Sprague, J. Vinyl, asphalt, rubber, anionic and nonionic polyacrylamide PAM , and biopolymers are examples of chemical stabilizers that can be sprayed onto an exposed soil surface to hold the soil in place and minimize erosion from runoff and wind EPA Chemical soil stabilizers can be used in areas where vegetation cannot be established, or on rough grading, cut and fill areas, tempo- rary stockpiles, temporary or permanent seeding, or for site winterization, dormant seeding in the fall, staging areas, or other disturbed soils IUM When asked to provide an example of an underutilized tool, technique or method of erosion control, one respon- dent Skip Ragsdale, personal communication, April 18, said, a disturbed area.
Straw bales are readily available in most locations. One disadvantage is that they are bulky and heavy when wet Caltrans Straw bale barriers are short-term erosion control mea- sures that are best used at the base of a slope or down-slope of disturbed soil. Straw bale barriers can be placed around stockpiles, such as a stockpile of topsoil that will be used again later in the project, and can be used to protect drain inlets and ditch lines Caltrans Straw bale barrier maintenance may include replacing damaged straw bales, repairing washouts, or removing accu- mulated sediment behind the straw bale.
The straw bales should be removed and accumulated sediment redistributed once work is complete Caltrans SILT FENCES Silt fences are a linear barrier of permeable fabric designed to intercept and slow the flow of sediment-laden runoff, allow- ing sediment to settle from the runoff before water leaves the site Caltrans Silt fences are difficult to construct and maintain, and their use is for short-term maintenance only Caltrans Although silt fences are widely used, they are often not installed correctly, not maintained, or not removed once the work is complete.
Additionally, silt fences are made of nonbiodegradable materials. Erosion control professionals have recently called for more stringent specifications to be placed on silt fence installation techniques Sprague and Carpenter Currently two techniques, static slicing and trench-based installations, can be used to achieve maximum silt fence performance. Static slicing requires the insertion of a.
There was a new Interstate project in which the sculpted road was going to sit unpaved from November through May. PAM creates an electrochemical reaction that draws fine particles close together, making larger particles that are more resistant to erosion and large enough to settle from suspen- sion Cohn Historically, PAM has been used in agri- culture to reduce soil loss in irrigation channels. When used for slope stabilization, PAM is only to be used where sheet flow is present. PAM is not be used on slopes greater than unless additional erosion-control measures such as mulch, geotextiles, or mats are used IUM PAM should not be applied to frozen soil or where ice is present.
It works best in soils with significant amounts of fine silts, clays, and colloidal particles, although overapplication can reduce soil infiltration rates. PAM breaks down over time, and areas of application need to be inspected regularly for signs of ero- sion. Biopolymers that chemically stabilize soil include chi- tosan, cellulose and starch xanthates, and cellulose micro- fibrils Orts et al.
Chitosan, a naturally occurring polysaccharide, is derived from chitin in shellfish. Historically, cellulose and xanthates have been used as soil stabilizers. Cotton microfibrils are a new product that shows potential for soil stabilization. The U.
Some countries, including Japan, Germany, and the Netherlands, have banned or highly restricted its use in drinking water treatment. The EPA permits chitosan use in drinking water, waste water, and industrial water. Divakaran, R. Code , [Online]. Nichols, E. Orts, W. Sojka, and G. Sojka, R. Bjorneberg, J.
Entry, R. Lentz, and W. Soil bioengineering is a technique that uses plants and plant material alone, whereas biotechnical techniques use plants in conjunction with more traditional engineer- ing measures and structures to stabilize slopes Gray and Sotir ; Schiechtl and Stern and alleviate shal- low, rapid landslides and eroding stream banks Lewis et al.
Both soil bioengineering and biotechnical tech- niques contribute to sustainable development practices, as they enhance the aesthetics of the highway environment and reduce the ecological impacts of highway construc- tion, maintenance, and operations. In soil bioengineering systems, plants grasses and shrubs, especially deep- rooted species are an important structural component in reducing the risk of slope erosion Jiang et al.
Soil bioengineering measures are designed to aid or enhance the reestablishment of vegetation USDA Properly designed and installed vegetative portions of systems should become self-repairing, with only minor mainte- nance to maintain healthy and vigorous vegetation. Soil bioengineering frequently mimics nature by using locally available materials and a minimum of heavy equipment, and is an inexpensive way to treat slope stabilization Lewis et al.
Faiz, personal communica- tion, May 6, Soil bioengineering has six main functions: 1. To catch eroded materials with physical barriers e. To armor the slope from erosion caused by runoff or rain splash using vegetative cover, partial armoring using lines of vegetation; 3. To reinforce soil physically with plant roots; 4. To anchor surface material to deeper layers using large vegetation with deep roots or rock bolts; 5. To support soil by buttressing with retaining walls or large vegetation; and 6. To drain excess water from the slope through the use of drains and vegetation Howell ; Schor and Gray When using soil bioengineering and biotechnical stabi- lization practices on slopes, consider a partnership among many disciplines, including soil scientists, hydrologists, bot- anists, engineering geologists, maintenance personnel, civil engineers, and landscape architects Lewis et al.
Consider topography, geol- ogy, soils, vegetation, and hydrology. Avoid extensive grading and earthwork in critical areas. Any materials removed from the site are to be kept on site and reused if possible. Soil bioengineering systems generally require minimal access for equipment and cause relatively minor site distur- bance during installation USDA The timing of implementation of a soil bioengineered and biotechnical treatments is an important part of plan- ning.
Native Roadside Vegetation that Enhances Soil Erosion Control in Boreal Scandinavia
Consider planting during the dormant season, usually. Installation of live cuttings should begin concurrently with earthmoving operations if they are carried out during the dormant season. All construction operations are to be phased together when possible. The selection of plant species is also important. Second, wherever possible, native plant species e. Over time, highway agencies could see significant savings in labor, fuel, maintenance equipment costs, and reduced chemical use. Chen et al. Finally, mixture seeding is a desirable method of establish- ing a viable plant community for roadside slope protection.
For this specific region, the field results indicated that the Indigo- fera pseudotinctoria and Pinus massoniana ranked the best and the worst, respectively. The authors suggested that the mixture seeding utilize woody plants featuring high stress resistance and outstanding growth potential as target species in conjunction with herbaceous plants featuring high early growth ability as protective species. Soil bioengineering and biotechnical projects ideally use on-site stockpiled topsoil as the planting medium USDA Soil bioengineering and biotechnical systems need to be installed in a planting medium that includes fines and organic material and is capable of supporting plant growth.
The same study also found that the addition of more water retainer and soil stabilizer instead of mulch improved the performance of ordinary spray seeding. The selected soil backfill does not need to be organic topsoil, but enough organic material needs to be present to support plant growth. On-site soil should be tested for nutrient content, metals, and pH before the vegetation is installed. Soil around the vegetation should be compacted to densities approximat- ing the surrounding natural soil densities, and soil around plants should be free of voids USDA Vegetation alone plays an important role in stabilizing slopes by intercepting and absorbing water, retaining soil below ground with roots and above ground with stems, retarding runoff velocity by providing a break in the path of the water and increasing surface roughness, and increas- ing water infiltration rates, soil porosity, and permeability Schor and Gray Each type of vegetation serves a critical function.
Grasses, or herbaceous cover, protects sloped surfaces from rain and wind erosion. Shrubs, trees, and other vegetation with deeper roots are more effective at preventing shallow soil failures, as they provide mechani- cal reinforcement and restraint with the roots and stems and modify the slope hydrology by root uptake and foliage interception Schor and Gray Where the main func- tion of structural elements is to allow vegetation to become established and take over the role of slope stabilization, the eventual deterioration of the structures is not a cause for con- cern USDA Field studies have shown instances where combined slope protection systems have proven to be more cost- effective than the use of vegetative treatments or struc- tural solutions alone USDA Lewis et al.
The average benefit-to-cost ratio in this study was 2. Soil bioengineering and biotechnical treatments should not be considered the solution to every slope failure and surface erosion problem USDA At some sites, hand seeding with grass seed will be the most cost-effective solution for the site, while at other sites a better solution may be an engineered retaining wall, with or without a vegetative component. Fox, P. Wu, and B. Gray, D. Ganabahal, Kath- mandu, [Online]. Sandhu, N. Vyas, R. Sheikh, and S. Lewis, L. Department of Agriculture, Wash- ington, D. Salisbury, and S.
Ramakrishna, A. Schiechtl, H. Baker, U. Schor, B. When correctly prepared and planted, or placed, the live stakes will root and grow. A system of stakes creates a living root mat that stabilizes the soil by reinforcing and binding soil particles together and by extracting excess soil moisture. In the United States, willow is a good woody plant that roots rapidly and begins to dry out a slope soon after installation USDA Live stakes are an appropriate technique for repair of small earth slips and slumps that are frequently wet. Live staking is a technique for relatively uncomplicated site conditions when construction time is limited and an inexpensive method is necessary USDA Live stak- ing can also be used to pin down, or anchor, erosion control materials on the surface.
Live stakes are also well suited for stabilizing intervening areas between other soil bioengi- neering techniques, such as live fascines. Live cuttings should be 0. Side branches are to be cleanly removed with bark intact. Basal ends are to be cut at a degree angle for easy insertion into soil and the top is to be cut square.
It is important that cuttings be installed as. Four-fifths of the length of the live stake should be installed in the ground and soil compacted around it after installation, with care taken not to split the stakes. In this technique, bundles of live branches are laid in shallow trenches and partially buried.
After burial in the trenches, they put out roots and shoots, forming a strong line of veg- etation, also called live contour wattling. Live fascines mechanically reinforce the soil with roots, deplete soil water through transpiration and interception, and buttress the soil with the embedded stems USDA ; Howell Live fascines also dissipate the energy of downward-moving water by trapping debris and providing a series of benches on which grasses, seedlings, and transplants establish more easily USDA In certain locations, fascines can be angled to provide drainage Howell Fascines immedi- ately reduce surface erosion or rilling and are well suited for steep, rocky slopes where digging is difficult USDA Woody species, such as shrub willow or dogwood, are made into sausage-like bundles, which are generally ori- ented parallel to the slope contour USDA Figure Portions of fascines will root and become part of the stabi- lizing cover.
Fascines are best used on consolidated debris and fill slopes or soft cut slopes Howell If the soil material is too hard, growth will be unacceptably slow. When time is an issue, brush layering may be a more appropriate option, as it establishes more quickly than fascines. Fascines can be used on slopes up to 45 degrees, whereas wattle fences can be used on slopes up to 30 degrees Howell Contour fascines work well in well-draining materials; for poor- draining materials a herringbone pattern is suggested, as this pattern aids in drainage. Little or no maintenance is expected to be necessary for fas- cines with the exception of thinning established vegetation as needed over time Howell Wattle fences are often too weak to support the volume of debris that is caught in them; fascines have been shown to be more effective Howell Brush layers form a barrier and prevent the development of rills, and trap sediment and debris moving down-slope.
Brush layer- ing is somewhat similar to live fascine systems in that both involve the cutting and placement of live branch cuttings on slopes, but the two techniques differ in the orientation of the branches and the depth to which they are placed in the slope USDA In brush layering, the cuttings are ori- ented more or less perpendicular to the slope contour, simi- lar to live stakes.
The brush branches reinforce the slope, and the portions of the brush that protrude from the slope face assist in retarding runoff and reducing surface erosion USDA The main function of brush layering is to catch debris and to armor and reinforce the slope Howell After installation, over time a terrace or bench will develop. In certain locations, brush layers can be angled to create a drainage channel. Bench excavation should start at the toe of the slope. The surface of the bench should be sloped so that the outside edge is higher than the inside.
Live branch cuttings should be placed on the bench in a criss- cross or overlapping configuration with the brush growing tips aligned toward the outside of the bench. Backfill is then placed on top of the branches and compacted to eliminate air spaces, with brush tips extending beyond the compacted fill.
Each lower bench is backfilled with soil from excavating the bench above. Consider brush layering on slopes up to in steepness and no greater than 15 ft 4. Mulching between benches is suggested. This technique can be used on a wide range of sites up to 45 degrees Howell It is particularly effective on debris piles, fill slopes, and high embankments. Avoid using this technique on soils that drain poorly or that frequently slump.
Spacing between brush layering depends on the steep- ness of the slope Howell There is generally no need for maintenance except to replace failures if they occur, or to thin vegetation once it is established Howell Brush layering can be complex, and careful tailoring to specific site and soil conditions may be needed USDA This method is very similar to brush layering.
The main dif- ferences been brush layering and branch packing is that. Live brush cuttings should be 0. Each layer of branches is followed by a layer of compacted soil USDA Soil should be moist or moistened to ensure that the live branches do not dry out.
Slope Stability and Erosion Control: Ecotechnological Solutions - Google книги
Branch packing is not effective in areas where slumping is greater than 4 ft 1. Another method, called live gulley repair Sotir and Gray , p. Live gully repair utilizes alternating layers of live branch cuttings and compacted soil to repair small rills and gullies USDA Joint planting works well with rock blankets and rock walls. This technique is very similar to live stakes. A steel rod or pry bar is used to open up a hole in the rock. Then the live stake is placed into the hole and driven into the ground. This will also punch a hole through any geotextile filter layer behind the rock.
Roots from the plants will improve drainage by removing soil moisture, and over time create a living root mat in the soil base and around rocks USDA The root system of the mat will help to bind or reinforce the soil and to prevent loss of fines between and below the rocks USDA The live cuttings should be 0. To install, plant live branch cuttings into the openings of the rock during or after construction by tamping them with a soft mallet or by hand.
Orient the live cuttings perpendicular to the slope with growing tips protruding slightly from the finished face of the rock. Pyles, D. Hibbs, and B. Washington, D. The structure is filled with suitable back- fill material and layers of live branch cuttings, which root inside the crib structure and extend into the slope NRCS Once the live cuttings root and become established, the resulting vegetation gradually takes over the structural function of the wood members USDA Crib walls provide immediate erosion protection, while the established vegetation provides long-term stability.
The technique is appropriate at the base of a slope where a low wall may be needed to stabilize the toe of the slope, to prevent small failures, and to reduce its steepness USDA Crib walls are useful where space is limited and a more vertical structure is needed USDA Timber crib walls cost less to construct than concrete crib walls, espe- cially when timber can be harvested or gathered from the site Shah Crib walls are not designed or intended to resist large, lateral earth stresses USDA Excavate the back of the stable foundation, at the slope, slightly deeper than the front; this will add stability to the structure.
Crib walls are to be built with round or square timbers, in. Repeat these steps for each additional course of crib wall, securing each course with nails or rebar. As the crib wall structure is built up, beginning at ground level, place live branch cuttings on the backfill perpendicu- lar to the slope, cover the cuttings with backfill, and com- pact it USDA Live branch cuttings should be 0. Live branch cuttings should be placed on each course to the top of the crib wall with growing tips coming out of the face of the crib wall USDA When the fill material is tamped into openings between the poles, large hollow spaces should be avoided to ensure that the branches will root properly Shah Vegetation should be planted at a density of 10 live stakes per 3 ft 0.
This may vary with the type of vegetation used for cuttings and the slope steepness. The constructed crib wall should be tilted back, or bat- tered, if the system is built on a smooth, evenly sloped sur- face USDA Live crib walls can be complex, and careful tailoring to specific site and soil conditions may need to be considered USDA Prefabricated concrete slabs or hollow bricks are used to cre- ate the wall Shah ; Zhang and Chen There are different types of concrete crib walls, but generally 4-ft-long 1.
The footer slabs have sockets on both sides and the header slabs have convex ends on both sides Shah Empty gabions are placed in posi- tion, wired to adjoining gabions, filled with stones, and then folded shut and wired at the ends and sides. Live branches. These will take root inside the gabion baskets and in the soil behind the structures USDA In time, roots consolidate the structure and bind it to the slope.
The technique is appropriate for the base of a slope where a low wall may be necessary to stabilize the toes of the slope and reduce its steepness USDA This technique is not designed or intended to resist large, lateral earth stresses. It is important that the gabion wall be constructed to a maximum height of 5 ft 1. This technique is used where space is limited and a more vertical structure is required.
Cuttings used should be 0. Exca- vate the back of the stable foundation, closest to the slope, slightly deeper than the front to add stability to the struc- ture. Place gabion wire baskets in the bottom of the exca- vation pit and fill with rock. Place backfill between and behind the wire baskets. Place live branch cuttings on the wire baskets perpendicular to the slope with the growing tips oriented away from the slope extending slightly beyond the gabion baskets USDA Extend the live cuttings beyond the backs of the wire baskets into the fill mate- rial.
Place soil over the cuttings and compact it. There are two types of gabions: stone-filled and earth-filled. Vegetated stone gabions tend to come about naturally where trees have seeded existing gabion walls, although they could be seeded artificially. There is little concern for distortion of the wire gabion boxes How- ell The benefit is that the trees will provide flexible binding to the structure once the wire has corroded.
For stone-filled gabions, trees are unlikely to contribute much to the strength of the structure until the wire has become seriously corroded. Vegetated earth-filled gabions are a lower-cost alterna- tive to stone-filled gabions Howell They are cre- ated by placing a fill of in-situ earth behind a single layer of dry stone within the gabion basket Howell Tree seedlings are then planted on the gabion Howell Plants should be spaced 1.
Maintenance may include thinning of veg- etation to maintain the site. This technique is not widely studied or implemented. Vegetated Soft Gabion Wall Another technique, called vegetated soft gabion walls, has been used successfully in Pakistan Figure 31 Shah Soft gabions are made of jute or synthetic fiber bags, origi- nally used for fertilizer or sugar, which are filled with soil or aggregate and placed to create a soft retaining wall. This technique can be used where stones are not available for gabion construction. Maintenance may include cutting back or pruning the established plants.
Vegetated rock walls differ from conventional retaining structures in that they are placed against relatively undisturbed earth and are not intended to resist large lateral pressures.
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Vegetated rock walls are useful where space is limited and natural rock is available USDA To build a vegetated rock wall, live cuttings should be 0. Excavate the back of the stable foundation, closest to the slope, slightly deeper than the front to add stabil- ity to the structure. Excavate the minimum amount from the existing slope to provide a suitable recess for the wall. Well-draining base material needs to be used if deep frost penetration may be an issue. Place rocks with at least three load-bearing points contacting the foundation material or underlying rock course USDA They should also be placed so that their center of gravity is as low as pos- sible, with the long axis slanting inward toward the slope if possible.
When a rock wall is constructed adjacent to an impervious structure, place a drainage system at the back of the foundation and outside the toe of the wall to provide an appropriate drainage outlet USDA The overall height of the rock wall including the excavated base should not exceed 5 ft 1. A wall can be constructed with a sloping bench behind it to provide a base on which live branch cuttings can be placed during construction USDA Live cuttings should be tamped or placed into the openings of the rock wall during or after construction. The base ends of the branches should extend into the backfill or undisturbed soil behind the wall.
Live cuttings should be oriented perpendicular to the slope contour with growing tips protruding slightly from the fin- ished wall face USDA The report address topic planning, site investigation, erosion control techniques, soil bioengineering and biotechnical techniques, mechanical stabilization, and earthwork techniques. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.
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Shakya , Karen Sudmeier-Rieux.
References Publications referenced by this paper. Erosion processes in steep terrain—Truths, myths, and uncertainties related to forest management in Southeast Asia Roy C. Sidle , Alan D. Wint , L. Cammeraat , James P. Cammeraat , Rens van Beek , Annemieke M. The use of live willow poles for. Comparison of three GIS-based models for assessment and prevention. For Ecol Manag engineering strategies for slope protection.