Land Reclamation, Landslide Treatment 453

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NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION PRACTICE STANDARD

LAND RECLAMATION, LANDSLIDE TREATMENT (No. and Ac.)

CODE 453

DEFINITION 2. Geologic profiles and cross sections showing attitude and conditions of strata Managing in-place natural materials, mine spoil and details of the slip zone (excavated over-burden), mine waste or overburden to reduce down-slope movement. 3. Soil classification and properties, including gradation, density, strength, and chemical characteristics PURPOSE 4. Ground-water conditions  Repair unstable slopes caused by slope 5. Depth extent, and volume of material failure, and reduce the likelihood of involved enlargement or renewed movement of 6. Estimated pre-slide profile and subsurface slope surfaces; conditions  Protect life and property; 7. Conditions where slopes are stable in  Prevent excessive erosion and similar materials sedimentation; 8. Extrinsic factors (e.g. land use activities  Improve water quality and landscape and/or precipitation events) that triggered resource quality; and or remobilized the failure.  Create a condition conducive to Extreme caution must be exercised and careful establishing surface protection and planning is required before permitting any beneficial land use. personnel, drilling equipment, or construction machinery, in the slide area. A slide is often active during wet periods and may be CONDITIONS WHERE PRACTICE APPLIES comparatively stable during dry periods. To areas where in-place material, mine spoil, Slope stability. Measures developed to waste, or overburden, or rock cut road banks prevent or stabilize slides shall be based on are unstable, moving, or judged to have engineering analysis and judgment made by potential of moving down slope in a manner an engineer trained and experienced in soil that will cause damage to life, property, or the mechanics and soil bioengineering. environment. It does not apply to constructed embankment surfaces such as road fills, dams, Slope stability analysis shall account for all dikes, levees and terraces. critical soil and loading conditions. The strength parameters of natural soil and rock or of waste materials shall be based on the CRITERIA appropriate conditions for each slide. Long- Investigations. Investigations shall include term strength parameters (c=0 and internal and extend beyond the area of the landslide friction based on residual shear) shall be used. and shall be made to determine: The methods of slope stability analysis are to be appropriate for the loading conditions and 1. Surface profiles, cross sections, and for the location and shape of sliding or topographic features potential failure surfaces.

Conservation practice standards are reviewed periodically, and updated if needed. To obtain NRCS, NHCP the current version of this standard, contact your Natural Resources Conservation Service State Office, or download it from the electronic Field Office Technical Guide. February 2005 453 - 2

Appropriate safety factors shall be provided Earth material control. The design shall take based on the degree of uncertainty in the soil into consideration the following factors on strength values used, the soil and water impacting loading, strength or counter- conditions assumed, and the detail of the buttressing as appropriate: analysis used.  earth material When there is a potential for loss of life or  internal water damage to farmsteads, residential areas,  rock material frequently traveled roads, and occupied  Loading control. Where appropriate, facilities, or important public utilities, the measures shall include removal of the material consider alternatives for loading control, subject to sliding or any other control to ensure including: removing excess material from safety. the upper portions of the slide mass; removing the entire slide mass; dewatering The requirements contained in the NRCS at least the upper portion of the slide, and National Engineering Manual Part 531.26 (a) removing excess weight associated with shall apply for the geologic investigations and development. Sites for safe disposal of seismic assessments. Criteria for minimum excavated slide material should be seismic coefficients and recurrence interval identified as part of planning and design. shall be as required in the state building code.  Slope reduction. Critical slopes within Water control. Sources of water that will the slide area shall be reduced by grading enter the landslide area shall be controlled to when practical. the extent possible in accordance with the following:  Increasing internal strength. The design shall analyze the impact of removing and  Surface runoff water. Runoff water that recompacting of material at designed would enter the landslide area is to be levels of moisture and compactive effort. It intercepted and conveyed to a stable shall also analyze the impact of outlet. biotechnical slope stabilization practices.  Water from direct precipitation.  External restraints. External restraints Infiltration shall be limited to the extent shall be used where slope movements possible by providing positive surface must be limited due to high-valued drainage and sealing surface cracks within improvements, and where manipulation of the area. Grading and shaping may be the earthen material may not achieve the required to provide positive surface desired results. External restraints shall drainage. Terraces structures and be designed to withstand overturning, waterways are to be installed as needed to sliding at or below the base, and bearing provide safe water disposal without failure of the foundation. All measures erosion and with positive grade to reduce shall include provisions for proper seepage. The surface of the treated area drainage. shall be protected from erosion as appropriate. Vegetative treatment. Vegetation shall be planted using selected soil bioengineering or  Ground water. Design measures, biotechnical slope stabilization techniques including vegetative treatment where appropriate to the site. Deep rooted grasses appropriate, shall be taken to intercept and shrubs with proven performance in soil ground water that contributes to instability bioengineering applications shall be used. The of the area. Drainage systems shall be transpiration potential and rooting depth of the designed in accordance with Part 633, vegetation applied shall be considered. Site Chapter 26 of the National Engineering conditions including soil pH, particle size, and Handbook, and the system shall be nutrient content shall be analyzed, and this designed to remain operational in the information used to select the appropriate event of limited movement of the area after vegetative treatment and plant materials for the construction. site.

NRCS, NHCP February 2005 453 - 3

Component practices. All individual practices reshaped and regraded to blend in with the installed as a component of landslide treatment surrounding land features. are to be designed and installed in accordance with applicable NRCS conservation practice PLANS AND SPECIFICATIONS standards and specifications. If NRCS standards are not available, the practice is to Plans and specifications for slide treatment be designed and installed using current shall be in keeping with this standard and shall engineering technology. describe the requirements for applying the practice to achieve its intended purpose. Environmental. All disturbed areas are to be provided with adequate water disposal systems and established to vegetative cover, OPERATION AND MAINTENANCE or otherwise protected, to control erosion and The maintenance plan is to include periodic sediment as soon as practicable. Temporary inspections for additional movement, failure of protective measures will be necessary if a long water disposal systems, vegetation, and other delay is anticipated in establishing permanent problems. The water disposal system, cover. Human, animal and vehicular traffic is subsurface drainage system, access roads, to be controlled to protect the area. and vegetative cover are to be maintained to accomplish their intended purposes. CONSIDERATIONS Necessary maintenance and repair activities are to be initiated promptly. Consider offsite water quality effects such as acid mine drainage. REFERENCES Consider designing drainage systems that remain operative after limited movement. Landslides: Investigation and Mitigation. Pipes should be used with caution because of Special Report 247. 1996. Transportation the potential of breaking and/or misalignment Research Board, National Research Council, with further movement. Flat or nearly flat National Academy Press, Washington, D.C., gradients should be avoided for the same 673 p. reasons. National Engineering Handbook. Chapters 16, Consider visual resources with other design 18, 26. USDA-NRCS. features during planning, design, and Rural Abandoned Mine Program (RAMP) installation. All disturbed areas can be Handbook. USDA-NRCS.

NRCS, NHCP February 2005