Effects of Cemented Porous Media on Temporal Mixing Behavior of Conservative Solute Transport

Dou, Zhi; Zhang, Xueyi; Zhou, C.; Yang, Yun; Chen, Zhuang; Wang, Chenxi

doi:10.3390/w11061204

Cited by 8 publications

(8 citation statements)

References 37 publications

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“…Since the preferential flow path development in the flow field is the result of the complex fractured space, the presence of the preferential flow is related to the heterogeneity of the flow field. To quantify the shear-induced flow field where the preferential flow occurs, the coefficient of flow velocity variation, a global measure of the velocity spatial variability [27,42], was calculated for all sheared fractures:…”

Section: Resultsmentioning

confidence: 99%

“…However, it is still a challenge to directly measure fluid flow and solute transport processes within fractures with small apertures and rough surfaces. Benefiting from the development of computer computing power, numerical simulations that can provide pore-scale details are widely adopted to investigate fluid flow in fractures or porous media [10,[26][27][28][29].…”

Section: Introductionmentioning

confidence: 99%

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Influence of Shear Displacement on Fluid Flow and Solute Transport in a 3D Rough Fracture

et al. 2021

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Fractured rocks in the subsurface are ubiquitous, and the dynamics of mass transfer in fractured rocks plays an important role in understanding the problem in engineering geology and environmental geology. In this study, the influence of shear displacement on fluid flow and solute transport in a 3D rough fracture was investigated. A 3D self-affine rough fracture was generated using the modified successive random addition (SRA) technology, and three sheared fractures with different shear displacements were constructed based on the mechanistic model. A direct numerical model based on the Navier-Stokes equation and the advection-diffusion equation was developed to solve the fluid flow and the solute transport. The results showed that shear displacement had a significant influence not only on the fluid flow but also on the solute transport. A global measure of the spatial variability of the flow velocity showed that the heterogeneity became weaker with decreasing shear displacement. All measured BTCs deviated from the Gaussian profile and exhibited the typical anomalous behaviors, such as the long tail and the early arrival. Although the best-fitted results of the advection-dispersion equation (ADE) model and mobile-immobile model (MIM) were generally consistent with those of the BTCs, the MIM was more capable than the ADE model for characterizing the shear-induced anomalous behavior of the BTCs. It was found that the mass exchange process between the immobile and mobile domains was enhanced in the sheared fractures while the fraction of the advection-dominant mobile domain decreased as the shear displacement increased. Furthermore, the deviation of the Taylor dispersion coefficient from the fitted dispersion coefficient by the ADE model and MIM in the sheared fractures was confirmed due to the influence of shear displacement.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Influence of Shear Displacement on Fluid Flow and Solute Transport in a 3D Rough Fracture

et al. 2021

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“…The coefficient of flow velocity variation, a global measure of the velocity spatial variability [30,54], was calculated in PM0-3 to quantitatively evaluate the velocity heterogeneity in the flow fields:…”

Section: Resultsmentioning

confidence: 99%

“…In order to investigate the influence of grain size transition zone on fluid flow and solute transport through layered porous media, the 3D layered porous media were generated. The generation approach of layered porous media combines a deposition process [52,53] under the force of gravity and a random packing process [54]. A sedimentation algorithm was adopted to simulate the deposition of solid grains.…”

Section: Methodsmentioning

confidence: 99%

Influence of Grain Size Transition on Flow and Solute Transport through 3D Layered Porous Media

et al. 2021

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Soils and other geologic porous media often have contrasting grain size layers associated with a grain size transition zone between layers. However, this transition zone is generally simplified to a plane of zero thickness for modeling assumption, and its influence has always been neglected in previous studies. In this study, an approach combining a deposition process and a random packing process was developed to generate 3D porous media without and with consideration of the transition zone. The direct numerical models for solving the flow and concentration fields were implemented to investigate the influence of the grain size transition on flow and solute transport. Our results showed that although the transition zone occupied 13.6% of the entire layered porous medium, it had little influence on the distribution of flow velocity at the scale of the entire layered porous medium. However, the transition zone had a significant influence on the local flow field, which was associated with the increased spatial variability of velocity and the varied distribution of flow velocity. This varied local flow field could increase the solute residence time and delay the breakthrough time for solute transport. Although using both the advection-dispersion equation (ADE) and the mobile and immobile (MIM) models to fit the breakthrough curves (BTCs) for solute transport through layered porous media resulted in trivial errors, the ADE model failed to capture the influence induced by the local flow field, especially the influence of the transition zone. In contrast, the MIM model was shown to be able to capture the influence of the transition on solute transport. It was found that the mass transfer rate α, a parameter of the MIM model, was significantly improved by the presence of the transition zone, while it decreased as the transition zone fraction increased. Our study emphasized that the transition zone can vary the local flow field at the pore scale, while it has little influence on the hydraulic properties (e.g., hydraulic conductivity) of the macroscale flow field. However, the local flow field varied by the transition zone has a significant influence on solute transport.

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“…where u is the mean flow velocity in the porous media (m/s), R is the characteristic length, for cement-based material, and R is the average diameter of particles [47]. According to the code for mix design of hydraulic concrete (DL/T 5330-2015), the average diameters of two-grade roller-compacted concrete, three-grade compacted concrete, and regular concrete are 0.02 m, 0.04 m, and 0.02 m. is study takes the average diameter of grout curtain as 0.01 m. D e is the molecular diffusion, m 2 /s.…”

Section: Calcium Compounds Decomposition Modelmentioning

confidence: 99%

Numerical Analysis of Concrete Gravity Dam Seepage Characteristics Evolution considering the Calcium Leaching Effect

Zhang

Qiu

et al. 2021

Advances in Civil Engineering

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During the long-term service life of hydraulic structures, the calcium compounds in cement-based materials decompose in the aqueous environment, leading to the continuous change of seepage characteristics. To study the influence of calcium leaching on the concrete dam seepage characteristics, we proposed a new mathematic model of the cement-based material calcium leaching model under advection-diffusion-driven leaching. A solid-liquid nonequilibrium model is adopted to model the decomposition of calcium hydroxide (CH) and calcium silicate hydrate gel (C-S-H). To calculate the porosity more accurately, the proposed model takes the effect of different calcium compound decomposition on the porosity increase in consideration, respectively. Shimantan dam is selected for the three-dimensional (3D) calcium leaching analyses. The 3D finite element model of this dam is analyzed using COMSOL Multiphysics software that is based on the finite element method. Based on the proposed model, seepage characteristics evolutions of the Shimantan dam are studied. Good agreement between the numerical results and the monitored data indicates the accuracy of this simulation. The result shows that after 100 a leaching duration, the uplift pressure increases by 40.8%, and the leakage quantities of the dam body and foundation increase by 48 and 17 times. The rise of uplift pressure and leakage changes caused by curtain deterioration are the main influences of calcium leaching on the dam seepage. The parameter sensitivity results show that it is necessary to reduce CH content in cement-based materials to obtain better calcium leaching durability. This model and simulation results can guide the operation of concrete dams under advection-diffusion-driven leaching.

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Effects of Cemented Porous Media on Temporal Mixing Behavior of Conservative Solute Transport

Cited by 8 publications

References 37 publications

Influence of Shear Displacement on Fluid Flow and Solute Transport in a 3D Rough Fracture

Influence of Shear Displacement on Fluid Flow and Solute Transport in a 3D Rough Fracture

Influence of Grain Size Transition on Flow and Solute Transport through 3D Layered Porous Media

Numerical Analysis of Concrete Gravity Dam Seepage Characteristics Evolution considering the Calcium Leaching Effect

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