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SLOPE STABILITY

Highway 194Avery County

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SLOPE STABILITY

SLOPE STABILITY

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SLOPE STABILITY

SUPERFICIAL SLOPE STABILITY

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SUPERFICIAL SLOPE STABILITY

SUPERFICIAL SLOPE STABILITY

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SUPERFICIAL SLOPE STABILITY

SUPERFICIAL SLOPE STABILITY

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SUPERFICIAL SLOPE STABILITY

SUPERFICIAL SLOPE STABILITY

• Superficial Slope Stability Analysis

• “RUSLE” A = R * K * LS * C * P

• “RUSLE” factors R, K, LS, C, and P

• Acceptable Soil Loss Tolerances

• Establish and Discuss Safety Factors

• Good Practice

• EXTRA, EXTRA!

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REVISED UNIVERSAL SOIL LOSS EQUATION (RUSLE)

Why RUSLE?

• “RUSLE is a science-based tool that has been improved over the last several years. RUSLE is a computation method which may be used for site planning purposes and to aid in the decision process of selecting erosion control measures.” (New York Standards and Specifications For Erosion and Sediment Control Manual)

REVISED UNIVERSAL SOIL LOSS EQUATION (RUSLE)

• “RUSLE” A = R * K * LS * C * P * 0.00595• A = Soil loss in tons/acre/year • R = Rain factor• K = Soil erodibility• LS = Topographic factor• C = Cover factor• P = Practice factor• 0.00595 = conversation factor for soil loss rate from

tons/acre to uniform inches.

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“RUSLE” FACTOR R

R Factor: The annual rainfall/runoff factor for a given location through a given time period. A conservative approach is to use the “average annual rainfall/runoff values.

Iredell County ~ 175 Johnston County ~ 300

“RUSLE” FACTOR R (PARTIAL)

• R Factor can be reduced for Partial Year Evaluations

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“RUSLE” FACTOR R (PARTIAL)

“RUSLE” FACTOR R (PARTIAL)

• Subtract Ending Date % from the Starting Date %

• Multiply Annual R value by the % of the Rain Energy for that given time period.

• Construction in IredellCounty will Start March and last through October. R = 175

• Rf = (93% – 7%) = 86%• Rpart = 175 * 0.86 = 150.5

• Construction in JohnstonCounty will Start March and last through October. R = 300

• Rf = (95% – 4%) = 91%• Rpart = 300 * 0.91 = 273

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“RUSLE” FACTOR K

Soil Erodibility Factor (K)

• The soil erodibility factor, K, provides a measure of the susceptibility of soil particles to detachment and transport by rainfall and runoff.

• The principal factors affecting K are texture, organic matter, structure, and permeability.

• Usually taken for the “B” Horizon

“RUSLE” FACTOR K

Permeability

• Permeability is a major factor influencing erosion. It refers to the soil’s ability to transmit water or air and depends on both the size and volume of pores. Deep, permeable soils are less erodible because more rainfall soaks in, reducing surface runoff.

• Compaction reduces permeability therefore increasing erodibility.

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“RUSLE” FACTOR K

“RUSLE” FACTOR K

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“RUSLE” FACTOR K

“RUSLE” FACTOR K

IREDELL COUNTY

Johnston County

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“RUSLE” FACTOR LS

Length-Slope Factor, LS

The length of slope factor, L and the slope gradientfactor, S are usually determined as a single value, theLS factor. Slope length, L is defined as the horizontaldistance (not the slope distance)from the point oforigin of overland flow to the point where the slopegradient decreases to the extent that depositionbegins to occur, or the point where runoff enters awell-defined channel.

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“RUSLE” FACTOR LS

12’

30’

30’ H to 12’ V 2.5 : 1 = 40%

“RUSLE” FACTOR LS

LS ~ 2.9

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“RUSLE” FACTOR C & P

Cover Factor & Practice Factor

• Cover factors for Erosion Control matting are usually assigned and can be located in the specifications.

• C = 1.0 for an unprotected state.

• Practice factors account for construction techniques such as tracking slopes, surface roughening.

“RUSLE” FACTOR C & P

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“RUSLE” FACTOR C

“RUSLE” FACTOR C

USE THE MANUFACTURE’S SPECIFICATIONS

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“RUSLE”

“RUSLE” A = R * K * LS * C * P * 0.00595Iredell CountyAbare = 150.5 * 0.1 * 2.9 * 1.0 *1.0 * 0.00595 = 0.26”Amat = 150.5 * 0.1 * 2.9 * 0.06 * 0.9 * 0.00595 = 0.014”

Johnston CountyAbare = 273 * 0.43 * 2.9 * 1.0 *1.0 * 0.00595 = 2.026”Amat = 273 * 0.43 * 2.9 * 0.06 * 0.9 * 0.00595 = 0.109”

Are these acceptable losses?

SOIL LOSS TOLERANCE (SLT FACTOR)

• The SLT factor is an estimate of the maximum average annual rate of soil erosion by wind and/or water that can occur without affecting crop productivity over a sustained period. The rate is in tons per acre per year.

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SOIL LOSS TOLERANCE (SLT FACTOR)

SOIL LOSS TOLERANCE (SLT FACTOR)

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SOIL LOSS TOLERANCE (SLT FACTOR)

• 0.00595 = conversation factor for soil loss rate from tons/acre to uniform inches.

• SLT = 5 * 0.00595 = 0.03”

SAFETY FACTOR (IREDELL COUNTY)“RUSLE” A = R * K * LS * C * P * 0.00595

Abare = 150.5 * 0.1 * 2.9 * 1.0 *1.0 * 0.00595 = 0.26”

Amat = 150.5 * 0.1 * 2.9 * 0.06 * 0.9 * 0.00595 = 0.014”

SLT = 0.03”

SF = SLT/A 0.03”/0.014” = 2.14 (STABLE)

If SF > 1.0 = Stable Design

If SF< 1.0 = Unstable Design

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NORTH AMERICAN GREEN

SAFETY FACTOR (IREDELL COUNTY)

American ExcelsiorErosion Works 9.1

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AMERICAN EXCELSIOR EROSION WORKS 9.1

SAFETY FACTOR (JOHNSTON COUNTY)“RUSLE” A = R * K * LS * C * P * 0.00595

Abare = 273 * 0.43 * 2.9 * 1.0 *1.0 * 0.00595 = 2.026”

Amat = 273 * 0.43 * 2.9 * 0.06 * 0.9 * 0.00595 = 0.109”

SLT = 0.03”

SF = SLT/A 0.03”/0.109” = 0.275 (UNSTABLE)

If SF > 1.0 = Stable Design

If SF< 1.0 = Unstable Design

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SAFETY FACTOR (JOHNSTON COUNTY)

SLOPE IS TOO STEEP!

GOOD PRACTICE!

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GOOD PRACTICE!

GOOD PRACTICE!

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GOOD PRACTICE!

GOOD PRACTICE!

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GOOD PRACTICE!

GOOD PRACTICE!

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GOOD PRACTICE!

GOOD PRACTICE!

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GOOD PRACTICE!

GOOD PRACTICE!

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GOOD PRACTICE!

GOOD PRACTICE!

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NEW STABILIZATION TIMEFRAMES!

GOOD PRACTICE!

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GOOD PRACTICE!

GOOD PRACTICE!

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GOOD PRACTICE!

GOOD PRACTICE!

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GOOD PRACTICE?

GOOD PRACTICE?

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GOOD PRACTICE?

RIPARIAN SEEDING

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RIPARIAN SEEDING

EXTRA! EXTRA!

FOX SQUIRREL

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REFERENCES

https://www.bae.ncsu.edu/bae/workshops/dot/ppts_level3/text.pdf

http://portal.ncdenr.org/c/document_library/get_file?uuid=076fbe07-5fd9-4d76-b1d6-2600efde8c99&groupId=38334

http://www.dec.ny.gov/chemical/29066.html

QUESTIONS

Matthew B. Poling, PE

Assistant State Sediment Specialist

Division of Energy, Mineral, and Land Resources

512 North Salisbury Street

1612 Mail Service Center

Raleigh, NC 27699-1612

Voice: (919) 707-9209

Fax: (919) 733-2876