Effective Stress Analysis Research Articles

Analysis of Liquefaction Susceptibility in the Nakdonggang Delta Region via Effective Stress Analysis

During the 2017 M5.4 Pohang earthquake, significant damage occurred because of liquefaction. However, South Korea is located in a stable continental region where earthquakes are rare, and the widely-used simplified liquefaction assessment methods have not been validated domestically. Hence, this study evaluates liquefaction at several locations in the Nakdonggang Delta region via effective stress analysis and compares the results with those of the simplified method of Boulanger and Idriss (2008). For the liquefaction assessment, a hypothetical earthquake scenario with a magnitude of 6.2 on the Dongnae Fault was assumed, and ground motions were generated via broadband hybrid ground motion simulation. The effective stress analysis was performed using OpenSeesPY and a multi-yield plasticity model. The results of the liquefaction assessment revealed significant differences between the two methods. The simplified method indicated that shallow sediments in the Nakdonggang Delta region were more susceptible to liquefaction, whereas the effective stress analysis indicated that loose, shallow sediments were more vulnerable. These results suggest that simplified liquefaction assessment methods must be carefully validated for application in South Korea. Future studies will need to accurately reflect dynamic soil properties based on experimental data to help validate effective stress analysis methods and assess the applicability of simplified methods for practical application in South Korea.

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.

Effects of Spatial Variation in Relative Density on Seismic Behavior of Saturated Sandy Ground

Proper consideration of variations in soil properties and their effects is necessary to enhance the seismic safety of structures. In this study, the effect of spatial variations in the cyclic resistance ratio on seismic ground behavior was investigated. Initially, dynamic centrifuge model tests were conducted on sandy ground featuring a 20% mixture of weak zones with low relative density and on homogeneous sandy ground with no mixture of weak zones. Subsequently, an effective stress analysis was performed by modeling the distribution of weak zones in the centrifuge model tests. Finally, after confirming the validity of the parameter settings, several analytical models with different weak-zone distributions were generated and numerically analyzed using random field theory. The results indicate that a local mixing of approximately 20% weak zones has only a limited effect on overall ground behavior. However, differences were observed in the rate of increase and dissipation of the excess pore water pressure ratio and in the residual horizontal displacement.

Optimal intensity measure for seismic performance assessment of shield tunnels in liquefiable and non-liquefiable soils

Relating the ground motion intensity measure (IM) and the structural engineering demand parameter is a crucial step in the performance-based earthquake engineering framework. This study investigates the selection of IM for development of probabilistic seismic demand model of urban shield tunnels subjected to earthquake ground motions in liquefiable and non-liquefiable soils. Nonlinear dynamic effective stress analyses are conducted to develop a database of the intensity measures and structural seismic responses exposed to ground shaking and soil liquefaction. Two advanced soil constitutive models (i.e., Pressure DependMultiYield03 and PressureIndependMultiYield for liquefiable and non-liquefiable soils, respectively) are employed to capture the nonlinear behavior. A suite of 23ground motion intensity measures is selected and assessed based on the evaluation criteria of correlation, efficiency, practicality and proficiency. Eventually, the multi-level fuzzy comprehensive evaluation method is employed to comprehensively consider the four evaluation criteria and establish the optimal ground motion IM suitable for probabilistic seismic demand analysis of shield tunnel structures. The obtained results show that the sustained maximum acceleration is the optimal IM for evaluating the structural seismic response, followed by the peak ground acceleration in both liquefiable and non-liquefiable soils. Peak pseudo velocity spectrum, displacement square integral and Housner spectral intensity are found to be not suitable for the probabilistic seismic demand analysis of shield tunnel structures.

Seismic performance of sheet pile walls in liquefiable soil using centrifuge tests and an assessment of nonlinear effective stress analysis using PM4Sand

Past earthquakes have revealed that damage to sheet-pile walls under saturated conditions is closely linked to excess pore water pressure buildup in the surrounding soil. Nonlinear effective stress analysis (ESA) is commonly employed to assess the seismic performance of sheet-pile walls in liquefiable soils, incorporating constitutive models for liquefaction simulation. However, ESA results are sensitive to uncertainties in input parameters, model calibration, and modeling techniques. Dynamic centrifuge tests conducted in the Liquefaction Experiments and Analysis Project (LEAP) offer valuable insights into important response mechanisms and validate ESA. Seven centrifuge tests on a cantilevered sheet-pile wall model showed that liquefaction did not occur in the backfill near the wall due to net seaward wall displacement but did occur farther away. In addition, the mechanism of wall displacement was mainly due to the shear deformation of the softened backfill, with the displacement magnitude depending on the relative density of soil, peak ground acceleration of base motion, and wall displacement during gravity loading. Nonlinear ESA was performed for three centrifuge tests using FLAC2D and the PM4Sand constitutive model for soil. Gravity analysis captured static wall displacement and initial stress distribution in the soil. Two calibrations of the PM4Sand model were pursued at the element level: C1 calibration for liquefaction strength and C2 calibration for liquefaction strength and the post-liquefaction shear strain accumulation rate. System-level simulations showed similar liquefaction behavior as observed in the tests for both calibrations. However, the C2 calibration provided closer predictions of wall displacements, while the C1 calibration (default for PM4Sand) resulted in larger and more conservative displacements. Overall, the PM4Sand model performed well with minimal calibration, making it suitable for nonlinear ESA of sheet-pile walls.

Numerical analysis of stress and distortion in bulk deposited structures of Inconel 625 alloy: Influence of deposition strategies

This study explores the numerical analysis of effective stress and distortion (dimensional variations) in bulk deposited structures of Inconel 625 alloy with seven different deposition strategies using wire arc additive manufacturing (WAAM) process. Due to the challenges in detecting in-situ stress changes during bulk deposition, numerical analysis is employed to approximate stress distribution. The goal is to investigate stress and distortion (dimensional variations) in the build direction (BD), longitudinal and transverse directions, and understand their impact on anisotropy and asymmetry. The findings reveal distinct patterns in effective stress, with initial decrease in bottom, followed by a gradual increase at the middle and rapid increase thereafter, regardless of deposition strategies. Parallel and contour deposition strategies exhibit lower effective stress compared to spiral strategies. Distortion (dimensional variations) along the BD increases with height, and parallel strategies result in higher distortion. The parallel strategies show increasing distortion from one edge to the other, while spiral and contour strategies lead to high distortion at the center. The parallel and contour deposition strategies exhibit higher compressive stress at the bottom and middle compared to the spiral strategies. Anisotropy analysis indicates higher stress anisotropy in parallel and contour patterns, but lower distortion anisotropy compared to spiral patterns. Empirical equations are developed to understand the relationship between stress, distortion (dimensional variations) and hardness. The study suggests that higher effective stress can adversely affect material yielding behavior. This study undertakes a comparison between FEA and analytical model which reveals a close alignment in the residual stress distributions in the build direction.

STATE-OF-THE-ART APPLICATION OF THE LOG-PILING METHOD IN THE ROLE OF SHALLOW GROUND IMPROVEMENT FOR LIQUEFACTION MITIGATION

<p>This research paper focuses on evaluating the log piling technique as a sustainable, cost-effective, and environmentally friendly solution for reducing soil liquefaction risks during earthquakes. Although this method has been used extensively in Japan, mainly aiming for complete soil layer penetration, its economic viability is questionable in cases requiring very deep soil improvements. The study highlights that shallow ground improvement can notably enhance the seismic behavior of the soil-improvement-structure system, as evidenced by the reduced total and penetration settlements caused by liquefaction. The paper presents a methodology for determining the optimal dimensions of the modified ground zone using both small and medium-scale 1-g shaking table tests. </p> <p>The small-scale tests involve a detailed parametric study, examining variables like improvement width, pile spacing, and the depth-to-thickness ratio of the improved layer. Medium-scale tests, on the other hand, are geared towards identifying the minimum effective pile length. This approach provides a practical guideline for engineers to implement log piling for small residential buildings. Additionally, the paper utilizes finite element method (FEM) effective stress analysis, incorporating a PLAXIS 2D-based constitutive model (PM4Sand) calibrated with laboratory undrained cyclic torsional tests. This model accounts for the changes in effective stress during seismic activities. Finally, the study correlates its numerical findings with the results from the 1-g shaking table experiments, offering a well-rounded perspective on the effectiveness of log piling in mitigating liquefaction risks during seismic events</p> <p> </p>

Large deformation analysis of spudcan settlement during operation

Jack-up rigs have been utilized to support booster stations in wind farms or to provide accommodation in oil and gas developments. In these scenarios, the dissipation of excess pore pressures and subsequent spudcan settlement during operation phase are of concern. However, predicting the spudcan settlement in naturally structured soil remains challenging. A large deformation finite element method, within the framework of effective stress analysis, has been developed to investigate the penetration and subsequent settlement of the spudcan footing. The inherent structure of cohesive soil and its degradation caused by spudcan penetration are described using the Structured Cam-Clay model. The large deformation approach is validated by comparisons with existing centrifuge tests. Parametric studies are then conducted with various operational loads and installation depths of spudcans. A backbone curve is provided, to estimate the history of spudcan settlement in kaolin with inherent structure. The distribution of excess pore pressures around the spudcan under different operation period is explored as well. A normalised dissipation curve at the largest cross-section of the spudcan during the operation phase is presented.

Effective Stress Analyses to Assess the Stability of Progressively Raised Upstream Dikes for Tailings Impoundments with Waste Rock Inclusions

Effective Stress Analyses to Assess the Stability of Progressively Raised Upstream Dikes for Tailings Impoundments with Waste Rock Inclusions

Bidirectional static loading tests on barrette piles. A case history from Ho Chi Minh City, Vietnam

Bidirectional static loading tests were conducted on two strain-gage instrumented barrettes installed to 72 m depth in Ho Chi Minh City, Vietnam. The barrettes were to support a 16-storey building with 5 basements. The soil profile comprised layers of medium coarse to fine sand, medium clay, firm to stiff clayey soil, and dense sandy silt. The region is experiencing an ongoing land subsidence affecting the upper about 40 m of soil and, on average in the city, the ground surface is currently settling 16 mm/year. The test records were processed by means of effective stress analysis to provide the axial pile force distribution, load transfer functions, and equivalent head-down load–movement curve. The analysis was then used to obtain the equivalent pile-head load–movement response adjusted to the planned 22 m deep basement excavation. Load transfer functions were back-calculated from the test records and indicate that the construction will show somewhat large load-transfer movement. However, because the equilibrium plane will be below the subsiding layers, below 40 m depth, downdrag is not expected to affect the building. The load response of the barrettes is compared to the results of a bidirectional (BD) loading test on a 1.8 m diameter bored pile at an adjacent project.

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.

Liquefaction vulnerability of Puketoka formation soil deposits using effective stress analysis

Liquefaction vulnerability of Puketoka formation soil deposits using effective stress analysis

An updated simplified pore water pressure model for loosely coupled effective stress analyses

An updated simplified pore water pressure model for loosely coupled effective stress analyses

Evaluation of seepage and seismic behavior in the earth dam based on effective stress analysis of unsaturated soil

Evaluation of seepage and seismic behavior in the earth dam based on effective stress analysis of unsaturated soil

Effective stress analysis of soil-structure systems in practice through strain space multiple mechanism model: validation through 15 case histories

Effective stress analysis of soil-structure systems in practice through strain space multiple mechanism model: validation through 15 case histories

Dynamic effective stress analysis of centrifuge tests on pile foundations and liquefaction countermeasure utilizing densification method

Dynamic effective stress analysis of centrifuge tests on pile foundations and liquefaction countermeasure utilizing densification method

Study on applicability of effective stress analysis considering large-strain liquefaction characteristics of sandy soils

Study on applicability of effective stress analysis considering large-strain liquefaction characteristics of sandy 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.

A general FSI framework for an effective stress analysis on composite wind turbine blades

The fluid-structure interaction (FSI) technique has been extensively used and developed in the past decades. Commonly, the reduced-order models are used in FSI analyses to assure the numerical robustness and efficiency. However, due to the increasing demand for higher numerical resolutions in modern wind turbine composite blade applications, intrinsic limitations of reduced-order models, such as their inability to account for complex aerodynamic flow interactions, multi-motion couplings, and sophisticated composite properties, have become the weaknesses in existing reduced-order FSI approaches. In this study, we propose a general FSI framework, which combines the advantages of high-fidelity Computational Fluid Dynamics (CFD) and robust Multi-Body Dynamics (MBD) methods, and detailed Finite Element Analysis (FEA) for analysing the detailed stress distributions on the composite structures. The results of predicted dynamics and the Von Mises stress on the composite blade structures under given operation condition are compared and reasonably agreed with the literature results, with a significant computational cost reduction by nearly 25% is achieved. The proposed FSI framework can be a general approach to investigate the multi-physical interactions where the composite structure specifications are involved, coupling with complex dynamic motions in three-dimensional space.

Investigation on strength and deformation properties of lateritic clay

Lateritic clay is often used as a construction material for roads in tropical and subtropical areas. However, these materials exhibit high compressibility, high rate of creep, and susceptibility to severe cracking due to swelling and shrinkage behavior. These traits are closely linked to its hydro-mechanical and deformation properties. In this study, firstly, a boundary line between the swelling and compression deformation zone was determined based on the results of wetting tests. This boundary line is crucial for identifying the specific deformation mechanisms observed in unsaturated lateritic clays under varying water conditions. Secondly, an analysis of the relationship between pore size distribution and the soil water retention curve (SWRC) were conducted. A simple bimodal SWRC model, using the normal distribution function, was proposed. Additionally, the strength characteristics of lateritic clay were investigated over a wide suction range. It was observed that the existing strength model significantly underestimated the tested values in the medium to high suction range. To address this, a segmented strength equation was introduced based on unsaturated effective stress analysis. This approach allows enables enhanced predictions of the strength properties of lateritic clay. Altogether, these findings have greatly contributed to a better understanding of the engineering properties of lateritic clay.