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The anisotropy of rockfill materials has a significant influence on the performance of engineering structures. However, relevant research data are very limited, because of the difficulty with preparing specimens with different inclination angles using traditional methods. Furthermore, the anisotropy test of rockfill materials is complex and complicated, especially for triaxial tests, in which the major principal stress plane intersects with the compaction plane at different angles. In this study, the geometric characteristics of a typical particle fraction consisting of a specific rockfill material were statistically investigated, and the distribution characteristics of particle orientation in specimens prepared via different compaction methods were examined. For high-density rockfill materials, a set of specimen preparation devices for inclined compaction planes was developed, and a series of conventional triaxial compression tests with different principal stress direction angles were conducted. The results reveal that the principal stress direction angle has a significant effect on the modulus, shear strength, and dilatancy of the compacted rockfill materials. Analysis of the relationship between the principal stress direction angles, change in the stress state, and change in the corresponding dominant shear plane shows that the angle between the compacted surface and dominant shear plane is closely related to interlocking resistance associated with the particle orientation. In addition, different principal stress direction angles can change the extent of the particle interlocking effect, causing the specimen to exhibit different degrees of anisotropy.

For geotechnical stability analysis involving non-associated plasticity, the Davis approach with internal friction angle and dilatancy angle updated during the strength reduction process can lead to an improvement over the Davis approach without updating the two angles, according to recent studies. However, the Davis approach with internal friction angle and dilatancy angle updated may be overly conservative, especially for those geotechnical stability analyses involving large friction and small dilation, which provides the motivation to modify the Davis formula. In this work, a modified Davis approach is proposed by enhancing the original Davis formula. Based on the enhancing approach, two modified Davis formulas – a theoretically modified Davis formula derived from the geometric relation and an empirically modified Davis formula by multiplying the original Davis formula by an enhancement function – are investigated. The appropriate values of the parameters in two modified Davis formulas for practical use are studied. Numerical investigations disclose that the modified Davis formulas in conjunction with the appropriate parameters can lead to improved estimations of the geotechnical stability.

Cracks are the visual manifestation of soil failure. Exploring the propagation process of soil cracks is of great significance to the safety of geotechnical engineering. However, this part...

This work studies the effects of coarse aggregate content on the paste rheological thresholds of fresh self-compacting concrete (SCC). A new mechanical model for highly flowable SCC was established, and a coefficient in the plastic viscosity threshold formula was modified after conducting experimental tests on Wu’s model. The threshold of the paste yield stress decreases while the threshold of the paste plastic viscosity increases with the increase of aggregate content. The bilinear interpolation method was used to process the paste and SCC results. Prediction accuracy formulae based on figure area were introduced to assess the predictive effect of the new model. The relative accuracies of the new model are greater than 70%, whereas the relative accuracies of Wu’s model are no greater than 45%. At last, Two types of cement were used to conduct the verification experiments and high prediction accuracies were obtained. The results show that the application of this method is independent of the type of cement used.

This paper presents a steady-state and transient heat conduction analysis framework using the polygonal scaled boundary finite element method (PSBFEM) with polygon/quadtree meshes. The PSBFEM is implemented with commercial finite element code Abaqus by the User Element Subroutine (UEL) feature. The detailed implementation of the framework, defining the UEL element, and solving the stiffness/mass matrix by the eigenvalue decomposition are presented. Several benchmark problems from heat conduction are solved to validate the proposed implementation. Results show that the PSBFEM is reliable and accurate for solving heat conduction problems. Not only can the proposed implementation help engineering practitioners analyze the heat conduction problem using polygonal mesh in Abaqus, but it also provides a reference for developing the UEL to solve other problems using the scaled boundary finite element method.

Nowadays, most slope stability analyses have been performed without considering the effects of shear band width. To improve the estimations, the shear band width was adequately modeled by introducing an internal characteristic length (lc) within the Cosserat continuum framework, and hence the recently developed second-order cone programming optimized Cosserat continuum finite element method (named CosFEM-SOCP) is employed to investigate the effects of shear band width on slope stability. Based on a homogeneous slope example, it can be recognized that neglecting the shear band width for a slope may lead to overly conservative estimations on the FOS of the slope.

Water inrush disasters are the main cause of karst collapse. In this study, a physical model test was conducted to investigate the mechanism of karst collapse. The formation, expansion, and...

Both experimental studies and engineering practices have indicated that shear effects significantly influence the permeability of clayey soil. In this study, to ameliorate the imperfections...

A comprehensive study is presented of the characteristics of calcareous concretions in the Connecticut Valley varved clay (CVVC), a glacial lake sediment, probed by an array of investigations, including compositional analyses via X-ray powder diffraction and energy-dispersive X-ray spectroscopy, mechanical property mapping by nanoindentation, selective dissolution, microstructure examination by optical and electron microscopy, and stable isotope analyses, with an objective to resolve some long-standing questions on their origin and growth mechanisms. Results show that these concretions are of a biogenic origin and consist of ~40 wt% primary host sediments and ~ 60 wt% secondary calcite post-depositionally precipitated as pore infills and inter-particle cement. The highly consistent layering and dry density between the carbonate-free host sediments in the concretions and in-situ varved sediments manifest that the precipitated calcite causes no disturbance to the original stratification and structure of the varved sediments. Moreover, both the mechanical properties (i.e., Young's modulus and hardness) and calcite concentration in concretions exhibit a radially decreasing pattern slightly disturbed by the sediments' layered textures. Further supported by the radial distribution patterns of stable carbon and oxygen isotopes, the CVVC concretions grow in a concentric pattern. A conceptual ion transport model is proposed to further interpret the growth mechanisms. These concretions grow radially in a nearly closed sediment system with diffusion-controlled transport of HCO3− from decaying organic matter and Ca2+ from porewater at direction-dependent rates dominated by the pore characteristics of the local host sediments. The diverse concretion morphologies are attributed to the different growth rates in different directions affected by the heterogeneous layering and pore sizes of the host sediments.

Soil-rock mixture(S-RM)is a widely distributed geotechnical medium composed of “soil” and “rock block” different both in size and strength. Internal rock blocks form special and variable meso-structural characteristics of S-RM. The objective of this work was to study the control mechanism of meso-structural characteristics on mechanical properties of S-RM. For S-RM containing randomly generated polygonal rock blocks, a series of biaxial tests based on DEM were conducted. On the basis of research on the effects of rock blocks’ breakability and sample lateral boundary type (rigid, flexible) on macroscopic mechanical behavior of S-RM, an expanded Mohr-Coulomb criterion in power function form was proposed to represent the strength envelop. At the mesoscopic level, the variations of meso-structure such as rotation of rock block, and the formation mechanism and evolution process of the shear band during tests were investigated. The results show that for S-RM with a high content of rock block, translation, rotating and breakage of rock blocks have crucial effects on mechanical behavior of S-RM. The formation and location of the shear band inside S-RM sample are also controlled by breakability and arrangement of rock blocks.

Triaxial tests on three types of soil–rock mixture (S-RM) samples with the same rock block content, but different grain size distributions, were performed in this study. To better understand the meso-mechanical behavior of soil–rock mixtures, one set of samples containing “oversized rock blocks” was designed. The oversized rock blocks in the other two sets were handled using the equivalent weight replacement method and the similar translation method. On this basis, the effect of the grain size distribution on the mechanical properties of the soil–rock mixtures was explored. The interlocking and the breakage of the large rock blocks were found to be two of the controlling factors of the mechanical properties of soil–rock mixtures. The deviator stress and the volumetric strain correlated well with the uniformity coefficient of the particle size distribution curve and performed differently under different confining pressure levels. Based on X-ray computed tomography (CT) slices of samples taken during the triaxial tests, the interaction of the internal rock blocks and the evolution of the sample meso-structure in the loading process were observed and analyzed; the present analysis provides explanations for the macroscopic mechanical behavior of soil–rock mixtures.

In this paper, we report a D-type optical fiber biosensor for human immunoglobulin G (HIgG) detection based on surface plasmon resonance (SPR). The SPR phenomenon was both simulated by COMSOL and observed experimentally. To fabricate the sensor, the cladding of a multimode optical fiber (MMF) was polished using a grinding wheel to obtain a D-type cross-section. Next, a gold film was sputtered on the surface of the MMF. The optimal gold layer thickness and grinding depth were determined through simulations. As per the experimental results, the optimized sensor exhibited high refractive index (RI) sensitivity, which ranged from 1590.9 nm/RIU to 3513.3 nm/RIU for RI values of 1.343 to 1.373. Subsequently, Poly dimethyl diallyl ammonium chloride (PDDA) and Poly(sodium-p-styrenesulfonate) (PSS) were deposited four times in sequence to form polyelectrolyte self-assembled multilayers for the surface functionalization of the fiber. HIgG and goat anti-HIgG (GaHIgG) were chosen as the bioconjugate pair for evaluating the functionality of the fabricated biosensor, and the sensitivity to IgG was determined to be 91 nm/(mg/ml). The specificity of the biosensor was also verified through comparison tests performed using gelatin, horse IgG, and swine IgG. The obtained results confirmed the suitability of the biosensor for use in various biochemical applications.

A novel superhydrophobic, chemical-resistant, hybrid inorganic-organic, polymer additive was recently synthesized as soil amendments to finely tune the flow behavior of various soils for functional applications. This paper presents an experimental investigation of the flow and conduction behavior of clays amended by the superhydrophobic additive with the consideration of water as the permeant. Results show that the superhydrophobic additive can transform a wetting, permeable, but dry clay powder into a non-wetting, impermeable barrier at low hydraulic gradients. However, when mixed with wet clay slurry, it can significantly accelerate the consolidation process of clays. The improvement to the water-based flow and conduction behavior enables the amended soils to function as an ideal material for many viable yet challenging applications.

This paper presents a novel nanoindentation technique that obtains massive data on the basis of large volume to extract the mechanical properties of both the individual mineral phases of shales and its bulk rock. Massive data collected on a given surface but extended to a depth of 8–10 μm with the statistical or grid indentation method were processed to extract the mechanical properties of individual mineral phases as well as the dependence of the mechanical behavior upon indentation depth. Large volume-based indentation was then applied at varying depths by the sacrificial removal of the previously indented surface layer. This method is now being implemented as a screening and optimization protocol for various chemical stimulants and additives used in hydraulic fracturing and oil/gas production operations.

It is well known that the trial process for seeking the safety factor in the shear strength reduction finite element method (SSRFEM) is quite expensive, particularly for large 3-D slope stability analyses. The search algorithm for the safety factor is crucial to the entire solution process for the shear strength reduction finite element method, but few studies have attempted to exploit it. Among search algorithms, the commonly used bracketing and bisection search has not been fully optimised. Consequently, to improve the search scheme for the safety factor associated with the shear strength reduction finite element method, two strategies are suggested. First, a generalised bisection search algorithm is proposed to reduce the possibility of encountering non-convergence from a statistical point of view. To further improve the efficiency, a new two-grid scheme, characterised by a coarse mesh search and followed by a fine mesh search, is developed. Based on the drained or undrained analyses of the 3-D slope examples, the new search algorithm can markedly outperform the commonly used bisection search algorithms based on a single finite element mesh.

The parameters of the constitutive model, the creep model, and the wetting model of materials of the Nuozhadu high earth-rockfill dam were back-analyzed together based on field monitoring displacement data by employing an intelligent back-analysis method. In this method, an artificial neural network is used as a substitute for time-consuming finite element analysis, and an evolutionary algorithm is applied for both network training and parameter optimization. To avoid simultaneous back-analysis of many parameters, the model parameters of the three main dam materials are decoupled and back-analyzed separately in a particular order. Displacement back-analyses were performed at different stages of the construction period, with and without considering the creep and wetting deformations. Good agreement between the numerical results and the monitoring data was obtained for most observation points, which implies that the back-analysis method and decoupling method are effective for solving complex problems with multiple models and parameters. The comparison of calculation results based on different sets of back-analyzed model parameters indicates the necessity of taking the effects of creep and wetting into consideration in the numerical analyses of high earth-rockfill dams. With the resulting model parameters, the stress and deformation distributions at completion are predicted and analyzed.

Six non-expandable, hydrous 2:1 phyllosilicate minerals with different layer charges, including pyrophyllite and talc from the pyrophyllite-talc group and biotite, two muscovites, and margarite from the mica group, were nanoindented to probe their nanoscale deformation behavior and hardness. Remarkably different deformation responses were obtained, which are highly dependent upon the type and strength of interlayer interactions controlled by Coulomb or van der Waals forces. Concave load–displacement curves were observed on the micas with stronger Coulomb forces as interlayer interaction, while convex curves on the other group with weaker van der Waals attractions as interlayer interaction. The hardness increases with layer charge both within each group and between the two groups, ranging from 3.86 GPa for talc to 16.34 GPa for margarite, with the highest being four times greater than the lowest. Owing to their layered structure that favors kink band formation and layer delamination, pop-ins of varied extensions occur randomly in the load–displacement curves. An observed apparent indentation size effect is attributed to the pop-in events. The dependence of hardness on interlayer interactions between 2:1 layers instead of the atomic bonds within the 2:1 layer suggests that the interlayer interactions can be used as a hardness or plastic signature for phyllosilicate minerals.

Soil–structure interaction problems are commonly encountered in engineering practice, and the resulting linear systems of equations are difficult to solve due to the significant material stiffness contrast. In this study, a novel partitioned block preconditioner in conjunction with the Krylov subspace iterative method symmetric quasiminimal residual is proposed to solve such linear equations. The performance of these investigated preconditioners is evaluated and compared on both the CPU architecture and the hybrid CPU–graphics processing units (GPU) computing environment. On the hybrid CPU–GPU computing platform, the capability of GPU in parallel implementation and high-intensity floating point operations is exploited to accelerate the iterative solutions, and particular attention is paid to the matrix–vector multiplications involved in the iterative process. Based on a pile-group foundation example and a tunneling example, numerical results show that the partitioned block preconditioners investigated are very efficient for the soil–structure interaction problems. However, their comparative performances may apparently depend on the computer architecture. When the CPU computer architecture is used, the novel partitioned block symmetric successive over-relaxation preconditioner appears to be the most efficient, but when the hybrid CPU–GPU computer architecture is adopted, it is shown that the inexact block diagonal preconditioners embedded with simple diagonal approximation to the soil block outperform the others.

A new type of geopolymer composite was synthesized from two industrial wastes, red mud (RM) and rice husk ash (RHA), at varying mixing ratios of raw materials and the resulting products characterized by mechanical compression testing, X-ray diffraction, and scanning electron microscopy to assess their mechanical properties, microstructure, and geopolymerization reactions. Prolonged curing significantly increases the compressive strength and Young’s modulus, but reduces the ductility. Higher RHA/RM ratios generally lead to higher strength, stiffness, and ductility, but excessive RHA may cause the opposite effect. The compressive strength ranges from 3.2 to 20.5 MPa for the synthesized geopolymers with nominal Si/Al ratios of 1.68–3.35. Microstructural and compositional analyses showed that the final products are mainly composed of amorphous geopolymer binder with both inherited and neoformed crystalline phases as fillers, rendering the composites very complex composition and highly variable mechanical properties. Uncertainties in the composition, microstructure, the extent of RHA dissolution, and side reactions may be potential barriers for the practical application of the RM–RHA based geopolymers as a construction material.

The variation of stress–strain state induces changes in the permeability of clayey soil and then affects the properties of seepage and consolidation. In previous studies, variations of the permeability of soil in shear process were mainly neglected, and there were no reasonable descriptions of the permeability in such a condition. To study the variation of the hydraulic conductivity of clayey soil in shear process, new triaxial seepage equipment was designed by changing the conventional triaxial apparatus. Based on a series of tests under different confining pressures carried out by this equipment, the influences of the stress–strain state of clayey soil on hydraulic conductivity were investigated. Furthermore, a mathematical model for the hydraulic conductivity of clayey soil under the condition of large shear deformation was proposed. The comparison between the seepage test results and the calculated values of the proposed model indicates that the mathematical model can calibrate the effects of ...

Several recent studies have suggested that maternal exposures to air pollution and temperature extremes might contribute to low birth weight (LBW), preterm birth (PTB), and other outcomes that can adversely affect infant health. At the time the current study began, most other studies had been conducted in the United States or Europe. Dr. Zhengmin Qian proposed to extend work he had done on ambient particulate air pollution and daily mortality in Wuhan, China (Qian et al. 2010), as part of the HEIsponsored Public Health and Air Pollution in Asia program, to study adverse birth outcomes. Wuhan is the capital city of Hubei province, has a large population of about 6.4 million within the urban study area, experiences temperature extremes, and generally has higher air pollution levels than those observed in the United States and Europe, thus providing a good opportunity to explore questions about air pollution and health.Qian and colleagues planned a cohort and nested case–control design with four specific aims, examining whether increased exposures to air pollutants (PM2.5, PM10, SO2, NO2, O3, and CO) during vulnerable pregnancy periods were associated with increased rates of PTB, LBW (2500 g), or intrauterine growth retardation (IUGR, defined as having a birth weight below the 10th percentile of singleton live births in Wuhan) after adjusting for major risk factors and whether the associations were confounded by copollutant exposures, affected by residual confounding, or modified by temperature extremes, socioeconomic status (SES), or secondhand smoke (SHS) exposure. The cohort study included 95,911 births that occurred from June 10, 2011, to June 9, 2013, and met typical prespecified inclusion criteria used in other birth outcome studies. The case–control study included 3146 cases (PTB, LBW, or both, but not IUGR) and 4263 controls (matched to the cases by birth month) for whom investigators were able to complete home visits and questionnaires. The investigators obtained air pollution and daily weather data for August 2010 to June 2013 from nine monitoring stations representing background air pollution sites in seven Wuhan inner-city districts. Only two of these stations provided PM2.5 data. For the cohort study, the investigators assigned exposures to mothers according to the daily mean concentrations from the monitor nearest the residential community in which the mother lived at the time of the birth. For the case–control study, they assigned exposures based on the inverse distance weighted average of daily mean concentrations from the three nearest monitors, for all but PM2.5 for which the method was not specified. They also collected data on various factors that might confound or modify the impact of the pollutants on the adverse outcomes, including data collected in the cohort from mothers at the time of delivery and, in the case–control study, from questionnaires administered to mothers. In the case–control study, covariates representing SES (as indicated by the mother’s educational attainment and household income) and SHS exposures were of particular interest. The primary statistical analyses of the pollutant associations with PTB, LBW, and IUGR were conducted using logistic regression models. In the cohort study, exposures during the pregnancy period of interest (full term, trimesters, and selected months) were included as continuous variables. In the case–control study, the exposures were modeled as binary variables (i.e., above or below the median pollutant concentrations). Numerous sensitivity analyses were conducted.Although originally planning a nested case–control study, the investigators encountered challenges that led them to analyze the cohort and case–control studies using different ways of assigning exposures and characterizing them in their statistical models. These decisions precluded direct comparisons between the sets of results, making it difficult to answer the questions about residual confounding that nested case–control studies are designed to answer. The odds ratios from the two study designs using different exposures also have different interpretations. Still, one can ask whether the sets of findings were qualitatively consistent with each other or with those of similar studies. There were some similarities. Both studies suggested that increased PM(2.5), PM(10), CO, and O(3) exposures over the full pregnancy were associated with small increases in the odds of PTB (the case–control study also showed an association with NO2) and that increased PM(2.5) exposures were associated with significantly increased odds of LBW. However, most of the other pollutants had no effect on LBW, except CO in the cohort study and O(3) in the case–control study, both of which increased the odds of LBW. The exposures over the entire pregnancy were generally associated with decreased odds of IUGR. Adjustments for potential confounders were greatest for the delivery covariates. The investigators found no systematic association of any of these outcomes with particular trimesters or months, another result that differed from those of some other studies. They found little evidence that their main results were confounded or modified by the presence of copollutants, although with the exception of O3, most of the pollutants were highly correlated, making it difficult to disentangle the effects of individual pollutants. Could the two sets of data be analyzed in a more comparable way, as in a standard nested case–control study? At the Committee’s request, the investigators reanalyzed the case–control data using the same exposures and models as in the cohort study. The results were strikingly different from those using the inverse distance weighted exposures, modeled as binary variables — the pollutants had either no effect or an apparent beneficial effect on PTB and LBW. The Committee was not convinced by the explanations offered for these differences, leaving the reasons for them unresolved.This study set out to answer important questions about the effects of air pollution exposure on three measures of adverse birth outcomes — LBW, PTB, and IUGR — in a large cohort of mothers and newborns in Wuhan, China. Given the cohort size, high pollution levels and temperatures, and detailed covariate data, the investigators were well poised to address these questions. They sought to pattern their work on other studies of birth outcomes, were very responsive to Committee questions, and provided many additional analyses and explanations. In the Committee’s view, however, the study was unable to address with confidence several of its specific aims. Most important, the differences in results when the case–control data were analyzed with different exposure metrics remain unexplained, raising concerns about the ability to draw conclusions from subsequent analyses assessing residual confounding and effect modification by temperature extremes, SES, and SHS exposure. Consequently, any individual findings from the cohort and case–control studies should be considered suggestive rather than conclusive, and should be interpreted carefully together.

A consolidation analysis method for an earth-rockfill dam based on the coupling of physical state, stress deformation, and seepage was established. In this method, a permeability coefficient model considering physical state and shear stress level was introduced, and it was integrated with Biot’s consolidation theory to simulate the coupling relationship. Taking the Nuozhadu high earth-rockfill dam as an example, a parameter back-analysis method using a neural network and evolutionary algorithm was applied to back-analyze the permeability coefficient model parameters of the core material based on observation data of pore water pressure in the dam. Then, consolidation numerical analyses were performed by using the back-analyzed parameters and the constant permeability measured in situ, respectively. The spatial and temporal distribution of pore water pressure calculated by the back-analyzed parameters coincided quite well with the monitoring data during construction and operation. However, the numer...

Because most geotechnical analyses may involve elastoplastic geomaterials, a robust solution scheme is of critical importance to the efficiency of the entire finite-element (FE) computation. To accelerate the Krylov subspace iterative methods, some preconditioning techniques have been developed based on the factorization of elastic stiffness. However, the idea of constructing a preconditioner based on elastic stiffness is heuristic. In this study, a class of Neumann expansion preconditioners constructed from the constant (elastic) partition and varying (plastic) partition of the elastoplastic stiffness matrix was proposed. Based on two numerical examples, the performances of truncated Neumann expansion preconditioners were examined with associated and nonassociated soil plasticity considered, respectively. It is interesting to note that the convergence behaviors of truncated Neumann expansion preconditioners closely depended on the approximation to the elastic stiffness part as well as the truncat...

The effects of source materials on the microstructure and mechanical properties were studied by comparing two types of geopolymers synthesized from metakaolin, a non-waste material, and the admixture of two wastes, red mud and fly ash. Unconfined compression testing was conducted to assess their curing time and mechanical properties, while X-ray diffraction and scanning electron microscopy employed to examine geopolymerization reactions and the composition and microstructure of the end products. For a given Si/Al ratio, the metakaolin-derived geopolymer exhibits higher compressive strength than the waste-based one. Both geopolymers contain a significant amount of voids and unreacted phases as inactive fillers within the geopolymer binder, resulting in complexity and variability in their mechanical behavior. The difference in strength and microstructure between the two geopolymers is attributed to the different reactivity of source materials, percentage of nonreactive fillers, and alkalinity for geopolymerization reactions.

Based on a force analysis, an expression is derived to describe the critical Shields number for incipient motion of uniform cohesionless sediment particles on a riverbank slope in terms of flow parameters, outflow seepage, and physical and mechanical properties of sediments. Parametric studies were conducted to investigate quantitatively the effects of hydraulic gradient of seepage, slope angle, and flow direction on the critical Shields number. The results show that the critical Shields number decreases with an increase in the hydraulic gradient. Where bank collapse is concerned, the most dangerous direction of hydraulic gradient of outflow seepage is at an angle equal to the effective internal angle of friction of the sediment mass with respect to slope surface. At a certain value of hydraulic gradient, the critical Shields number decreases with increasing slope angle. Open flow becomes more erosive when the current direction changes from horizontally parallel with the riverbank line to turning downward.

An intelligent method for the effective displacement back-analysis of earth-rockfill dams was proposed by combining artificial neural networks and evolutionary calculation. This method employs artificial neural networks, with optimal architecture trained by the evolutionary calculation and Vogl’s algorithm, instead of the time-consuming finite element analysis. In the back analysis, the soil parameters were optimized by performing evolutionary calculations on the tested neural network. The proposed method was verified by applying it to the displacement back-analysis of two projects in China, and the influence of generation number and set size on the simulation ability of neural networks was investigated.