**7.2. Internal stability check**

to' for the tests specified in ISO 22157-1 [15, 16]. On a number of issues, this standard refers to existing national and supranational standards which should be followed, especially for bamboo application in temperate climates (e.g. W. Europe, Canada). This standard contains a

The above ISO standards provide the basis for design with bamboo culms. However, they do not include content relating to living bamboo (design and testing) and the use of a combination of living and inert bamboo in a structure. The existing standards need to be updated and expanded to reflect the growing research on test methods and material characterization of both living and inert bamboo, especially covering the durability and evolution of load transfer mechanisms with time. This update could be partially covered by an attempt to use the existing timber-based test methods for characterization and design [29] which could be beneficial in engaging engineers and architects [31] in the use of bamboo for bioengineering purposes.

The analysed structures can be classified as soft engineering structures [24] with a certain durability and change in stress transfer mechanism over the lifetime of the structure. The durability of the structure will depend on the used bamboo species and the biological activity of local degrading mechanisms but also on air temperature, humidity and soil moisture variability. In the bioengineering design approach, the load transfer between the initial structural elements and the developing structural vegetation elements can be calculated using a bioen-

number of examples, templates and backgrounds to the tests specified in [15].

**7. Stability checks for bamboo retaining structures**

• Determination of the mechanical properties of the wooden elements

• Determination of the stress diagrams of the different structural elements

• Determination of the decay rate of the wooden element and their design service life • Determination of the plant root system growth and the roots' mechanical properties

progression of decay and development of the live elements in the structure [26]

• Stability assessment of the structure at different periods of its design lifetime reflecting the

As with any stabilization structure, soil bioengineering solutions must be checked from a structural point of view to ensure that both external (sliding, overturning, bearing capacity and slope failure; **Figure 1**) and internal stability conditions are satisfactory. These checks must include both decay and living plant effects, in order to reflect the changes during the lifetime of the bioengineering solution. The external stability checks are usually performed in line with existing geotechnical engineering design standards and the stability is expressed in terms of a factor of safety (FoS; e.g. [32]). In this book chapter, both the FoS expressions for bare and vegetated soil [24] and the use of lumped global FoS for the sliding and overturning checks

value with time across the sliding plane [33], while the resistance to overturning (FoS<sup>o</sup>

) will be affected by the evolution of the RAR

) will

gineering design scheme for durability [26]:

are proposed. The resistance to sliding (FoS<sup>s</sup>

**7.1. External stability checks**

120 Bamboo - Current and Future Prospects

Internal stability analysis consists of checking the mechanical capacity of the bamboo culms which are fulfilling structural functions within the ground bioengineering work.

The characteristic strength values should be obtained according to ISO 22157 [15, 16]. Suggested characteristic strength values for any bamboo species can be found in [35]. These values should be adapted to the bamboo moisture content by using the moisture content correction factor included in [35] which is based on NSR [36] and EN 384 [37]. Bamboo live pole (pegs) strength characteristic values have been shown in preceding epigraphs (see **Table 3**). The values for the material factor of safety are specified in ISO 22156 [30]. Recommended values for this factor can also be found in [35].

In soil bioengineering works, bamboo culms work under Service Class 3 conditions (relative humidity >85%) and in-ground conditions. This situation can be reflected by means of the service class and load duration factor (Kmod) which can be determined from the existing standards [30, 35].

Other factors making allowance for other conditions (e.g. earthquakes, connection between elements of different rigidity, etc.) can also be found in [35].

Bamboo structures' internal stability checks follow Eurocode 5: Design of timber structures. This design scheme is detailed in ISO 22156 [30] and in [38]. Because of the specific bamboo culm shape, the cross-sectional area to be used in the design calculation is the following:

$$A = \frac{\Pi}{4} (De^2 - (De - 2t)^2) - \sum area \text{ of any holes} \tag{2}$$

where *A* is the net area of section; *De* is the bamboo culm outer diameter; *t* is the bamboo culm average thickness.

Accordingly, the elastic section modulus (*Selastic*) for the bamboo case will be.

$$
\Gamma\_{\text{elastic}} = \frac{\Gamma\_{\text{elastic}}}{\Gamma\_{\text{elastic}}}
$$

$$
\mathcal{S}\_{\text{elastic}} = \frac{\Pi(De^4 - (De - 2t)^4)}{32De} \tag{3}
$$

By comparing the existing stress values with the element bending capacity, shear, axial tension or axial compression, the internal stability check can be fulfilled.

Additionally, Eqs. (2) and (3) can also be useful for determining the minimum bamboo culm dimeter fulfilling the internal stability condition [29].

The forces exerted on the bamboo culms can be determined by using traditional structural calculation theory (**Figure 5**). Typically, the moment, shear and axial stress diagrams should be generated and their maximum values used for internal stability checks [29].

**8. Plant material quality control, maintenance and monitoring of** 

including inspection and test records, test data, corrective actions, etc.

Quality assurance manual (QAM) covering the bamboo application and approved by the overseeing organization should form an integral part of soil bioengineering project documentation [30]. For the purposes of soil bioengineering works, the QAM should record the control of plant material (including incoming material, inspection and acceptance requirements), personnel, design, construction, quality assurance testing and acceptance procedures, sampling and inspection frequencies and procedures to be followed upon failure to meet specifications or upon out-of-control conditions. The QAM should be supplemented by relevant records,

The Use of Bamboo for Erosion Control and Slope Stabilization: Soil Bioengineering Works

http://dx.doi.org/10.5772/intechopen.75626

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There are a large number of species of bamboo native to different world regions, mainly in the warm and moist tropical and warm temperate climates. Current standards recognize that methods of identification of bamboo through anatomical characteristics have not been perfected. To mitigate against the risk of selecting inadequate/untested species, experienced sorters should be employed in identification through morphological characteristics on full

Quality control must ensure that only matured bamboo of at least 4 years of age shall be used in construction, preferably after at least 6 weeks after felling. Experienced quality assessors should ensure that solid bamboo culms or culms with thicker walls and closely spaced nodes are selected for structural use. Conversely, the quality assurance control must ensure that any broken, damaged or collapsed bamboo shall be rejected while dead/immature/infected

If living bamboo is to be used in the structure, the origin/provenance of the bamboo seeds/ seedlings/plantings should be recorded in the QAM together with the species name(s), application/planting rate/density, fertilizer, mulching, soil preparation and maintenance requirements. This must be supported by certificates relating to type, origin, quality and validity of

Knowing that the natural durability of bamboo is relatively low (12–24 months when used in the open and in contact with the soil but depending on the species and environmental conditions), and its strength decreases rapidly with the onset of fungal decay, suitable treatment (traditional treatments if possible) for preserving bamboo must be applied considering the environmental impact and health aspects of labour and all users of the structure. The samples for testing the effect of preservatives must be cut from treated bamboo for chemical analysis

Air-dried bamboo should be used whenever possible in order to ensure it deteriorates more slowly. QC should ensure that, if the bamboo delivered to site is wet, there is an opportunity

**bamboo structures in soil bioengineering**

standing culm and the results recorded in the QAM.

**8.1. Plant material quality control**

bamboos shall be avoided.

seeds/plants and quality of fertilizers.

(e.g. a weight of approx. 100 g per 100 kg bamboo treated).

to dry again before it is applied in the soil bioengineering structure.

**Figure 4.** (A) Sliding check and (B) overturning check. The bamboo root effect (if applicable) is highlighted within the circle (adapted from [26]).

Given the low natural durability value of bamboo species, an adapted design scheme making allowance for the wooden element deterioration process can be adopted [26]. In order to give answer to cross-sectional losses because of decay processes at the internal stability design level, different strategies can be followed:


In the last two cases, lower forces will be exerted on the bamboo culms, and, therefore, lower diameters will be able to withstand them and ensure the internal stability of the bamboo structure. A complete example of the preceding design approach can be found in [26, 29].

**Figure 5.** Example of stress diagrams for the vertical and horizontal elements in a bamboo palisade [29], where q is the distributed load (kN/m<sup>2</sup> ), L is the length of the element (m), H is the height of the vertical element and Ka is the coefficient of active earth pressure (dimensionless).
