Various production and construction projects are increasingly implemented along with
increased investment in China's infrastructure construction projects.In the process of
construction, plenty of vegetation is destroyed as well as surface and underground soils are
disturbed,detached,removed and loosely packed, which has caused serious man-made water
and soil loss.Owing to be short of protective measures,massive waste soils and residues
forming in the process of construction namely engineering accumulations became the most
serious places subject to water and soil loss and the main sediment origins for the
newly-added soil and water loss by human,which severely deteriorates local eco-environment.
The calculation of water and soil loss still adopt analogy in our country’s program of water
and soil conservation,which lack of experimental basis and model support.It is essential to
refer to the basical ideas involved in the Universal Soil Loss Equation (USLE) and revise
such factors as soil erodibility, slope steepness, slope length and rainfall erosivity to construct
a water and soil loss calculation model suitable for production and construction projects in
China.At present, research on these fields still has many works to do in China.In this study,
by taking the slope length factor of engineering accumulation of production and construction
projects in the loess area as the research object, runoff yield, sediment yield and
hydrodynamics on indoor simulated engineering accumulation were focused through an
artificially simulated rainfall experiment. Specific objectives were to understand the
mechanisms of soil erosion and the processes of soil and water loss and find the relational
expression and the method to define fixed value for slope length factor (L) incorporated in the soil and water loss calculation model. Our study may provide a scientific basis for the
calculation model and the supervision and law enforcement by governmental departments in
charge. The study is of important significance in science and practical values in application.
The main conclusions are as follow:
(1)In the condition of slope steepness 25º,runoff rate first increases with the time then
maintain fluctuate around a average value with the range of slope length from 3m to 12m.Soil
detachment rate decreases rapidly with the time,then fluctuate in different level of
tendency.The probability of rill ersion on slope is decrease with the enlargement of gravel
(2)For the different gravel content,runoff rate and soil detachment rate increase with
increasing rainfall amount.On the same rainfall amount,runoff rate varies gravel content
unconspicuously.With the gravel content increase,soil detachment rate has a tendency of
decrease,which indicates the increase of rock can reduce soil erosion.The runoff rate has a
linear relation with rainfall amount and rock content.The relationship between soil
detachment rate and rainfall amount can be described using exponential function.
(3)The level of fluctuation range between runoff rate and soil detachment rate under the
condition of different slope length.The groove has a evident increase with the slope length
increase,meanwhile the fluctuation increase.The runoff rate has a significant increase with the
slope length increase,but this law for soil detachment rate is different.Slope length λ≤5m or
λ≥6.5m,increase of soil detachment rate is not significant with slope length;Slope length
5≤λ≤6.5m,the soil detachment has a rapid increase with the slope length increase.Rill erosion
has a critical slope length,rill erosion will emerge exceeding this value,the value maybe
between 5~6.5m.The conclusion will play an important function in practice.
(4)For the same slope length,the runoff shear stress、Reynolds number(Re)、Froud
number(Fr) and runoff power increase with increased rainfall amount,which has different law
with increased rock content.Runoff shear stress decrease with increased rock content for the
slope length of 5m,which has no significant law in other slope length.Slope length
≤5m,Reynolds number(Re) decrease with increased rock content;Slope length ≥6.5m,this law
is not evident.Slope length ≤6.5m,Reynolds number(Re)Re≤500,runoff of slope belong to
layer flow.Slope length ≤6.5m,Froud number(Fr) belong to slow flow in the condition of little
precipitation but display as rapid flow in the condition of strong rainfall.For the slope length
of 12m,the runoff of slope all belong to rapid flow.
(5)Runoff shear stress、Reynolds number(Re)、Froude number(Fr) and runoff power
increase with increased slope length,and build the experienced equation between parameter of water motive power and slope length and rock content.The relationship between parameter of
water motive power and rainfall amount can be described as linear equation.By means of grey
related analyse between soil detachment rate and such factors under different slope
length,prove that runoff power has the most effection on soil detachment rate,while the
Reynolds(Re) ranks second.Buildidng the linear relationship between soil detachment rate
and runoff power,the relation is significant.
(6)The standard plot and slope length factor used in the water erosion calculation model
are defined in combination with the characteristics of the engineering accumulation under the
basis of refer to USLE/RUSLE.
(7)A power function between slope length factor(L) and slope length is established
under the condition of different gravel content in the basis of soil-gravel Mixture.Result
indicate that slope length factor(L) is 0.65 exponentional relation of slope length,the value is
higher than our country’s and similar with the value of RUSLE.
(8)A simple relationship between slope length factor( L i ) of Soil-gravel Mixture and
slope length factor( L 0 ) as well as gravel content(
P ) is established. A check spreadsheet of the L
values for the slope length of 3m to 20m is established using the simple relationship of
slope length factor.
Key words:production and contribution project, engineering accumulation, runoff and
sediment, slope length factor, hydrodynamic parameters