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The Journal of Geotechnical and Geoenvironmental Engineering (JGGE) is a prestigious journal that recently celebrated its 150th volume. Published by ASCE and sponsored by ASCE's Geo-Institute (G-I), it stands out from other journals in the field. The journal has a strong international presence, with contributors and editorial board members from various countries. To mark this milestone, the journal made 10 important papers available for free and organized a special session at a conference. Over the years, the journal's name has changed to reflect the expanding focus on environmental considerations in geotechnical engineering. It has published groundbreaking research in areas such as soil mechanics, geotechnical earthquake engineering, geoenvironmental engineering, and ground engineering. The field of geotechnical engineering is adapting to address global challenges like climate change and the shift to low-carbon energy. The journal maintains its commitment to the peer review process and remains a valuable resource for researchers, practitioners, and students worldwide. [Extracted from the article]

Although non-isothermal tests are important for many applications in geotechnical engineering, there is no standard for conducting such tests and interpreting the resulting data. This paper describes the development of a temperature-controlled triaxial apparatus, focussing on its thermal performance, and discusses relevant protocols to perform and interpret hydraulic conductivity tests on granular materials at different temperatures. With the aid of thermal cameras, hot spots on the surface of the equipment and instruments were identified. Subsequent modifications to minimise and mitigate heat reaching volume gauges and pore water pressure transducers were introduced. After modifications to reduce the system’s intrinsic head losses, the thermal expansion of the system proved to be significant and needed to be accounted for avoiding overestimation of thermally-induced mechanical strains. The addition of a new probe at the centre of the specimen allowed the characterisation of the temperature field within the system and specimen, as well as assisting with the identification of thermal equilibrium. Significant drops in temperature were flagged by this probe, though these proved to be unimportant in terms of hydraulic conductivity. The use of the average temperature for each pressure step is advised when a specimen probe is available. Alternatively, the use of target temperatures can be chosen, leading to minor underestimations of the intrinsic permeability.

Geotechnical engineers need to predict the macroscopic behaviour of clays in terms of strength, stiffness, and permeability and the variation in these properties during deformation. Engineers also need to predict the influence of environmental variables (temperature, pressure, pore-fluid chemistry) on these engineering properties. Particle-based methods, which explicitly model individual clay platelets and their interactions, can help identify the fundamental mechanisms that govern the engineering behaviour. Virtual samples can be created, and simulations can consider application of mechanical loading or change in the environmental conditions to generate data on particle kinematics and interparticle interactions. Particlebased models can be used to simulate stress and strain paths that are not easy to reproduce in physical experiments. This approach to simulation also enables parametric studies to understand the sensitivity of the overall behaviour to various particle characteristics and the nature of the particle interactions. This contribution provides a review of the state-of-theart of existing particle-based models for clays, namely Discrete Element Method (DEM), Monte Carlo method (MC), and Molecular Dynamics (MD). The technical challenges, advantages, and disadvantages of each method for the simulation of clays are presented and discussed, together with the technical developments we would like to see over the next decade to realize the full potential of these modelling tools.

In principle, numerical simulations of boundary value problems that involve fluid-soil interaction should account for the evolution of permeability due to soil deformation. For many applications of interest in geotechnical engineering, an accurate assessment of the permeability is key to an accurate prediction of settlements and pore water pressure changes. Finite element models rely on laboratory or field testing to characterise permeability; however, these methods cannot easily evaluate anisotropy or moderate variations of permeability. Current testing tools have a limited accuracy and a rigid experimental set-up, and are usually restricted to consider one flow direction. In this study, the influence of shearing on the intrinsic permeability and the anisotropy of permeability in medium-loose liquefiable sands is investigated. The discrete element method (DEM) was used to simulate monotonic undrained and drained triaxial test simulations on model soils comprising spherical particles. The particle positions were recorded at discrete strain levels and the data were taken as input into finite volume method (FVM) simulations which were used to evaluate intrinsic permeability in selected subsamples. In the FVM simulations, permeability was evaluated in the three orthogonal directions. The results indicate that shear deformation induces an anisotropy in permeability, in both drained and undrained triaxial conditions and this anisotropy increases with axial strain. Specifically, the results show an increase in permeability in the direction of the major principal stress, whereas a reduction permeability is observed in the orthogonal plane. Undrained simulations exhibit a jump in vertical permeability around the liquefaction onset; this can be attributed to the sudden loss of particle contacts.

Characterisation of the permeability of soils is of practical importance and, for cohesionless or granular soils, it can be predicted from the void ratio and the particle size distribution (PSD). However, the effect of fabric anisotropy on the permeability is rarely discussed. Restricting consideration to granular (cohesionless) soil, this study combines a variety of numerical methods to investigate (1) how the anisotropy of the permeability evolves as the soil fabric anisotropy evolves in triaxial deformation and (2) establish a link between the anisotropy of the permeability and the fabric anisotropy. The Discrete Element Method (DEM) was employed to create linearly graded virtual samples of spheres (Cu of 1 to 2). Initially isotropic sphere packings were subjected to triaxial compression or triaxial extension up to 30% of absolute axial strain to induce an anisotropic fabric. Pore Network Models (PNMs) present a computationally efficient option for simulation of flow through the pore space. A PNM models fluid flow between pores (nodes) connected by pipes (edges) whose geometry is defined by the topology of the connected pores and the mass balance equation is solved at each pore. After demonstrating the accuracy of the PNM framework adopted here, this contribution presents data from PNM simulations that used the positions of individual particles in the sheared spherical packings as input data. The fabric and permeability anisotropies during triaxial shear deformation were compared at axial strain intervals of 1%. Detailed microscale analyses suggest that the anisotropy in the permeability can be attributed to an increase in the local conductance of fluid pipes in the direction of the major principal stress, which is related to the evolution of the pore topologies during the shear deformation.

It is now viable to use coarse-grained molecular dynamics (CGMD) to model interacting clay particles in simulations of soil mechanics element tests. In CGMD, particle interactions are described by the Gay-Berne (GB) potential, which can approximate the potential energy between clay particles as a function of their separation and relative orientations; however, a previous study identified a significant shortcoming of the GB potential, which is that it lacks a local maximum called the “energy barrier” that the true interaction possesses at very close range. In this study, we propose a modified GB potential which can capture the energy barrier at and we use this new potential function to simulate the clay mineral kaolinite under isotropic compression. Our simulations show that the energy barrier is a crucial ingredient required to reproduce the elastoplastic behaviour observed in laboratory tests upon unloading from an isotropic normally consolidated state. Our data show that the difference in mechanical behaviour between normally consolidated clay and overconsolidated clay can be explained by the fact that, during the initial loading, some pairs of interacting particles surmount the energy barrier so that they then experience a large attractive force. Effectively, these particles become bounded and do not separate when the stress applied to the sample is released. The response of overconsolidated clay to applied stress is stiffer than that of normally consolidated clay because a larger proportion of the clay particle interactions exist in this bonded state.

The ability to predict thermal-induced stresses in granular materials is of practical importance across a range of disciplines ranging from process engineering to geotechnical engineering. This study presents an analytical formula to predict thermal-induced stress increments in mono-disperse granular materials subject to an initial isotropic stress state. A complementary series of DEM simulations were carried out to explore the applicability of the proposed analytical formula. The comparative analysis showed that the proposed expression can accurately predict stress changes in packings where there are negligible particle displacements as a consequence of the thermal loading (e.g. regular packings and medium/dense random packings); however large errors were observed in loose samples with a random packing.

Objective: To analyze comparative treatment persistence for first‐line baricitinib (BARI) versus first‐line tumor necrosis factor inhibitor (TNFi) in patients with rheumatoid arthritis (RA) and for first‐line BARI initiated as monotherapy versus first‐line BARI initiated with at least one conventional synthetic disease‐modifying antirheumatic drug (csDMARD). Methods: Patients with RA who initiated BARI or TNFi as first‐line biologic or targeted synthetic DMARD from October 1, 2015, to September 30, 2021, were identified in the OPAL data set. Drug survival times to 6, 12, and 24 months were analyzed using restricted mean survival time (RMST). Multiple imputation and inverse probability of treatment weighting were used to address missing data and nonrandom treatment assignment. Results: A total of 545 patients initiated first‐line BARI, including 118 as monotherapy and 427 as csDMARD combination therapy. Three thousand five hundred patients initiated first‐line TNFi. There was no difference in drug survival to 6 or 12 months for BARI compared with TNFi; differences in RMST were 0.02 months (95% CI: −0.08 to 0.013; P = 0.65) and 0.31 months (95% CI: −0.02 to 0.63; P = 0.06), respectively. Patients in the BARI group had 1.00 month (95% CI: 0.14 to 1.86; P = 0.02) longer drug survival to 24 months. There was no difference in drug survival for BARI monotherapy compared with combination therapy, with differences in RMST to 6, 12, and 24 months of −0.19 months (95% CI: −0.50 to 0.12; P = 0.12), −0.35 months (95% CI: −1.17 to 0.42; P = 0.41), and −0.56 months (95% CI: −2.66 to 1.54; P = 0.60), respectively. Conclusion: In this comparative analysis, treatment persistence up to 24 months was significantly longer for first‐line BARI compared with TNFi, but the effect size of 1.00 month is not clinically meaningful. There was no difference in persistence for BARI monotherapy versus combination therapy. [ABSTRACT FROM AUTHOR]

The nature of the link between macro-scale yield and particle scale interactions is poorly understood. This contribution addresses this knowledge gap using discrete element method (DEM) triaxial test simulations performed with a modified version of the granular LAMMPS code, employing a simplified Hertz-Mindlin contact model. Each sample comprised monodisperse spheres and these samples were sheared from different initial density states. The positions of the yield surfaces were identified from the overall load:deformation behaviour, just as in a laboratory test. The overall sample responses observed in these DEM simulations confirmed that the size and positions of the sub-yield surfaces largely depend upon the sample density. The particle-scale parameters monitored included the coordination number, the second order fabric tensor and the proportion of sliding contacts (the sliding fraction). A correlation was established between the variation in coordination number with strain and stiffness degradation with strain. The sliding fraction data information showed that, in contrast to conventional understanding, the particles start to slide relative to each other even within the linear elastic zone

This study aims to develop a fundamental understanding of the role of fine particles on the small-strain stiffness of gap-graded granular soils. Stiffness was measured using cyclic triaxial probes, which give a measure of static stiffness, and dynamic wave propagation data, from which the dynamic stiffness can be measured. Assemblies of loosely packed spherical particles were considered. In the laboratory, local deformation transducers were used to measure the static stiffness, while the dynamic stiffness was calculated from stress wave velocities, measured using planar piezoelectric elements. To relate the particle-scale responses to the overall soil stiffness, complementary discrete element method (DEM) simulations were performed in which both static and dynamic stiffnesses were measured. Both the laboratory and the DEM data indicate that at low fines contents (< 30%) the stiffness decreases with increasing fines content. When the fines content increases from 30% to 35% there is a sharp increase in stiffness with increasing fines content; this is understood to mark the transition point at which the fines start to contribute significantly to the overall behaviour. Analyses of the frequency domain response of shear wave signals revealed that the lowpass frequency increases significantly at this transition point. This observation can be used to develop experimental interpretation protocols to assess to what extent fines are contributing to the overall soil stiffness.

The behaviour of gap graded soils comprising non-plastic fines (sand or silt) mixed with a coarser sand or gravel fraction has received attention from researchers interested in internal instability under seepage loading (a form of internal erosion) as well as researchers interested in load:deformation responses. Skempton and Brogan [1] postulated that resistance to seepage induced instability depends upon the proportion of the overall applied stress that is transmitted by the finer fraction. Shire et al. [2] explored Skempton and Brogan’s hypothesis using DEM simulations to look at the proportion of the applied stress transmitted by the finer fractions (α) in ideal isotropic samples. They showed that at low fines contents (FC< FC*) the average stress transmitted by the finer grains is less than the applied stress (αFC+ the fines play a key role in stress transmission (α>1); for FC*

Geotechnical engineers are well aware that the particle surface chemistry and the pore fluid composition can significantly influence the mechanical behaviour of clay. Reference is often made to the Derjaguin-Landau-Vervey-Overbeek (DLVO) theory, which enables the electrochemical interactions between charged particles to be estimated. Hitherto, the absence of an effective framework for particle-scale simulation of clay has inhibited a direct link between these electrochemical interactions and clay behaviour (e.g. load:deformation response) or fabric (i.e. the development of a disperse or flocculated fabric). Ebrahimi [1] demonstrated the viability of using molecular dynamics simulations where the clay grains are simulated as ellipsoidal particles whose interactions are described by an analytical expression called the Gay-Berne (GB) potential. While promising when compared to other approaches documented in the literature, Ebrahimi's work considered only a single clay mineralogy and did not explicitly account for the pore fluid composition. This paper considers the use of the Gay-Berne potential in particle-scale modelling of clay from a more general perspective. Calibration of the GB model parameters to predict kaolinite particle interactions reveals a lack of generality in Ebrahimi's approach. The Gay-Berne potential cannot simulate situations in which attractive and repulsive interactions co-exist, which lead to the classical “cardhouse” fabric, as is the case of kaolinite particles interacting via an acidic pore fluid.

This paper puts forward a perspective or opinion that we can demonstrate Darcy's law is valid at any scale where fluid can be modeled/analyzed as a continuum. Darcy's law describes the flow of a fluid through a porous medium by a linear relationship between the flow rate and the pore pressure gradient through the permeability tensor. We show that such a linear relationship can be established at any scale, so long as the permeability tensor is expressed as a function of adequate parameters that describe the pore space geometry, fluid properties, and physical phenomena. Analytical models at pore scale provide essential information on the key variables that permeability depends on under different flow regimes. Upscaling techniques based on the Lippman-Schwinger equation, pore network models, or Eshelby's homogenization theory make it possible to predict fluid flow beyond the pore scale. One of the key challenges to validate these techniques is to characterize microstructure and measure transport properties at multiple scales. Recent developments in imaging, multiscale modeling, and advanced computing offer new possibilities to address some of these challenges. [ABSTRACT FROM AUTHOR]