The effective stresses in saturated soils are crucial for geotechnical engineering, particularly in the ocean environment, but no current transducers can directly measure both vertical and lateral effective stresses. Thus, a novel effective stress transducer based on fiber Bragg grating (FBG) technology is developed to directly measure three-dimensional (3D) effective stress in saturated soils. The design of the transducer ensures that pore water pressures inside and outside the transducer are balanced, allowing the strain to solely reflect the effective stress sustained by the soil skeleton. Two FBG sensing elements of the 3D effective stress transducer are designed to measure the vertical and lateral effective stresses by sensing the strain in the thin plate and the sensing cylindrical shell through the porous disk, respectively. Experimental results indicate that the transducer accurately captures the evolution of effective stress under complex static loads and precisely tracks cyclic stress variations under cyclic loadings. Compared to traditional transducers, the lateral earth pressure coefficient derived from the measurement data of the new effective stress transducer shows advanced accuracy and stability. Moreover, the FBG-based transducer effectively monitors effective stress changes during the excavation, capturing soil stress variations and enabling precise excavation stability assessments. The novel 3D FBG-based effective stress transducer offers a vital method for directly measuring the vertical and lateral effective stresses of saturated soils.

The unified effective stress equation based on suction stress, a widely accepted method for calculating effective stress in unsaturated soils, provides a closed-form solution that enables the characterization of soils in both saturated and unsaturated states. The effect of desaturation on the water content of natural and treated soils was studied with respect to unconfined compressive strength (UCS) and indirect tensile strength (ITS). The soil's moisture-dependent behavior was characterized by the van Genuchten (Soil Sci Soc Am J 44:892-898, 1980. https://doi.org/10.2136/sssaj1980.03615995004400050002x) and Lu et al. (Water Resour Res, 2010. https://doi.org/10.1029/2009wr008646) models and implemented using the equation. Suction tests were conducted using the dew point and filter paper methods, alongside UCS and ITS tests, on silty clay soil and microsilica-treated soil with microsilica contents of 5%, 10%, and 15%. The equation was validated by comparing mean total stress (p) and mean effective stress (p ') to deviatoric stress (q) and analyzing the friction angle at different suction levels. It proved applicable to both natural and treated soils, with valid moisture content ranges of 4-17.5% and 6-20%, respectively. This study experimentally confirms the equation's effectiveness in characterizing the hydro-mechanical behavior of soils under varying moisture conditions.

The majority of existing effective stress-based constitutive models approach thermal effects through the temperature dependency of surface tension and its effects on the soil-water retention curve (SWRC) and effective stress. Experimental tests and theoretical studies, however, suggest that the temperature effect on surface tension alone is not sufficient to properly explain thermal-induced changes in the effective stress and SWRC. This study focuses on the temperature-dependent elastoplastic behavior of low plasticity unsaturated soils by developing a set of constitutive-level relations that incorporate temperature-dependent SWRC and effective stress models. These models account for the effect of temperature on the enthalpy, contact angle, and surface tension. The application of the presented constitutive relations was demonstrated and validated for low plasticity soils, specifically incorporating temperature effects into the hardening modulus, specific volume change, yield stress of the modified Cam-Clay model, and stress-strain relationships. The proposed relationships are incorporated in any effective stress-based constitutive model for modeling temperature dependency of elastoplastic response in low plasticity unsaturated soils. Employing these relationships can enhance the numerical simulation of low plasticity unsaturated soils under thermo-mechanical or other coupled processes involving temperature-dependent conditions.

The shear strength of compacted bentonite is crucial for preventing tilting and damage of the waste canisters in deep geological repositories (DGRs). The shear strength evolution along the confined wetting path also needs to be investigated, given the long saturation time of the bentonite buffer. This study conducted direct shear tests on densely compacted Gaomiaozi bentonite after suction control under confined conditions to determine its peak shear strength and strength parameters. Furthermore, the shear strength evolution along the confined wetting path was modeled on the basis of the effective stress principle. The results show that, for a given dry density, the peak shear strength at a given vertical pressure and the strength parameters exhibit an overall decrease along the confined wetting path. Moreover, the peak shear strength of the specimen that underwent confined wetting was considerably lower than that of the as-compacted specimen with the same total suction, indicating that the suction value and microstructure codetermine the peak shear strength of compacted Gaomiaozi bentonite. For this reason, the peak shear strength in the as-compacted state and the dual-porosity water retention curves established along the confined wetting path were used to model the shear strength evolution along the confined wetting path. The substitution equation for the effective stress parameter chi was selected on the basis of the experimental evidence. Finally, the model parameters were calibrated from the shear strength evolution at a given vertical pressure, and they reasonably reproduced the shear strength evolution under other vertical pressures. These findings can be helpful for the design and safe operation of DGRs under extreme geological conditions.

The effective stress principle is the fundamental theory of soil mechanics. The effective stress transmitted between particles dominates the mechanical properties of soil, such as strength, deformation, and drainage. However, there remains a paucity of research on the effective stress in the compression of nano-scale clay minerals. This study explored the application of the effective stress principle in the consolidation behavior of kaolinite through the Molecular Dynamics method. The calibration and correction for micro effective stress and pore water pressure were first proposed. Micro-effective stress is the stress on the mineral itself in the contact part of two particles, while micro-pore water pressure always represents that on the weakly bound and free water in the same part. The strongly bound water film between particles can indirectly transmit the micro-effective stress through the electrical double-layer repulsion. The calculation of micro stress has been corrected according to the derivation of macro theory, and the results obtained corresponded well with that in the macro experiment. Moreover, the evolution of effective stress was analyzed by observing the interparticle water film. The increase in effective stress during consolidation was mainly due to the compression of the strongly bound water and the drainage of weakly bound and free water.

The design of steel catenary risers (SCRs) is mainly affected by fatigue performance in the touchdown zone (TDZ), where the riser cyclically interacts with the seabed. This cyclic motion leads to seabed soil softening and remoulding. However, over an extended period of riser operations, the seabed soil undergoes a drainage because of small motion amplitudes of the floating vessel during calm weather or a limited contact with the seabed due to vessel relocation. This may cause recovery of the soil strength associated with excess pore pressure dissipation resulting in an extra fatigue damage accumulation in the TDZ. In the current study, a global SCR analysis has been conducted using a series of coded springs along the TDZ to model advanced SCR-seabed interactions. The instantaneous undrained shear strength of the soil is determined by using a recently developed effective stress framework. The effects of soil remolding and consolidation were integrated during both the dynamic motion of the SCR and intervening pause periods within the critical-state soil mechanics. The model updates the SCR-soil interaction spring at every time increment of dynamic analysis, calculating the cross- stress range while taking into account the overall configuration of the riser on the seabed. The study showed that the consolidation may result in an increased fatigue damage of about 23 %, which is currently neglected by the existing non-linear SCR-soil interaction models.

Loess is susceptible to loading effects such as significant changes in strength and volume variation caused by loading and wetting. In this study, considering the different connection states of pore water and gas in loess fabric, the gas phase closure case is incorporated into a unified form of the generalized effective stress framework, introducing a damage parameter considering the effects of closed pore gas. The loading effects of unsaturated loess under wide variations in saturation are described in a unified way, and the model performance is verified by corresponding stress and hydraulic path tests. The results indicated that the collapse response involves the initial void ratio of loess, and the coupled outwards motion of the loading-collapse (LC) yield surface under loading enhances its structural strength. Suction-enhanced yield stress requires a greater tensile stress to counteract its structural stability. The nucleation of bubbles at high saturation causes a decrease in yield stress. The loading effect exhibits a smaller collapse behavior when the influence of closed gas is considered, whereas the suction path does not cross the LC in the stress space under hydraulic action for the same parameters, which amplifies the influence of closed gas on loess deformation. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

At present, the widely used bishop stability analysis method does not consider the unsaturated effective stress, and the effective stress theory is unclear. To address these questions, this study initially explores a novel methodology for determining pore water pressure via the phreatic line. Subsequently, this study integrates the unified effective stress equation for both saturated and unsaturated soils, known for its clear physical significance, to propose an enhanced Bishop method(EBM) that accounts for effective stress in unsaturated soils. This EBM features a comprehensive theoretical framework, enabling direct stability analysis based on the phreatic line and demonstrating significant value for engineering applications. The reliability of the computational procedure of the EBM is validated through a saturated slope case study. Building upon this validation, the study further investigates the impact of incorporating unsaturated effective stress on slope stability. The results show that the deeper most dangerous sliding surface corresponds to an increase in the factor of safety(FOS) from 1.01% to 20.51% when considering the unsaturated effective stress. Overall, the integration of unsaturated effective stress exerts a positive influence on slope stability, underscoring the significance of this method for stability analysis and engineering design applications.

This paper presents a novel analytical framework to predict short-term pile setup in natural structure clay, considering the influence of soil destructuration in installation and consolidation. Based on the cavity expansion method, a simulation of pile installation has been conducted, with an analytical solution formulated for cavity expansion under undrained conditions to capture soil destructuration effectively. The flow rate in the unit cell is determined by Darcy's law based on the soil mass volume change, leading to the consolidation equation, which is obtained in a fully analytical form for excess pore water pressure (EPWP) dissipation. The utilization of the average compression curve aimed to depict a partially disturbed state due to the effects of installation. Based on the rewritten effective stress method (beta method), which involves the time-dependent factor while properly incorporating the effects of relaxation and thixotropy by introducing the requisite parameters. Finally, the analytical framework for predicting short-term pile setup is established and validated through a comprehensive pile field test conducted at St-Alban. The close correspondence between the analytical results and the empirical data indicates the effectiveness of the proposed framework in forecasting short-term pile behaviour with reasonable accuracy.

Seismic fragility analysis can quantitatively evaluate the seismic performance of structures from a probabilistic viewpoint and accurately characterize the relationship between the degree of structural damage and ground motion intensity. This study investigates the seismic fragility of shield tunnels in three different liquefiable and non-liquefiable soils. A plane-strain finite element model of the saturated soil and shield tunnel is established via the OpenSees computational platform employing the multi-yield surface elastoplastic PressureDependMultiYield and PressureIndependMultiYield models to simulate the constitutive behaviour of liquefiable and non-liquefiable soils. The developed model is utilized to conduct nonlinear dynamic effective stress time history analyses to generate the seismic fragility curves and surfaces based on the incremental dynamic analysis method. Meanwhile, appropriate scalar- and vector-valued intensity measures are identified based on their correlation, efficiency, practicality and proficiency. Compared with the fragility curves based on scalar-valued intensity measures, the fragility surfaces based on the vector-valued intensity measures can better describe the effect of ground motion characteristics on the structural seismic demand, and thus can more accurately assess the structural seismic performance. The seismic damage probabilities derived from the fragility curves and surfaces reveal that the seismic damage risk of the shield tunnel in sandwiched liquefiable soil deposit is higher than that of the tunnel structure located in entirely liquefiable or non-liquefiable soil profiles. This finding underscores the importance of carefully evaluating the seismic safety of shield tunnels situated in sandwiched liquefiable soil deposits.