4.3 Discussion on application of newly proposed model in
predicting erosion from tests conducted in literature
To further verify the applicability of the proposed model, the available
data from literature work is collected and performed the redetermination
of erosion characteristics, as shown in Fig. 10 and Fig. 11. The studies
of Indraratna et al. (2008) and Xie et al. (2018) recorded the temporal
variation of the concerned parameters in the HET. The current model
shows considerable consistency and adaptation in predicting erosion
variation. The instantaneous recording included erosion rate, hydraulic
shear stress, water pressure, eroded depth, and radius. Indraratna et
al. (2008) plotted logarithmic coordinates to find the linear
relationship between erosion rate/hydraulic shear stress and logarithm
of time. Since the equations of concerned parameters are found as power
functions in this study, it is reasonable to obtain the linearity in the
logarithmetic scale. Although the experimental results of Xie et al.
(2018) indicated that the hole enlargement was not perfectly symmetrical
and uniform during continuous erosion due to the friction loss at the
entrance of the hole (Říha and Jandora 2015), the erosion process
appears to be generally predicted by the new model. It might be
attributed that the energy loss at the entrance of the hole is minor as
compared to the energy dissipation of sediment detachment and transport.
Nguyen and Indraratna (2020) also suggested that a large percentage of
the input energy in the fluid flow was dissipated by soil erosion.
Further, the energy was transferred to the kinetic component of soil
particles was negligible. Ouyang and Takahashi (2016), Fattahi et al.
(2017), Jiang and Soga (2019), and Zhang et al. (2020) also performed
HETs and explored internal erosion process on various soils. Cumulative
eroded soil loss (from equation [36]), shows considerable
performance of fitting. However, it should be noted that prediction
ability cannot be judged completely since, the soil properties and
experimental setups in the above studies were different. The erosion
trend of these studies can be generally captured. However, the
cumulative eroded soil loss at the final phase is slightly overestimated
by proposed equations, as shown in Fig. 10 (d) and Fig. 11 (a-d). This
might be resulted from the effects of sediment clogging in long-scale
soil pipes (Wilson and Fox 2013). Soil particles were accumulated and
entrapped in the latter part of soil pipes, when the residual fluid
energy after dissipating in the sediment detachment could not support
the entire process of sediment transport. Therefore, the estimated soil
loss is marginally larger than the measured sediment and the water
pressure is subtly higher than the prediction.
Seepage tests have been used to investigate the influence of internal
erosion (Tomlinson and Vaid 2000). New model might be useful to estimate
the settlement and strain of the soil body subjected to internal erosion
by following the mass conservation law. The dynamic measurement of soil
settlement and strain in the previous studies (Tomlinson and Vaid 2000;
Marot et al. 2010; Ouyang and Takahashi 2016; Sato and Kuwano 2018;
Indiketiya et al. 2019) was approximately observed to obey the equation
[36]. This is because the deformation of soil body is attributed to
the soil loss. If the subtle change of soil strength properties is
ignored, the prediction of the soil loss would roughly explain the
settlement and strain of the soil (Indraratna et al. 2009). Hence, the
theoretical model might be significant to explain the mechanism and
influence of erosion process in the HET, soil erosion, soil deformation,
and even the instability of earth structures.