International Journal of Geomechanics

Biogeotechnical research has inspired revolutionary ideas to claim the status of a distinctive branch of geotechnical engineering. Most notably, underground carbonate mineralization, most commonly referred to as microbially induced carbonate precipitation (MICP), has been seen as a promising solution to mitigate multiple problems, most notably increasing the bearing capacity of soils, slope stabilization, liquefaction mitigation, and erosion protection. To date, it is fair to say that MICP has moved past the proof-of-concept phase and is growing in terms of technology readiness. In this work, a comprehensive review is provided, ranging from MICP’s core fundamentals to recent breakthroughs and milestones, specifically targeting three core axes, namely, the achieved mechanical performance, modeling approaches, and upscaling considerations. From the return of experience in over two decades of research and considering the most recent opportunities and challenges, this review covers more than 150 articles published after 2019, introduces a synthesis of the trends in mechanical performance captured for biocemented materials, and concludes with a holistic overview of the future prospects of biocementation.

Mud slurries are characterized by high water content and low strength; therefore, treatment (which included volume reduction and strength improvement in this study) was required before they could be transported, handled, and reused more easily. This study presented a method that combined prefabricated horizontal drains, vacuum preloading, and solidification (PHDVPS) for the rapid treatment of mud slurry with high water content. The performance of the PHDVPS method was experimentally investigated and compared with traditional methods that used only vacuum preloading or only solidification. Settlement and the mass of the discharged water (m_vw) were monitored in model tests to investigate the dewatering efficiency (i.e., volume reduction). Then, unconfined compressive strength (UCS), permeability, X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) tests were conducted to investigate the mechanical, hydraulic, and microstructural properties of the PHDVPS-treated soils. The results indicated that the PHDVPS method significantly outperformed the traditional vacuum preloading and direct solidification methods for volume reduction and strength improvement. In addition, parametric studies indicated that the initial water content (w_o) of mud slurry, cement content (A_w), duration of vacuum preloading (t_p), and magnitude of vacuum pressure (σ_vp) had a significant influence on the performance of the PHDVPS method.

The expansion and shock wave coexisting failure theory has been widely recognized. However, it is not clear whether the main cause of rock mass blasting failure is the shock wave or gas pressure. In this paper, the contribution proportions of both loads to rock mass failure were investigated in bench blasting. First, the blasting damage in rock mass was simulated with a fluid-structure interaction (FSI) method. Then, a novel method to quantitatively distinguish between the rock-breaking effects (RBEs) of the shock wave and gas pressure was proposed that was based on the damage results. In addition, under different free surface conditions, the blasting failure volume that was caused by both loads was obtained for three typical rock masses, which included poor, middle, and good rock masses. The results showed that the range of the tensile failure zone by reflected waves was small, and the favorable effects of free surfaces on the failure induced by shock waves were limited. The free surface had a minor beneficial influence on the rock mass failure that was induced by the shock waves. In addition, it had a more favorable influence on the failure that was induced by the gas pressure. Finally, the influence of the free surface and rock mass conditions on the contribution proportions of both loads was discussed. A higher proportion of the RBEs of the shock wave was in the good mass with large wave impedance compared with the poor rock mass with small wave impedance. According to the contribution proportions under different rock masses and free surface conditions, the main cause of rock blasting failure was the gas pressure action, which was verified through the field high-speed photography data. The findings revealed the main cause of rock mass failure in bench blasting and could provide a theoretical basis when seeking effective engineering measures to give full play to the gas pressure action.

Abstract

Slopes are rarely homogeneous. However, stability solutions for homogeneous slopes are still useful because simple assumptions on ground conditions have to be made when there is no or little site investigation, typically at the early design stage of a project. Many stability charts have been developed for slope stability analysis since the pioneer work of 1937, however, stability charts are a product of the 20th century and not very compatible with the digital design workflow in the 21st century. Instead, closed-form solutions (CFS), which are more compatible with modern digital design workflow, are developed in this study for dry, saturated, and unsaturated slopes. The CFS can directly be used for deterministic analysis. Limit state surface (LSS), which separates the failure and safe domains, is ultimately important for probabilistic analysis. With the proposed CFS, LSS can be defined analytically, therefore conducting a probabilistic analysis is as straightforward as a deterministic analysis. Four methods are considered in this study: first-order reliability method (FORM), second-order reliability method (SORM), direct integration method (DIM), and Monte Carlo simulation (MCS). Two examples are used to illustrate the application. In the first example, probability of failure obtained by FORM in this study (defining LSS by the proposed CFS) agrees well with those reported in the literature (defining LSS by the strength reduction finite-element method). It is shown that LSS in the uncorrelated normalized u-space can be highly nonlinear, in such a situation FORM is less accurate, while SORM still performs well compared with DIM and MCS. In the second example, it is demonstrated that with the proposed CFS, digital automation of slope design can readily be implemented in a computer spreadsheet using various design methods.

Practical Applications

This study presents a series of simple analytical solutions for dry, saturated, and unsaturated slopes. These analytical solutions are more convenient to use than the conventional slope stability charts, as analytical solutions can be incorporated into a spreadsheet program and readily be used for parametric studies and design automation. With the proposed analytical solutions, carrying out a probabilistic analysis is as simple as a deterministic analysis. Therefore, slope stability can be evaluated through probability of failure, which better captures the uncertainty of the ground parameters. An Excel spreadsheet that contains automation scripts and practical examples is provided in the Supplemental Material, which can be directly used or adapted for specific design problems.

Weathering processes such as dry–wet (DW) cycles affect the hydromechanical properties of soils for earthen sites, in which significant proportions of the cross section could be influenced by climatic weathering, such as basal erosion of earthen sites. This study investigated the effects of the hydraulic history of silt samples that were subjected to nine DW cycles for ≤270 days on their mechanical properties. The results indicated that the proposed method of DW cycles was appropriate when determining soil strength profiles in earthen sites through soil column experiments. The mechanical properties of silt samples that were subjected to the same drying water content (w) under the same consolidation stress were significantly different when they had different hydraulic histories. When the wetting w was lower than the shrinkage limit, the silt in the upper soil layer that experienced lower wetting w generated a higher shear strength than samples that were not subjected to DW cycles. In contrast, silt samples in the lower soil layer that had been exposed to a higher wetting w than the shrinkage limit yielded a lower shear strength than the initial specimen. The hydraulic histories had a threshold effect on the strength profile of silt, where this was caused by the coupled effect of a stronger connection between its particles and the propagation of microcracks due to the DW cycles that intensified the heterogeneity of the strength profile of silt. These findings could help better understand basal erosion formation in earthen sites and protect our cultural heritage.

The stability of slopes subjected to vertical embedded strip footing loads under static and seismic conditions was investigated. The pseudostatic method was considered to represent an earthquake load. Two-dimensional lower-bound finite-element limit analysis (LB-FELA) and the strength reduction method (SRM) were employed to investigate the stability and failure mechanisms of the slopes subjected to the footing loads. It was found that the factor of safety (FOS) started to decrease rapidly after a certain load (defined as a threshold load). The critical location of the footing on the slope (where the FOS was at a minimum) was examined. In addition, a series of numerical analyses were carried out to check the effect of edge distance on slope stability. Changes in the FOS were evaluated for a particular footing edge distance for varying slope angles. The effects of variation in the shear strength parameters and the location of the water table on the slope stability under footing loads were also examined. It was found that the effect of loading intensity on the FOS was significant for gentle slopes, with this effect decreasing for steeper slopes. The influence of footing width on the FOS, for a given slope angle and loading intensity, was also insignificant. The footing near the slip surface at the top of the slope was the most critical location. The effect of the water table on the FOS diminished as the loading intensity on the footing increased. To demonstrate the practical application of this study, we also examined the slope failure that occurred during the 2011 Tohoku, Japan, earthquake.

To investigate the failure process of fault rock burst in tunnels, a large-scale physical model test is conducted. Using the 3D printing technology of the wet-material extrusion deposition molding process, a 2 m × 2 m × 1.5 m model with a rigid closed fault is successfully printed. The mechanical similarities between the printed model and natural rock are quantitatively evaluated based on similarity theory. Based on the printed model, gradual excavation and multistage loading tests under true-triaxial stress conditions are conducted, and the failure process of the Jinping 11.28 rock burst is simulated. The test process is monitored with distributed fiber optical sensing, acoustic emission (AE), and video observation systems. During the excavation process, the surrounding rockmass is stable. The compressive strain concentration of the optical fibers near the fault is obvious. The AE events are mainly distributed along the fault and nucleated near the tunnel face. During the multistage loading process, the left sidewall primarily exhibits surface cracking accompanied by local spalling and slight rock burst, while several local intense rock bursts occur on the right sidewall, indicating the controlling effects of the fault on the failure modes. In the critical period of the intense rock bursts, the monitored stain of the optical fibers penetrating the fault changes from compressive to tensile suddenly, which can be related to the slip and dislocation of the fault. In addition, the AE events increase sharply and concentrate in the footwall of the fault. Failure mechanism analysis of AE events indicates that tensile failure is dominant during the excavation process, and shear failure increases significantly in the following multistage loading process. The research results can provide an important reference for better understanding of the fault rock bursts.

The liquefaction of sands remains an important topic in geotechnical earthquake engineering. The most widely used evaluation method is based on in situ testing means such as cone penetration test, standard penetration test, and dynamic penetration test. Recently, machine learning has emerged as a promising approach for evaluating liquefaction potential problems. Due to the complexity of the site and the different standards of the available measurement methods, however, the problem of small sample liquefaction data severely restricts the development of machine learning in the prediction and mitigation of soil liquefaction. Here, we propose the Wasserstein Generative Adversarial Networks (WGAN) to expand the sample size of the liquefaction data set. The result shows that the proposed method (WGAN) learns the feature distribution of the original data set effectively and improves the accuracy of the model. By comparing with Synthetic Minority Oversampling Technique, the superiority of Wasserstein Generative Adversarial Networks in data generation is demonstrated, especially for discrete data. The effectiveness of the method (WGAN) on soil liquefaction prediction is further analyzed using the K-means algorithm. The method (WGAN) provides a good solution for earthquake engineering where it is difficult to obtain comprehensive data and improves further the application of deep learning.

Frame–shear wall buildings with multiple basements are the most commonly used structural form of high-rise buildings in the world today. In the traditional design method, structures are usually assumed as rigid base structures without considering soil–structure interaction (SSI), since incorporating the dynamic SSI tends to prolong natural periods and increase the damping of the system, which are considered beneficial for the seismic response of structures. However, recent studies exposed a potentially harmful aspect of SSI. In this study, a soil–foundation–structure model developed in finite-element software and verified by shaking table tests is used to critically investigate the influence of SSI on high-rise frame–shear wall structures with a series of superstructure and substructure parameters. The beneficial and detrimental impacts of SSI are identified and discussed. Numerical simulation results indicate the rise in the stiffness of subsoil can dramatically amplify the base shear of structures. As the foundation rotation increases, interstory drifts are increased and base shears are reduced. In general, SSI amplifies the interstory drifts showing detrimental effects of SSI. However, as for the base shear, SSI exerts detrimental effects on most piled foundation cases as well as classical compensated foundation structures founded on C_e soil, whereas for classical compensated foundation structures founded on soil types D_e and E_e, effects of SSI are beneficial since the base shear is reduced. Moreover, regarding structures with different foundation types, minimum base shear ratios considering the SSI reduction effect are presented.

Earthquakes are recognized as one of the main causes of slope instability. Hence, assessment of slope seismic stability has attracted considerable attention from researchers. However, most studies currently focus on the seismic stability of dry or saturated homogeneous slopes and do not consider the spatial and time effect of the seismic waves. To fill this gap, under the framework of kinematical approach of limit analysis, this paper presents an analytical procedure for assessing the three-dimensional seismic stability of slopes in unsaturated and inhomogeneous soils, in which the variations in suction and effective unit weight profiles of soil were considered, and the soil cohesion was assumed to increase linearly with depth. A pseudodynamic approach was employed to take the dynamic characteristics of seismic waves into account. The expression of the factor of safety (F_s) for the slope was derived by the energy balance equation combined with the gravity increase method, and the minimum of F_s was optimized by a genetic algorithm. The methodology was well demonstrated by comparing the results with previous solutions and numerical simulations. Parametric analysis revealed that the sensitivity of slope stability with earthquake intensity becomes smaller with the increase in infiltration rate, whereas this does not vary with soil inhomogeneity. The enhancement of seismic intensity significantly weakens the influence of suction and soil inhomogeneity on slope stability. The soil amplification factor poses a great impact on F_s, especially for higher horizontal seismic coefficient and infiltration rates, while the effects of the shaking period and wave velocity are very small.

Abstract

The present study is carried out to investigate the traversing of a Love-type wave in a prestressed anisotropic magnetoelastic stratum (PAMES) bounded between a prestressed anisotropic porous upper substrate (PAPUS) and prestressed anisotropic porous lower substrate (PAPLS). The exact solution of the governing equations is acquired and explained in detail for various effective parameters. Irregular boundary conditions have been employed for both the interfaces of the sandwiched layer. The variable separable technique has been used to determine the exact solution of the governing equations. The impacts of diverse parameters such as prestress, anisotropic porosity, anisotropic magnetoelasticity, irregularity parameters on phase, and damped velocity of Love-type wave have been discussed. This model contains huge potential to deal with many commercial and industrial applications in acoustical engineering, geotechnical engineering, ultrasonics, earthquake engineering, and geophysics. Results indicate that the anisotropic magnetoelastic parameter possesses a positive impact on phase and damped velocity. The damped velocity converges to some constant magnitude for distinct values of the porosity parameter.

Practical Applications

This is a theoretical work on the seismic wave propagation of surface waves. In this work, the seismic tremor, the soil components, and the transducers are made with the help of both theoretical and numerical calculations. This research could have also been used in acoustic design, earthquake engineering, geophysics, and ultrasonics. Seismic waves are also applicable for forecasting. This can be improved by putting a porous material on the structure's free surface. The goal of looking at different physical situations is to find ways that the results of this study can be used in science, technology, or the field of geotechnics. Geotechnical engineering is an integral part of civil engineering that looks at how earth materials work in engineering. Geotechnical engineers use soil properties, such as porosity, void ratio, permeability, and so forth, to analyze site conditions and plan earthworks, retaining structures, and foundations. The surface wave survey method is under continuous evolution. On a small scale, it can be used to describe a medium without touching it. On a large scale, it can be used to do a geotechnical survey after an earthquake. Even though the sizes of these applications are very different, they all use the way surface waves move along the edge of a layered medium.

The vacuum preloading combined flocculation and solidification method (VP-FSCM) has been proposed in recent years to increase the efficiency of high-water-content slurries. The characteristic of the strength development of cement-treated mud, especially in the early stage, has significant effects on the consolidation process in the application of the VP-FSCM. An appropriate model for strength development can help decide the design scheme for the combining method to ensure that a high stabilization efficiency of high-water-content slurries is achieved. In this work, laboratory tests are conducted to investigate the strength development of mud with low cement dosage from a very early stage using vane shear tests and unconfined compression tests. After integrating the strengths obtained from the two approaches, the strength development behavior is analyzed, and the offset time is valued by performing a back-analysis using a modified Gallavresi’s equation. It is found that a linear model can be built between the offset time and the water–cement ratio for a series of samples with the same soil type and binder type. Based on the model, the actual and predicted strength values fit well with a correlation coefficient of above 0.998. The model also agrees well with the test data from other literature, thereby testifying to its accuracy. By implementing the proposed model using consolidation theory, the consolidation proceeding time in the combined improvement method is determined.

Two traditional methods when calculating slope failure risk (R) are the rigid body limit equilibrium (LEM) and finite-element methods (FEM). However, the LEM requires the previous assumption of the location and shape of the sliding surface; and the FEM needs to carry out postprocessing to estimate the slope sliding surfaces. This paper proposed an element failure risk method (EFR) to calculate R based on plastic limit analysis. The proposed method did not require any assumptions about the failure modes. The safety factors and velocity fields were first computed based on the stochastic programming model that used random soil shear strength parameters. The failure of the elements and R was evaluated and calculated. An efficient upper bound method (UBM) parallel computation was programmed based on Python, which enhanced computational efficiency. Two classic cases were conducted to validate the proposed method. The results showed that the proposed method could accurately calculate the probability and R. This broadened the applications of the EFR method in the risk assessment of slope stability.

A nonlinear large strain consolidation model for unsaturated soils is presented in this paper. The model uses the Lagrangian–convective coordinate to track the flow of air and water through a deformed layer and the state surface approach to approximate the hydromechanical behavior of unsaturated soils. The model comprises a set of governing equations to integrate the water flow, airflow, and layer consolidation where large strain deformation of the layer occurs. The governing equations were discretized and solved using the finite-difference method, with the solutions verified against the analytical answers. The model was implemented to surcharge preloading studies with a focus on the effects of the initial wet degree of layers on consolidation. The results suggest that the initial wet degree affects the consolidation curves. Higher consolidation settlement occurs in the wet soil layers than in the less-wet layers. In the same layer, the pore air pressure dissipation is completed earlier than the pore-water pressure.

Due to good corrosion resistance and high tensile strength, glass fiber–reinforced plastic (GFRP) bolts are widely used in mining operations. However, GFRP bolts are susceptible to blast load damage, so it is important to understand their dynamic mechanical behavior. This experiment constructed a dynamic testing system to simulate the in situ rock bolt dynamic loading conditions. Using strain gauges, the axial load signals at different locations along the bolt were recorded and the corresponding axial stresses were analyzed. Moreover, a numerical model was established to analyze the axial stress distribution along the bolt under dynamic loading. The results showed that the maximum axial stress of GFRP bolt occurs at the bolt collar position and increases approximately linearly as the impact load increases. The axial stress decreased within a short distance from the bolt collar position following approximately an exponential function. In addition, the stronger the mechanical properties of the surrounding rock, the faster the axial stress decreases along the bolt and the greater the increasing rate of the maximum axial stress with an increase of the impact load. The location and increased characteristics of the maximum axial stress in metal and GFRP bolt were similar, but the dynamic load significantly affected the existence range and decreasing rate of axial stress in GFRP bolts than in metal bolts.

A database was compiled to establish the site-specific measured load–displacement responses of piles from different sites across the globe, which contains 188 curves from 12 sites. A curve-fitting technique was applied to each measured curve by using a two-parametric power law regression modeling. For an entire construction site, the scatter in the load–displacement behavior of multiple curves was incorporated in the uncertainty of the regression pairs. Consequently, environmental contours for regression pairs were developed by using the Nataf transformation or a normal copula. Such a contour was generated to quantify the uncertainty in the regression pairs in which the target reliability index of piles is specified, as demonstrated in various cases with two, three, and four variables. Most importantly, the environmental contour bounded by the serviceability limit state of piles at each site was presented and the reliability index was solved through an evolution of the environmental contours. The computed reliability index of the bearing resistance for piles was compared with the values yielded by the geometric reliability analysis and the first-order reliability method (FORM). Since the reliability index was solved in the original physical variable space, it made the reliability theory easy to understand. Such a site-specific reliability assessment of piles could be helpful for a practical project to implement quality control during the construction of pile foundations.

Abstract

The tension and slide of surrounding rock are highly inclined to cause dynamic disasters, thus seriously threatening the safety of mine resource recovery. This study proposes a novel method based on the global–local dissipation energy time-series variation coefficient in order to analyze the relationship between local deformation and global stability of rock. The localized light-force monitoring test method is used to analyze the tensile-sliding effect, and the evolution characteristics of the global–local dissipative energy time-series variation coefficient are compared. The results indicate that the strength reduction of rock is affected by the deformation accumulation of the loading displacement field. As for the stable damage specimen, the sliding displacement occurs 5.5 s earlier than tensile displacement, which is 4.4 s longer than the case of the transient damage specimen. The node spring model theory is further proposed to determine whether the global–local dissipation energy relationship of rock under load conformed to the linear function distribution. The global–local dissipation energy time-series variation coefficient range is always in the [1, 0.9] range. Rock instability can be predicted based on the slope and inflection point changes in the time-series variation coefficient curve, and increasing the number of effective monitoring points can significantly improve the monitoring effect and accuracy of the local time-series variation coefficient.

Practical Applications

As an important component of safe mining space, the roadway surrounding rock is prone to instability due to tensile and sliding failure, which seriously affects the safe and efficient mining of mine resources. Based on global–local energy, a new method of time-series variation coefficient is proposed in this study according to the local tensile and sliding deformation tests. By fitting the rock global–local energy relationship, the internal relationship between the local time-series variation index and the overall stability is determined. The result shows that the point measurement data in practical application are almost invariably local information because the rock deformation and stress data monitored in the roadway surrounding rock are almost reflected in the form of measuring points. Therefore, it is crucial to study the feedback of the local time-series variation coefficient on global stability, which provides an important index for early warnings of surrounding rock instability and failure. Meanwhile, it also points the direction for further improving the rock stability control theory in rock mechanics.

Anisotropy of the soil is responsible for its noncoaxial response. In simple shear and hollow cylindrical torsional shear tests, considerable noncoaxial responses were detected as a result of the stress-induced anisotropy caused by the rotation of the principal stress axis, while true triaxial tests on the noncoaxial and anisotropic response of perfectly spherical particles have seldom been reported. In consideration of the influence of the three principal stress orientations, true triaxial tests were conducted on uniformly sized spherical glass balls using the stress path of fixed-axis shear with constant values of p′ and b in the deviatoric plane. Samples with inherent anisotropy were prepared to study the evolution of noncoaxiality and anisotropy as a result of the loading process across the entire deviatoric plane. Test results indicate that the glass bead samples exhibit minor deformation and strength anisotropy in various sections of the deviatoric plane. The noncoaxial behaviors exhibit apparent orientation-dependent and b-dependent properties. This study would provide a valuable reference for granular materials with different shapes and gradations in nature that are subjected to true triaxial stress conditions.

A novel semianalytical method is proposed to estimate the earth pressure exerted on rigid retaining walls supporting a narrow granular backfill in this study, which is based on the assumption of a log-spiral failure surface. This study adopts the differential element limit equilibrium method, coupled with the stress analysis considering the deflection of principal stress trajectory, to obtain the stress distribution against retaining walls. The resultant earth pressure, the point of application, and earth pressure distribution can be obtained by the finite-difference method. The method proposed in this study is verified via comparisons with model test results, centrifuge test results, and discrete-element method results. Furthermore, a series of extensive parameter studies are conducted to investigate the effect of backfill width and interface friction on resultant earth pressure, the point of application, and earth pressure distribution for further studies.

In order to compare and study the creep mechanical behavior of quartz sandstone under the action of different cooling methods in high temperature, firstly, triaxial creep tests of quartz sandstone after natural cooling and water cooling are carried out, and creep curves under two conditions and different temperatures are obtained, respectively. Meanwhile, the mesodamage characteristics of quartz sandstone under the action of different cooling methods are analyzed. Based on experimental data and statistical damage theory, an improved Burgers creep damage model is proposed, and the model parameters are subjected to sensitivity analysis. The test results show that the creep process of quartz sandstone under different cooling methods has three-stage characteristics, and the creep rate increases gradually with temperature, whereas the long-term strength decreases gradually. Under the same temperature, the creep rate of quartz sandstone under water cooling is higher than that under natural cooling, whereas the long-term strength is lower than that of natural cooling. The mesoscopic test also shows that the damage degree of water cooling to the rock is higher than that of natural cooling. Finally, by comparing with the experimental data, it is found that the proposed improved Burgers creep damage model can effectively reflect the influence of different cooling methods on the creep properties of quartz sandstone. The results of this paper can provide important scientific significance for the damage assessment, repair, and reinforcement of tunnel surrounding rock and other structures under high temperatures.

A meter-scale model test with microbially induced calcite precipitation (MICP) is an efficient method to validate this sustainable soil reinforcement technique. Mechanical and physical testing methods for evaluating the biocementation efficiency of model tests are still being explored. In this study, a meter-scale calcareous sand base was treated with MICP. The mechanical and physical characteristics of the sand base, such as strength, shear-wave velocity (SWV), and acoustic emission (AE) signals, were measured via cone penetration tests (CPTs), bender element tests, unconfined compression tests (UCTs), and AE tests. The CPTs showed that the strength of the sand base increases with the biotreatment level, and the maximum strength could be reached at eight-cycle treatment. The biotreatment showed heterogeneity within the sand base, which can be reflected by the differences in the dry density, SWV, and unconfined compression strength of the segmented specimens. The AE signals from both the CPTs and UCTs with avalanche analysis showed that the damage model in the tests involves both fracture and friction.

Rock formations experience strength and stiffness degradation or enhancement, which is often reflected by an increase or decrease in the elastic constant. Such elastic constant variation in rock mass often causes the redistributions of the stress and strain; therefore, the geostructure stability is affected. However, to the best of the authors’ knowledge, no studies have been conducted to investigate this problem analytically. Therefore, based on Hooke’s law, this paper analyzed the stress, strain, and energy density distributions in a rock formation with such a variation in the elastic constant. Then, a general analytical solution was presented for two scenarios. One scenario was the elastic constant variation over the whole domain of rock mass, and the other was the elastic constant variation over the partial domain of interest. According to the law of thermodynamics, the elastic constant and stress components could be expressed as a function of the elastic strain energy density (ψ). Then, the stress and strain components distributions after the elastic constant variation could be directly correlated to those that developed before the elastic constant variation. The analysis showed that the stress components before and after the elastic constant variations were unchanged for the case with a variation in the elastic constant over the whole domain of interest. In contrast, in this case, the strain components after the elastic constant change were equal to 1/R times the strain components before the elastic constant change. In this paper, the ratio of elastic constants after the change to before the change was R. The analysis showed that the strain components before and after the elastic constant changes were the same for cases where the elastic constant varied over the partial domain of interest. However, in this case, the stress components after the elastic constant change were equal to R times the stress components that developed before the elastic constant change in this partial domain. The analytical model was verified through numerical simulation with the help of ABAQUS.

A sand compaction pile (SCP) with a high area replacement ratio (>50%) has been recently employed to improve the soft clay ground in offshore projects, but its performance is still not completely known. Therefore, to provide a comprehensive understanding of the SCP method, a series of laboratory model tests were performed on the SCP-improved clay ground using high (70% and 100%) and the low-to-medium (0%, 14%, and 38%) area replacement ratios. The internal stress and strain responses of SCP-improved ground with a high area replacement ratio were different from those with a low-to-medium ratio. Typically, under high ratios, the loaded SCPs bulged, resulting in the bending of the adjacent SCPs, while under low-to-medium ratios, the SCPs deformed individually. Essentially, the additional lateral confinement is provided by the adjacent SCPs under the high replacement ratio. An improved model to predict the bearing capacity of the SCP-improved ground was proposed by incorporating a coefficient of lateral pile interaction that reflects the failure mechanism. The prediction using the proposed model showed good agreement with the observations in the west artificial island of the Hong Kong–Zhuhai–Macao Bridge project. This study provides a universal mathematical model to predict the bearing capacity of the clay ground improved by SCP varying from low to high area replacement ratios, leading to a comprehensive understanding of the performance of this modern technique.

Abstract

The traditional chemical vacuum preloading method for landfill sludge (LS) often has problems of pollution, deformation, and blockage of the drainage plate. Consequently, we proposed a freeze–thaw process with vacuum preloading via prefabricated horizontal drains (PHDs). First, the LS was pretreated by freeze–thaw. Then, a comparative model test of prefabricated vertical drains (PVDs) and PHDs was carried out to investigate the anticlogging mechanism and vacuum consolidation effect of PHDs from macro- and microaspects. The results showed that the water discharge of PHD was 13.4% higher than that of PVD, the settlement of PHD was 16% higher than that of PVD, the volume reduction ratio of PVD was 58.2%, and that of PHD was 67.5%. The initial water content of LS was 86%, the minimum for PVD was 61%, and the minimum for PHD was 56%. The particles of PVD were mainly transported in the radial direction, PHD was transported primarily in the vertical direction, and there were more small particles in the center of the PVD. PHD had a high degree of consolidation, mainly with micropores and mesoporous distribution, and the PVD consolidation degree was low, primarily the distribution of small pores. The study found that freezing, thawing, and vacuum preloading with PHDs may efficiently minimize the amount of LS.

Practical Applications

As a special biological colloid, landfill sludge (LS) has the characteristics of high moisture content, limited permeability, and a very low load-bearing capacity, resulting in low efficiency of vacuum drainage and consolidation, and construction personnel and heavy machinery are often unable to carry out direct operations, which greatly reduces the efficiency of vacuum preloading construction operations. In view of this, this study proposed a more environmentally friendly and efficient method of freeze–thaw combined with vacuum preloading using prefabricated horizontal drains (PHDs) for LS treatment. Using PHD can effectively improve the efficiency of drainage and consolidation and significantly improve construction efficiency. At the same time, the freeze–thaw method can effectively avoid the secondary pollution caused by the use of chemicals, reduce the cost of later sewage treatment, and improve the way of sludge resource utilization. The method of freeze–thaw combined with vacuum preloading using PHDs can effectively achieve in situ volume reduction treatment of LS, which is a guideline for the treatment of LS.

A group of well-designed centrifuge model tests were conducted to analyze the influence of drying–wetting cycles on the failure and deformation behavior of the slope. The full-field displacement was measured via the image correlation-based analysis and was used for the coupled analysis of the deformation and failure process. The drying–wetting cycles caused the slope to exhibit a shallower slip surface and lower safety limit. The drying–wetting cycles induced a remarkable progressive failure downward to the toe of the slope that was driven by the coupling development mechanism in the local failure and deformation localization of the slope. The slope deformation tended to localize in an area and then was aggravated, which led to the local failure there. The derived progressive failure mechanism highlighted the diversity in the slip surface and safety limit of slopes with the application of various water variation conditions. The drying–wetting cycles decreased the slope stability by aggravating the degree of deformation localization. The drying–wetting cycles induced significant deformation near the slope surface, where the direction of slope displacement exhibited a reversible change within a drying–wetting cycle and changed from vertical to horizontal as the elevation decreased. The drying–wetting cycle caused the soil to consolidate; therefore, the slope deformation that was due to the drying–wetting cycles decreased as the number of drying–wetting cycles increased.

The magnitude of seismic displacement is an important index to evaluate the safety of slopes. The traditional Mohr–Coulomb failure criterion may overestimate the slope stability in seismic displacement calculation. Some analyses under plane-strain (2D) conditions reveal a significant effect of tension cutoff on slope displacement. This paper aims to carry out a three-dimensional (3D) analysis to investigate the seismic displacement of slopes affected by tension cutoff. Within the framework of limit analysis, a 3D rotational failure mechanism is adopted here for homogeneous slopes consisting of c–φ soils. A series of parametric analyses are conducted to explore the influence of the reduction coefficient on the yield acceleration coefficient, displacement coefficient, and seismic displacement. The results are more comprehensive and accurate compared with 2D analysis.

The existence of weak interlayers (WIs) in slopes results in slope failure with multiple possibilities. The most likely failure modes include sliding along a curved slip surface, linear slip surface, and composited slip surface. As such, WIs are highly sensitive to slope stability results, and dense slice division is necessary for limit-equilibrium (LE) stability analysis of the slopes with WIs. However, considering the stability of a complex slope dependent on the dense slice division, the traditional rigorous LE methods have the problem of nonconvergence calculation for possible interference from unreasonable interslice moment results. Thus, this study established a novel LE method based on increments in interslice forces (ISFs). The proposed method had good convergence with the introduction of the overall moment equilibrium condition and rigorously satisfied the end boundary conditions of both normal and shear ISFs. Thereafter, the reliability of the proposed method was verified by comparing and analyzing several examples. Furthermore, stability charts for slopes with WIs were realized based on a large amount of statistical data on typical occurrence and strength parameters to provide guidance for slope design.

Accurate and reliable predictions of debris-flow runout are essential for debris-flow hazard assessment. Debris-flow runout distances are commonly estimated by empirical relationships for their simplicity. However, existing empirical models have been developed by traditional regression analysis, which generally require a large amount of data to guarantee their accuracy and predictability. Owing to the unpredictability of debris flows and lack of data referencing historic events, the amount of debris-flow data is usually very limited and associated with measurement errors. How to develop a reliable runout prediction model and simultaneously quantify the uncertainties still remains a difficult task. This paper proposed Bayesian approaches to develop the runout model of site-specific debris flow in basin-based limited investigation data and prior information. The proposed approaches can select the most suitable model of debris-flow runout among various alternatives based on field data and prior information, and simultaneously characterize the predictive uncertainty of runout distance. To overcome the limitation of the Metropolis–Hastings algorithm in inefficient sampling, a multichain method, specifically the DREAM_(ZS) algorithm, is used to obtain the posterior distribution to solve the sampling problem on complex and high-dimensional target distributions. Copula theory is applied to calculate the model evidence based on the random samples of model parameters generated from the DREAM_(ZS) algorithm, providing a promising tool for calculating the model evidence in Bayesian inference. The proposed approaches are illustrated using the debris-flow data in the Wenchuan area. Results show that the proposed approaches accurately estimate the runout distances in the study area, and reasonably consider the measurement noise and modeling errors in the empirical relationship. Based on the limited site-specific data sets, the Bayesian approaches perform better than the preexisting empirical relationship and favor a simple model in terms of balance between data fitting and model complexity.

This paper utilized an advanced surrogate modeling technique known as adaptive kriging (AK) for the probabilistic design of foundations. The quantile-based approach accounted for the variability in soil and foundation dimensions with an adequate level of safety, and the AK algorithm replaced the theoretical or numerical models with surrogate models to improve the computational efficiency. The AK model had the advantage of considering the design dimensions and their variability in its optimization algorithm. For the design of shallow foundations, the variability in the design dimensions and its optimization was carried out by introducing the width-to-length ratio as the design parameter. This meant that a surrogate model for different foundation dimensions did not need to be developed separately. This paper showed that the computational time for the AK model was much less compared with the probabilistic analysis that used numerical models. A quantile-based design and optimization procedure that used the AK model was illustrated through a shallow foundation example and provided economical design parameters.