International Journal of Geomechanics

Abstract

Among other reasons, studies of the liquefaction potential of gravelly soils are limited because of the difficulties involved in preparing uniform specimens, without particle segregation, especially for a well-graded gravelly soil in a dry state for simple shear testing. Errors and difficulties are also involved in compensating for membrane penetration to a gravelly soil specimen in triaxial testing to get reliable data. Thus, innovative approaches for preparing triaxial and simple shear specimens for gravelly soils are introduced and implemented in this study to overcome experimental problems in acquiring accurate test results. In addition to the aim of obtaining reliable testing data on the liquefaction of gravelly soils under initial static shear stress for simulating sloping ground conditions, a study of the effect of various stress paths on the liquefaction resistance of gravelly soils was another goal of this research. In this regard, two sets of cyclic tests using medium-size triaxial and simple shear devices are conducted on a unique soil to compare the liquefaction potential of the tested gravelly soil using these two devices. Results of simple shear tests indicate that as the value of initial static shear stress increases, the cyclic resistance of the tested gravelly soil decreases. However, the results of the triaxial tests show that the variation of cyclic resistance for the tested soil depends on the initial static shear stress level and associated stress reversal conditions. Furthermore, the observed value of the pore water pressure ratio at failure using the strain-based liquefaction criteria for the tested gravelly soil was about 0.85, regardless of the type of testing. In addition, the relationship between the liquefaction resistance of gravelly soils using cyclic triaxial and simple shear devices was obtained.

Practical Applications

There is a common belief among practitioners that gravels have a far lower potential for liquefaction than sands. Results of experimental tests in this study reveal that gravels containing sands, known as gravelly soils, may have a high potential for liquefaction as well. However, the condition of zero effective stress, typically linked to liquefaction triggering in sandy soils, might not occur in gravelly soils. Rather, it is observed that the condition of excessive soil deformation leads to liquefaction triggering in gravelly soils. In addition, there are several observations on liquefaction triggering in sloping ground conditions. In this condition, initial static shear stress is present in the liquefiable soil; investigating the effects of such initial static shear stress on the liquefaction triggering of gravelly soils is strongly recommended, to ensure careful attention in design processes.

Abstract

Because of the complexity of geological conditions and disturbance of external factors, the process of instability of open-pit landslides is very complicated. To illustrate this complex process, taking an open-pit coal mine landslide as an example, an accurate landslide geological section was established via detailed field investigation, remote sensing image interpretation, and field borehole data, in this study. A two-dimensional discrete-element model was established by the Fast CPU Matrix Computing of Discrete-Element Method (MatDEM, Version 1.60). The failure evolution of the landslide was investigated; then, the deformation behavior and dynamic characteristics of the landslide were systematically studied. The analyses of the failure process, velocity, displacement, and heat showed that the evolution of the landslide could be divided into the stages of initial deformation, accelerated deformation, and deceleration and stabilization. During the movement of the landslide, the gravitational potential energy of the landslide gradually converted into kinetic energy, heat, and elastic potential energy. The kinetic energy in the initial stage was small but rapidly increased and occupied the dominant position in the second stage. The kinetic energy gradually decreased and tended to be stable in the third stage. The final geometry and accumulation characteristics of the landslide obtained by numerical simulation were consistent with the corresponding field investigation and remote sensing interpretation. This work can provide a reference for the study of the evolution and prevention of open-pit mine landslides.

Practical Applications

In view of the observation that the open-pit slope is prone to catastrophic damage, taking the West Open-Pit Mine in Pingzhuang city, Inner Mongolia Autonomous Region, China, as an example, the discrete-element geological model of the slope is established to determine the relevant calculation parameters, and the deformation behavior and dynamic characteristics of the landslide are revealed with the help of the rich information (failure, velocity change, and energy change processes of the landslide) obtained from the simulation results. The geometric shape and accumulation characteristics simulated by the mesoscale discrete-element technique are in good agreement with the terrain features observed after the actual landslide. Through a comparison and analysis of the monitoring data from the monitoring points arranged on site, the limitations of monitoring feedback landslide information are determined. These findings provide a certain reference for the numerical simulation study of open-pit coal mine landslides with discrete elements.

Caissons are rigid foundation systems with huge mass that support a large variety of load combinations. Most studies ignore the resistance provided by the periphery of a caisson in providing resistance to applied external loading. In this study, the variation of resistive stresses generated on the base and sides of a caisson under various loading, interface, and seismic conditions, obtained from numerical analysis, is explored using finite-element method–based computer program ABAQUS. The shear forces and resistive moments thus generated have been studied to identify the resistive forces required for stability for different input parameters. The percentage of resisting moment shared by the caisson sides (lateral soil pressure, horizontal and vertical skin friction) has then been compared with that due to the caisson base (base reaction and base friction). Empirical correlation has been obtained using multiple linear regression analysis for the load shared by the caisson sides. It is observed that, with an increase in the horizontal and vertical seismic acceleration coefficients, the percentage of resisting moment contributed by the caisson sides increases.

Modeling of fluids in deformable geoformation media has gained much attention in the past decades due to significant applications such as groundwater prediction, and shale gas and carbon capture and storage. However, considerable research has been focused on the porous media concept, and dual network (fracture and pores) multiphysics coupled modeling has remained a challenge due to the lack of a systemic theory to bridge the physical deformation of the media (e.g., rocks) and the interaction of water flow in pores and fractures. This paper adopts the nonequilibrium thermodynamics-based approach, the mixture coupling theory, to develop a thermodynamics consistency constitutive model for the fully coupled hydromechanical behavior in double porosity formation. The energy dispassion due to fluid flow in matrix pore and fracture is given through nonequilibrium thermodynamics, and the relationship between the solid and fluid is linked through the Helmholtz free energy. The dynamic evolution of stress, porosity change of the matrix pores, and fracture are derived with respect to mechanical strain, pore pressure, and fracture pressure to account for the flow–deformation interaction. The developed constitutive equations are then solved numerically to show the hydraulic and mechanical behavior of double porosity formation, as well as their sensitivity to parameters.

The paper aims to evaluate the pseudostatic seismic bearing capacity of shallow foundations on geosynthetic-reinforced granular soil subjected to inclined/eccentric combined loading. This is achieved through a comprehensive set of lower-bound finite-element limit analysis (LB FELA) simulations adopting the second-order cone programming. The pseudostatic seismic loading is incorporated into the element equilibrium equations as body forces. Both sliding and structural modes of geosynthetic failure are simulated within the FELA framework. The influences of pseudostatic acceleration, embedment depth (u), and the ultimate tensile strength (T_u) of the reinforcement layer on the failure mechanism, bearing capacity ratio, and failure envelope of the overlying obliquely/eccentrically loaded shallow foundation are thoroughly investigated and discussed. It is generally concluded that at a given reinforcement embedment depth, failure envelopes shrink substantially with the increase of the seismic horizontal acceleration and the reduction of the geosynthetic ultimate tensile strength.

The use of reclaimed asphalt pavement (RAP) for the production of asphalt mixtures has become a common practice in the pavement industry. However, there have been limited studies on the long-term performance of RAP in the unbound layers of pavements. The main objective of this study was to characterize the resilient modulus (Mr) and long-term permanent deformation responses of RAP blends with recycled concrete aggregate (RCA) in the unbound base and subbase courses of pavements. To this end, up to 70% RAP by dry mass was mixed with RCA to characterize the resilient modulus, long-term permanent deformation, and shear strength responses of the blends through an extensive experimental program. The behavior of RAP/RCA blends was classified according to their permanent deformation responses and the shakedown concept, which indicated that adding up to 30% RAP could provide desirable performance in the unbound pavement layers. The support vector regression (SVR) approach was utilized as a machine learning technique for predicting the Mr and permanent deformation behavior of RAP/RCA blends. Three different kernel types, including linear (linear_svr), radial basis function (rbf_svr), and polynomial (poly_svr), were utilized in developing the machine learning models. The performance of the optimal SVR models for Mr and PS was compared with that of a random forest regression model to evaluate their predictive performance further. Further analyses were provided to validate the developed models. This study aims to promote an increased proportion of recycled aggregates in the design and construction of pavements justified through extensive laboratory characterizations backed up with robust machine learning modeling.

Due to the different structural characteristics and in situ environment, jointed rock masses encounter different failure mechanisms. Because of the joints, jointed rock masses show peculiar characteristics such as anisotropy and weakening. To describe the deformation and failure mechanism in jointed rock masses, a novel damage constitutive model of rock mass is proposed here considering the geometric parameters and mechanical properties of joints. A total damage variable is derived on the basis of the strain equivalence hypothesis, which combines the Weibull statistical damage theory for the strength of the rock elements and the fracture mechanics model for joints. This new damage variable reflects the coupled damage inflicted by two damage states, one is initial damage induced by prefabricated joints and the other is joint damage and rock mesoscopic damage under loading. The damage evolution path revealed by the new damage variable corresponds to the evolution of mechanical properties and behaviors induced by changes in the rock mass structure. Afterward, the computational formulation scheme for the model parameters is deduced using the extremum method. The model parameters, m and F₀, have a clear physical meaning. The parameter m describes the ductility–brittleness characteristics of jointed rock masses, and F₀ reflects the level of strength. This model describes the effect of joints and strain on the evolution of rock mass damage, model parameters, deformation, and failure characteristics. The mechanical behavior of rock mass described by the damage model and the change law of model parameters are consistent with the published experimental results.

Stone columns are constructed in soft soil to speed up the consolidation process. However, clogging of the column during the consolidation period can adversely degrade the drainage performance of the improved ground. The use of a suitable geotextile encasement may decrease clogging by preventing the movement of fine soil particles during the dissipation of water through the column. In this study, an analytical model is developed to investigate the filtration capability of a geotextile encasement used to prevent clogging. Permeability and retention criteria are suggested for the geotextile encasement to minimize stone column clogging. The spacing between the columns notably influences the selection of geotextile properties for reducing stone column clogging during consolidation. The difference in stiffness between the stone column material and soft soil, the capture coefficient of the column, and the smear effect also influence the selection of geotextiles. Under most critical conditions, the selection of a maximum size of geotextile opening that is less than or equal to r_s,10 or D₁₀ (where r_s,10 or D₁₀ indicates the soil particle size at which 10% of particles are finer than it) is effective to mitigate the column clogging during soil consolidation.

In this paper, a small strain numerical procedure, the press-replace method (PRM), is adopted to model the monotonic, quasi-static installation of a jacked-in pile under an undrained condition. Numerical simulations are carried out using the small-strain geotechnical finite-element software PLAXIS 2D (version 20.03.00.60). The PRM implementation for modeling jacked-in pile installation is described. This paper aims to demonstrate and assess the prediction potential and limitations of the PRM for modeling the pile installation process followed by the subsequent load testing, using published information from two well-known field case studies. It is shown that the combination of the PRM with the modified Cam-clay constitutive model can not only capture the penetration resistance experienced by the pile during jacking but also simulate realistic stress and pore-pressure changes around the pile caused by the jacking process. The pore-pressure response during postinstallation consolidation, which leads to the pile setup phenomenon, can also be reasonably captured. Subsequently, the importance of incorporating installation effects in the numerical simulations of pile load tests is demonstrated, using a wished-in-place (WIP) pile model and another with the installation process simulated via the PRM. The PRM model predicts a significantly higher pile capacity than the WIP model. The different load-settlement behavior of the two piles can be attributed to the different soil states present in the two models at the start of the load test, in which the WIP model does not capture the changes occurring in the stresses, overconsolidation ratios, and void ratios of the surrounding soil caused by the pile jacking process.

When a tunnel boring machine (TBM) excavates in the mudstone layer, the slacking mudstone will be formed under the action of the disc cutter due to the argillization effect. Therefore, the cutter wear mechanism differs significantly from that in the hard rock layer, and the hazard of flat wear increases rapidly. To predict the cutter wear in the mudstone, a novel prediction model based on the “mixture lubrication-cavity expansion” theory is established in the present study, which takes the argillization effect into consideration. Initially, the cutter wear mechanism in the mudstone was revealed by the mixture lubrication theory. Then a modified cavity expansion model was proposed and the thickness of the slacking mudstone in the rock was determined. Subsequently, according to the force acting on the disc cutter, the motion of disc cutter during the rock breakage process, and the critical condition for flat wear, formulas for the normal and flat wear of a disc cutter considering the argillization effect were derived. Finally, the proposed model was employed to predict the wear loss of a disc cutter in a tunnel project in Chongqing. The effectiveness of the proposed model was verified. It was found that the force acting on the disc cutter is borne by the slacking mudstone and the cutter simultaneously. In the modified cavity expansion model, the zone of the rock beneath the cutter is divided into the core zone (0 ≤ r ≤ T/2), argillization zone (T/2 ≤ r ≤ r_a), plastic zone (r_a ≤ r ≤ r_p), and elastic zone (r ≥ r_p). The stress caused by the cutter is equal to the stress at the argillization zone. The argillization effect can reduce the wear loss to some extent due to the mixture lubrication, however, it aggravates the risk of flat wear. This study will enrich the understanding of the cutter wear mechanism during the tunneling. Furthermore, it will provide some references for the design of the TBM and the scheme of the tunneling project.

The ultimate bearing capacity is one of the most important mechanical parameters in the mining and geotechnical fields and has a vital influence on the stability of slopes and the safety of constructions and structures. The determination of the ultimate bearing capacity has become a controversial issue in slope engineering. This study proposes a way to obtain the ultimate bearing capacity of a multilayer slope with horizontal stratification. According to limit analysis theory, three typical multiblock sliding failure modes for a multilayer slope with horizontal stratification are established. The upper limit solution of the ultimate bearing capacity of a multilayer slope, considering the influence of horizontal stratification, is derived. The optimization procedure is carried out to obtain the optimal value of the ultimate bearing capacity by using the sequential quadratic programming algorithm. The accuracy of the present method is proven based on a comparison of calculation results using other analytical methods and the numerical simulation method. The influence analysis of the parameters, involving the slope angle, soil strength, and distance of the foundation from the slope shoulder, is performed. The results indicate that the error between the calculated results of the present method and those of numerical simulation, as well as the error between the calculated results of the present method and those of other existing methods, is less than 10%. The ultimate bearing capacity linearly decreases with increasing slope angle, while it linearly increases with increasing distance of the foundation from the slope shoulder. The analytical method provides a method to analyze the ultimate bearing capacity of a multilayer slope, which effectively solves the problem of heterogeneity of soil layers observed in the natural slope. The results from this study can be used as a guide to estimate the stability of the slope and design of the foundation on a slope considering the load action near the slope.

The assessment of the behavior of the ground is highly critical for any geotechnical and geological projects. Uniaxial compressive strength (UCS) is an essential mechanical parameter for any rock mass characterization, whereas the elastic properties of rocks help us understand the deformational behavior of the rocks. However, the determination of these parameters is challenging, time-consuming, destructive, and expensive and requires a skilled workforce. In contrast, the dynamic elastic properties require P-wave velocity (V_P), S-wave velocity (V_S), and density (ρ) for calculation, which are easy, quick, nondestructive, and cost-effective to determine. Therefore, in this paper, to understand the behavior of different rocks, UCS has been correlated with the dynamic elastic properties, including dynamic bulk modulus (K_D), dynamic shear modulus (G_D), dynamic Young’s modulus (E_D), and dynamic Poisson’s ratio (µ_D) for carbonate, serpentinite, shale, sandstone, volcanite, and ignimbrite rocks incorporated from the databases of eight previous studies. Based on the lithology, different correlation equations have been proposed to predict the UCS from dynamic elastic properties using simple regression (SR) analysis. From SR analysis, it was observed that the coefficient of correlation (R) values depended on the type of rock. The R-values for the overall rocks, including all six rock types, for different correlations, were observed to be inferior to the R-values obtained on the basis of lithology. The principal component analysis (PCA) reduced the dimension of the data sets, and the trendline obtained for each rock type was observed to be dependent on the lithology. Moreover, descriptive statistics were also used to validate the lithological control for six different rock types.

Granular materials, such as rockfill materials and carbonate sand, exhibit complex mechanical behavior, which is affected by particle breakage under elevated pressures. In this study, we present a relative breakage model based on mean stress, void ratio, and strain. We further consider the effect of relative breakage on the critical state line. A hypoplastic constitutive model is developed by incorporating the critical state. The validity of the constitutive model is shown by comparing the numerical and experimental results of drained triaxial tests.

The mechanical properties of a connection are essential for the structural performance of a prefabricated bridge pier because the connection is located in the weakest part of the pier structure. Among different types of connections, a large-diameter grouted sleeve connection with a connection bar of 40 mm diameter has been widely exploited in recent years. However, past experimental researches and the latest corresponding industrial standards barely pay much attention to the mechanical properties of this large-diameter grouted sleeve connection. Therefore, a series of experiments and numerical simulations were conducted to address the critical issue. First, the static tension tests were carried out on fabricated specimens considering the eccentricity of the bar, and then the internal conditions of the sleeve were detected using industrial computed tomography. Experiment-based tests showed that the bearing capacity of all connections exceeds the standard value of the tensile strength of connection bars and mainly depends on the bearing capacity of connection bars. The eccentricity of the bar could increase the local stress of the sleeve, which must be addressed during the design and construction progress. The inner bonding interface between the bar and the grouting material was destroyed when the bar was fractured or pulled out. Moreover, the results of experiments and numerical simulations revealed that some geometry-related parameters about the sleeve and the bar could be properly optimized for further design. The sleeve design parameters considering the eccentricity of the bar was recommended as 1.27, and a new sleeve structure with variable thickness was proposed.

In the standard Lagrangian finite-element framework, the “remeshing and interpolation technique with the small strain” (RITSS) method has been applied increasingly in geotechnical engineering. However, the mapping algorithm of the RITSS method suffers from either the onerous division of unique element, such as the modified unique element divisional method, or frequent mapping of the stress and other information between integration points and nodes, resulting in the loss of precision, such as superconvergent patch recovery (SPR) and recovery by equilibration of patches. In this study, within the original RITSS, the radial point interpolation method (RPIM) mapping algorithm is implemented to improve accuracy and convenience. The RPIM-RITSS method is integrated into the ABAQUS (6.14) commercial software package. With a master Python script, the whole analysis process is performed automatically and continuously without any intervention from the user. The efficiency and robustness of the RPIM-RITSS method are verified through three numerical examples: penetration of the strip footing, the pullout and the rotation of the anchor plate, and deep penetration of the T-Bar. Consequently, the RPIM-RITSS method is an alternative, powerful, and easily extensible way to tackle large deformation problems in geotechnical engineering.

The frame beam anchor plate (FBAP) is a new supporting structure to reinforce backfill. The current studies of slope stability concentrate on homogeneous isotropic dry or saturated slopes according to two-dimensional assumptions. In engineering practice, however, the soils are heterogeneous and anisotropic and exhibit evident unsaturated characteristics, and the failure surface shows obvious three-dimensional (3D) characteristics universally. A new method for evaluating the 3D stability of unsaturated soil slopes reinforced with FBAPs is established in this paper. The upper-bound analytical solution of slope safety factor (Fs) is derived based on the energy balance equation incorporated with the 3D spiral failure mechanism and the gravity increase method (GIM). Comparisons verified the effectiveness of the methodology and the optimization program. The influence of unsaturated characteristics, support structure design parameters, and seismic force on the 3D slope stability is evaluated through parameter analysis. The results show that the shear strength prediction model is crucial in slope stability assessments. The stability of slopes can be significantly improved by about 29%–52% by using FBAPs. Seismic action has a significant negative impact on the slope stability. When k_h increases from 0 to 0.3, Fs generally decreases by about 40%–55%.

Geotechnical engineers are faced with great uncertainty with regard to the stability design of soil structures such as retaining walls, foundations, and slope stability. Instead of using a deterministic approach by replacing the design parameter with a single mean number, Monte Carlo simulations could be used to provide better decisions by considering all possible outcomes under parametric uncertainty. This paper studies probabilistic failures of classical passive trapdoors in shallow depths with spatially random soils. The effects of soil strength variability are investigated for various spatial correlation lengths and trapdoor depths using the latest adaptive finite-element upper-bound limit analysis with second-order cone programming. In addition, probabilistic stability results are compared with those published in renowned literature, and a comprehensive probability of design failure (PF) charts is developed for a practical range of deterministic factors of safety. The extensive results reported in this paper would be of great interest to engineering practitioners because better decisions can be made in the design process and design confidence improved.

The application of the compressible layer in linings provides a feasible and safe solution to addressing the problems of the excessive deformations of surrounding rocks and support failure in the deep soft-rock tunnels. However, there still has not been a well-constructed method to report the mechanical responses of the tunnels supported by such a support system. The objective of this study is to provide an analytical approach to estimating the influence of the compressible layer on the tunnel performance. The mechanical model of the tunnel supported by the compressible layer and concrete lining within the viscoelastic–plastic geomaterial was established. The corresponding analytical solutions for the tunnel displacement and lining pressure are provided, where the influences of the stress path, tunnel face advancement, and installation delay of supports are considered. The effectiveness and reliability of the proposed model are validated by using the numerical calculation, and a good agreement between the analytical and numerical results are obtained. Finally, a comprehensive parametric investigation is carried out, including the influences of the yielding stress, yielding length and elastic modulus of the compressible layer and the lining installation time. The important findings are provided and several useful recommendations are proposed for the design of this supporting system.

Cement composite soil is a more stabilized method in expansive soil foundation projects, but it is essential to find an ecofriendly modification material to reduce the content of cement and its pollution for the environment. A series of unconsolidated–undrained (UU) triaxial tests were conducted to investigate the modification effect of graphene oxide (GO) on cement-stabilized expansive soil (CS), and the contents of GO were 0.05%, 0.1%, 0.15%, and 0.2%, respectively. The test results show that (1) the deviatoric stress–strain curves of CS gradually change from a weakly softening type to a strongly softening one after adding GO. (2) The compressive strength, shear strength, and toughness of GO-modified cement-stabilized expansive soil are better than CS, and the optimal GO content is 0.05%. (3) Microscopic tests show that GO can promote the hydration reaction of cement and reduce the internal pores of CS. Consequently, the mechanical properties and microstructure of CS can be significantly improved after adding GO, and it is feasible to replace a part of the cement with GO in expansive soil foundation projects.

This manuscript documents an exploratory study aimed towards the development of a mix-less technique to reduce heave caused by soil swell. The technique involves the placement of compressible inclusions in the soil mass, such that the swell deformation that would otherwise displace or distort a proximate structure is accommodated by the inclusions (i.e., is consumed in compressing them). Experimental results have confirmed that the swell-induced displacements of a free boundary in the vicinity of an inclusion are reduced in proportion to the extent to which the soil compresses the inclusion and in proportion to the inclusion’s compressibility. Simulation results have indicated that swell accommodation can produce stress reductions on fixed boundaries and reductions in the heave experienced by a slab resting on an expansive soil layer that houses compressible inclusions. Stress arching around inclusions emerges as a potential contributor to the minimization of settlements incurred by susceptible structures upon the retrofitting of their foundation soils with inclusions horizontally trenched at depth.

For soft soils, creep settlement plays an important role in the full life cycle performance of infrastructures, which is a serious concern for engineers and researchers. Columns such as deep cement mixed (DCM) soil columns are commonly adopted to treat soft grounds in order to reduce the life cycle settlement of the infrastructures. However, the creep behavior of soft grounds treated by DCM soil columns is often ignored, inducing underestimated total settlements or unexpected differential settlements. In this study, a new calculation method is developed for the life cycle settlement of column-improved soft grounds by considering the creep of soft soils and load transfer between the columns and the surrounding soils. A physical model test with double-layer soil improved by DCM soil columns is designed and performed to demonstrate the feasibility of the calculation method. It is found that the settlements calculated by the proposed method show good agreement with the measured data in the physical model. A parametric study is conducted, revealing that the calculated settlement of the double-layer soil improved by DCM columns can be largely influenced by the stress concentration ratio, the permeability of the DCM columns, and the area replacement ratio. Finally, the proposed method is applied to calculate the settlement in a real project.

Understanding initial in situ stress is important for studying rock burst or large deformation problems in tunnels under high geostress. Field measurements and inversions of the in situ stress field in the Baima tunnel were taken to determine key controlling factors on disturbance of the in situ stress field in fault areas. The measured results showed that the magnitude of the maximum principal stress at the fault decreased and the direction deflected. Numerical experiments showed that the fault type, fault direction, fault width, rock bedding direction, elastic modulus ratio of the surrounding rock to the fault, and principal stress ratio all had different effects on the stress field in the fault area. The on-site rock mass parameters were obtained through the conversion of the geological strength index, and the in situ stress field distribution in the fault area under the influence of combined factors was clarified by using the inversion method of multiple linear regression. This study showed that the more the actual geological characteristics of the site are considered, the more realistic and accurate the inversion results of the site stress field are.

Abstract

Municipal solid waste (MSW) landfills using leachate recirculation optimize the waste stabilization process by providing nutrition and moisture for biological activity. However, the leachate recirculation creates an environment with complex processes due to accelerated biodegradation and generated heat. Additionally, different timing in waste placement and the heterogeneous nature of MSW cause significant variations in properties throughout the intercalated layers. In this study, a settlement framework model employing Thermal–Hydraulic–Mechanical–Biochemical processes is proposed, which considers multiple MSW properties including temperature, pH, and saturation. The framework model includes a modified Cam-clay model to simulate short-term settlement and adopts mechanical and biological creep models for long-term settlement estimation. A long-term biological creep model that uses a single decay rate constant is revised to account for environmental factors such as temperature, pH, and saturation in estimating MSW decay rates. The framework model was calibrated using the data of large-scale column experiments, which were conducted at different temperatures and saturation conditions considering biodegradation rates. Also, an MSW placement strategy was developed to consider the effect of different waste layer placement timing in the progression of MSW landfill total settlement. The modeling framework was validated using settlement data from a landfill in Canada. The results showed that temperature and saturation have a significant influence on MSW settlement and therefore should be considered in MSW landfill settlement prediction models.

Practical Application

In municipal solid waste (MSW) landfills, leachate recirculation increases biological activity and heat and therefore results in further breakdown of waste material and, subsequently, large settlements. Also, different climates and waste placement seasons, in addition to the nonhomogenous nature of MSW, create variations in landfill layers that need to be addressed. This study investigated a settlement model that was verified with an experiment where different temperature and saturation was applied to MSW. The settlement was divided into short-term settlement (from the compression of material) and long-term settlement from the breakdown of material with time. Additionally, since the whole MSW is not placed in a landfill at once, a strategy was developed to consider the different stages of waste placement in the developed model. The developed framework was verified using the data collected from a landfill in Canada. The results show that when we consider temperature and the amount of saturation in MSW, we can have a better prediction of MSW settlement and prevent unwanted consequences of landfill failure.

The incident angles of seismic waves have a significant influence on the seismic response of asphalt–concrete core rockfill dams. This paper constructs the free field of elastic semispace under P waves with arbitrary incident angles and clarifies the variation law of the seismic intensity on the ground surface with incident angles γ and α. The free field on the foundation boundary under arbitrary combinations of angles γ and α are derived according to the wave-field superposition principle. Combined with the viscoelastic artificial boundary, the free field is transformed into the equivalent load on the boundary node, and the input method of the P wave with arbitrary incident angles is established. Finally, the seismic response of the asphalt–concrete core dam under P waves with arbitrary incident angles is studied. The results show that when the incident direction is perpendicular to the dam axis, the dynamic shear stress is the highest, and the local seismic safety factor of the dam is the largest. When the incident direction is parallel to the dam axis, the tensile stress of the asphalt core is the highest, there is a possibility of cracking at the contact part of the lower part of the asphalt core with the canyon, and the seismic subsidence rate of the dam crest is the highest. For the tensile stress of the asphalt core and the dam-crest subsidence rate, the most unfavorable incident angle α is 75° when the incident angle γ is the same.

The issue of water blocking by grouting in coastal areas has engendered the need for a novel numerical simulation method for grouting with a flowing water under tidal action, two-fluid tracking (TFT). This paper proposes such a method. First, based on the material derivative, the transport model of the residence time of injected slurry was derived. In addition, the residence time of injected slurry microgroups at any grouting time was obtained by solving the transport model. Further, the numerical characterization of slurry viscosity during grouting in flowing water was realized by introducing a time-varying viscosity function obtained from previous experiments. Then, based on the generalized tidal action model, the diffusion behavior and blocking mechanism of slurry under tidal effects were studied. The results show that: (1) under tidal action, the water velocity fluctuates and decreases, whereas the grouting pressure fluctuates and increases; (2) at the early stage of grouting, the diffusion pattern of slurry appears as a droplet, and the tailing phenomenon becomes more serious with an increase of tidal intensity; with the progress of grouting, the diffusion pattern gradually changes to U-shaped or elliptical; (3) the strong tidal action will reduce the retention rate of slurry, which is not conducive to the grouting blocking. The research results have been applied to the grouting treatment of a China Resources Cement (Hepu) limestone mine. This research can provide some useful guidance for grouting treatment engineering of water inflow in coastal areas.

Abstract

Internal instability means that finer particles pass through the constrictions of coarser particles at a hydraulic gradient well below that of heave or piping, rendering the soil ineffective for its intended purpose. The soil could make a transition from an internally stable state to an unstable state or vice versa due to shear-induced deformation. The discrete element method (DEM) is adopted in this study to examine and quantify soil behavior by simulating the quasi-static shear deformation of internally stable and unstable soils at the micro- and macroscales. The dense bimodal specimens were sheared under drained conditions following a constant mean stress path in order to investigate the influence of stress heterogeneity. At the macroscale, the peak deviatoric stress was found to be a function of the fines content and the initial void ratios of the specimens. The development of the average number of contacts per particle and the stress transfer to the finer fraction during shearing are discussed. The simulation results innovatively show that a dense specimen could undergo a transition from an internally stable to an unstable soil as it dilates during shear. These numerical results have significant implications on the importance of real-life situations, such as predicting mud pumping in railroad tracks.

Practical Applications

Microscale investigations enabled a better understanding of the mechanism of internal instability of soil, which can be helpful in the design and construction of substructures in railways. To demarcate internally unstable and stable soils, the microscale criterion based on the coordination number and the stress reduction factor can be used to estimate the probability of internal instability in the field at different stress state. Internal instability is a problem in railways that results in significant maintenance costs. The findings of this study can be used to avoid the huge maintenance cost associated with internally unstable capping layer in railways.

The appropriate prediction of horizontal earth pressure against retaining walls can lead to a safer and more efficient design of such structures. Retaining walls are among the structures in which the arching phenomenon plays an essential role in distributing horizontal earth pressure. In this research, based on the limit equilibrium condition and considering the arching effect, a new theoretical method is proposed to estimate the earth pressure against a battered wall under translation movement with a cohesive-frictional backfill soil. A parametric study is conducted for assessing the effect of the surcharge pressure, cohesion, internal friction angle, wall–soil friction angle, and wall inclination on lateral earth pressure. In addition, a series of numerical models is employed to implement the finite difference method. The development of shear bands inside the backfill and the changes in earth pressure behind the wall are studied. The outcomes of the suggested analytical solution are compared with the numerical data as well as with some other theories. It is concluded that the proposed method is applicable to a wide range of cohesive-frictional soils retained with walls, covering a variety of batter angles and face frictional conditions.

The sleeve-valve pipe grouting technique is widely used in railway, highway, and house construction in China for its outstanding advantages in recent years. However, as the key parameter of sleeve-valve pipe grouting, the open-loop pressure of sleeve body material is still mainly determined by engineering experience. A sophisticated and reliable calculation theory and method have not been established. The role of sleeve body material used in sleeve-valve pipe grouting and the transformation of the acted object by the slurry pressure during the grouting process were systematically analyzed. The stress calculation method of the soil layer around the slurry outlet of the sleeve valve pipe in any inclined state and sleeve body material was obtained. Then, the open-loop failure condition of sleeve body material was proposed, and finally, the theoretical calculation method of open-loop pressure for sleeve-valve pipe grouting, considering the comprehensive influence of multiple factors, was established. Based on these calculation methods, the influence law of some factors of the open-loop pressure was studied deeply, and it was found that the open-loop pressure increases with the increase of the strength of sleeve body material, the elastic modulus ratio of sleeve body material to grouted soil, and the depth of grouting and decreases with the increase of the ratio concerning with Poisson’s ratio of sleeve body material and grouted soil. The orientation (characterized by α and β) of the grouting hole in sleeve-valve pipe grouting has a noticeable effect on the open-loop pressure. When α is constant, the open-loop pressure increases obviously with the growth of β, and when β is constant, the open-loop pressure increases with the increase of α. Taking the DK107 + 105 frame jacking culvert project of the newly built Daye North–Yangxin railway as an example, the theoretical calculation method of open-loop pressure established in this paper was applied and verified. The calculated results showed that the outcomes calculated by using the method proposed in this paper are more consistent with the measured values of open-loop pressure at the engineering site and are better than the values of open-loop pressure calculated by these existing methods. The research results can support the development and improvement of sleeve-valve pipe grouting theory.

Displacement and factor of safety are two crucial pieces of information about slope stability, but the traditional limit-equilibrium slice method has a significant defect; that is, it cannot reflect slope displacement. In this paper, a displacement-dependent limit-equilibrium slice method is proposed based on the soil shear constitutive model and Morgenstern–Price assumption of interslice forces to establish the relationship between the factor of safety and displacement. In addition to the overall factor of safety, point factors of safety and point displacements can also be obtained using the proposed method to characterize the displacement-dependent slope stability. The point factor of safety and shear displacement of each soil slice calculated using the proposed method are slightly higher and smaller than those calculated by the modified displacement-dependent Janbu method. The iterative process of the proposed method is simpler and more stable than that of the modified displacement-dependent Janbu method. Calculation results of four examples show that the point factors of safety at the upper and lower ends of the slide mass are generally smaller than those at the middle part of the slip body, and the shear displacement of the soil slice near the slope top is generally larger than those at the other positions. The proposed method associates the factors of safety with slope displacements, which allows us to quantitatively assess the slope stability immediately in practice by monitoring the displacements of some key points on it.

Multiseam mining generates enhanced characteristics of strata movement and surface subsidence (CSMSS) than single seam mining, which strongly increases the possibility of mine water disasters and surface deformation. In this study, the effect of seam separation distances and key stratum (KS) configurations on CSMSS is evaluated using the discrete-element method. The results of the analyses indicated that control function loss of the KS aggravated the failure of the overlying strata and expanded the original water-flowing fractured zone, which grew by 91.49% and 23.40% in short-distance and medium-distance multiseam mining. In addition, the subsidence was higher in the first two cases and also in the tilts and strains. The separation and penetrating tensile cracks determined the upper boundary of the caved and fractured zones in the discrete-element method simulation analysis supported by field data. Finally, this study provides a method for identifying the multiseam category according to the CSMSS resulting from multiseam mining operations, which is the first step toward effective disaster prevention and management.