*6.2.1 Design parameters for soil and reinforcement*

Allowable Tensile Strength (Tall) for reinforcement is chosen such that strain in reinforcement does not exceed 3–5% during design life to ensure satisfactory serviceability. φ d = φ*<sup>c</sup>* . Porewater pressure to be considered should include the worst condition expected in design life. Design values of φ d, ru, β and H are used to


**21**

**Figure 8.**

*Design chart for ru = 0 after Jewell [14].*

*Geoysynthetic Reinforced Embankment Slopes DOI: http://dx.doi.org/10.5772/intechopen.95106*

used for design.

determine required earth pressure coefficient, Kreq, and reinforcement length, LR/H, from the design charts. Design charts for ru = 0, 0.25 and 0.50 are shown in **Figures 8** and **9**. Large strain or critical state shearing resistance <sup>c</sup> ( ) φ of soil is to be

Various LE Methods such as Bishop's Simplified, Janbu's Simplified, Spencer, Morgenstern-Price, Janbu Generalized, Sarma, etc., have been developed for slope stability analysis. The problem is considered in two dimension i.e. plane strain case. The primary difference among all these methods lies in the equations of statics considered, which interslice normal and shear forces are included, and the assumed relationship between the interslice forces. **Tables 3** and **4** summarize the conditions

**6.3 Limit equilibrium (LE) method of stability analysis**

for some of the common methods of stability analysis.

#### **Table 2.**

*Salient improvements over Jewell et al. [14].*

#### *Geoysynthetic Reinforced Embankment Slopes DOI: http://dx.doi.org/10.5772/intechopen.95106*

*Slope Engineering*

ru = *u z* / γ

**Figure 7.**

**6.2 Revised design**

1 Slope angle (

3 Direct Sliding coefficient (fds)

*Salient improvements over Jewell et al. [14].*

The interslice forces are assumed to be zero. Design charts calculate total reinforcement force and length of reinforcement in terms of slope angle, β,

1.3 to 1.5 for the slope is achieved by applying the same to the reinforcement strength as well. All reinforcement layers are of equal length. Surcharge and

φ

 . The strength of reinforcement is the strength of geogrid at the end of design life for most severe condition expected during service life. Factor of safety of

Jewell [14] revised the previous design for geotextiles and geogrids as reinforcement. Interaction between soil and horizontal reinforcement has been considered in terms of bond coefficient (fb) which governs the load transfer between reinforcement and soil. The basic philosophy of design is that available stress from the reinforcement exceeds the required stress for equilibrium in soil. Improvements

Allowable Tensile Strength (Tall) for reinforcement is chosen such that strain in

friction = 50% design friction angle of soil

Friction resistance to direct sliding = 80%

4 Reinforcing material Geogrid Geogrid and Geotextile

90 30 °≤ ≤ °

β

fds = 0.80 and correction factor applied whenever fds takes a value less than 0.8.

1 0 ≥ ≥ *fb*

reinforcement does not exceed 3–5% during design life to ensure satisfactory serviceability. φ d = φ*<sup>c</sup>* . Porewater pressure to be considered should include the worst condition expected in design life. Design values of φ d, ru, β and H are used to

**SN Parameter Jewell et al. [8] Jewell [14]**

design friction angle of soil

β

c, and porewater pressure parameter,

effective critical state friction angle of soil,

*Steep slope embankment (after [8]).*

earthquake loads are not included in the analysis.

over previous design method are given in **Table 2**.

*6.2.1 Design parameters for soil and reinforcement*

β

) 80 30 °≤ ≤ °

2 Bond coefficient (fb) Reinforcement bond angle of

**20**

**Table 2.**

determine required earth pressure coefficient, Kreq, and reinforcement length, LR/H, from the design charts. Design charts for ru = 0, 0.25 and 0.50 are shown in **Figures 8** and **9**. Large strain or critical state shearing resistance <sup>c</sup> ( ) φ of soil is to be used for design.
