An integrated constitutive model has been developed for rock-like materials, incorporating confinement-sensitive damage and bi-mechanism plasticity. The model aims to improve the capability of the conventional damage model in depicting the strengthening and brittle-to-ductile transitions that occur under both active and passive confinement conditions. A thermodynamic analysis of energy transformation and dissipation, considering both damage and plasticity, underpins the model's development. The model, rooted in damage-plastic theory, has been divided into two sub-models: (1) Confinement-Sensitive Model: This sub-model addresses the strengthening and ductility enhancements due to active confinement stress. It effectively captures the mechanical responses of rock-like materials under various levels of active confining stresses. (2) Endochronic Dilatancy Model: Based on endochronic theory, a separate dilatancy strain model is proposed, which effectively facilitates the interplay between lateral dilatancy and the growth of passive confining stress. Both sub-models, as well as the integrated model, have undergone validation using experimental data, including uniaxial tests, cyclic loading tests, actively confined tests, and passively confined tests of rock-like materials. These validations confirm the model's accuracy and reliability in predicting the mechanical behavior of rock-like materials under complex loading conditions.

Cemented paste backfill (CPB) is a cemented void filling method gaining popularity over traditional hydraulic or rockfill methods. As mining depth increases, CPB-filled stopes are subjected to higher confining pressures. Due to the soil triaxial apparatus limitations, as the conventional method of triaxial testing on CPB, no confining pressures higher than 5 MPa can be applied to CPB over a range of curing time. This lack of data introduces uncertainty in predicting CPB behavior, potentially leading to an overestimation of the required strength. To address this, this study introduces a new testing method that allows for higher confinement beyond traditional limitations by modifying the Hoek triaxial cell to accommodate low-strength materials. This study then investigates the coupled influence of confining pressure and curing time (hydration) on CPB characteristics, specifically examining the impacts of different curing times and confining pressures on the mechanical and rheological properties of CPB. A total of 75 triaxial tests were conducted using 42 mm cylinder shape samples at five various curing times from 7 to 96 days, and applied at low and high confinement condition levels (0.5 to 30 MPa). The results reveal that hydration and confinement positively impact the CPB strength. The modified structured Cam-Clay model was selected to predict the behavior, and its yield surface was updated using the experimental results. The proposed yield model can be utilized to describe CPB material subjected to various curing and pressure conditions underground.

Record-breaking rainfall from February to July 2022 caused widespread damage to multiple road sections within the local government area of Shoalhaven NSW, Australia. With approximately 2059 mm of rainfall in the Kangaroo Valley area alone, which was more than double the rainfall what residents would normally experience, Shoalhaven City Council experienced the wettest year on record. As a direct result of this rainfall, multiple sections along several roads have been severely affected by slope instability resulting in road damage (including 98 landslips affecting 23 roads) restricting local residents from accessing even nearby towns. Accordingly, the local Council sought feasible options that could provide temporary yet safe access to local residents. Among a number of feasible options considered, the proposed use of geocell reinforcement was selected as the preferred short-term remediation option to temporarily restore road use and facilitate safe passage. This paper presents a case study of the performance of a landslide-impacted of Wattamolla Rd, Woodhill, NSW that was stabilised with geocell reinforcement. Limit equilibrium method and finite element analysis were undertaken to design the temporary access through the landslide affected of the road. This study showed that geocell can effectively be used as a temporary solution and has feasibility as a permanent solution, where roads are impacted by landslide. Results showed that by confining infill material, geocell minimised axial deformations and lateral spreading and provided a semi-rigid platform that improved the stability of the road embankment.

This study compares how geosynthetics behave under load, under strain, and over time when subjected to confined tensile tests in soil, employing two commonly used mechanisms in research. One test type simulates a reinforced layer, where tensile loads are indirectly applied to the geosynthetic via stresses transferred from the soil. In contrast, the other test applies tensile loads directly to the geosynthetic material using clamps while under soil confinement. The objective is to elucidate how these testing mechanisms might yield differing in-soil tensile characteristics for different geosynthetics. The study involved conducting load-strain-time tests on samples of nonwoven and woven geotextiles, as well as a geogrid, under varying sustained loads over a 120-h period within a sand clay soil providing soil confinement to geosynthetics at different surcharge levels. The results suggest that soil confinement plays a significant role in shaping the load-strain-time behavior of geosynthetics. Furthermore, it was noted that the impact of testing mechanisms on this behavior is contingent upon the type and stiffness of the geosynthetics, as well as their interaction with the confining soil. In general, in-soil tests in which tensile loads are mobilized by geosynthetics and transferred from the soil provide more confident results for better simulating operation conditions. Tests that directly apply tensile loads to the geosynthetic while maintaining stationary soil confinement may yield misleading results, especially for geosynthetics that have poor interaction with the soil.

Geocell has a confinement effect, limiting the deformation of soil and enhancing the strength of reinforced soil, and has a wide range of application prospects in traffic transportation subgrade engineering. To investigate the confinement effect of geocell on the mechanical characteristics of reinforced sand subgrade, this paper analyzes the macro-mechanical properties of reinforced sand subgrade using triaxial tests, investigates the micro- reinforcement mechanism employing discrete element method (DEM)-based simulations. The potential macro- -micro linkages are studied. The experimental results revealed that the volumetric strain of the geocellreinforced samples increased with the material's elastic modulus, exhibiting a shear shrinkage phenomenon. The deformation pattern of the reinforced samples presented segmental deformation, which differed from that of the unreinforced sand samples. The geocell enhanced the cohesion intercept of the sand samples while having a minimal impact on friction angle. Through the analysis of numerical simulation results, it was found that the geocell constrained the displacement of the soil particles, altering the shear band development trend of the sample and resulting in segmental deformation. The geocell facilitated the concentration of force chains, enhancing their stability and resulting in improving the strength in the macro. Additionally, it was observed that the confinement effect of the geocell significantly reduced the fabric and force anisotropy of the granular soil, promoting consistent vertical alignment of force chains. This, in turn, enhanced the vertical force transmission capacity of the sample, explaining the micro-mechanism by which the confinement effect of the geocell increases the peak shear strength of the samples.

Erosion in loess is a widespread phenomenon, as loess covers about 10% of the Earth's land surface. While erosion of loess soil has been intensively studied, the mechanisms controlling erosion in gullies and pipes in loess are poorly understood. Cohesion plays an important role in erosion in loess. Interactions between erosional processes and stabilizing mechanisms in loess are poorly understood. This study focuses on the interaction between air slaking and stabilization by confinement to improve leaching techniques for identifying cohesion sources in undisturbed loess from four sites in Czechia. The decrease in tensile strength of samples after leaching in distilled water, dithionate, HCl, and hydrogen peroxide was used to selectively remove cohesion sources such as Fe-Al oxides and hydroxides, carbonates, and organic matter. Experiments showed that confinement and overburden stress are important but neglected stabilizing mechanisms in loess. Leaching of unconfined loess samples gave misleading results because of ubiquitous air slaking. To reliably identify cohesion sources, samples confined in compacted sand were used. Leaching of confined samples showed that Fe-Al oxides and hydroxides are major sources of cohesion (60-90%), while carbonates and organic matter are of minor importance (0-30%). To avoid misleading results, examination of loess structure after leaching is critical to identify samples with damaged structure due to enhanced air slaking caused by bubbles generated during leaching. Air slaking is a powerful and rapid damage mechanism, but it occurs only in dry or semi-dry loess near the soil surface. In contrast, chemical weathering is able to remove cohesion sources in deeper parts of the loess profile. Reduction of tensile strength after leaching used to quantify cohesion sources. Stabilization of loess by confinement needed during leaching tests. Al-Fe oxides and hydroxides are major source of loess cohesion. image

Natural habitats of most living microorganisms are distinguished by a complex structure often formed by a porous medium such as soil. The dynamics and transport properties of motile microorganisms are strongly affected by crowded and locally anisotropic environments. Using Chlamydomonas reinhardtii as a model system, we explore the permeation of active colloids through a structured wall of obstacles by tracking microswimmers' trajectories and analyzing their statistical properties. Employing micro-labyrinths formed by cylindrical or elongated pillars, we demonstrate that the anisotropy of the pillar's form and orientation strongly affects the microswimmers' dynamics on different time scales. Furthermore, we discuss the kinetics of the microswimmer exchange between two compartments separated by an array of pillars. Quasi-2D PDMS-channels with arrays of pillars are used as a model system for a porous medium to study the effect of environmental anisotropy on the behavior of motile microalgae. The geometry of the surrounding gives rise to preferred swimming directions and affects the permeation probability. image

The small strain shear modulus is an important parameter in the assessment of soil dynamics problems. Studies on the small strain shear stiffness of volcanic ash remain rare probably because globally they cover just under 1% of the land surface. However, on a regional scale, this figure may be consequential as in the case of Japan, where about one third of its total land surface is covered by andosols. In this research, we aimed at understanding the influence of confinement time, a non-negligible parameter, contingent on the soil type, which needs to be accounted for when assessing the shear modulus. Bender element tests were conducted on allophanic volcanic ash, kuroboku soil sampled from the southern island of Kyushu in Japan. The allophanic ashes present all the characteristics of a non-textbook soil, notably high natural water content, high liquid and plastic limits and high void ratios. From the micrographic images, it was observed that the soil structure consisted of different types of porous particles (allophane, imogolite, volcanic glass and so on) at different internal spatial scales. Strong electrostatic bonding between the allophane particles means that in normal conditions the soil material exist as aggregates. The consequence is that the end of the consolidation stage is reached within a few minutes. Thus, the threshold demarcating the onset of the creep stage is different compared to sedimentary materials or other clayey soils. Based on the test results, empirical equations for predicting the time-dependent behaviour of the shear modulus were proposed.