为了更好地理解在滤饼形成过程中以及形成后泥浆与土壤的相互作用机制，耦合计算流体动力学（CFD）和离散元方法（DEM）数值方法是目前最优选择
，其中
固相被视为离散的泥浆颗粒
，而
流体相则被视为连续的牛顿流体
。
CFD-DEM方法已被广泛应用于模拟泥浆颗粒在液体中的沉降、泥浆颗粒渗透柱试验、颗粒渗流以及颗粒堵塞等方面。例如，Dong et al.研究了不同液体-颗粒相互作用力和液体性质对滤饼形成的影响。Zhang et al.考虑了泥浆颗粒之间的凝聚效应，并建立了压力降比与滤饼孔隙率之间的线性关系。Yin et al.识别了泥浆和沙粒颗粒之间不同尺寸比组合下形成的四种滤饼类型。Zhou et al.研究了细颗粒与粗颗粒直径比、质量流量和滚动摩擦系数对填充床中细颗粒堵塞行为的影响。
Fig. 1. Schematic diagram of slu
rry
shield tunnelling
.
Fig. 2. Laboratory test of slurry infiltration Subfigures taken fro
m
Min et al. (2019)
. (a
) Schematic of apparatus for an infiltration column test; (b) Photographs of typical filter cakes formed.
Fig. 3
.
The CFD mesh used to represent the sand column: (a) plan view; (b) front view.
Fig. 4
.
Particle form characterisation and examples used in simulations. (a) Indices of sphericity, flatness and compactness; (b) Combinations of aspect ratio of the slurry particles and size ratio
d
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𝑑
d
:
D
D
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𝐷
between the slurry and sand particles.
Fig. 5. Position of an ellipsoid at different times as it settles under gravity within a
quiescent fluid
.
Fig. 6. y-component of the angular velocity of the ellipsoid settling under gravity sho
wn in
Fig. 5
.
Fig. 7
.
Comparison of the simulation results for pressure drop versus fluid velocity with the Ergun equation for a packed bed of non-spherical particles.
Fig. 8
.
Illustrations of filter cake morphology with different combinations of size ratio and aspect ratio.
Fig. 9
.
Mean distance of the slurry particles from the bottom of the sand column in the filter cakes with different combinations of size ratio and aspect ratio.
Fig. 10
.
Comparing the (a) void fraction and (b) pore pressure distributions of external filter cake at a size ratio of 1:3.
Fig. 11
.
Normalised permeabilities of the uppermost region of the sand column after the formation of external filter cakes.
Fig. 12
.
Polar histograms indicate the orientations of slurry particles of size ratio 1:3 in the
x
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x–z
z
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𝑧
plane. 90° would represent a particle with its minor axis oriented vertically.
Fig. 13
.
Comparing the (a) void fraction and (b) pore pressure distributions of filter cake formed by particles with a size ratio of 1:5.
Fig. 15
.
Comparing the (a) void fraction and (b) pore pressure distributions of filter cake formed by particles with a size ratio of 1:6.
Fig. 16
.
Polar histograms indicate the orientations of slurry particles of size ratio 1:6 in the
x
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𝑥
x–z
z
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𝑧
plane. For aspect ratios of 1.2 and 1.5, particles which have migrated to the bottom of the sand columns have been excluded to eliminate the influence of particle stacking on the orientation distribution analysis.
Fig. 17. Proportion of particles with orientation angles ranging from 0° to 15° as a function of aspect ratio. For size ratio 1:5, (a)
sectional view
of aspect ratio 3 case; (b) sectional view of aspect ratio 7 case.
Fig. 18
.
Sectional views of filter cakes formed by slurry particles with an aspect ratio of 7. (a) and (b) are filter cakes formed by particles with and without cohesion, respectively, at a fixed size ratio of 1:5. (c) and (d) are filter cakes formed by cohesive particles with size ratios 1:3 and 1:6, respectively.
