D14

Modelling Internal Erosion with the Finite Different Method〇Tanawat TANGJARUSRITARATORN, 宮﨑祐輔, 澤村康生, 岸田潔

INTRODUCTION

comparison with an experimental model test for

According to the widely utilized undergroundcalibration in erosion modeling.

infrastructure, the shallow under groundwater isCurrently, this research is still working on thesometimes unavoidable for geotechnical construction

erosion simulation part which concerns the erodible

which could be leading to the need for the dewateringtransport through porous media.

process. The seepage flow is generally occurred andstimulating an erosion process in accordance with theErosion simulation

dewatering. Eventually, the severe erosion behind

According to the suffusion or internal erosion type,retaining wall even in embankment structure might be

the soil mass has been divided for 4 main parts, asa collapse following the soil strength changed.

shown in Figure 3., which is quite different from theIn order to identify the erosion, three mechanisms

conventional concept. The fluidized particle will be

are generally defined; 1) Suffusion, 2) Contact erosion,

added into the soil model for representing an erosion

and 3) Concentrated leak erosion (Molinder, G., 2016)

particle in the fluid state which is ready to move due

as in Figure 1. This study is going to aim at theto the seepage flow. In addition, the erodible part isinternal erosion or suffusion type.

needed as well to store the limitation of the erodible
particle. The convective form is used to govern

METHODOLOGY

erosion transportation as follow in Equation 1 (Liang,To approach erosion behavior by using numerical,Y., 2017). According to the particle transport inside

analysis conventional numerical analysis might not be

porous media, the erodible soil must be moving whileable to illustrate erosion behavior, therefore, thethe drag force is enough to move the fine particle.

calculation scheme of erosion must be added into theTherefore, the shear stress is used to define anmain calculation scheme. Besides, the mechanicalinitiation of erosion and rate of erodible particle

calculation and water flow calculation will be

detachment as follows Equation 2 and Equation 3

calculated by Finite Different method operated in(Wan and Fell, 2004; Reddi et al., 2000).

FLAC3D. Hence, coupling simulation of mechanicalbehavior and flow simulation from FLAC3D together
with erosion simulation will be used as following

Internal erosion Contact erosion Concentrated(Suffusion)leak erosion

Figure 2.
Besides, the erosion calculation, which is standing
for particle transported and detachment of particle
from the soil mass, will be executed by either Finite
Different method or Finite Volume method. Finally,
thenumericalsimulation

willbetaken

intoFigure 1. Erosion mechanism

10 KPa (fixed)

0 KPa (Fixed)

Air phase (disregarded)

Eroded ratio stored extra zone
Seepage vector [qi]S=mErosionUpdate Mechanical parameters
Density, rBulk modulus, KShear modulus, GHydraulic conductivity, kCoarse soil

Erodible soil

mFigure 2. Calculation
schemeSolid phase

FLAC3D

Fluidized particle

Figure 3. soil model
concept

Calculation steps of fluid flow

Water (fluid phase)

Figure 4. Seepage flow vectors, pore pressure andsource term contour.

Equation 1.
Equation 2.

REFERENCE

Equation 3.

• Reddi, L. N., Lee, I., and Bonala, M. V. S. (2000).
Comparison of internal and surface erosion using

RESULT AND DISCUSSION
Currently, the simple simulation has been calculated

flow pump test on a sand-kaolinite mixture. J.
ASTM Geotech, 23(1), 116–122.

to test the source term propagation due to the seepage• Reddi, L., Lee, I.-M., & Bonala, M. (2000).

as in Figure 4. The fluid flow is simulated inside

Comparison of Internal and Surface Erosion Using

FLAC3D which will continue for 20,000 steps toFlow Pump Tests on a Sand-Kaolinite Mixture.

show steady state. Besides, the erosion simulation isGeotechnical Testing Journal, 23(1), 116. doi:

calculated at each step of flow simulation to define a

10.1520/gtj11129jzone that will be changed in skeleton mass to fluidized• Molinder, G. (2016). Internal erosion in the pervious

particle phase. From the simulation, the mass changefoundation of an embankment dam: A case study on

is observed at several steps of flow simulation. For thethe Lossen dam.

first 100 steps, high seepage flow zones are located• Liang, Y., Yeh, T.-C. J., Wang, Y.-L., Liu, M., Wang,

near to the left boundary, therefore, the source term isJ., & Hao, Y. (2017). Numerical simulation ofstarting to generate from the left side boundary as well.

backward erosion piping in heterogeneous fields.

Furthermore, the seepage velocity or shear flow is

Water Resources Research, 53(4), 3246–3261. doi:

distributed uniformly all over the domain, therefore,

10.1002/2017wr020425

the source term is produced linearly at a steady state.