Hydraulic Characteristics and Sediment Yielding on Engineering

Excavated Soil Slope under Simulated Rainfall

Xi Li, Chongqing Wang, Shixiong Jiang, Sunxian Weng, Yanhong Che,

and Yao Chen

Electric Power Research Institute of State Grid Fujian Electric Power Co., Ltd., Fuzhou 350007, P. R. China

Keywords:

Engineering excavated slope, Simulated rainfall, Hydrodynamics, Inter rill erosion, Model

Abstract: Engineering excavated soil slopes play an important role in artificial soil loss. In order to assess the impact of

these engineering excavated soil slopes, hydraulic characteristics and sediment generation must be quantified.

Field rainfall simulation experiments were conducted under five rainfall intensities (0.6, 1.1, 1.61, 2.12 and

2.54 mm/min) and three slope gradients (10°, 15°and 20°) on engineering excavated soil slopes. The

precipitation of each rainfall was set to 50 mm, the duration of rainfall was 83, 45, 31, 24 and 20 min for

simulated rainfall intensities of 0.6, 1.1, 1.61, 2.12 and 2.54 mm/min respectively. Plots used in this study

were laid out to be 3 m in length and 1 m in width. Calibration of rainfall intensities was conducted before

each experiment. Totally, 45 simulated rainfall events were performed. Three indices were used to research

the soil erosion processes, including surface and subsurface runoff volume and the sediment yield. Results

showed that: 1) both surface and subsurface runoff varied depending on slope gradient and rainfall intensity.

Surface runoff and subsurface runoff were 33.6~42.7 mm and 0.15~ 1.24 mm, respectively. The process of

surface runoff yield was the main hydrological process, accounting for 67.2~85.4% of the precipitation. Under

conditions of low (0.6 mm/min) and high (2.12 and 2.54 mm/min) rainfall intensity, surface runoff increased

with slope. 2)The averaged flow velocity, Reynold number, Froude number, Darcy-Weisbach friction

coefficient, Manning roughness coefficients and stream power were 0.047~0.104 m/s, 48.985~392.918,

0.355~0.581, 1.317~5.171, 0.044~0.101 m

-1/3

·s, 0.029~0.457 kg·s

-3

, respectively. In addition, flow velocity

and Reynold number had a greatly significant correlation with rainfall intensities, Manning roughness

coefficients, Darcy-Weisbach friction coefficients and stream power a week correlation with rainfall intensity,

Froude number had a week correlation with rainfall and slope. There was no obvious relationship between

Darcy-Weisbach friction coefficient and the Reynolds number and there was a “increase resistance”

phenomenon in engineering excavated soil slopes. 3) Interrill erosion was the main erosion form on

engineering excavated soil slopes. Rainfall intensity, runoff rate and slope gradient are key factors to model

sediment yield rate. Three commonly interrill erosion models were evaluated and compared, the fitness of

model followed the pattern: model 1(NSE=0.977)>model 2(NSE=0.966)>model 3(NSE=0.924). A further

comparison between the models showed that the convex curvilinear slope factor (model 1) was more precise

than the power (model 3) and linear (model 3) slope factor in describing the effect of slope gradient for this

data. Interrill erodibility adopted in the WEPP model was determined as 0.332×10

kg·s·m

-4

. The results

provide valuable data for establishing water erosion prediction model of engineering excavated slope.

1 INTRODUCTION

Erosive rainfall is one of the main driving factors of

slope hydraulic erosion. Rainfall indicators such as

rainfall volume, rainfall intensity and rainfall

ephemeris jointly influence the slope erosion process.

Pruski and Nearing

(2002) found that soil loss

increased by 0.85% when the total rainfall increased

by 1% for the same rain intensity conditions. The

raindrop striking splash not only causes separation

and displacement of soil particles, but also increases

the turbulence of water flow in the thin layer of the

slope. The boundary conditions of water flow in

indoor soil tank test are easy to control. It is a more

common method to study soil erosion dynamics of

slope, but it has large differences with natural slope.

As one of the most widely distributed and hazardous

sources of anthropogenic soil erosion, soil excavation

slopes are mainly excavated after topsoil stripping for

construction projects. The disturbed soil is generally

composed of weathered crust or parent material

458

Li, X., Wang, C., Jiang, S., Weng, S., Che, Y. and Chen, Y.

Hydraulic Characteristics and Sediment Yielding on Engineering Excavated Soil Slope under Simulated Rainfall.

In Proceedings of the 7th International Conference on Water Resource and Environment (WRE 2021), pages 458-466

ISBN: 978-989-758-560-9; ISSN: 1755-1315

(parent rock) (Zhang et al., 2013). Soil excavation

slopes have high soil capacity, high compactness, and

steep slope, thus resulting in a soil loss process that

differs significantly from that of natural slopes. Under

the erosive rainfall, the water flow along the

excavated slope of the project constantly has the

convergence of mass sources, and the temporal and

spatial changes of runoff are obvious, and the soil

porosity of the lower bedding surface is lower, and the

infiltration capacity is poorer than that of the natural

slope surface, which is more complicated.

At present, there are relatively few studies on the

erosion characteristics of engineering excavation

surfaces and their erosion mechanisms. Most studies

have focused on the erosion of loose piles generated

by mineral extraction and road construction. For the

prediction model of soil erosion on excavated slopes,

the current research is still in the initial stage.

Therefore, this study analyzes the hydrodynamic

characteristics of erosion between fine trenches on

soil excavation slopes and its loss prediction under

erosive rainfall conditions by field artificial rainfall

test method, with a view to providing a theoretical

basis for the prediction and control of anthropocentric

soil erosion caused by engineering construction

excavation.

2 MATERIALS AND METHODS

2.1 Experimental Design and

Observation

Three slope plots of 3 m in length and 1 m in width

were selected for this experiment on a highway slope

in central China, with the slopes of 10°, 15° and 20°.

The wall of the slot is made of stainless steel plate of

2 mm thickness to cut off the channel of runoff

exchange inside and outside the cell. A "V" shaped

catch basin was inserted at the lower end of the plot

and connected to a runoff collection barrel through the

catch basin to collect surface runoff, the structure of

which is shown in Figure 1.

The test uses a spray-swing simulated rainfall

device. The rainfall height was 2.5 m, the rainfall

uniformity was 85%, the effective rainfall area was

about 2 m×3 m, the simulated rain intensity range was

20~170 mm/h, and the simulated rainfall

approximated natural rainfall. In view of the range of

erosive rainfall occurring at the test site, the rainfall

intensities of 0.6, 1.1, 1.61, 2.12 and 2.54 mm/min

were finally designed for the combined tests. The total

amount of rainfall for each rainfall test was controlled

at 50 mm, and the rainfall ephemeris was set

according to the rainfall intensity, i.e., the rainfall

intensities for 83, 45, 31, 24 and 20 min were 0.6, 1.1,

1.61, 2.12 and 2.54 mm/min, respectively.

Figure 1: (a) Sampling point location;(b) Diagram of runoff and sediment collection system in the field.

The soil capacity of the road excavation slope of

the test site was measured by the ring knife method to

determine 1.54~1.58 g/cm

. The average capacity of

the test plot was 1.56±0.21 g/cm

and the average

water content was 17.6±0.18%. The slope of the

excavated surface is between 10° and 70°, with 40° to

70° accounting for 19%, 20° to 40° accounting for

75% and 20° accounting for 6%. Through particle

sieving of the collected soil samples, it was found that

the soil on the excavated slope was dominated by 1~2

Hydraulic Characteristics and Sediment Yielding on Engineering Excavated Soil Slope under Simulated Rainfall

459

mm soil particles with coarse texture, and the basic

soil properties are shown in Table 1.

Table 1: Physical-chemical properties of the test soil.

Soils

Particle composition/%

Particle size/ mm Mass percent/%

Disturbed soil

<0.01 0.19

0.01~0.1 4.48

0.1~0.5 22.10

0.5~1 21.68

>1~2 51.56

2.2 Test Process

A rain shelter was used to cover the plot before the

start of each test. Rain barrels were placed around the

perimeter of the plot to filter the rain intensity until

the rainfall intensity reached the test requirements.

Soil samples were collected on the excavated surface

to determine the pre-soil water content. When the soil

moisture content of the repeated tests showed a large

difference, it was left to stand for 24 hours after a light

rainfall in advance to eliminate the effect of soil

moisture content. From the beginning of the

experiment to the full production of flow on the slope,

the flow rate and sand content at the outlet were

measured and the time was recorded. During the test,

the water flow temperature is used to calculate the

water flow viscosity coefficient, while the total time

of rainfall is also recorded. Further, the sampling

interval was determined as one sample every 1 minute

at the beginning of the birth flow. After 3-7 minutes,

a sample was taken every 2 minutes. After 7-10

minutes, one sample was taken every 3 minutes. After

10 minutes, a sample was taken every 5 minutes. The

sediment content in the sample is determined by

drying method. The surface flow velocity was

determined by KMnO

pigment tracer method in three

measurement sections at the top, middle and bottom,

and each test was repeated three times to ensure the

test accuracy. After the test, the new plot was

rearranged for the test.

2.3 Data Analysis Method

1) Surface runoff velocity (V). The maximum surface

flow velocity was measured at three observation

sections using KMnO4 solution and an electronic

stopwatch to determine the time required to pass the

1 m measurement distance, and the average value was

taken and multiplied by a correction factor of 0.67 to

obtain the average surface runoff flow velocity (Li et

al., 2015), m·s

-1

2) Average water depth (H). Since the erosion of

the soil excavation slope during the test was

dominated by the erosion between fine trenches and

the water depth was small, it was difficult to

determine directly. Therefore, equation (1) was used

for calculation (Wang et al., 2016):

VBt

⋅⋅

(1)

Where, h is the average water depth on the slope,

m; Q is surface runoff flow, m

; B is the cross-section

width, m; t is the time, s.

3) Calculation of hydrodynamic parameters. The

hydrodynamic parameters involved in this paper

include Reynolds number Re, Darcy-weisbach drag

coefficient f, Manning's roughness coefficient n and

flow power w. The above parameters were calculated

using the open channel flow equation (Luo et al.,

2009).

4) Soil denudation rate (D

) is the mass of soil

transported by surface runoff per unit area per unit

time, kg·(s

-1

-2

), which is calculated as follows:

⋅

(2)

Where, Ms is the soil loss from the slope in the

time period t(s), kg, obtained from runoff sediment

samples. A is the area of the test plot, m

5) In this paper, three commonly used statistical

models of inter-groove erosion on slope surfaces are

used to study their applicability in predicting inter-

groove erosion on soil excavation surfaces.

Model 1 adopts WEPP inter rill erosion equation

(Flanagan & Nearing, 1995):

iif

KQS I=

(3)

In which, Ki is the erodibility factor between

rills,kg·s·m

-4

; Q is the average runoff intensity, m·s

-1

;

is the slope factor and the slope of the test plot; I is

rain intensity, m·s

-1

Model 2 adopts the inter rill erosion equation

including runoff factor proposed by Kinnell (1993):

KQSI=

(4)

Where, Q is the average runoff intensity, m·s

-1

; S

is the slope of the test area, m·m

-1

WRE 2021 - The International Conference on Water Resource and Environment

460

Model 3 adopts the inter rill erosion equation

proposed by Bulygin et al. (2002):

(5)

SPSS 20.0 was used for data analysis, and LSD

(lowest extreme difference method) was applied in

ANOVA for multiple comparisons with a significance

level of p<0.05. The model accuracy evaluation

metrics were selected from the complex correlation

coefficient (R

) and the Nash-Suttclife efficiency

coefficient (NSE), where the NSE was calculated

using the following equation (Bulygin et al., 2002):

(6)

Where Oi is the measured value, Oc is the

calculated value and Om is the average value of the

measured value.

(a) Surface flow (b) Sediment

ield rate

Figure 2: Surface runoff volume and sediment yield rate for different slope gradients and rainfall intensities. For each

treatment, means with the same lower-case letter are not significantly (p<0.05, least significant difference) different.

3 RESULTS AND ANALYSIS

3.1 Analysis on Characteristics of

Water and Soil Loss on Soil

Excavation Slope

Surface runoff from soil excavation slopes varied

between 33.6 and 42.7 mm under different slope and

rain intensity conditions (Figure 2a). Surface runoff,

as the main hydrological process under erosion

conditions, accounted for 67.2 to 85.4% of the total

rainfall. A study by Defersha and Melesse (2012)

indicated that the effect of slope and rain intensity on

sand and flow production on slopes varies with

changes in soil properties on the subsurface. In this

study, an artificially simulated rainfall scheme was

adopted to control the total rainfall of 50 mm with

rainfall intensities of 0.6, 1.1, 1.61, 2.12 and 2.54

mm/min. Under the same slope condition, the surface

runoff volume shows a phenomenon of decreasing

and then increasing with the increase of rain intensity,

Hydraulic Characteristics and Sediment Yielding on Engineering Excavated Soil Slope under Simulated Rainfall

461

which is due to the fact that when the soil on the slope

surface produces crust, it will make the slope surface

flow production mechanism become more

complicated. When the rain intensity changes from

small to medium rain intensity, the splash of raindrops

is further enhanced. The soil compacted by the

excavation is further transported and the soil porosity

increases, thus increasing the soil infiltration. With

the further increase of rainfall intensity, the rainfall

intensity is greater than the infiltration rate, forming

superinfiltration production flow and accelerating the

formation of surface runoff. The increase of surface

runoff flow rate will reduce the chance of infiltration

of slope surface flow. Therefore, the surface runoff

appears to decrease and then increase with the

increase of rainfall intensity.

There were significant differences in sand yield

per unit area under different slope and rain intensity

conditions (Figure 2b), and the sand yield per unit

area increased with the increase of slope and rain

intensity. When the slope of excavation slope

increases from 10° to 20°, the sand production rate per

unit area increases by 2.92, 2.12, 1.96, 1.57 and 1.88

times when the rain intensity is 0.6 mm·min

-1

, 1.1,

1.61 mm·min

-1

, 2.12 and 2.54 mm·min

-1

, respectively.

On the other hand, the sand production rate per unit

area increased 16.87, 20.48 and 10.88 times when the

rainfall intensity increased from 0.6 mm min

-1

to 2.54

mm min

-1

at slopes of 10°, 15° and 20°, respectively.

This is consistent with the findings of Ziadat and

Taimeh

(2013). The effect of variation in rainfall

intensity on sand production rate is greater than the

effect of slope variation on sand production rate.

3.2 Analysis on Hydrodynamic

Parameters of Soil Excavation

Slope

Table 2 shows the correlation coefficient statistics of

hydrodynamic parameters with slope S, rain intensity

I and rain intensity-slope interaction (I×S). Under

different rain intensity conditions, the surface runoff

velocities V of 10°~20° soil excavation slopes were

0.047~0.084, 0.052~0.092 and 0.054~0.104 m·s

-1

respectively. The flow velocity V increased with

increasing rain intensity at the same slope. There is a

significant linear relationship between the two

=0.58-0.92, P<0.01). Under the same rainfall

intensity, the runoff flow velocities of slopes of 15°

and 20° were 0.84-1.19 times and 0.92-1.23 times

higher than those of slopes of 10°, respectively. The

differences between the runoff velocities of excavated

slopes with different slopes of soil were not

significant (P>0.05). The results of correlation

analysis showed that the soil excavation slope flow

velocity was not significantly correlated with slope

(P>0.05) and was highly significantly correlated with

rain intensity I and the interaction of slope and rain

intensity I×S (P<0.01).

Table 2: Correlations between flow hydrodynamic parameters and coupling effects of rainfall intensity and slope gradient.

Variable V/(m·s

-1

) Re Fr f

/(m

-1/3

·s)

w/(kg·s

-3

)

I 0.892** 0.954** -0.199 0.091 0.397 0.759

0.198 0.213 -0.052

I×S 0.878** 0.918** -0.109 / / /

The Reynolds number of soil excavation slope

runoff under different rain intensity and slope

conditions is between 48.985 and 392.918, and the

soil excavation slope runoff flow pattern belongs to

the category of laminar flow according to the criteria

for determining the flow pattern of open channel flow.

In the test, it was observed that no matter what the

combination of rain intensity and slope, there was

obvious sand-holding phenomenon in the process of

slope flow movement. The sand concentration of the

water body at the outlet of surface runoff is between

1.2% and 23.7%. The slope runoff flow pattern should

belong to the category of turbulent flow. The

traditional criteria for determining the flow pattern of

open channel flow are not applicable to the soil

excavation slope. Re had the highest correlation with

rainfall intensity I and insignificant correlation

(P>0.05) with slope S (Table 2), indicating that the

magnitude of rainfall intensity determines the

variation of runoff patterns on the soil excavation

slopes. The Froude number Fr is between 0.355 and

0.581, all of which are less than 1 and are slow flow.

Correlation analysis showed that the correlation

between Fr and the interaction of rain intensity I,

slope S and rain intensity I × S was not significant

(P>0.05).

The Darcy-Weisbach resistance coefficient f and

the Manning coefficient n are hydraulic parameters

commonly used to characterize the resistance to water

flow on a slope. Under different rain intensity

conditions, the runoff resistance coefficient of

excavation slope at slope of 10° ranged from 1.317 to

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462

3.527. Under the same rain intensity conditions, the f-

values of 15° and 20° soil excavation slopes are 1.04-

2.18 times and 1.46-2.97 times higher than those of

10° slopes. The f-value of soil excavation slope

increases with the increase of slope. At the same slope,

there is no significant trend in the f-value of soil

excavation slope with rain intensity. The Manning

coefficients n of 10°~20° soil excavation slope is

0.044~0.084, 0.057~0.090 and 0.079~0.101

respectively. The correlation between the f and n

values of the soil excavation slope and the rain

intensity was not significant. A power function

relationship exists between the slope flow resistance

coefficient f and the Reynolds number Re (Nearing et

al., 1997). The results of this test show that there is no

significant relationship between f and Re (see Figure

3a). The Reynolds number is not the main factor

affecting the resistance coefficient because the

particle resistance of the soil excavation slope does

not dominate. This is in agreement with the findings

of Nearing et al. (1997). On rough slopes, there is no

single relationship between f and Re As can be seen

from Figure 3b, the resistance of slope flow under

rainfall conditions is greater than that under non-

rainfall conditions, and the extent of its effect is

influenced by the depth of water flow, slope and

surface morphology. There is an obvious

phenomenon of "increasing resistance" of water flow

on the slope of soil excavation.

The water flow power w incorporates the role of

slope and runoff rate. Soil flow can be predicted in

terms of water flow dynamics. The water flow power

ranged from 0.029 to 0.457 kg·s

-3

for different slope

and rain intensity conditions. Under the same

conditions of rain intensity, the water flow power (w)

of slope 15° and 20° is 1.517~1.745 times and

2.282~3.379 times than that of slope 10°. The w value

increases as the slope increases. The correlation

between w value and rain intensity is not significant.

The relationship between the power of water flow and

the amount of soil loss per unit was obtained from the

regression analysis, as follows:

(7)

Where, qs is the unit soil loss, g·s

-1

·m

-1

; W is the

water flow power,g·s

-3

From equation (7), it can be seen that the linear

relationship between water flow power and unit soil

loss has a high coefficient of determination and can

be used to predict soil loss from soil excavation

surfaces. Meanwhile,the water flow power must reach

a certain critical value for soil loss to occur on the

slope surface.

(a) Scatter plot

(

)

Double-Lo

lot

Figure 3: Relationship between Darcy-Weisbach resistance

coefficient and Reynolds number.

Figure 4: Soil loss rates as functions of runoff rates.

3.3 Analysis of Rill Erosion Model on

Soil Excavation Slope

Figure 4 shows the relationship between runoff rate

and soil denudation rate on the soil excavation slope.

Runoff rates of 4.92×10

-5

to 3.01×10

-4

·s

-1

for

excavated surfaces with a slope of 10°. When the

slope is 15° and 20°, the runoff rate is 0.86 to 1.21

times and 1.14 to 1.74 times, respectively. There was

a good linear relationship between soil denudation

Hydraulic Characteristics and Sediment Yielding on Engineering Excavated Soil Slope under Simulated Rainfall

463

rate and runoff rate. Among them, the slopes of the

fitted equations were 1.36 and 1.33 times higher for

slopes of 15° and 20° than for slopes of 10°,

respectively. Therefore, the slope is the key factor

affecting soil loss on the slope of soil excavation, and

the degree of its influence increases with the slope

showing the characteristics of first increasing and

then leveling off.

The relationship between soil erosion rates

between fine channels on soil excavated slopes and

the rainfall runoff factor and topographic factor was

obtained by predicting the soil erosion rates between

fine channels based on the equations used in the

WEPP model for calculating fine channel erosion:

(8)

Where, Di is the soil erosion rate between rills on

the soil excavation slope, kg·s

-1

·m

-2

; Q is the average

runoff rate of surface runoff, m·s

-1

; Sf is the slope

factor; I is the rain intensity, m·s

-1

The soil erodibility factor Ki of the soil excavation

slope is 0.332×106kg·s

-1

·m

-2

obtained from the

regression coefficient of equation (8).

The prediction results of the fine intergully

erosion models selected in this study are shown in

Figure 5. The Nash efficiency coefficients of model 1,

model 2, and model 3 were 0.977, 0.924, and 0.966,

respectively, indicating that all three models

performed well in predicting soil denudation rates on

soil excavation slopes under the rainfall intensity and

slope conditions of this study. Model 1 was the best in

predicting soil denudation rate on soil excavation

slopes. The comparison of the model structures

reveals that the calculation results using the convex

curve type slope factor index are more accurate.

(

)

Model 1

(

)

Model 2

Figure 5: Comparison between measured and predicted soil

losses from the excavated soil slope.

4 DISCUSSION

In this paper, the hydrodynamic characteristics of the

soil excavation slope are analyzed for its fine

interchannel erosion process under rainfall conditions.

The soil excavation slope has the characteristics of

high compactness, high capacity, low infiltration rate

and steep slope, etc. Its process of producing flow and

sand is quite different from the natural slope. The

erosion mode of the soil excavation slope during the

sampling stage of this test is mainly interfine gully

erosion, and the hydrological process is mainly

surface runoff, which accounts for 67.2~85.4% of the

total rainfall. Under the test rainfall conditions, the

surface runoff flow pattern on the soil excavated slope

with slope of 10°~20° still belongs to laminar flow.

However, there is obvious tumbling of fine sand in the

test slope surface runoff, which contradicts with the

non-mixing of masses between the layers of laminar

flow. At the same time, the resistance coefficient of

surface runoff from soil excavated slopes is greater

than that in open channel laminar flow (Figure 3), and

for this phenomenon can be explained from the

perspective of slope flow resistance composition. The

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464

slope surface flow resistance includes four

components: particle resistance, morphological

resistance, wave resistance and rainfall resistance,

and these four components can be superimposed on

each other. In this study, field rainfall tests were used,

with no ground cover on the excavated slope and the

slope flow depth h ranging from 1.04 to 4.03 mm. The

median diameter of raindrop is 2.30 mm, because

when h ≦ 3mm, the raindrop striking force can

penetrate the water layer and affect the topsoil. At the

same time, raindrops disturbing the thin layer of water

flow on the slope increase the turbulence of the water

flow, thus increasing its resistance (Proffitt et al.,

1993).

Through the test observation, the erosion process

of soil excavation slope surface shows that the thin

layer of water flow erosion is dominant, i.e., fine

inter-groove erosion. Therefore, the conclusions

obtained from this study are applicable to the surface

erosion stage of the slope without erosion ditch. Water

flow power is suitable for describing the erosion

process of thin water flow on slopes, and can reflect

the effect of slope water runoff rate and slope factor

on soil denudation rate. The sand transport process of

slope surface flow caused by rainfall is influenced by

the water depth, while the size of the water depth is

influenced by the slope. Rain intensity is also an

important parameter that influences the erosion

process between fine trenches on the slopes of soil

excavations (Kinnell, 1988). Through the above

analysis, we further added the rain intensity factor

into the equation for predicting soil denudation rate.

The results show that the prediction accuracy of the

model in Table 3 is greater than that of Eq. (7), and

the model in Table 3 takes into account the effects of

rainfall, runoff and slope on soil denudation rate at the

same time. Models 1 and 3 performed better in

predicting soil denudation rates compared to model 2,

indicating that the convex curve type slope factor

index is more suitable for soil denudation rate

calculation on soil excavation slopes. The slope of the

fitted equation between soil denudation rate and

runoff rate under different slope conditions is not a

single linear relationship with increasing slope

(Figure 4), which is similar to the results of Parson

and Abrahams (1993). The amount of erosion

between fine trenches showed a tendency to increase

and then decrease with increasing surface slope, i.e.,

there was a critical slope, and this phenomenon was

also present on the soil excavation slopes.

Due to the limitation of experimental conditions,

only the soil excavation slope was selected for this

study to investigate the hydrodynamic characteristics

during the erosion between fine trenches. In reality,

there are various forms of engineering excavation

slopes, and the composition of the sub-bedding

material, the depth of the excavated soil layer and the

length of the excavated slope will affect the process

of slope hydraulic erosion, and the way of erosion is

also diversified, including sheet erosion, fine ditch,

shallow ditch and other erosion methods. In this paper,

the field excavation surface plot size is small, the

material composition of the lower bedding surface is

relatively single, the test is not designed separately for

different slope lengths, and the erosion process of the

excavation slope under the condition of water and

sand coming from above is not considered. The later

research needs to further study the test plot size,

material composition of the lower bedding surface,

erosion mode and other aspects, so as to provide

reference for the establishment of erosion prediction

model for the engineering excavation slope.

Table 3: Efficiency of selected models.

Equation NSE

Model 1 D

=332775QS

I 0.977

Model 2 D

=1.63504×10

QSI 0.924

Model 3 D

=753568QS

2/3

I 0.966

5 CONCLUSION

By establishing excavated slope plots with different

slopes (10°, 15° and 20°) of soil in the field and

studying the hydrodynamic characteristics of fine

interchannel erosion on excavated slopes under

different simulated rainfall intensities (0.6, 1.1, 1.61,

2.12 and 2.54 mm/min) and a design total rainfall of

50 mm, the main conclusions are as follows:

1) The surface runoff from the soil excavation

slope is 33.6~42.7 mm, and surface runoff is the main

hydrological process, accounting for 67.2~85.4% of

the total rainfall. The influence of rainfall intensity on

sediment yield is greater than that of slope change.

2) The flow velocity and Reynolds number of the

soil excavation surface were highly significantly

correlated (P<0.01) with the interaction of rain

intensity I and slope and rain intensity I×S. Interaction

between Froude number and rain intensity I, slope s,

slope and rain intensity I×S was not related; Manning

coefficient, Darcy weisbach resistance coefficient and

flow power are not related to rain intensity. There is

no obvious relationship between Darcy-Weisbach

resistance coefficient and Reynolds number, and the

phenomenon of "increasing resistance" exists on the

soil excavation slope.

Hydraulic Characteristics and Sediment Yielding on Engineering Excavated Soil Slope under Simulated Rainfall

465

3) All three fine intergully erosion models were

able to predict the soil denudation rate of soil

excavated slopes better. In terms of fitting effect,

model 1 (NSE=0.977) > model 3 (NSE=0.966) >

model 2 (NSE=0.924). The convex curve type slope

factor index is more suitable for the calculation of soil

denudation rate of soil excavation slope. The soil

erodibility factor Ki of the soil excavation slope is

0.332×106 kg·s·m

-4

calculated from the WEPP inter

fine gully erosion equation (Model 1).

ACKNOWLEDGMENT

This work is supported by the State Grid Corporation

of China (WBS NO.501304200006)

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