Total Stress Analysis Research Articles

Nonlinear seismic response analysis of liquefiable sites based on effective stress method

In this study, the one-dimensional nonlinear Matasovic model was extended to the two- and three- dimensional stress space by replacing the shear strain with the generalized shear strain. The extended Matasovic model was subsequently combined with Dobry’s excess pore water pressure generation model, and the reliability of the proposed loosely coupled effective stress analysis model was verified through undrained cyclic triaxial tests and a one-dimensional site response analysis. Finally, this method was applied to an engineering site in China to evaluate the nonlinear seismic response of liquefiable sites. The results show that the proposed effective stress analysis method can capture the dynamic behavior of the soil and the generation of pore water pressure during strong shaking. Moreover, there are differences between the proposed effective stress analysis method and the total stress analysis method for liquefiable sites, which indicates the need for careful selection in practical applications.

Evaluating and validating 3-D simulated MASW and SPAC in situ tests in Argostoli, Greece

SUMMARY Geophysics and Geotechnical Engineering commonly use 1-D wave propagation analysis, simplifying complex scenarios by assuming flat and homogeneous soil layers, vertical seismic wave propagation and negligible pore water pressure effects (total stress analysis). These assumptions are commonly used in practice, providing the basis for applications like analysing site responses to earthquakes and characterizing soil properties through inversion processes. These processes involve various in situ tests to estimate the subsurface soil’s material profile, providing insights into its behaviour during seismic events. This study seeks to address the limitations inherent to 1-D analyses by using 3-D physics-based simulations to replicate in situ tests performed in the Argostoli basin, Greece. Active and passive source surveys are simulated, and their results are used to determine material properties at specific locations, using standard geophysical methods. Our findings underscore the potential of 3-D simulations to explore different scenarios, considering different survey configurations, source types and array sets.

Fraction of Pore Pressure and Calculation of Earth Pressure for Saturated Cohesive Soils

Earth pressure for saturated cohesive soils is closely related to the effective stress expression. For cohesionless soils, previous research indicated that the fraction of pore pressure (factor η) in the effective stress expression is below unity at high pressures. However, for cohesive soils, reliable η‐value has not been reported. In this study, experimental data from direct shear and triaxial tests were analyzed in order to derive the η‐values of two cohesive soils. It was shown that η‐value of cohesive soils decreases significantly with increasing effective stress, and the values of η derived from different experiments were consistent with each other. The obtained values of η were applied to the calculations of lateral earth pressure. The lateral earth pressure based on real η was compared with the results of traditional methods, i.e., effective stress analysis (ESA) and total stress analysis (TSA). The traditional ESA was conservative because of the overestimation of active earth pressure. Such conservatism was more significant for high plasticity clay. Contrastingly, TSA results were risky for both of the two cohesive soils.

A limit analysis approach to uplift bearing capacity of shallow plate anchors in marine environments

AbstractOffshore oil and gas exploration activities involve the installation of various subsea infrastructures on the ocean floor, often supported by shallow foundations such as anchor plates or mudmats. These foundations must be designed to withstand applied service loads along the structure lifecycle, including decommissioning loads required for subsequent removal. In this context, this work is dedicated to the evaluation of uplift bearing capacity of shallow anchors within the theoretical framework of limit analysis and its related kinematic approach. Based on the implementation of 3D failure mechanisms, rigorous upper bound estimates for the uplift force viewed as ultimate load for the material system are derived from either total or effective stress analyses. In that respect, emphasis is given to the formulation of limit analysis problem in the context of effective stresses, showing how the effect of seepage flow may be accounted for by means of driving body forces derived from the gradient of excess pore pressure distribution and how suction forces arise from pore pressure difference between upper and lower anchor surfaces. Evaluation of suction forces developed during anchor lifting is addressed by resorting to a simplified modeling applied to circular and rectangular anchors. The accuracy of the upper bound predictions derived for uplift force is assessed by comparison with available experimental data. Several numerical results are also provided to investigate the effects of relevant problem parameters on the uplift bearing capacity.

One-Dimensional Reverse Consolidation Model for Basal Soil from Deep Excavation Based on the Continuous Drainage Boundary

Excavation-induced unloading effects and dewatering-induced groundwater seepage inevitably result in basal soil reverse consolidation in deep excavation. However, this reverse consolidation process is rarely considered because most previous analytical methods were developed based on total stress analyses. This study proposes a one-dimensional reverse consolidation model for basal soil of deep excavation. Based on the consolidation theory proposed by Terzaghi, governing equations of soil reverse consolidation caused by excavation and dewatering were separately established. The continuous drainage boundary was introduced to describe the construction processes. The reverse consolidation responses of basal soil were obtained by superimposing analytical solutions of the excess pore-water pressures that resulted from excavation and dewatering. The proposed model was verified by existing solutions and a well-documented excavation case history. Moreover, the reverse consolidation characteristics of basal soil were investigated by parametric analyses. Results indicate that the excavation-induced variations in pore-water pressure decreased with increasing excavation depth. The final pore-water pressure and effective stress were predominantly affected by excavation duration rather than interval distribution. In addition, a smaller coefficient of consolidation led to lower pore-water pressure and greater effective stress at a given excavation depth.

English

Inflammatory bowel disease (IBD) is the persistent inflammation of GIT (Gastrointestinal tract). IBD mainly divided into ulcerative colitis and Crohn’s disease while the Crohn’s disease involves the whole gastrointestinal tract while ulcerative colitis is limited to the colon. The current experimental study elucidates the antioxidative and microbial homeostatic efficacy of monolaurin, monolaurin with butyric acid and propionic acid in DSS (Dextran sulfate sodium) induced acute colitis in rat model. The results revealed that total antioxidant capacity was raised significantly (P<0.05) in all the treatment groups comparative with positive control group. While the results of total oxidative stress and relevant gene expression analysis revealed that mRNA expression of cell stress pathways such as, Traf-4, Traf-6 and MAPK-8 genes (Mitogen activated Protein Kinase) pathways and Calm-2, Gerk-2 and Pias-2 genes (Calcium signaling pathways) were significantly (P<0.05) higher expressed in the positive control group as compared to negative and all the treatment groups. While as, the total antioxidant capacity and NFR-1, Keap-1 and Nef-212 were significantly (P<0.05) down expressed in positive control group as compared to all the treatment groups. Histopathological study revealed that disruption of intestinal mucosa and immune infiltration in positive control group while, restoration and regeneration of intestinal parenchyma was observed in all the treatment groups. Overall study results concluded that monolaurin, monolaurin with butyric acid, and propionic acid can develop innovative customized remedies against DSS-induced acute colitis.

Cross-anisotropic stiffness characteristics of a compacted lateritic clay from very small to large strains

Lateritic clay is widely distributed in tropical and subtropic regions, with distinct engineering properties from other clays. Its stiffness properties, which are often anisotropic and crucial for analysing the serviceability limit state of earthen structures, have not been well understood. This study investigated the cross-anisotropic stiffness of compacted lateritic clay through comprehensive isotropic compression and consolidated drained and undrained shear tests. Both vertically and horizontally cut specimens were tested using triaxial apparatus equipped with bender elements and local strain measurements. The results show that compared with other clays, the lateritic clay shows a weaker dependency of shear modulus to confining pressure, a higher shear modulus at the same confining pressure, and a higher degradation rate of stiffness with strain. The lateritic clay behaves like granular material due to its large-size aggregated microstructure and 42% sand content. The widely used correlations between stiffness parameters and plasticity index seem unsuitable for it. Furthermore, the elastic shear modulus in the vertical direction is slightly higher than that in the horizontal direction, and the anisotropy evolves during shearing. A complete set of cross-anisotropic stiffness parameters for both effective and total stress analysis were determined. They are useful for developing constitutive models and analysing earth structures' serviceability involving lateritic soils.

Analysis of simplified time of liquefaction triggering methods by laboratory tests, physical modelling and numerical analysis

The damage resulting from earthquakes can result from the combination of seismic excitation and/or due to a build-up of excess pore pressure in the soil (liquefaction). These two effects are related since the reduction of soil stiffness due to a decrease in effective stress, modifies the seismic response of the soil deposit. Therefore, the expected level and type of damage is dependent on the amount of seismic energy reaching the ground surface before liquefaction. The development and validation of simplified liquefaction assessment methods to provide reasonable estimates of the build-up of excess pore pressure is essential for improving estimates of the level of seismic demand (ground shaking and permanent ground deformation) that may be experienced by a building. This paper presents two methods, one based on equivalent cyclic stress loading, and another based on the cumulative strain energy, which are used to predict the evolution of the pore pressure build up throughout time. The centrifuge tests performed in ISMGEO (Italy) during the LIQUEFACT project (www.liquefact.eu) were used as a benchmark to evaluate the predictive performance of the methods. Additionally, a series of one dimensional soil column effective stress and total stress analyses and single soil element simulations were run. Available laboratory tests were used to calibrate the parameters of the simplified methods, as well as input parameters for the numerical simulations. The results showed that both simplified methods had considerable bias. A direct comparison of the effective stress analyses, a set of effective stress analyses with limited drainage, and the centrifuge results, highlighted that the centrifuge experiments exhibited significant pore water flow that was not captured in the simplified models. Comparisons between the irregular loading in the one dimensional analyses compared to the uniform loading in the element tests highlighted shortfalls in the conversion from irregular to equivalent uniform loading. Comparisons between stress demands from total stress, effective stress and the simplified methods illustrated the limitations of relying on the total stress acceleration to estimate demands on a soil in a liquefying deposit.

A Numerical Study of Ground Displacement and Stress Conditions of Small and Medium Circular Diaphragm Wall during Excavation

In the present study, a dimensional total‐stress elasto‐plastic FEM analysis was conducted, which was based on the Mohr‐Coulomb constitutive model. The model was combined with a practical engineering case in order to investigate ground displacements and stress conditions during the installations of a medium‐sized and a small‐sized circular diaphragm wall, as well as the subsequent soil excavations within the walls. The distribution characteristics of the lateral radial displacements and stress conditions in the ground following the wall installations and excavations within the walls were investigated. Also, two different excavation methods, as well as three different soil depths for the walls, were considered. The distributions of the internal forces along the depth directions of the radial sections of the walls were also analyzed in this study. The analysis results showed that the slotting order had made the model nonaxisymmetric, which had further influenced the distribution characteristics of radial stress and displacements. It was found that the distributions of the horizontal radial displacements, along with the stress levels of the soil behind the walls, were only minimally affected by the excavations of the soil in the shaft. The internal force distribution of the wall radial section caused by the direct excavation method and the reverse excavation method is very small, that is, the wall bending moment generated by the reverse excavation process is larger, and the most obvious near the rock‐socketed depth. The distribution pattern of the bending moment depth corresponding to different excavation construction methods is similar. Furthermore, the soil penetration depths of the walls were determined to have had little influence on the internal force distributions of the radial sections of the walls above the foundation pit. However, there was a greater influence observed on the internal force distributions of the radial sections of the walls below the foundation pit.

Creep Behavior of Saturated Clay in Triaxial Test and a Hyperbolic Model

As one of the basic mechanical properties of soil, the creep property of a given type soil is related to stress path, and stress level. In this paper, triaxial shear creep tests under different deviatoric stress levels were performed on both intact sample and the reconstituted sample of clay taken from Hangzhou, China. Based on the Boltzmann linear superposition principle, the creep curves of the clay sample under different levels of deviatoric stress were obtained, and the creep characteristics of the intact sample and the reconstituted sample were compared in both total stress creep analysis and effective stress creep analysis. Furthermore, the creep curves were fitted using a hyperbolic creep model. The results show that (1) under the same stress level, the creep of intact sample evolves more than that of reconstituted sample; (2) the hyperbolic creep model is suited to describe the creep characteristics of intact and reconstituted clay, and the model parameters A s and B s can be linearly correlated to the stress level D r ; (3) for the application of the hyperbolic model, the total stress analysis works better, and the model parameters A s and B s can be determined by a linear relationship with Dr.

Simplified kinematic hardening plasticity framework for constitutive modelling of soils

A simplified kinematic hardening plasticity framework for the constitutive modelling of soils is presented. In contrast to conventional kinematic hardening plasticity, the yield surfaces do not enter explicitly into the governing equations but are used only for the purpose of computing an effective hardening modulus. This leads to models reminiscent of conventional nonlinear elastic/perfectly plastic models, thus facilitating an efficient numerical implementation. The framework is detailed both with respect to total and effective stress analysis. Its capabilities are illustrated by the development of a simple model for undrained total stress analysis of clays.

Nonlinearity evaluation considering the uncertainty of S-wave velocity based on total stress analyses and diffuse field assumption: the Mw 9.1 great Tohoku Taiheiyo-Oki earthquake at 05:46 UTC on 11 March 2011

In this study, the inversion modeling method variability of S-wave velocity structure results by inverting/forward-modeling waveforms and HVSR curves is investigated. For this purpose, eight KiK-net seismic stations using 636 foreshocks, mainshock of the 2011 Tohoku earthquake, and 4983 aftershocks obtained from KiK-net are used. The most reliable and representative inverted S-wave velocity structures are based on close fitting of the theoretical to the observed data of waveforms and HVSR curves. The inverted S-wave velocity structures derived from the total stress analyses are showing high degrees of similarity and consistency using both EW and NS components and evidenced by the isotropic HVSRs directionality related to the linear and nonlinear site effects. Conversely, stiffness variations due to nonlinearity, inferred from inverted S-wave velocity structures derived from the diffuse field assumption, significantly correspond with stiffness variations evaluated from the observed fundamental resonance frequencies. The corresponding percent of reduction and recovery reflect low variability in S-wave velocities that result from inversion modeling based on diffuse field assumption. Qualitatively, the presence of the stiffness degradation process due to linear and nonlinear site responses could be obviously detected using both inversion modeling methods based on total stress analyses and diffuse field assumption. Quantitatively, the precision of the nonlinearity evaluation is questionable due to significant uncertainties in the inverted S-wave velocity structures inferred from both inversion modeling methods. These uncertainties are strongly dependent on the theory of each inversion modeling method. The use of complementary methods with more prior information is suggested to resolve the nonuniqueness of the inverted S-wave velocities and hence overconfidence in the precision of the nonlinearity evaluation.

Constant water content direct shear testing of compacted residual soils

Mechanical behavior of residual soils are studied by performing constant water content direct shear tests on reconstituted specimens using total stress analysis. The testing program involves initial degree of saturation (Sr) and applied normal stress as the control parameters. For three different soil samples, a total of 55 direct shear tests are conducted at Sr = 60%, 80%, and saturated conditions, in the normal stress range of 15–60 kPa. The results showed that shear strength increases with decreasing Sr and the relationship between shear strength and Sr is nonlinear. More dilative response is observed with decreasing Sr and decreasing applied normal stress. Maximum dilatancy and Sr relationship is nonlinear. At large displacements, samples prepared at different Sr levels showed similar ultimate shear resistances under similar applied normal stresses. It is concluded that Sr and applied normal stress dramatically influence the mechanical behavior of compacted residual soils studied.

The in vitro cytotoxic, genotoxic, and oxidative damage potentials of the oral artificial sweetener aspartame on cultured human blood cells

Background/aimAspartame (APM, L-aspartyl-L-phenylalanine methylester) is a low-calorie, nonsaccharide artificial sweetener widely used in foods and beverages. When metabolized by the body, APM is broken down into aspartic acid, phenylalanine amino acids, and a third substance, methanol. Since the amino acid phenylalanine serves as a neurotransmitter building block affecting the brain, and methanol is converted into toxic formaldehyde, APM has deleterious effects on the body and brain. Thus, its safety and, toxicity have been the subjects of concern ever since it was first discovered. Although many studies have been performed on it, due to the presence of conflicting data in the literature, there are still numerous question marks concerning APM. Therefore, the safety of aspartame was tested using in vitro methods.Materials and methodsWe aimed to evaluate the in vitro cytotoxic effects by using 3-(4,5-dimetylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase release tests, genotoxic damage potential by using chromosome aberration (CA) assay, and antioxidant/oxidant activity by using total antioxidant capacity (TAC) and total oxidative stress (TOS) analysis in primary human whole blood cell cultures.ResultsThe results of the MTT test showed that APM led to significant decreases in cell viability in a clear concentration-dependent manner. Moreover, an increase in CA frequency was found in the cells treated with APM. However, APM treatments did not cause any significant changes in TAC and TOS levels in whole blood cultures.ConclusionOverall, the obtained results showed that APM had genotoxicity potential and a concentration-dependent cytotoxic activity in human blood cells.

Prediction of time of liquefaction using kinetic and strain energy

The time of liquefaction triggering during a strong ground motion can have a large influence on the expected level of foundation and superstructure damage. To enable simple, yet accurate estimates of the triggering time, the build-up of pore pressure needs to be understood in terms of cumulative measures of ground motion intensity. This paper develops a theoretical framework and simple procedure to predict the build-up of excess pore pressure based on the principles of conservation of energy. The liquefaction resistance is first quantified in terms of cumulative absolute change in strain energy, which is shown through the evaluation of experimental cyclic simple shear tests to be insensitive to loading amplitude. A ground motion intensity measure is presented that uniquely calculates the cumulative absolute change in kinetic energy. This intensity measure is then used to provide an exact analytical solution for the cumulative absolute change in strain energy at any depth in a homogenous linear elastic soil deposit using the novel, nodal surface energy spectrum (NSES). A simple reduction to the NSES is proposed for viscous and nonlinear soil deposits, as well as a correction for changes in stiffness between layers of soil. The estimation of strain energy and build-up of pore pressure using the simple NSES method was applied to 500 randomly generated soil deposits using a range of different ground motions and validated against nonlinear total stress and nonlinear effective stress time-history analyses, with the NSES method providing a high level of accuracy. The proposed spectrum based solution provides an efficient and physically consistent procedure for the prediction of excess pore pressure build-up.

Determination of slurry density required for stability of slurry-supported trenches excavated in partially submerged soils

Stability of slurry-supported trenches is investigated in this study, with a discretization-based kinematic analysis procedure. Such a procedure retains the merits of discretization technique (discretizing the problem of interest into infinitesimal elements for the ease of considering complicated scenarios) and upper-bound analysis (deriving a rigorous upper bound solution at limit state with a sophisticated procedure). Semi-analytical solutions are derived for the upper-bound formulations of safety factor and the slurry density required for trench stability, based on the work rate balance equation. Conventional upper-bound analysis yields a closed-form solution when considering simple problems. To encompass more scenarios, drained effective stress and undrained total stress analyses are performed. Two examples are given to investigate the effect of slurry height, pore water pressure, soil strength and excavation process on trench stability, in normally consolidated and layered soil strata.

Application of the Hilbert–Huang transform to identify the dynamic characteristics of a caisson foundation during liquefaction

This paper presents the application of a Hilbert–Huang transform data processing technique in a dynamic response analysis to identify the dynamic characteristics of a caisson foundation during liquefaction. The degradation of structural modal frequencies during liquefaction under strong earthquakes directly related to a reduction in the stiffness of the soil-foundation structure due to the loss of strength, and the nonlinearity of the liquefied soil layer always occur in a short time. Thus, the short-duration variation of frequencies provided a good indicator for the occurrence of the liquefaction and geometric distortion of a soil foundation system during strong earthquakes and was a very important step in the structural health monitoring work of foundation structures. This study shows that the proposed approach was effective in identifying the instantaneous downshift of frequency of caisson foundation system during liquefaction. This study was based on the measured acceleration response data of a test foundation model from a 1-G shaking table test. Additionally, 2D numerical modeling using a total stress analysis stipulated in the highway bridge specification (JRA 2002), an equivalent linear method in the liquefaction calculation of foundation, was conducted to evaluate the consistency with vibration testing.

Total Stress Analysis of Soft Clay Ground Response in Centrifuge Models

This paper presents one-dimensional ground response simulations of centrifuge models involving soft clay deposits subjected to ground motions of varying intensity. Total stress ground response simulations were performed using equivalent-linear (EL) and nonlinear (NL) methods. Shear strains higher than 10% were mobilized during large ground motions; therefore, undrained shear strength of the clay is an important parameter for the simulations. Testing shows that the San Francisco Bay Mud materials used in centrifuge modeling have monotonic shear strengths that increase by 13% per log cycle of shear strain rate. A comparison of simulation results to observations reveals the importance of incorporating shear strength into the development of stress-strain backbone curves, with appropriate consideration of rate adjustments to shear strength and stiffness. NL ground response simulations provide a good match to observed pseudospectral accelerations only when rate-adjusted shear strengths are properly accounted for; otherwise, the NL simulations have significant underprediction bias at oscillator periods less than the soil column period. EL modeling, even with the incorporation of shear strength, leads to unrealistic spectral shapes and overprediction at short spectral periods for tests involving large-strain site response.

2-D P-SV and SH spectral element modelling of seismic wave propagation in non-linear media with pore-pressure effects

SUMMARYIt has long been recognized that the effects of superficial geological layers, or site effects, can play a major role on the seismic ground motion at the free surface. In this study, we compute wave propagation in a 2-D asymmetrical basin considering both soil non-linearity and pore-pressure effects. Equations of elastodynamics of wave propagation are solved using the spectral element method (SEM). The geometry of the basin gives rise to basin-edge generated waves, that are different for in-plane (P-SV) and out-of-plane (SH) wave propagation and resulting in different non-linear response. Moreover, the excess-pore pressure development in superficial liquefiable layers (effective stress analysis) brings larger deformation and loss of strength than the analysis without pore-pressure effects (total stress analysis). The coupling of vertically propagating waves and the waves specifically generated in 1-D model leads to waves whose amplitude and duration are higher than the 1-D case. This multidimensional effect increases material non-linearity. Such complex wavefield provokes larger deformation and higher pore-pressure rise that cannot be predicted by 1-D modelling. Therefore, our paper suggests the use of multidimensional modelling while studying seismic wave propagation in both linear and non-linear complex media.

A 3D RITSS approach for total stress and coupled-flow large deformation problems using ABAQUS

A large deformation finite element (LDFE) method is implemented in a commercially available finite element software in three dimensions using a re-meshing and interpolation technique. The method allows fully coupled pore fluid effective stress analysis as well as decoupled total stress analysis to be performed. The method is described step by step following its application to offshore pipeline penetration analysis in full 3D. The results indicate versatility of the approach, showing reasonable agreement with existing solutions.