25-07-2012, 01:09 PM
Bioengineering for The Protection of Soil Erosion
Bioengineering for The Protection of Soil Erosion.pptx (Size: 4.11 MB / Downloads: 59)
Definition
Bio-engineering is the use of vegetation, either alone or in conjunction with civil engineering structures, to reduce instability and erosion on slopes. It should be a fundamental part of the design and construction of all roads in rural (and urban) hill areas, mainly because it provides one of the best ways to armour slopes against erosion. Because of the steep and dynamic slopes , most hill roads are engineered near to the margin of safety. Bio-engineering is an effective way of enhancing civil engineering structures to increase stability as far as possible. It is relatively low in cost uses local materials and skill, and provides livelihoods benefits through, economically useful products.
Effects of plantation on soil
Plants have a number of effects on soils and slopes, which can be categorised as hydrological and mechanical.
plants used in combination can provide much greater effects than single plants, but with a similar increase in complexity. For example, a single grass plant can catch a small amount of debris and reinforce a small volume of soil with its roots.
If a line of grasses is planted across a slope, together they form a continuous chain to catch debris, and can provided a linear rather than a point of reinforcement.
In the process of serving these functions, however, the contour line of grass will also increase the infiltration capacity of the soil.
If the material characteristics are such that this may lead to a critical condition of saturation, then another function, that of drainage, will be required.
Grass planting
Large clump grasses can be planted in various configurations, such as contour, diagonal or even down slope lines, depending on the characteristics of the materials, and perhaps combined with a jute or synthetic geotextile. This provides erosion control and shallow reinforcement.
Grass seed is spread on to the slope, armouring the surface. Alternatively, grass is hand-planted in lines across the slope. The lines armour the slope and catch debris. Angled lines planted by hand may also help to drain the surface, but catch little debris.
Shrub and Tree Planting
Shrubs or trees are planted at regular intervals on the slope. As they grow, they create a dense network of roots in the soil. The main engineering functions are to reinforce and, later, to anchor. In the long term, large trees can also be used for slope support.
Brush Layering, Palisades and Fascines, etc
Composite Systems
A range of composite systems are commonly used. Examples are: Live check dams, which armour and reinforce gully beds and catch debris; vegetated stone pitching, which provides strong armouring for water courses; planted geotextiles, where the geotextile provides armouring, later supplemented by the vegetation, which also reinforces the soil.
Site Assessment
The geological element in slope structure, geomorphologic processes, the identification of erosion and landslide causes and mechanisms, and determination of treatment strategies.
Integration with standard civil engineering measures, plant species selection, propagation and construction techniques.
• Bio-engineering planning and implementation: the programming of bio-engineering works in relation to the seasonal calendar and construction schedules, critical paths for plant propagation, site preparation and works implementation; and the options for phasing works over more than one year.
Steps for the Process
Initial plan,
Prioritise works,
Divide the site or slope into segments ,
Assess the site ,
Determine conventional civil engineering works,
Choose the right bio-engineering technique,
Design the civil and bio-engineering works,
Select the species to use ,
Calculate the required quantities and rates ,
Finalise priority against available budget ,
Steps for the Process
Plan plant needs (i.e. order seeds, nursery stock) ,
Decide implementation/prepare documents,
Prepare for plant propagation,
Site arrangements ,
Prepare the site for work ,
Implement the civil engineering works ,
Implement the bio-engineering works,
Monitor the works .
Issues keep in mind
The main issue that has to be grasped by engineers is that plants cannot be procured without some advance preparation, and that works have to be scheduled more precisely in line with seasons; this is particularly important under the monsoon climate that prevails in northern India.
Quality Control
Quality control is also important due to the fact that bio-engineering techniques have low margins of safety. Inert materials (such as stone, concrete and steel) allow the engineer to over-design slope stabilisation measures where there is doubt over the factor of safety
Vegetative structures using hardwood cuttings: brush layers, fascines and palisades, with the angle of the lines determined by the type of material and slope on which they are applied. These also control erosion, catch debris and provide strong, fibrous root reinforcement.
Tree planting, as part of a plant community with under storeys of shrubs and grasses: a wide range of possibilities are available, to suit all environmental conditions. Tree roots offer greater reinforcement and anchorage.
Without any protection
Support a weak soil mass by the provision of toe support.
This can be achieved either by creating a heavy, immovable weight at the base of the slope, or by altering the slope to create an effect of buttressing and arching (where the soil between buttresses is supported from the sides by compression). The buttresses and arches of a building have similar engineering functions.
Toe Support at the Start Of The Work
Grasses had been effective at stabilizing surface erosion. To maintain surface stability and to prevent shallow rapid land sliding, trees (20%) and shrubs (80%) would be planted at a minimum of 4-foot x 4-foot spacing.
Benefit: root development increases soil strength and slope stability
Future Expectations
1- Increase its use in India,
2- lesser damages in the hill roads,
3-Economic growth,
4-Improves countries greenery which attracts foreigners.