ASTM D 6459 State-of-Practice
Presented to D18.25.02
June 2011
By
Joel Sprague, P.E.
TRI/Environmental
D 6459 Overview
ASTM D 6459 is an international standard that simulates full-scale
conditions “typically found on construction sites” as outlined in the
standard’s significance and use statement.
Test results have been correlated with “real world” performance and
reported in, Slope Erosion Testing – Identifying “Critical”
Parameters, (2008 IECA). The paper presented an analysis of
large-scale slope erosion testing protocols used by three different
labs and demonstrated that at least one protocol (ASTM D 6459)
produces actual performance results that correlate with the
theoretical results predicted by the Revised Universal Soil Loss
Equation (RUSLE). Tilting bed protocols did not correlate well.
This correlation validates that the test provides relevant input to the
Revised Universal Soil Loss Equation.
Numerous, comprehensive test reports of products independently
tested in accordance with the standard are publically available at
www.NTPEP.org.
D 6459 Overview
ASTM D 6459 sets the following specific test parameters:
– 8 ft wide x 40 ft long bed;
– 3:1 slope;
– 12 inches of compacted soil veneer (over underlying natural soil layer);
– Soil veneer is to be compacted to 90 ±3% Std Proctor density when first placed;
– The soil surface is to be tilled to a depth of 4-inches, raked level, and lightly compacted with a turf
roller (TRI uses an empty 24-in diameter x 48-in long turf roller that weighs 160 lbs.);
– The same soil preparation applies to slopes that receive an erosion control treatment (RECP) and
to unprotected (control) slopes;
– The erosion control treatment is to be installed as directed by the client and reported;
– Rainfall drop size distribution range is dictated (and based on natural rainfall) and must be
calibrated/documented and reported;
– Rainfall uniformity over the test bed is dictated and must be calibrated/documented and reported;
– Rainfall intensity is dictated and must be verified/reported during the test;
– Wind must be not be over 5mph when testing. The wind speed must be measured and reported.
(TRI’s test slopes are fully enclosed and not subject to wind.)
– All runoff is collected (water and sediment), quantified, and reported;
– 1 control slope is to be tested for every 3 protected slope;
– Test results are to be reported as the ratio of soil loss from the protected slopes to soil loss from
the control slopes.
Soil Loss vs. RUSLE R
(bare soil control tests to develop K factor for TRI-Loam test soil)
8 x 40 slopes
6 x 30 slopes
2 x 20 slopes
Linear (8 x 40 slopes)
Linear (6 x 30 slopes)
Linear (2 x 20 slopes)
70.00
8 x 40 ft slope
K=m/LSCP
K=m/2.80*1*1
K=.2018/(2.80)
K=.072
60.00
Soil Loss (T/A)
50.00
6 x 30 ft slope
K=m/LSCP
K=m/2.23*1*1
K=.1849/(2.23)
K=.083
2 x 20 ft slope
K=m/LSCP
K=m/1.62*1*1
K=.1522/(1.62)
K=.094
40.00
y = 0.2018x
R² = 0.9421
y = 0.1849x
R² = 0.9594
y = 0.1522x
R² = 0.8965
30.00
20.00
10.00
0.00
0.0
50.0
100.0
150.0
200.0
RUSLE R
250.0
300.0
350.0
Product
Type
Application Rate
Anchorage
C-Factor
Comment
Single net straw
RECP
7.69 osy
1.5 staples/sy
0.053
Pitting and Rilling
Double net straw
RECP
8.08 osy
1.5 staples/sy
0.012
Pitting
Wood fiber mulch
HECP
9.92 osy
Hydro-colloid tackifier
0.290
Mass wasting
Wood fiber mulch with
crimped interlocking fibers
HECP
11.57 osy
Cross-linked Tackifier
0.003
Localized “slumping”
Double net coconut
RECP
11.02 osy
1.75 staples/sy
0.006
Pitting
Double net straw
RECP
6.22 osy
1.2 staples/sy
0.024
Pitting
Straw/Cotton (70/20) fiber
mulch
HECP
11.57 osy
Hydro-colloid tackifier
0.003
Minor rilling
Straw/Cotton (65/25) fiber
mulch
HECP
11.57 osy
Hydro-colloid tackifier
0.001
No apparent erosion
Single net straw
RECP
7.68 osy
1.8 staples/sy
0.005
Pitting
Double net coconut
RECP
6.99 osy
1.1 staples/sy
0.010
Pitting
Single net excelsior
RECP
8.47 osy
1.1 staples/sy
0.039
Pitting and minor rilling
Soil Loss vs RUSLE R
(Control Testing of TRI-Loam; 3:1 Slope)
70.00
C= m / (2.78*K)
K = m / (C*2.78)
K = 0.2369 / (2.78*1.0) = 0.085
60.00
Slope 1 - 10/29/09
y = 0.2369x
R² = 0.9619
Slope 2 - 8/17/09
Slope 3 - 10/29/09
Slope 1 - 16Apr10
50.00
Slope 2 - 16Apr10
Slope 3 - 8Apr10
Soil Loss (T/A)
40.00
Slope 1 - 21Apr10
Slope 2 - 23Apr10
30.00
Slope 3 - 23Apr10
Slope 1 - 8/6/10
20.00
Slope 2 - 8/6/10
Slope 3 - 8/6/10
10.00
All
Linear (All)
0.00
0
50
100
150
200
250
300
RUSLE R (US Customary Units)
350
Insufficient Differentiation?
One historical objection has been that the test method does not
sufficiently differentiate between product types. Some believe that
this is a deficiency in the test protocol. However, others believe it
more likely that when very different products perform similarly, it is
because they have been installed using installation details uniquely
designed (by the manufacturer) for the test conditions, i.e. 3:1 slopes,
sandy-loam soil, high intensity rainfall. Most product literature
provides guidance in selecting installation details for the specific
conditions. Such variations as anchor density, size, pattern, and type
(RECPs) and coverage rate and curing time (HECPs) can dramatically
influence product performance. Thus, the installation details are
reported along with the resulting test results. The data presented
above reasonably supports the test’s ability to differentiate products
appropriately for the conditions tested.
Seriously Flawed?
Another objection that has been heard is that the test method is
“seriously flawed” and the ASTM balloting process has been too
slow to make changes. As noted above, like all test methods,
this method should be continuously improved based on
experience. Yet, results of this test have been shown to
correlate well with “real world” performance, so any proposed
changes are being thoroughly investigated by the ASTM task
group governing the standard before being implemented. Work
is ongoing in this regard.
D 6459 vs. Tilting Beds
All other currently used slope testing protocols use tilting beds
that allow for the soil layer to drain from below. This prevents
the soil layer from becoming saturated under heavy rainfall
simulations. This also creates a soil condition that cannot exist in
the real world. The ballot author references Lal, 1994, as
recommending the use of bed drainage when testing where
“runoff and soil loss are the primary indicator of differences in
the treatments”. While Lal was referring only to small plots, he
goes on to clarify that these “small [drained] plots do not give
complete information about the erosion process”. Clearly, there
are times when the primary indicator of differences in the
treatments is whether mass wasting occurs or not. Thus, it
would not be appropriate to have drained beds when testing
these products.
D 6459 vs. Tilting Beds
The tilting bed slope test configuration has been used to isolate
surface dynamics from full-depth slope stability issues, and thus
has been shown in this limited context to segregate between
surface-treatment technologies. However, global erosion
phenomenon, including infiltration and associated hydraulic
loading, warrant the use of large – real world slope tests, such as
ASTM D 6459, for field performance investigations. For example,
it has been documented that erosion control products that resist
surface erosion dynamics by preferentially encouraging
infiltration may also increase the risk of slope instability via mass
wasting.
D 6459 vs. Tilting Beds
Other commonly used protocols use large, uniform sized
raindrops rather than a range of drop sizes as found in nature.
The rainfall is then reported in terms of a hypothetical amount
of kinetic energy that has been applied. The argument for using
large drop sizes has centered on the need to maximize the
aggressiveness of the rain storm event in order to delineate
between competing erosion control technologies, especially
those that rely on a chemical agent to provide localized fiber-tofiber bonding. While calculating the kinetic energy of singlesized spheres is quite straight forward, it is not at all clear how,
or if, this can be accurately done for an actual rainfall distribution
until the measurement of drop sizes and their proportional
makeup of the rainfall can be more definitively measured.
D 6459 vs. Tilting Beds
Finally, all other testing protocols use test slopes that are shorter
(< 40 ft) and narrower (< 8 ft) limiting the extent to which natural
erosion mechanisms can develop. The ballot author references
Lal, 1994, as noting that “experience has shown that 5 m is about
the minimum slope length that will adequately represent a rill
system in an up-and-down-hill plot.” In the very next sentence
Lal goes on to say, “A better length is at least 10 m.” It seems
clear that longer is better (i.e. less flawed).
Improving D 6459
• Since the standard test protocol requires construction of
the test slopes in-situ, and rainfall drop size and distribution
representative of actual rainfall, definition and control of
these variables can and should be refined with continuing
development of control mechanisms.
• Slope construction, especially final surface compaction, is
currently only qualitatively defined in the standard. This
could be better quantified based on experience to-date.
• Rainfall drop size distribution requires balancing flow,
pressure, and spray head selection. The proper balance is
then judged by a periodic drop size measurement
technique using pans of flour and the sifting of dried
“beads”. An improved drop size measurement technique,
such as real-time measurements, would make continuous
controls possible.
Dysdrometer Measurements of Natural Rain at DDRF - 28Feb11
200 mm/hr
150 mm/hr
100 mm/hr
50 mm/hr
50%
40%
% of Drops
30%
20%
10%
0%
0
1
2
3
Drop Size, mm
4
5
6
Dysdrometer Measurements of Natural Rain vs. Flour Pan Measurements of Test Rain
at DDRF
150 mm/hr
100 mm/hr
50 mm/hr
DDRF - 6 in/hr
DDRF - 4 in/hr
DDRF - 2 in/hr
60%
% of Total Drop Mass
50%
40%
30%
20%
10%
0%
0
1
2
3
Drop Size, mm
4
5
6