Variation Of Shear Strength Research Articles

A two-step dynamic FEM-FELA approach for seismic slope stability assessment

AbstractThe determination of the factor of safety (FoS) of slopes during seismic excitation can be complex if the relevant effects of pore water pressure accumulation, nonlinear material response and variable shear strength are duly accounted for. A rational two-step approach to tackle this task based on a hydro-mechanically coupled dynamic simulation and finite element limit analyses is henceforth introduced. To ensure accurate transfer of the hydro-mechanical soil state, a mapping concept is presented, accounting for spatial distributions of stresses, excess pore water pressures, inertial forces and shear strength. The proposed approach is compared to limit equilibrium method (LEM) for the case of a large-scale water-saturated open cast mine slope subjected to seismic loading. In comparison with LEM, the new approach to assess seismic slope stability proves to be simpler in its implementation and straightforward, which could be an important asset for practitioners.

Characterisation of the spatial variability of underconsolidated Singapore Marine Clay using random field theory

ABSTRACT This paper characterised the spatial variability of Singapore Kallang Formation Marine Clays using piezocone penetration test (CPT) data from the Marina South area. Both vertical and horizontal scales of fluctuation in undrained shear strength for two distinct clay units, Upper Marine Clay (UMC) and Lower Marine Clay (LMC), are calibrated for autocorrelation and semi-variogram functions. The Marina South area was reclaimed from the sea using fills placed in three phases from 1970s to 1990s and remains underconsolidated up to date. This study identified variations in the degree of consolidation across the area, which has led to variations in the undrained shear strength in this area. However, the variations in the degree of consolidation were found to have no noticeable influence on the vertical and horizontal scales of fluctuation of either UMC or LMC unit. The vertical scales of fluctuation of UMC and LMC units are 0.57 ± 0.3 m and 0.48 ± 0.17 m , respectively, while the horizontal scales of fluctuations are 148 ± 26 m and 138 ± 28 m , respectively. The present study contributes to the database of the statistical and spatial variability of marine clays and can provide useful guidance for assessing reliability of excavations and foundations in Marina South as well as other areas with similar geological settings.

Role of particle shape in sheared granular media: Roundness and elongation

Particle shape is an intrinsic characteristic of soil particles that significantly influences mechanical responses. In this investigation, a meticulously calibrated and validated two-dimensional discrete element method (DEM) model of a biaxial shearing test was employed to simulate the shearing response of forty distinct particle shapes. The systematic evolution of particle roundness (R) and aspect ratio (AR) was achieved by utilizing idealized polygonal-shaped particles, aiming to comprehend their effects on the macro and micromechanical behaviors of granular materials. The results suggest that a reduction in R limits free rotations and enhances interlocking, thereby promoting relatively stable force transmission between particles and leading to a monotonic increase in shear strength. However, this effect diminishes as particles become more elongated. Conversely, a decrease in AR from 1.0 (increased elongation) constrains particle rotations, increases the coordination number, and enhances fabric anisotropy initially resulting in increased overall shear strength, reaching a maximum before exhibiting a decreasing trend, indicative of non-monotonic variation. For high elongations, notable fabric anisotropy impedes clear force transmission between particles thus facilitating interparticle sliding and overall strength diminishes. The extent to which AR impacts depends on the angularity feature of particles. Finally, a nonlinear equation has been proposed to predict the variation in critical state shear strength of granular samples, based on the R and AR values of the constituent particles.

Monotonic simple shear characteristics of K0 highly over-consolidated and remolded Wenzhou clay

The over consolidated clay is widely distributed in the seabed. Monotonic simple shear tests on K 0 consolidated clays with an over consolidation ratio (OCR) of 1 ∼ 14 were conducted through a multidirectional cyclic simple shear apparatus. The stress–strain relationship, pore pressure evolution, and shear strength variation under different OCRs were revealed, and differences between over and normally consolidated clay were compared. When OCR is below 8, peak values of shear stress and negative excess pore pressure both increase linearly with increasing OCR. However, the peak values tend to stabilize when OCR is above 8. Correspondingly, the occurrences of peak values no longer delay linearly, and the failure line is also shifted towards stronger strengths. An exponential formula is purposed and validated on accordance with numerous experimental data to describe the aforementioned pattern more precisely compared with the traditional power formula. Therefore, shear strengths of over consolidated clays with various OCRs and consolidation pressures can be accurately predicted according to the exponential formula and the shear strength of a normally consolidated sample with a certain consolidation pressure.

Effects of clay grains on the shear properties of unsaturated loess and microscopic mechanism

Different clay grains affect the structural strength of loess through the cementation of skeletal particles. This study investigates both clay-clay grains and quartz-clay grains. Clay-clay grains mixed loess (CM-L) and quartz-clay grains loess (Q-L) samples were prepared, and their unsaturated shear properties analyzed. X-ray diffractometry (XRD) analysis was conducted to determine the types and proportions of clay grains. Ball mill grinding and laser particle size analysis were employed to ensure comparable sizes of clay grains, while mercury intrusion porosimetry (MIP) tests confirmed similar pore characteristics. Scanning electron microscope (SEM) and unsaturated triaxial consolidation and drainage tests explored the impact of different clay grains on loess shear characteristics, assessing both microscopic and macroscopic performance. The results indicate that CM-L loess exhibits higher cohesion and a lower internal friction angle at the same matric suction level. The cohesion and internal friction angle of both CM-L and Q-L loess exhibit a linear relationship within the range of 50–200 kPa matrix suction. The cohesive force ranges for CM-L and Q-L loess are 60.31–80.07 kPa and 43.01–69.60 kPa, respectively, while the ranges for internal friction angles are 19.95°-19.59° and 25.91°-25.06°, respectively. Compared to Q-L loess, CM-L loess exhibits an average difference in cohesion of 23.18 kPa and in internal friction angle of -5.72°. The microscopic variation in shear strength can be attributed to the “fish scale-like” interlocking state between clay-clay grains and the “tower-like” scattering arrangement of quartz-clay grains. In conclusion, the effect of different clay-grain types on the shear strength of loess varies significantly. The present study elucidates the relationship between the influence of different clay grains on the mechanical properties of loess and their microscopic structural characteristics, thereby providing crucial data for investigating the microscopic effects on the structural strength of loess.

Variation of Shear Strength of Cohesive Soils Subjected to Cyclic Loading at Different Rates of Loading

Variation of Shear Strength of Cohesive Soils Subjected to Cyclic Loading at Different Rates of Loading

Laboratory investigation of the influence of fines content on the mechanical behavior of sand

The present article seeks to examine and discuss the experimental results that were obtained from a series of straight box shear tests. For this, different soils were prepared with clean sand, which was brought from the Wilaya (Province) of Chlef that is located in northern Algeria, mixed with silt from the same site, clay from the town of M'zilla or clayey loam that is composed half of this same clay and half of silt. The percentages of sand replacement by the selected additions were 0, 10, 20, 30, and 40% in mass ratio. The samples thus prepared were then tested with respect to dry shear, under the normal stresses equal to 100, 200, and 400 kPa. The results obtained showed that the shear strength of the sand from Chlef decreases when the silt content increases from 0 to 40%. With regard to the sand-clay and sand-silt-clay mixtures, it was found that the shear strength decreases until reaching a threshold value that coincides with the addition content of 20%. Then, beyond that value, it begins to increase as the addition fraction increases. Likewise, it turned out that cohesion increases with increasing silt content, while for sand-clay and sand-silt-clay mixtures, this cohesion increases until reaching a maximum value which coincides with the addition of 20% silt content. The same trend was observed for the variation of the direct shear strength, while the friction angle exhibited an inverse behavior.

Unsaturated soil nailing wall system reliability analysis using random finite element

This study focuses on the evaluation of stability for a typical unsaturated Soil Nailing Wall System (SNWS), considering variations in soil shear strength, suction, and elasticity modulus. The Random Finite Element Method (RFEM) is employed to derive the reliability indices for stability modes, including Global Stability (GS), Lateral Displacement Stability (LDS), Tensile Strength Stability (TSS), and Pullout Resistance Stability (PRS), which serve as essential components of the SNWS. Finally, the Sequential Compounding Method (SCM) is utilized to combine these modes of stability and their direct influence on the system reliability index. The results show although the maximum Coefficient of Variation (COV) of the soil parameters was 11%, the COV of lateral displacements at the top of the wall was obtained as 19%, which shows the significant influence of considering the soil heterogeneity. Furthermore, uncertainties of elasticity modulus and matric suction lead to an increase in GS, LDS, and PRS. The calculated system reliability index was found to be lower than the lowest reliability index of the individual components. The findings indicate that while the inclusion of matric suction and elasticity modulus may enhance the mean values of stability modes, there is a possibility that the system reliability index could decrease.

Probabilistic assessment of bearing capacity of skirted foundation under combined loadings with a rigid base

Skirted foundations are critical components in offshore applications where combined loads are common in deep‐water environments. Their ultimate capacity under VH (vertical‐horizontal) combined loading is traditionally determined using VH failure envelopes, which are primarily constructed using numerical methods. These methodologies, however, frequently ignore the spatial variability inherent in seabed soils due to geological formations. This paper investigates the effect of spatial variability of undrained shear strength and embedment ratio impact on the capacity of skirted foundations subjected to VH combined loading. For this, OptumG2 software is used to perform Monte Carlo simulation combined with random finite element limit analysis. This paper investigates the stochastic analysis of bearing capacity and failure envelopes, with a particular emphasis on understanding the effect of spatial correlation on undrained shear strength. The study focuses on the horizontal scale of fluctuation and the soil strength heterogeneity index, shedding insight on previously undiscovered areas. Novel findings highlight how a rigid base affects VH failure envelopes and offer insights into evaluating the vertical bearing capacity of skirted foundations. [Correction added on 8 July 2024, after first online publication: The above statement has been updated in this version.]

Selection of long-term shear strength parameters for strain-softening geosynthetic interfaces (2023 IGS Rowe Lecture)

The behavior of strain-softening geosynthetic interfaces that can lead to progressive failures in lined containment facilities has been a source of confusion in slope stability evaluations for over 30 years. This paper presents 15 mechanisms that can potentially induce displacements along strain-softening interfaces, along with measures that can be considered to reduce strain-softening displacement. New quantifications of shear strength variability that can be caused by manufacturing, installation, and construction practices are introduced. Guidance and recommendations are given that are applicable to numerical continuum as well as limit-equilibrium approaches to assist in selecting appropriate geosynthetic shear strength parameters for containment facilities that have strain-softening interfaces. While most of the paper focuses on deep-seated critical interfaces for high-normal-stress bottom liners, low-normal-stress veneer covers are also addressed.

Counter-intuitive mechanical performance variation in aged low-temperature interconnections in electronic packaging

Different from the conventional aging induced continuous mechanical performance deterioration in solder joints, a counter-intuitive “decrease-increase-decrease” variation in shear strength with a peak value 12 MPa higher than the initial state was captured in aged low-temperature BGA structure Cu/Sn–58Bi/Cu solder joints. The first decrease in shear strength was dominated by the coarsening of Sn and Bi phases. The following increase in shear strength was rooted in the concurrent Bi subgrain strengthening, solid solution strengthening of Bi element in Sn-rich phase and precipitation strengthening induced by the Bi-rich phase particles. The eventual decrease in shear strength was ascribed to severely deteriorated interface between the solder matrix and intermetallic compound layer being the weaker site in the long time aged solder joint. This aging induced strengthening phenomenon is inspiring in mechanical performance optimization and reliability elevation of SnBi-based solder joints for the coming chiplet and heterogeneous integration packaging.

Effect of air exposure time on erodibility of intertidal mud flats

This study investigates the influence of air exposure time on the erodibility of intertidal mud flats, emphasizing the role of evaporation in altering sediment strength and cohesion. Through a comprehensive approach combining laboratory experiments, fieldwork, and numerical modelling, it explores the dynamic interactions between sediment properties and environmental conditions. The research reveals that drying significantly reduces sediment erodibility, with pronounced effects observed during the initial hours of air exposure. Laboratory tests demonstrate a direct correlation between drying time and increased yield stress for both artificial and field-derived mud samples. Field observations further support these results, showing spatial and temporal variations in water content and shear strength across various locations on a tidal flat. The study emphasizes the critical impact of mud content on water retention and the subsequent effect on sediment stability. The incorporation of drying time into erosion formulations within a numerical model highlights the importance of considering evaporation processes in predicting the morphological evolution of tidal flats. This research contributes to a better understanding of sediment transport dynamics in intertidal zones, offering insights into the mechanisms driving the growth and stability of mud flats. It underscores the necessity of integrating evaporation effects into cohesive sediment transport models to enhance the accuracy of predictions concerning the erosion and accretion of intertidal environments.

Experimental investigation on fractal mechanism and shear failure characteristics of cement mortar at different curing ages

In this paper, the NMR and direct shear tests were conducted successively on cement mortar specimens with different curing ages (7 days, 14 days and 28 days). The porosity, shear strength, shear stiffness and shear energy of cement mortar are measured and analyzed through interpreting the pore distribution patterns and their corresponding fractal dimensions. The cross-sections of shear surface were characterized into point cloud data via 3D laser scanning and quantified by three dimensionless parameters (the root mean square value of the first derivative, root mean square value and joint roughness coefficient). The grey relation analysis (GRA) method and principal component analysis (PCA) is employed to analyze the relationship between the pore structures (i.e., gel pores, transition pores, capillary pores and pores or cracks) and distribution and the fractal dimensions. The results indicate that the shear peak strength is linearly correlated with the joint roughness coefficient. Compared to the fractal characteristics of pore size (T2 spectra) and pore distribution (MRI), we demonstrated that there is a strong correlation between the peak shear strength and the fractal dimension of shear fracture surface, which suggests that the quantitative characterization of internal pores and shear strength variations in cement mortar specimens can be achieved through the numerical values of fractal dimensions.

Lateral holding behaviour of torpedo piles in spatially variable soil: Development of a probabilistic design approach

Offshore torpedo piles are increasingly being utilised in deepwater oil and gas development as part of a taut-leg mooring system. As these piles commonly experience inclined loading in service, accurately determining their lateral holding capacity is crucial. Despite the fact that natural soil characteristics exhibit significant spatial variability, existing studies are mostly deterministic in nature. This paper presents probabilistic analyses of the lateral holding capacity of torpedo piles, explicitly considering the spatial variability of soil shear strength. Large deformation finite element calculations are combined with three-dimensional random field generation in a Monte Carlo framework. The results show that while spatial variability does not apparently alter the failure mechanism of laterally loaded torpedo piles, it significantly influences their holding capacity. The routine deterministic calculation, neglecting spatial variability, would probably yield unconservative estimates. To address this challenge, a probabilistic Broms method is developed, which enables engineers to produce lateral holding capacity estimates with varying confidence levels, using local strength data rather than central tendency. Furthermore, endeavours are also made to calibrate the safety factor, extensively employed in deterministic design practices, from a probabilistic perspective, providing practicing engineers with a viable alternative in scenarios where a local strength profile is unavailable.

Characterisation and statistical modelling of shear strength in 12 hardwood timber species from the Congo Basin

Shear strength is a wood property which is fundamental to the design of wood-based products and constructions. This property cannot be predicted at present for lack of sufficient knowledge, mainly because of the large number of timber species that occur in the Congo Basin. The main aim of this study was to provide a preliminary qualification of shearing in Congo Basin timber species, with consideration for its variability. For this purpose, we studied 12 timber species with very different properties, from the least dense to the densest. Their shear strength was determined experimentally using European standards specifications, on the scale of the wood material used. A statistical analysis was conducted. To reduce shear strength variability, the species were assigned to four distinct clusters defined according to FCBA Institute specifications. With a view to developing allowable design stresses to facilitate decision-making, we evaluated the relative goodness-of-fit of five probabilistic shear strength distributions (normal, lognormal, exponential, Weibull 2 parameters and Weibull 3 parameters) that are used in wood-related applications. The results of geometric regression (R2 = 0.81) show that shear strength is well correlated with density. Shear strength can be more reliably predicted with the three-parameter Weibull distribution than with the other distributions. The findings of this study open up new prospects to be considered for the design of wood-based products with regard to shear, when using tropical timber species from the Congo Basin.

Reliability-based evaluation of ultimate embedment depths of torpedo anchors in spatially variable clay

In this study, a large deformation random finite element (LDRFE) method was used to investigate the dynamic penetration of anchor piles in spatially variable clay. Validation of the rationality of the proposed methodology using data from published studies. The randomness of the undrained shear strength of the soil in the system is considered by three-dimensional random fields to investigate the anchor penetration mechanism and quantitatively assess the ultimate embedment depths (Hran ) of the anchor in spatially variable clay. The strain softening and strain rate effects of the soft clayey soil were considered. The findings indicate that the variability in soil strength significantly affects the flow pattern and failure mechanism of the soil, consequently influencing the Hran of the anchor. Furthermore, according to the computed Hran results, a coefficient of variation of soil shear strength φ can be used to connect the deterministic (Hdet ) and random analysis results. This correlation may facilitate further development of reliability-based designs.

Using soil tuff-modified polymetallic lead–zinc tailings sand to facilitate sustainable development of subgrade engineering

The use of soil tuff, an industrial solid waste, for the modification of lead–zinc tailings as subgrade fillers presents a sustainable solution for concurrently addressing the negative impacts of tailings accumulation and resource depletion resulting from road construction. To demonstrate this, we conducted a thorough series of macroscopic and microscopic experiments, including the physical performance, durability, and microstructural behaviors of soil tuff-modified lead–zinc tailings sand (STM-LZTS) and cement-modified LZTS with varying modifier dosages, compaction degrees, and curing ages. Furthermore, we conducted a comprehensive comparison of the sustainability performance of these two modified LZTSs in terms of cost, CO2 emissions, and energy consumption. The results indicate that the incorporated 6% soil tuff filled the voids with the hydrated calcium silicate gel generated during the hydration process, which improved the structural stability. The CBR value was further enhanced to over 4% upon modification. With an increase in compaction degree to 96%, the CBR value escalated to over 8% (＞4%). The STM-LZTS specimens exhibited compressive strengths ranging from 0.818 to 0.958 (＞0.3 MPa). The variations in shear strength ranged between 200 and 550 kPa. Meanwhile, the modification of LZTS with soil tuff considerably delayed the deterioration of specimens under dry–wet, freeze–thaw, and salt-solution immersion conditions. Furthermore, compared with the cement-modified LZTS, the modified material formed a denser binder and a more robust nonparticle gel due to its lower calcium–silica ratio and higher aluminum–silica ratio, exhibiting superior performances in terms of compressive strength and resistance to salt corrosion. In addition, the use of soil tuff substantially reduced the cost, carbon emissions, and energy consumption, making it a promising and ecofriendly alternative for waste management and achieving carbon neutrality goals in subgrade engineering.

Assessing Column Stability: A Comparative Study of Machine Learning Regression Models for Shear Strength Prediction

This research presents a comprehensive investigation into the accurate estimation of shear strength in rectangular reinforced concrete columns through advanced machine learning (ML) models. The study addresses the intricate challenge posed by shear strength complexity, which is crucial for evaluating column stability and ensuring structural integrity. Building upon a substantial dataset comprising 545 experimental observations sourced from diverse literature, this research establishes a robust foundation for predictive modeling. Four distinct ML regression models, Random Forest, Decision Tree, XGBoost, and LightGBM, are meticulously evaluated for their performance. The evaluation employs established metrics, including R2, RMSE, MAE, and MAPE to quantify their predictive capabilities. The outcomes highlight the models' robustness in capturing nuanced variations in shear strength, with impressive R2 values ranging from 93.6% to 93.9%, showcasing their exceptional ability to elucidate intricate shear behaviors. Furthermore, comparative analysis indicates the slightly superior performance of the Random Forest over the Decision Tree, highlighting the efficacy of ensemble methods in this context. Extending the exploration to include XGBoost and LightGBM, the study showcases their potential as accurate shear strength predictors. The performance of the models is validated through scatter plots and error distribution plots, confirming accurate shear strength predictions across various scenarios. This research contributes significantly to the advancement of structural engineering methodologies by highlighting the potential of ML to improve the accuracy of shear strength estimation. The findings not only underscore the exceptional performance of ML models but also provide valuable insights into their comparative effectiveness, paving the way for enhanced structural assessments in columns.

Molecular dynamics for optimizing interfacial properties of carbon fiber-reinforced polycarbonate: molecular conformation

ABSTRACT Molecular dynamic simulation along with experiments was used to study polycarbonate (PC) molecular conformation on composite interfacial properties. The interlaminar shear strength (ILSS) variations of composites with carbon fiber roughness were quite different between sized and unsized carbon fibers, which seem to conflict with the theory that rougher surface is harder to wet. By the results of molecular dynamic simulation, it was found that the conformation of PC molecules through solvent intervention could be higher, which is conducive to the formation of π–π stacking conformation between PC and carbon fibers and benefits the interface interaction, resultantly affecting the ILSS more when the carbon fiber surface area was low. When the specific surface area was high enough, the ILSS gets to a saturation value, because the fracture area changes from the interface to the matrix. It is concluded that the effects of sizing on ILSS varied with carbon fiber surface roughness, and the molecular conformation of the matrix affected by sizing or processing must be considered. Therefore, it is important to enhance the physical interactions with carbon fiber for thermoplastic resin matrixes.

THEORETICAL FRAMEWORK FOR LARGE-STRAIN SHEAR RESISTANCE OF KAOLIN CLAYS UNDER CHEMO-MECHANICAL LOADINGS

The normal stress, strain rate, and pore-fluid chemistry significantly influence the large-strain shear response of clays and received great attention for engineering practice. The effect of inundation pressure, consolidation pressure, pH of aqueous solutions, and di-electric on the shear response of kaolin was experimentally investigated. The strain-softening behaviour was observed under normally consolidated (NC) conditions as observed in the past studies on different clays. However, this anomalous shear response with volumetric contraction is not understood. Thus, for the first time, the strain-softening behaviour of NC clays was addressed from an effective stress approach using physico-chemical analysis of kaolin. In this study, the drained shear strength response of NC kaolin was investigated under physico-chemical influence using ring shear tests. A theoretical framework was developed by including micro-mechanism of clay fabric evolution during shear and explicit expressions for electro-chemical forces. The proposed framework provides useful expressions for predicting the shear strength behaviour of kaolin clays, which were validated with experimental data from the present study and literature studies. The new conceptual framework satisfactorily explained the peak and residual shear strength variations under different chemo-mechanical loading for NC conditions. The proposed model adequately predicted the effective stress paths, peak, and residual envelopes in ring shear stress conditions for normally consolidated kaolin soils