International Journal of Geomechanics

The present model is established to analyze the characteristics of SH wave propagation in a fluid-saturated porous layer interfaced between a corrugated heterogeneous layer and an orthotropic half-space under an initial stress. The combined effect of two distinct types of irregular boundary, that is, a rectangular form of irregularity at the common interface and a corrugated upper boundary, on the propagation of SH waves has been undertaken and seems to be an innovative idea. The dispersion equation has been obtained by imposing compatible boundary conditions employing Fourier transformation and first-order perturbation techniques. The prime goal of this study is to analyze the impact of corrugation, initial stress, depth ratio of two layers, porosity, and irregularity on the propagation of SH waves. Some special cases are deduced that agree with the pre-established result; one particular case reduces to the classical case that validates the undertaken study. In addition, some noteworthy factors are assessed graphically. The authors have used the software MATHEMATICA for graphical representation and mathematical determination to solve systems of equations throughout the manuscript. The results obtained from this study will be useful to geophysicists, seismologists, and civil engineers for the design and construction of sensors, as well as for undertaking nondestructive testing.

This paper proposes a semianalytical solution to analyze the long-term settlement of a single pile embedded in fractional derivative viscoelastic soils under time-dependent loading. In this paper, a three-dimensional (3D) fractional derivative viscoelastic model will be introduced to describe the rheological behavior of soils around the pile. Based on the shear deformation compatibility between the pile and soils, the semianalytical solution will be strictly derived using the correspondence principle and the Laplace transform technique. Three well-documented cases will be used to verify the correctness and reliability of the proposed semianalytical solution, all of which show a very close agreement. Furthermore, worked examples that include instantaneous and ramp loadings will be carried out to capture the influence of six dimensionless parameters, that is, a, b, c, d, κ, and α, on the long-term settlement of a single pile. The results indicate that: the dimensionless settlement for fractional derivative viscoelastic models is larger in the early stage and smaller in the later stage than those for conventional viscoelastic models; the dimensionless settlement capacity of the pile is controlled by the parameters a and d, and the dimensionless settlement rate is controlled by the parameters b and α, which means the selection of these four parameters has a great influence on the long-term settlement; and the parameter c causes little variation in the results.

In reservoirs and embankment areas, frequent water-level fluctuations, especially water drawdowns, often produce instability problems or landslides in the slopes overlying bedrocks. A series of centrifuge model tests were conducted on three slopes overlying bedrocks with different shapes and a slope without the bedrock under drawdown conditions. Full-field displacement of the slopes was obtained for analyses using an image-based system during the tests. The slip surfaces of the slopes overlying bedrocks all emerge at the top of the slopes and then extend to the bottom under drawdown conditions. The slip surface of the slope without the bedrock is the bounding surface for those slopes overlying bedrocks under drawdown conditions. The drawdown-induced deformation area of the slopes is first restricted to a certain range and then gradually expands during drawdown and finally stabilizes. The coupling development of the deformation localization and local failure during drawdown illustrates the progressive failure mechanism of the slope overlying the bedrock. Different shapes of the bedrocks would change the deformation localization characteristics of the slopes and hence significantly change the failure characteristics of the slopes, such as the slip surface, failure process, and safety limit.

This paper investigates the effects that the spatial variability of a soil's undrained shear strength has on lateral wall movements and ground surface settlements when performing a deep excavation stability analysis. A random finite-element method is employed to statistically assess a deep excavation. A case study based on an actual deep excavation project in Bangkok's subsoils was used to validate the methodology. The two-dimensional spatial variability of the undrained shear strength in the clay layers of Bangkok's subsoil is simulated using the random field theory and Monte Carlo simulation. The Mohr–Coulomb model is used to predict lateral wall movements and ground surface settlements, while the stability analysis of the deep excavation is evaluated by the factor of safety using the strength reduction approach. The results show that spatial variability highly affects the distribution of lateral wall movements and ground surface settlements, as well as the scatter of the factor of safety corresponding to progressing stages of excavation.

Cracks will be introduced into mortar specimens and embedded copper sheets to simulate fractured concrete according to the designed 20 mm crack lengths and angles. By taking into consideration the actual environment of a hydro-fluctuation belt for a typical bank slope in the Three Gorges Reservoir Region of the Yangtze River, China, a dry–wet cycle testing program will be designed to study the mechanical properties of the fracture mortar specimens immersed in different sulfate solutions. The failure characteristics and modes of the fracture mortar specimens will be measured and analyzed. The tests results show that the strength initially decreased and then increased with an increasing crack angle from 0° to 90°, and this was the smallest for the specimens with a 45° angle. Deterioration occurred in the specimens subjected to dry–wet cycles in different sulfate solutions. The damage extent is expressed as the change in elasticity. A formula for damage evolution of the fracture specimens will be proposed and the relationship between the deformation properties and damage properties of the specimens will be developed for the combined action of dry–wet cycles and sulfate attack. Based on the proposed damage model, the damage evolution equation and elastic damage constitutive model will be derived under the combined action of dry–wet cycles and sulfate attack, and this damage constitutive relation could be used to the study damage evolution for the fracture mortar specimens under the combined effects of dry–wet cycles and sulfate attack.

A new installation method for micropile is introduced, called driven grouted micropiles (DGMs), in which closed-end perforated steel pipes are driven to the refusal depth using a light hammer and grout is injected incrementally into the pipe using pneumatic packers. The increased bearing capacity and ease of construction of these micropiles recommend them over conventional micropiles. A total of 102 full-scale static loading tests were analyzed to evaluate the geotechnical performance of the DGMs in both sandy and clayey soil. The load–deformation curves were analyzed, and the ultimate bearing capacity of the DGMs was extracted using micropile failure criteria. The results show that, although existing micropile design manuals do not recommend consideration of the tip resistance of micropiles, the proposed DGM method recommends consideration of end bearing. The contribution of end bearing to the bearing capacity of the DGM is approximately 30%. In order to design a DGM that meets FHWA formulas for conventional micropiles, an incremental coefficient (λ = 1.3) is proposed to apply to the theoretical micropile diameter. Another incremental coefficient (η = 1.25) is proposed to apply to FHWA recommendations for bond strength that relate to the soil type.

A sensitivity analysis method is proposed for the water inflow assessment and prediction of underground water-sealed oil storage caverns in fractured porous media. First, sensitivity analysis was carried out based on the full factorial design of the seven influencing factors, i.e., the water pressure in the water curtain holes, the spacing of the water curtain holes, the rock permeability, the fracture permeability, the dip angle, the spacing, and the aperture of the fractures. Not only the main effects of the factors but also the interactions and cross effects were analyzed. Second, water flow coupling in porous media and fractures was investigated by sensitivity analysis of the water inflow. Third, two prediction models were proposed for the water inflow in porous media and fractures based on the sensitivity analysis. The results show that water inflow of the caverns was mainly concentrated in the fracture development area. Water inflow in the fractures was mainly affected by five factors in descending order of importance: fracture permeability, aperture, dip angle and spacing of fractures, and water pressure in water curtain holes. Water inflow in porous media was mainly affected by two factors in descending order of importance: rock permeability and water pressure in the water curtain holes. In addition, interactions and cross effects of the double and triple factors also significantly affected the water inflow, which cannot be neglected in the water inflow prediction model. Effectiveness evaluation of the prediction models and an engineering application were carried out. The present study can provide some reference for the site selection and preliminary design of the underground water-sealed oil storage caverns.

Research performed on pile foundations installed over sloping ground has consistently reported a reduction in the lateral load capacity. Therefore, identifying ideal solutions for the related circumstances is imperative. This paper explores the possibility of socketing piles into rock as a viable solution for piles being installed in the vicinity of sloping ground. A parametric study has been conducted on freestanding and rock-socketed piles on sloping ground by varying the position of the pile and the direction of loading. Tests have been performed on loose sand of 35% relative density by maintaining a slope of 1V:1.5H. The positions of the pile from the crest were planned at increments of five times the pile diameter on both sides. The behavior of the pile installed at the crest of the slope, that is, 0D, was also of interest as part of this study. The direction of loading was varied with either forward (toward the slope) or reverse (away from the slope) loading for all positions of the pile. The depth of socketing was established to a height of three times the diameter from the bottom of the pile. The socketed pile behavior was compared with that of freestanding piles that were installed and tested with identical parameters. Based on the experimental results obtained, it was observed that the rock-socketed pile at even +5D distance from the crest achieved the lateral load capacity of an unsocketed pile installed on uninfluenced horizontal ground. It was also observed that the socketed piles exhibited a significant increase in the lateral load capacity relative to the unsocketed piles in all positions considered.

Deformation assessment and control are important issues in the construction of concrete face rockfill dams (CFRDs). The design and construction of CFRDs require deformation behavior that can be estimated rapidly to support engineering optimization and safety assessment. This study aims to develop robust empirical prediction models with physical meaning for predicting key indices of CFRD deformation behavior based on in-service case history data. A database of 87 case histories of in-service CFRD constructed over the past 50 years was compiled. A multiple regression method is adopted to develop empirical relationships between three key indices (crest settlement, internal settlement, and face slab deflection) and six dam construction-related control variables (dam height, void ratio, foundation condition, intact rockfill strength, valley shape, and operation time). The internal correlation between the key indices and control variables is discussed. Dam height, intact rockfill strength, and foundation condition are found to be the important factors influencing the three key indices. The developed models are compared with some published methods to discuss model rationality and accuracy. The feasibility and application of the models are further validated considering one case study.

An analytical method will be proposed to investigate the bearing mechanism of piles in an anisotropic discontinuous rock mass. Based on the characteristic line method, the discontinuous part of the rock is considered as the boundary condition of the plastified zone, and Riemann's invariant governing equation will be applied at the boundary conditions to link these boundaries. It was found that four different failure mechanisms exist that depend on the inclination angle of weakness planes (χ): (1) conditioned by the planes of weakness in the intermediate zone (MC), (2) conditioned by the planes of weakness close to Boundary 2 in the active zone (M2), (3) conditioned by the planes of weakness close to Boundary 1 in the passive zone (M1), and (4) not conditioned by the planes of weakness (MI). Each pile failure mechanism contains four failure modes under different pile embedment and geostatic loads: (1) deep pile with minor overburden (DL), (2) deep pile and large overburden (DH), (3) semideep pile and small overburden (SL), and (4) semideep pile and large overburden (SH). Therefore, 16 pile failure modes exist and are distinguished by χ and the embedment ratios (n). The friction angles of the weakness planes (φ) have significant effects on the pile failure mechanisms. Under the failure mechanism of MC, M2, and M1, the peak of the percentage of pile bearing capacity in anisotropic discontinuous rock over that in isotropic continuous rock (N_βP,DL/N_βP,MI ) increased with φ.

This paper presents an elastoplastic damage constitutive modeling method in the thermodynamic framework for geomaterials. The model within this method starts from a strength criterion and shall well describe the full-spectrum stress–strain curves (i.e., curves of Classes I and II). First, a yield function is constructed in the stress space, on the basis of the strength criterion. A heuristic continuous and smooth unified hardening or softening parameter is then introduced into the yield function, which ensures that the yield function has the same form as the strength criterion at the peak stress state. Finally, an appropriate damage criterion is developed to consider the development of microcrack-induced damage. Unlike existing elastoplastic damage models, the yield function in stress space is not related to the damage. In this case, the model established using this modeling method shall derive some analytical solutions under several loading paths, which could be used to calibrate the model parameters and to validate the accuracy of the numerical algorithm. For application, the proposed method is utilized to construct an elastoplastic damage model based on the generalized Hoek–Brown strength criterion. The analytical stress–strain relations of the proposed model are used to predict the mechanical behavior of several types of rock. Comparisons between model predictions and experimental data show that this model can well describe the mechanical behavior of the investigated materials, including strength nonlinearity, strain hardening or softening, volume dilation, and brittle–ductile transition.

Based on the existing unified hardening model, the double-state parameters unified hardening (DPUH) model is proposed, which can take into account the initial density and confining pressure dependent characteristics and stress-induced anisotropy of geotechnical materials. The DPUH model uses 11 material parameters, whose physical significance is clear. It has the following characteristics: (1) the state parameter χ is introduced to reflect the effect of initial density on deformation and shear strength under monotonic loading; (2) the stress state parameter R is used to reflect the influence of stress history on the current elastoplastic modulus and strength; (3) in order to reflect the influence of stress-induced anisotropy on the stress–strain relationship, the rotational hardening rules are introduced to establish the mixed hardening parameters that meet the critical state condition and take into account the isotropic compression and rotation-hardening characteristics; (4) the double-state parameters model can be used to describe the cyclic mobility phenomenon under cyclic loading conditions. By comparing the test data with prediction results of sand, it can be adopted to simulate the stress–strain relationship for sand with a different initial density and confining pressure under complex loading conditions.

The prediction of the pile response near a slope has not been fully explored and remains challenging for designers. In this study, an experimental investigation is planned to explore the behavior of laterally loaded pile groups near sloping ground. This study will report the outcome of a series of 23 tests in sandy soils under three different relative densities, three ground slopes, and four positions of the pile group from the crest of the slope. Similarly, the response of a pile group in the level ground case will be examined to investigate the effect of sloping ground. The pile response in the form of displacements and moments will be considered for comparison. Compared with the leveled ground case, noticeable changes in the pile response were observed for the pile group near a slope. Pile deflection and maximum moments substantially increased for the pile group near a slope. As the edge distance from the slope crest increased, the pile response approached that of the level ground case. From the bending moment data at each load level, p–y curves, p-multipliers, and reduction factors are derived for sloping ground conditions.

This paper aims at analyzing the active and passive lateral earth pressures exerted on retaining walls due to the anisotropic medium of dry and noncohesive backfill subjected to the modified pseudodynamic earthquake loading. To this end, the well-established lower bound limit analysis in conjunction with the finite-element discretization method using second-order cone programming is exploited to evaluate the corresponding states of seismic earth pressures on the retaining structure. The earthquake loading is simulated by the propagation of the shear and primary waves through nonconstant inertia forces in the horizontal and vertical directions, respectively. The inherently anisotropic behavior of the soil medium is also accounted for by differentiating between the internal friction angles in different directions. Results generally show that, unlike the active state, inherent anisotropy bears a notable influence on the passive earth pressure; however, the effect of seismic loading on the lateral earth pressure is more pronounced in the active state. The dominant influence of anisotropy occurs at the critical state of seismic loading, i.e., the resonance condition. Using the results of numerical simulations, the influence of internal friction angle, soil–wall roughness, imposed wavelength, material damping, and inherent anisotropy on the lateral earth pressures is thoroughly evaluated and discussed.

The shear behavior of intact cubic sandstones was studied under constant normal stiffness (CNS) conditions using self-designed equipment. A series of direct shear tests on intact sandstone blocks was conducted with initial normal forces of 0, 20, 40, 60, and 80 kN at a constant normal stiffness of 400 kN/mm that came from the sandstone specimen. The results show that the deformation of intact sandstones at the prepeak elastic stage is independent of the boundary condition. The progressive shear failure process of intact sandstone specimens under the CNS condition can be divided into three stages: the prepeak stage including the prepeak elastic stage and the prepeak yielding stage; the postpeak shear wear stage; and the residual shear sliding stage according to the relationship between shear stress and normal stress. Under the condition of CNS, shear yielding failure occurs in the prepeak stage, while under the condition of constant normal load (CNL), no obvious shear yielding failure was observed. Under the condition of CNS, normal force would not stop increasing due to normal dilation after failure of some local positions in the shearing process until complete coalescence of the failure plane. The higher the initial normal force, the closer the peak shear strength point of specimens under the CNL condition approaches the yielding point of specimens under the CNS condition. Under the condition of CNS, the shear failure surface of intact sandstone is mainly formed by tension in the prepeak shear stage. The shear failure apparent friction angle at shear wear stage is smaller than the basic friction angle at residual shear sliding stage and decreases with the increase of the normal stress. The specimens under the CNS condition have a unified basic friction angle in the residual shear sliding stage regardless of the initial normal force.

The New Zigana Tunnel is, at 14.5 km long, the longest highway tunnel project in Turkey. In this project, it is planned to construct two service shafts to provide access to outside the tunnel and temporary ventilation. Service Shaft 2 (Ø = 2.60 m), which is 220 m in depth, was opened by the raise boring machine (RBM) method. In this study, the wall stability of Service Shaft 2 was investigated using empirical analysis, analytical analysis, and numerical simulation methods. To define the rock masses on the shaft route, the rock mass rating (RMR), Q, and geological strength index (GSI) classification systems were utilized as an empirical approach. The rock-support interaction and convergence-confinement methods were applied in the analytical analysis of wall stability. To determine the plastic zones that occurred around the unsupported shaft walls, 2D and 3D numerical simulations (FEM-based) were used. According to the results of empirical analysis, there is no need for support to ensure the stability of shaft walls. Conversely, the analytical and numerical methods exhibited more conservative results than other methods and suggested support application for stability. According to the convergence-confinement method and 2D FEM simulation, the plastic zone around the shaft walls developed after depths of 105 and 81 m, respectively. Finally, the results obtained from these analyses were compared with actual field situations, and their compatibility was investigated. It was concluded that, of these analysis methods, 2D FEM simulation is most compatible with the actual field data.

A probabilistic study on the bearing capacity of two parallel strip footings on a spatially variable soil where the mean of undrained shear strength increased linearly with depth was performed. For the comparative purpose, the single footing case was also investigated. Stationary and nonstationary random fields obeying log-normal distribution of undrained shear strength were generated and further mapped into nonlinear finite-element analysis. Monte Carlo simulations were then performed to evaluate the bearing capacity for the selected ranges of the degree of nonstationarity and the spatial correlation length in undrained shear strength. The normalized bearing capacities derived from two different random field models for the cases of single and two footings were compared, and the effect of footing interference was also discussed.

A ring foundation is a cost-effective circular beam foundation that is used to support tall and heavy circular onshore industrial structures, such as chimneys, cooling towers, storage tanks, and silos as well as offshore structures, such as wind turbines, and annular platforms. Compared with circular footings, ring foundations are more suitable and economical because they use less construction material. This study focuses on obtaining an undrained capacity for a ring foundation. A parametric finite element (FE) analysis will be carried out for circular and ring footings to evaluate the bearing capacity factors (N_c), which could be used by practicing engineers when designing foundations for onshore and offshore circular structures in cohesive soil. Variations in the geometry of ring foundation such that the ratio of inner to outer radius (R_i/R_o) was 0.2, 0.4, 0.6, and 0.8, the footing side roughness factors (α) of 0.2, 0.5, and 1, the foundation embedment depths (D/B) of 0, 0.25, 0.5, and 1 and the linearly increasing soil heterogeneity (kB/S_u) of 0, 2, 5, 10, and 30 will be considered in this study. The results show variations of N_c with the varying R_i/R_o, roughness coefficient, embedment depth, and increasing shear strength of the soil. Based on the results of the analyses, a simplified equation is proposed using dimensional analysis to evaluate the undrained bearing capacity of a ring foundation. From the sensitivity analysis, the undrained shear strength of the soil was the most significant parameter followed by footing side roughness factor and R_i/R_o ratio in the evaluation of undrained bearing capacity.

Stress conditions and preflaws are prominent conditions influencing the cuttability of deep hard rock. This study aims to investigate the cuttability of intact, prefractured, and drilled rocks under biaxial confining stress, uniaxial confining stress, and stress-free conditions using a conical cutter in rock fragmentation tests on true triaxial loading apparatus. Peak cutter force and penetration depth at rock initial fracture and final failure of the rock specimen were used to reflect rock cuttability. The results show that the rock cuttability increases with stress in one direction decreasing under biaxial confining stresses, and presents a decreasing trend followed by an initial increase as uniaxial confining stress increases. The prefractures and boreholes in rock can further improve the rock cuttability, compared with intact rock. A series of cuttability improvement measures were proposed to provide a suitable condition for the application of nonexplosive mechanized mining in hard rock. Finally, comparative field tests were performed on a single-face entryway and a peninsula-shaped pillar, in which the mean value of cutting efficiency increased from 32.6 to 107.7 t/h, and the dust production and cutter wearout failure reduced significantly.

The compression line of structured soils is highly nonlinear in the space of void ratio against logarithmic mean or vertical effective stresses. The variation in the compressibility with loading is attributed to the structure degradation. In this paper, the degree of structure is newly defined, and a new volume change equation for structured soils is established by using the modified mean effective stress and degree of structure as variables. The influence of the structure degradation on mechanical behavior of structured soils is explained by a degree of structure dependent normal compression index. The validity of this approach is examined via incorporating the newly defined volume change equation into the Modified Cam-Clay model. Simulations were carried out on four different types of structured soils under isotropic consolidation conditions and consolidated-drained triaxial shear conditions. Comparisons of simulation results with experimental data demonstrate that the new model provides satisfactory predicting of mechanical behavior of structured soils.

The study of the influence of foundations, placed adjacent to slopes, on the bearing capacity is of great importance in geotechnical engineering. The available analytical and empirical methods have some limitations in considering the soil properties and the location of the footings on the top surface of the slope. To overcome these limitations, finite element analysis (FEA) is usually performed. However, FEA requires significant computational effort and, therefore, the need for an analytical solution that can consider all the effective parameters on bearing capacity of the foundation still exists. Hence, a new analysis is proposed. In this regard, the stress distribution within a slope, due to the placement of a footing on the upper surface of the slope, is evaluated in this study. Following that, the minimum value of the vertical footing load required to destabilize the slope is computed. The strength properties and unit weight of the soil, the width and location of the footing, and the slope geometry are all taken into account in the analysis. The results show good agreement with the literature, including numerical, analytical, and empirical approaches. Thus, the proposed method that is more comprehensive compared with previous solutions can help both researchers and engineers to verify the FEM model or conducting a parametric study of the ultimate bearing capacity of the footing near the slope.

This paper presents a new model for predicting the fluid flow through a Marsh funnel. Based on the Herschel-Bulkley fluid model, the model considers both the friction force and the dynamic force. Pressure drop due to the yield stress in the conical section is accounted in the model. In addition, an improved testing system is proposed for the validation of this new model. Experiments were conducted with several Newtonian fluids as well as some non-Newtonian fluids. Experiments and model results on dynamic forces show good agreement. Although the model slightly underpredicts the Marsh funnel time, the overall match is good. The general agreement suggests that the new model can be used for a fast estimation of the rheology parameters of a liquid using Marsh funnel test results and can be used in field applications.