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ItemUnveiling air pollution-related health inequality in China’s food system(Georgia Institute of Technology, 2024-03) Zheng, Lianming ; Adalibieke, Wulahati ; Zhou, Feng ; He, Pan ; Chen, Yilin ; Guo, Peng ; He, Jinling ; Zhang, Yuanzheng ; Xu, Peng ; Wang, Chen ; Ye, Jianhuai ; Zhu, Lei ; Shen, Guofeng ; Fu, Tzung-May ; Yang, Xin ; Zhao, Shunliu ; Hakami, Amir ; Russell, Armistead G. ; Tao, Shu ; Meng, Jing ; Shen, HuizhongFood consumption contributes to the degradation of air quality in regions where food is produced, giving rise to an often-neglected form of environmental inequality, i.e., the contrast between the environmental health burden caused by the food consumption of a specific population and that they encounter as a consequence of food production activities. Herein, we explore this inequality within China’s food system, by linking air pollution–related health burden from the production side to the consumption side at high levels of spatial and sectorial granularity. Our findings reveal that low-income groups bear a 70% higher air pollution-related health burden from the food production than is caused by their food consumption, while high-income groups benefit from a 29% lower health burden relative to their food consumption. This discrepancy can be primarily attributed to the significant concentration of the low-income population residing in food production areas, thereby exposing them to higher emissions from agricultural activities. Our study indicates that comprehensive interventions targeting both production and consumption sides can effectively reduce health damages and concurrently mitigate associated inequalities, while singular interventions exhibit limited efficacy. This emphasizes the need for a combination of measures to establish a sustainable and equitable food system.
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ItemEffect of the intermediate principal stress on pre-peak damage propagation in hard rock under true triaxial compression( 2022) Wu, Zhuorui ; Xu, Tingting ; Arson, ChloéIt is of foremost importance to understand the mechanisms of damage propagation in rock under true triaxial stress. True triaxial compression tests reported in the literature do reflect the effect of the intermediate principal stress (σ2), but predictive models are still lacking. In this paper, an enhanced version of the Discrete Equivalent Wing Crack Damage (DEWCD) model initially proposed in (Jin and Arson, 2017) is calibrated and tested to bridge this gap. The original DEWCD model can predict most mechanical nonlinearities induced by damage but it cannot capture dilatancy effects accurately. To overcome this limitation, a dependence of the energy release rate on the first and third stress invariants is introduced in the damage potential. The enhanced DEWCD model depends on eight constitutive parameters. An automated calibration procedure is adopted to match pre-peak stress-strain curves obtained experimentally in (Feng et al., 2019) during true triaxial compression. The model successfully captures the differences in deformation and damage in the three principal directions of loading and accurately predicts that an increase of compression σ2 yields a decrease of the intermediate (tensile) deformation, a triggering of damage at a lower value of σ1 −σ2, as well as a decrease of cumulated damage in the direction of σ2 and an increase of cumulated damage in the direction of σ3 at the stress peak (pre-softening). During the true triaxial compression stage, a higher intermediate principal stress hinders dilatancy such that the volumetric strain at the peak of σ1 changes from dilation to shrinkage. The enhanced DEWCD model shows good performance in axis-symmetric compression and true triaxial compression, both for monotonic and cyclic loading. A comparison of three true triaxial stress paths at constant/variable mean stress/Lode angle suggests that: (i) the mean stress controls damage hardening and the sign of the volumetric strain rate at damage initiation, (ii) the second stress invariant is the primary control factor of the direction of the irreversible deviatoric strain rate during triaxial loading and of the sign of the total volumetric strain rate at failure; (iii) the Lode angle controls the direction of the total deviatoric strain rate.
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ItemA perspective on Darcy's law across the scales: from physical foundations to particulate mechanics( 2022) O’Sullivan, Catherine ; Arson, Chloé ; Coasne, BenoîtThis 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 permeablity 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, multi-scale modeling and advanced computing offer new possibilities to address some of these challenges.
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ItemAnisotropy and microcrack propagation induced by weathering, regional stresses and topographic stresses(American Geophysical Union., 2022) Xu, Tingting ; Shen, Xianda ; Reed, Miles ; West, Nicole ; Ferrier, Ken L. ; Arson, ChloéThis paper presents a new model for anisotropic damage in bedrock under the combined influences of biotite weathering, regional stresses, and topographic stresses. We used the homogenization theory to calculate the mechanical properties of a rock representative elementary volume made of a homogeneous matrix, biotite inclusions that expand as they weather, and ellipsoidal cracks of various orientations. With this model, we conducted a series of finite element simulations in bedrock under gently rolling topography with two contrasting spatial patterns in biotite weathering rate and a range of biotite orientations. In all simulations, damage is far more sensitive to biotite weathering than to topographic or regional stresses. The spatial gradient of damage follows that of the imposed biotite weathering rate at all times. The direction of micro-cracks tends to align with that of the biotite minerals. Relative to the topographic and regional stresses imparted by the boundary conditions of the model, the stress field after 1,000 years of biotite weathering exhibits higher magnitudes, wider shear stress zones at the feet of hills, more tensile vertical stress below the hilltops, and more compressive horizontal stress concentrated in the valleys. These behaviors are similar in simulations of slowing eroding topography and static topography. Over longer periods of time (500 kyr), the combined effects or weathering and erosion result in horizontal tensile stress under the hills and vertical tensile stress under and in the hills. These simulations illustrate how this model can help elucidate the influence of mineral weathering on Critical Zone evolution.
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ItemMicro-mechanical Modeling for Rate-Dependent Behavior of Salt Rock under Cyclic Loading( 2021) Shen, Xianda ; Ding, Jihui ; Arson, Chloé ; Chester, Judith S. ; Chester, Frederick M.The dependence of rock behavior to the deformation rate is still not well understood. In salt rock, the fundamental mechanisms that drive the accumulation of irreversible deformation, the reduction of stiffness and the development of hysteresis during cyclic loading are usually attributed to intracrystalline plasticity and diffusion. We hypothesize that at low pressure and low temperature, the rate-dependent behavior of salt rock is governed by water-assisted diffusion along grain boundaries. Accordingly, a chemo-mechanical homogenization framework is proposed, in which the Representative Elementary Volume (REV) is viewed as a homogeneous polycrystalline matrix that contains sliding grain-boundary cracks. The slip is related to the mass of salt ions that diffuse along the crack surface. The rate of diffusion is calculated by a pressure solution model. The relationship between fluid inclusion-scale and REV-scale stresses and strains is established by using the Mori-Tanaka homogenization scheme. The proposed rate-dependent homogenization model is calibrated against cyclic compression tests. It is noted from the model that a lower strain rate and a larger number of sliding cracks enhances stiffness reduction and hysteresis. Thinner sliding cracks (i.e. thinner brine films) promote stiffness reduction and accelerate stress redistributions in the crack inclusions. Higher roughness angles lead to an increased difference of normal stress along the different segments of the crack plane and to a reduced diffusion path, which both amplify the reduction of stiffness and the development of hysteresis. The larger the volume fraction of the crack inclusions, the larger the REV deformation and the larger the hysteresis. Results presented in this study shed light on the mechanical behavior of salt-rock that is pertinent to the design of geological storage facilities that undergo cyclic unloading, which could help optimize the energy production cycle with low carbon emissions.
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ItemDeformation and failure mechanisms of granular soil around pressurised shallow cavities( 2021) Patino-Ramirez, Fernando ; Ando, Edward ; Viggiani, Gioacchino ; Caicedo, Bernardo ; Arson, ChloéThe deformation patterns and failure mechanisms of pressurised cavities at shallow depth are of relevance to many geotechnical applications, including tunneling and horizontal directional drilling. In this paper, we present an experimental study of a reduced-scale pressurised cavity under geostatic stress, in order to measure the effect of cavity length, vertical stress and soil density on soil deformation and failure. x-ray computed tomography is used to acquire images of the system at key stages of the cavity inflation process. A closed shaped failure region developed around the cavities, beyond which, shear planes of elliptic paraboloid shape formed, extending from the bottom of the cavities all the way to the free surface. The plane strain assumption did not hold beyond the central portion of the longest cavity tested (L = 6D). The volumetric strain and porosity changes inside the shear bands showed significant dilation in dense specimens, but contraction in loose specimens. The average orientation and the thickness of the shear bands were in agreement with those found in the literature for passive arching mechanisms (anchoring). The orientation of the principal strains around the cavity follows catenary shapes, similar to those displayed in active trapdoor mechanisms.
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ItemTransportation networks inspired by leaf venation algorithms( 2020) Patino-Ramirez, Fernando ; Arson, ChloéBiological systems have adapted to environmental constraints and limited resource availability. In the present study, we evaluate the algorithm underlying leaf venation (LV) deployment using graph theory. We compare the traffic balance, travel and cost efficiency of simply-connected LV networks to those of the fan tree and of the spanning tree. We use a Pareto front to show that the total length of leaf venations is close to optimal. Then we apply the LV algorithm to design transportation networks in the city of Atlanta. Results show that leaf-inspired models can perform similarly or better than computer-intensive optimization algorithms in terms of network cost and service performance, which could facilitate the design of engineering transportation networks.
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ItemMicro-mechanical Modeling for Rate-Dependent Behavior of Salt Rock under Cyclic Loading(Georgia Institute of Technology, 2020) Shen, Xianda ; Ding, Jihui ; Arson, Chloé ; Chester, Judith S. ; Chester, Frederick M.The dependence of rock behavior on the deformation rate is still not well understood. In salt rock, the fundamental mechanisms that drive the accumulation of irreversible deformation, the reduction of stiffness and the development of hysteresis during cyclic loading are usually attributed to intracrystalline plasticity and diffusion. We hypothesize that at low pressure and low temperature, the rate-dependent behavior of salt rock is governed by water-assisted diffusion along grain boundaries. Accordingly, a chemo-mechanical homogenization framework is proposed, in which the Representative Elementary Volume (REV) is viewed as a homogeneous polycrystalline matrix that contains sliding grain-boundary cracks. The slip is related to the mass of salt ions that diffuse along the crack surface. The relationship between fluid inclusion-scale and REV-scale stresses and strains is established by using the Mori-Tanaka homogenization scheme. It is noted from the model that a lower strain rate and a larger number of sliding cracks enhance stiffness reduction and hysteresis. Thinner sliding cracks (i.e. thinner brine films) promote stiffness reduction and accelerate stress redistributions. The larger the volume fraction of the crack inclusions, the larger the REV deformation and the larger the hysteresis. Results presented in this study shed light on the mechanical behavior of salt-rock that is pertinent to the design of geological storage facilities that undergo cyclic unloading, which could help optimize the energy production cycle with low carbon emissions.
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ItemModeling root system growth around obstacles(Georgia Institute of Technology, 2020) Jin, Wencheng ; Aufrecht, Jayde ; Patino-Ramirez, Fernando ; Cabral, Heidy ; Arson, Chloé ; Retterer, ScottState-of-the-Art models of Root System Architecture (RSA) do not allow simulating root growth around rigid obstacles. Yet, the presence of obstacles can be highly disruptive to the root system. We grew wheat seedlings in sealed petri dishes without obstacle and in custom 3D-printed rhizoboxes containing obstacles. Time-lapse photography was used to reconstruct the wheat root morphology network. We used the reconstructed wheat root network without obstacle to calibrate an RSA model implemented in the R-SWMS software. The root network with obstacle allowed calibrating the parameters of a new function that models the influence of rigid obstacles on wheat root growth. Experimental results show that the presence of a rigid obstacle does not affect the growth rate of the wheat root axes, but that it does influence the root trajectory after the main axis has passed the obstacle. The growth recovery time, i.e. the time for the main root axis to recover its geotropism-driven growth, is proportional to the time during which the main axis grows along the obstacle. Qualitative and quantitative comparisons between experimental and numerical results show that the proposed model successfully simulates wheat RSA growth around obstacles. Our results suggest that wheat roots follow patterns that could inspire the design of adaptive engineering flow networks.
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ItemMechanisms of anisotropy in salt rock upon micro-crack propagation( 2020) Shen, Xianda ; Arson, Chloé ; Ding, Jihui ; Chester, Frederick M. ; Chester, Judith S.