fault vertically polarized shear (SV) waves. Several near-fault pulse-like records were selected, and their decomposed nonpulse (residual) components were used to guarantee the similarity of the response spectra. Furthermore, a seismic input model of the SV wave oblique incidence was developed based on the viscous-spring artificial boundary method, and its accuracy was verified using a numerical application. The effects of the incident angles of SV waves (−30° to 30° at 5° intervals), seismic intensity, and polarity on the damage and displacement responses of a gravity dam–reservoir–foundation system under pulse-like and nonpulse motions were studied. Additionally, the relationships between the incident angle, seismic characteristics [including the peak ground velocity to peak ground acceleration (PGV/PGA) ratio and spectral acceleration S_a(T₁)], and the proposed RDVR were established. The most unfavorable incidence angles for different cases were derived. The numerical results showed that the negative direction (from downstream to upstream) has a significant effect on the nonlinear responses of a dam. The seismic features of PGV/PGA exhibited a better correlation with RDVR than S_a(T₁). Subsequently, the damage to the gravity dam was estimated using the multivariate fitted method according to the proposed prediction model. The results showed that the proposed prediction model with arbitrary incident angles provides a good estimation of the real results. Thus, it is important to consider the coupled effect of incident angles and seismological characteristics in the seismic assessment of concrete dams located in near-fault regions.

Water flow experiments in single tensile and shear granite fractures were conducted to investigate the nonlinear flow behavior. Fracture geometry parameters based on single fracture wall (R_p, Z₂, Z₃, Z₄, JRC) and two fracture walls (aperture distribution, cluster coefficient) were calculated and compared. The effect of these fracture geometry characteristics on nonlinear flow behavior was explored. Fracture transmissivity, critical Reynolds number, pressure gradient, and normalized transmissivity were analyzed in detail. The result shows that shear fracture geometry has the characteristics of higher mean aperture with higher standard deviation, more clustering contact, and rougher fracture surface. The shear to tensile fracture transmissivity ratio increases from 2.3 to around 370 with the increase of confining pressure from 2 to 60 MPa and the stress-dependence coefficient of shear fractures is close to 1/22 of tensile fractures. The critical pressure gradient increases as confining pressure, indicating that it requires a higher pressure gradient to drive the linear flow to nonlinear flow, namely, when the injection pressure gradient keeps unchanged, high confining pressure causes the nonlinear flow to turn to linear flow. The critical gradient of the shear fracture is 0.004–0.527 MPa/m on average, which is much lower than that of tensile fractures (0.011–26.862 MPa/m), meaning that a lower pressure gradient can drive the linear flow to nonlinear flow in a shear fracture. The average Forchheimer coefficient β for tensile fractures is 0.133, which is about half of the shear fracture (0.253). Regression analysis indicates that a linear relationship exists between β and the fracture geometry parameters (mean aperture η and cluster coefficient ς) and the correlation coefficient is about 0.925 and 0.920, respectively. Further investigation confirms the “weak inertial effect” with the (T₀/T − 1)/Re data points falling in a straight line before the “strong inertial effect,” where the data points fall in an approximately horizontal line.

Abstract

This paper has proposed a closed-form solution for two-dimensional (2D) plane strain consolidation in unsaturated soils with lateral and vertical semipermeable drainage boundaries under time-dependent loading. By using the eigenfunction expansion technique, the governing equations are expanded into coupled ordinary differential equations, and the final solution of pore pressures is obtained by the integral transform method. The degraded proposed solution is then verified with the existing solution. The results show full agreement with the solutions, which indicates the proposed solution and program are completely correct. Meanwhile, the comparison between the analytical solutions and the finite-element simulations also demonstrates the correctness of the proposed solution. Subsequently, the effect of semipermeable parameters and loading parameters on the consolidation behavior has been investigated through the obtained analytical solution. And the distribution of consolidation profiles along two different directions has also been studied. It can be concluded that time-dependent loading changes the dissipation process obviously compared with constant loading.

Practical Applications

As the soil above the water table line is unsaturated, when constructing structures (e.g., houses and highways) on unsaturated soft soil, assessing the joint deformation of the structure and the foundation soil is essential to prevent excessive settlement and perhaps even cracking of the structures. When constructing on this soil, the foundations are often treated by some measures to avoid settlement and cracking. For example, vertical drains are used to accelerate the consolidation of the foundation soil. However, the presence of factors that impede drainages, such as the well resistance effect and the smear effect, brings some difficulties in calculating the coordinated deformation of the structure and the foundation soil. To integrate the effects of these factors, the research in this paper provides an analytical solution to evaluate the coordinated deformation of buildings and unsaturated soil. The analytical model can provide guidance for the construction of structures on such foundations by taking into account the unsaturated soil, the impeded drainage boundary, and the construction process.

Construction of a large water reservoir can trigger an earthquake. The event of the earthquake can lead to the propagation of a destructive Love-type waves (LT-wave). Therefore, the area near the reservoir is prone to the propagation of LT-waves. Due to this, it is crucial to examine the propagation of LT-wave propagation in the geological structure found in these areas. The present analysis adduces the propagation of LT-waves in the anisotropic double-porous rock structure that is generally found the area of water reservoirs. The said rock structure consists of three different regions: the uppermost viscous liquid region, transversely isotropic double-porous (TIDP) rock layer in the middle, and the lowermost half-space region comprised of isotropic double-porous (IDP) rock medium. The expressions for the dispersion and damping characteristics have been derived for parabolicalal and rectangular interfacial irregularity. The profound efficacy of distinct physical parameters, such as irregularity parameter, interfacial bonding parameter, porosity parameter of said middle double-porous layer, and porosity parameter of said lowermost double-porous half-space on the phase velocity and attenuation coefficient of LT-waves, are also discussed.