International Journal of Geomechanics

When applying the artificial ground-freezing method in a shield-driven tunnel, the design of the freezing zone and freezing time is of practical interest. Therefore, the distribution and evolution of heat transfer in a frozen soil wall are key issues in the examination of the freezing effect. In this study, the horizontal ground-freezing method for soil reinforcement in shield-driven tunneling was considered. A cup-shaped freezing scheme was adopted at the launching shaft of the shield-driven tunnel. Three-dimensional (3D) finite-element analysis was used to examine the heat transfer within the cup-shaped frozen soil wall. By this method, the feasibility of the artificial ground-freezing method in the shield tunneling of Nanjing Subway Line 10 was demonstrated. Four types of soil were considered as the in situ soils surrounding the shield machine: sandy, cement-admixed sandy, soft clay, and cement-admixed soft clay. The simulation results indicate that the cement-admixed sandy soil was the most favorable material in terms of ground freezing; it had the highest decreasing rate of temperature in the process of ground freezing. In contrast, the soft clay was the most unfavorable material in terms of ground freezing. The results imply that the closure time of the cup-shaped frozen soil wall was sensitive to the thermal physical properties of soils in addition to the in situ water content.

Stability of slurry trenches is an important issue during the construction of groundwater cutoff and diaphragm walls and, thus, has gradually drawn additional attention. With the aim of controlling the stability and collapse mechanism of slurry walls better, an analytical approach based on interactions between horizontal and vertical arching effects was conducted to estimate the stability factors for general and local stability of a slurry-supported trench panel in cohesionless soils. The results show that arching has certain characteristics that affect soil behavior near the trench, including directions of loading and unloading of soil, variation of active pressure coefficient on the sidewall interface, and a created downward load transfer mechanism. The trench stability depends on two types of safety factors; the first factor prevents sliding collapse (overall stability), and the second factor prevents collapse of the soil interface (local stability) because local interface instability triggers overall trench collapse in cohesionless soil. The solution was compared with field measurements and three-dimensional (3D) finite-element analyses (with the effect of the third dimension), which permitted study of the influence of the arch located in the third direction. The satisfactory correspondence validates this approach and shows that the 3D analytical analysis perfectly describes the phenomenon.

Weathered granite soils are abundant in China and used extensively as backfill materials. However, there is less systematic research on weathered granite compared with sedimentary types of soils, such as sand and clay. In this study, a series of laboratory tests was performed, including X-ray diffraction, sieving, expansion potential, compaction, California bearing ratio (CBR), and large-scale triaxial tests, to study the basic physical properties and mechanical behaviors of weathered granite soil. Results of the laboratory tests indicate that a clay content of 8% could be a good indicator to determine the compaction characteristics of weathered granitic soil with differing clay content. Thus, weathered granite soil with a clay content of approximately 8% would be advantageous to reach and maintain the compaction rate of subgrade and the stability of roads. However, the weathered granite soil with a clay content of approximately 4% had the largest mean value in the CBR tests, which was 95%. The critical confining pressure (100–200 kPa) is an indicator to determine the hardening characteristics of compacted weathered granitic soils under different pressures. The experimental results show that the samples exhibited different dilatancy characteristics under different confining pressures because the internal particles of the samples might have been compacted, dislocated, overturned, or broken and that the increase in peak deviatory stress resulting from an increase in mean stress was nonlinear because of particle breakage.

Recent experimental findings highlight the impact of anisotropic consolidation on triggering flow liquefaction failures. Results of a series of undrained tests on isotropic and anisotropic consolidated Firoozkuh sand are reported. It was observed that very loose and loose samples are very prone to flow liquefaction; however, the samples in a medium-loose state can withstand flow and limited flow liquefaction effectively for an initial mean principal effective stress less than 300 kPa. The mechanical behavior of isotropically and anisotropically consolidated samples of Firoozkuh sand in very loose, loose, and medium-loose states was simulated realistically by a state-dependent elastoplastic constitutive model. For highly anisotropic consolidated samples, numerical simulations confirmed that flow liquefaction in very loose and loose samples may be triggered easily without any warning. In addition, the stress ratio at the onset of flow liquefaction is not unique and greatly depends on the initial state and consolidation history.

Backfilling is commonly applied to aid pillar recovery in open stope mines. The backfill must then remain self-standing in the primary stope when mining an adjacent secondary stope. The design of exposed fill is often based on a solution proposed by Mitchell and coworkers over 30 years ago. Several modifications of this solution have later been reported. These solutions have been partly validated against a few physical model test results, and they have also been compared with numerical simulations. The analyses have shown that these solutions cannot completely capture the response of the exposed backfill, particularly when the required cohesion of the cemented backfill is relatively large. New simulation results presented here indicate that the sliding plane tends to change from planar at small fill cohesion to spoon shaped [three-dimensional (3D)] at larger cohesion. In the former case, the failure mechanism is controlled by shear stress along the sliding plane near the base of the stope; this corresponds well to existing analytical models. In the latter case, however, failure of the backfill is controlled by both shear (near the base) and tensile (near the top) stresses. This feature is not represented by existing analytical models. In this paper, a new analytical solution is proposed for assessing the stability of exposed cemented backfill with a vertical face. An instability criterion is also introduced for estimating the critical strength of side-exposed backfill. Additional numerical simulations are then conducted to validate the proposed analytical solution. The results show that the newly developed solution correlates well with the numerical simulations for representative stope geometry and backfill strength. This new solution is thus regarded as an improvement over existing solutions. Further calculations are made to illustrate the effect of key parameters on the stability of side-exposed fill. A discussion follows on the limitations and effect of various influence factors on the design of exposed cemented backfill.

Particle breakage modifies a rockfill structure, influencing its dilatancy, friction angle, strength, and permeability, as well as generating creep deformation, wetting deformation, and residual strain under a seismic load. However, the breakage laws of rockfill during shearing remain unclear. This paper investigates the particle breakage of the basalt rockfill that is used in the Gushui concrete face rockfill dam during specimen preparation, consolidation, and drained triaxial shearing. The results indicate that the hammer compaction during specimen preparation generates a considerable amount of particle breakage, whereas isotropic consolidation generates negligible particle breakage. Under a low confining pressure (100 kPa), rockfill particle sliding and roll over are loosely constrained, and negligible particle breakage occurs during triaxial shearing. Under a high confining pressure (greater than 500 kPa), rockfill particle sliding and roll over are more constrained. Thus, the contact force significantly increases and significant particle breakage occurs. During triaxial shearing, larger diameter particles break first and smaller diameter particles begin to break as the confining pressure increases. The percentage of particles with diameters below 0.25 mm always increases with increasing shearing strain, and the amplitude increases with increasing confining pressure. Particle breakage during shearing in the triaxial test is affected by both the shear strain and stress. Additionally, the relationship between the relative particle breakage index and plastic work can be simulated with a hyperbolic formulation.

For landfills situated in regions of high seismicity, seismic inertial forces may be a triggering factor for the translational stability of municipal solid waste (MSW) landfills. This paper applies a modified pseudodynamic method to the seismic translational stability analysis of landfills. In the present study, a closed-form solution is proposed to obtain the factor of safety and the yield acceleration coefficient for a typical side-hill-type landfill resting on a rigid base using limit equilibrium method. The acceleration ratio obtained in the present study compares well with that obtained using popular ground response analysis software for a given set of input parameters. The acceleration ratio is the ratio of seismic acceleration at the top of the landfill to the seismic acceleration at the base of the landfill. From parametric study, it is observed that the landfill is vulnerable to seismic damage in low-frequency input motions. At low frequencies, the seismic inertia force is in phase at all depths. The seismic force acting on the landfill mass is reduced at higher frequencies, where landfill mass is entering into higher modes of vibration, where some portion of landfill is moving in one direction and the remaining portion is moving in opposite direction. The results obtained are compared with the available literature sharing the same input parameters. The values of the factor of safety obtained in the present study are higher than those calculated using pseudostatic and pseudodynamic approaches. For the input parameters assigned in the comparison, the landfill mass in the third mode of vibration is the reason for the greater values of the factor of safety. Material damping may be also a reason for the higher factor of safety values.

Debris flows that entrain sediment by undermining channel beds or scouring channel banks can become exceptionally mobile and destructive. Therefore, the calculation of entrainment plays an important role in debris flow runout analysis. An entrainment model is proposed that takes into account surface erosional effects by considering progressive scouring and shear failure on the channel surface. By considering simple geometry and particle configurations, the equations for the progressive scouring are developed. In deriving the equations for the progressive-scouring mode of erosion, two types of motions are considered: rolling motion and sliding motion. Newton’s law of motion is applied to calculate the acceleration, velocity, and displacement of the particles. A probability-density function (PDF) is used in the calculation of the entrainment rate for different configurations of particle contact. Measurements from flume experiments were used for model verification. It was found that the entrainment rate can be calculated using a normal-distribution PDF. The proposed entrainment model has been shown to be effective in calculating debris flow entrainment.

The analysis of the complex kinematics of fine-grained masses, from the moment they rapidly slide along mountain streams until they stop, is crucial to the identification of potentially vulnerable areas and the design of adequate mitigation structures for their protection. For this purpose, the speed evolution and runout length of these material flows were analytically modeled in this research by taking into account (1) the (curved) geometry of the sliding surface; (2) the evolution of the excess pore-water pressures (generation, initially attributable to several factors/phenomena and during the motion to the slope curvature, coupled to undrained and oedometric conditions; dissipation, attributable to consolidation); (3) the physical and mechanical parameters of the sliding material; and (4) the mass variation attributable to possible erosion or deposition processes. The governing ordinary differential equation was analytically and numerically solved. The role played by the main parameters in the kinematics of rapid fine-grained material flows and the range of their admissible values were evaluated. Model validations using laboratory measurements and the analysis of specific documented cases were developed and carried out.

In the present paper two analytical models are proposed for the estimation of slope stability in homogeneous intact and jointed rock masses with strain-softening behavior and a single joint, as nonlinear functions of basic slope parameters (slope height H and angle β), and physicomechanical properties of rock mass (unit weight γ, peak cohesion c, peak friction angle φ, joint inclination α, joint cohesion c_joint, and joint friction angle φ_joint). Research was performed using the Box-Behnken design, for which the input data were provided by stability analyses of different slopes using the shear strength reduction method. For intact rock masses, the safety factor is given as a function of H and β, γ, c, and φ, whereas c_joint, φ_joint, and α, along with H and β, were also included for jointed rock masses with a single joint. Developed models provide reliable estimation of slope stability with high statistical accuracy and a small value of the predicted residual error sum of squares (PRESS) statistics. Robustness of developed models is verified against experimental modeling errors using a Monte Carlo simulation. Real-world application of the derived model for jointed rock mass is tested for a characteristic case from engineering practice.

The purpose of this study was to investigate the deformation-induced stability of earthen embankment dams to explosive airblast loading. This study specifically investigated the effects of close-in explosive airblast loads on the downstream toe of a homogeneous earthen embankment dam composed of cohesive soils. Small-scale explosive airblast experiments on cohesive soils from a previous study were compared with numerical analyses. Finite-element simulations of airblast loading on a cohesive soil embankment dam were performed using multimaterial arbitrary Lagrangian Eulerian (MM-ALE) methods. Blast effects on varying reservoir levels and engineered drainage were investigated to determine the impact on dam stability. The airblast simulations created craters on the downstream slope and reduced the toe length. Although larger explosive masses removed more material, crater dimensions did not significantly increase with explosive mass due to energy loss in air. Circular slip surfaces intersected the crater and reduced stability for dams with no engineered drainage. A horizontal toe drain effectively lowered the phreatic surface away from the blast crater and increased structural stability. It was concluded that explosive airblasts posed a possibility of slope failure only for dams with no engineered drainage that were close to full reservoir capacity.

The current study focused on the propagation behavior of horizontally polarized shear waves (SH wave) in a corrugated fiber-reinforced layer loosely bonded with an isotropic elastic half-space. Both the layer and half-space were assumed to be heterogeneous and acted upon by horizontal initial stresses. The heterogeneity in both the layer and half-space were caused by exponential variation of the elastic parameters and density as a function of depth. The closed form of the dispersion relation was obtained and reduced to the classical Love wave equation as a particular case of the problem. The substantial effects of reinforcement, anisotropy, heterogeneities, corrugation, loosely bonded interface, and initial stresses on the dispersion curve were studied extensively with the aid of graphical illustrations and discussions accomplished by numerical computation. Moreover, a comparative study was performed to meticulously compare the case of presence of reinforcement in the layer (anisotropic case) to the case of reinforced free layer (isotropic case), the heterogeneous case to the homogeneous case, and the case of loosely bonded interface to the case of perfectly bonded planar interface.

Three-dimensional (3D) slope stability analysis is a present research interest for geotechnical engineering. This work established a new 3D limit equilibrium method (LEM) to solve 3D slope stability with general-shaped slip surfaces. In the proposed method, a simple initial normal stress on a slip surface is used by analyzing the stresses on a vertical microcolumn. To ensure the accuracy of the results, a dimensionless variable is adopted to amend the initial normal stress. Then, by using the Mohr-Coulomb (M-C) criterion, the shear stress on the slip surface is also assumed. Different from the traditional LEM, global limit equilibrium (LE) conditions are used to avoid the effect of intercolumn forces on slope stability. Moreover, the Cartesian coordinate system is constructed on the basis of the main direction of a 3D sliding body; thus, strict solutions of 3D slope stability can be achieved with only three equations of static equilibrium on the sliding body. After contrasting the results in several classic slope examples, the proposed method’s feasibility is verified with the following advantages: (1) it has a simple derivation process to obtain rigorous results, and compared with the same simple 3D nonrigorous method, the improvement of more than 10% on the slope factor of safety (FOS) is achieved; (2) it is easy to program with a fast solution speed, and compared with the conventional 3D Morgenstern-Price (M-P) method, the calculation speed is increased more than 1.5 times; and (3) it can directly obtain the distribution of normal and shear stress on the slip surface and can also visually draw the global and local sliding trends of a 3D sliding body.

The lower- and upper-bound finite-element limit analysis in conjunction with second-order conic programming (SOCP) was used to estimate the ultimate bearing capacity of strip and circular footings with an inclusion of a layer of dense sand over existing loose sand strata. The analysis followed the Mohr-Coulomb yield criterion and an associated flow rule. The results are expressed in terms of an efficiency factor that increases quite significantly with increases in the (1) thickness and (2) friction angle of the upper densified layer. While keeping the same thickness of the upper dense sand layer, the circular footing exhibits greater efficiency-factor values as compared to strip footing. The numerical results compare well with data available from the literature.