**3. Use of bamboo in soil bioengineering techniques**

The strength of bamboo culms and roots and their straightness, lightness combined with hardness, range and size of hollowness make them potentially suitable for a variety of both structural and nonstructural applications. With good physical and mechanical properties, low shrinkage and good average density, bamboo is well suited to replace wood/timber in soil bioengineering applications but also to act on its own as a living material providing rapid ground coverage and sediment trapping, increasing surface roughness, increasing soil strength and decreasing pore-water pressures in the soil by evapotranspiration.

The selection of appropriate techniques is based on a specific site assessment and design criteria. Local climate conditions (precipitation regimes, seasonal variation, averages and extremes of temperature and rainfall), topography (slope gradient, terrain shape, elevation, sun exposition), soil (types, permeability, moisture and nutrient conditions), hydrological conditions and the most relevant erosion processes define the set of feasible techniques for a particular site. In a following step, the evaluation of the existing surrounding vegetation is most important for the design, in terms of project limitations, opportunities and potential long-term achievements. Even when bamboo is the main vegetal constructive element, the long-term success of any bioengineering implementation work is based on a wide range of plant species. It is also important to take into account the bioengineering-specific local logistical and economic constraints. Finally, all this gathered and specific site information forms the basis for selection of the appropriate bioengineering technique, plants and materials to use.

These limitations imply the need for the use of complementary structures to help overcome temporarily or permanently—the local adverse conditions. This situation determined the development of a particular segment of the industry related to complementary materials (e.g. organic geotextiles) aimed at reducing the impact of water and soil erosion in the initial development phases of the construction and interventions and to the conception of construction techniques using classical civil engineering approaches and materials in combination with the

The main concerns for soil bioengineering are related to soil support, cover, and consolidation, as well as the regulation of the forces and processes (mainly hydrological, hydraulic, and

• Support functions, in terms of building or fostering the development of structures able to stabilize slopes affected either by an increase on their slope angle or by an increase of the

• Regulation functions in terms of hydrological processes such as interception, evapotranspi-

These functions are performed mainly through the action of plant aerial parts and roots as well as the associated soil biota, through their action in soil anchoring, structuring, aggregating, draining, buttressing, and reinforcement. All of these functions, mainly ensured by living autochthonous vegetation, have the complementary advantages of promoting biodiversity

but also because the techniques and the nature and quantities of the complementary materials used imply a lower production of greenhouse gases and natural resource consumption.

The strength of bamboo culms and roots and their straightness, lightness combined with hardness, range and size of hollowness make them potentially suitable for a variety of both structural and nonstructural applications. With good physical and mechanical properties, low shrinkage and good average density, bamboo is well suited to replace wood/timber in soil bioengineering applications but also to act on its own as a living material providing rapid ground coverage and sediment trapping, increasing surface roughness, increasing soil

The selection of appropriate techniques is based on a specific site assessment and design criteria. Local climate conditions (precipitation regimes, seasonal variation, averages and extremes of temperature and rainfall), topography (slope gradient, terrain shape, elevation, sun exposition), soil (types, permeability, moisture and nutrient conditions), hydrological

strength and decreasing pore-water pressures in the soil by evapotranspiration.

emissions, not only through its capture during construction

• Consolidation functions in terms of soil protection, structuring, and reinforcement

The main functions fulfilled by the bioengineering approach are the following:

• Cover functions in terms of protection against erosion and trampling

**3. Use of bamboo in soil bioengineering techniques**

advantages brought by vegetation.

108 Bamboo - Current and Future Prospects

wind-related) that act as disturbance factors.

external or internal acting forces

ration, infiltration, and runoff control

and strongly reducing the CO<sup>2</sup>

The use of bamboo to make retaining structures for soil mass or for stream bank erosion control has been practiced in traditional way in various places around the world for long time. Live bamboo stakes, wattle fence, hedge brush layering techniques and bamboo crib walls are most commonly used bioengineering techniques. Several handbooks describe these techniques and can be used as references [4]. However, an engineering design of bamboo retaining structures, such as bamboo crib wall, has not been detailed so far. For this reason, this section is focused on this bamboo bioengineering technique.

A live bamboo crib wall is a three-dimensional structure created from untreated bamboos, fill material and live cuttings. Morgan and Rickson [5] described the crib wall as 'a specialized form of gravity-retaining structure using on-site fill material, held within a constructed framework, to provide most of the necessary mass to resist overturning by the weight of both the slope and the materials'.

This crib structure, once filled, acts as a retaining structure and supports the slope. The bamboo and other installed plants provide immediate protection and stability to the structure. However, it has to be taken into account that the structure stability and resistance to failure will be gradually decreasing as its construction materials decompose. As the bamboo elements of a crib wall decompose, the live cuttings of plants or bamboo clumps will grow and proliferate. The resulting root mass will then bind the fill material and the parent soils of the slope into a single continuum, which will have enhanced strength and contribute towards the stability of the slope. **Figure 1** shows the construction steps from a practical application of a bamboo crib wall in Nepal [6, 7].
