**8. Slope - reinforcement interaction and length optimization**

The inclusion of geosynthetic reinforcement in soil slope for improving stability leads to change in behavior of reinforced soil mass due to induced stresses as compared to that in unreinforced slope so far as critical slip circle is concerned. Hence there is a need to understand slope-reinforcement interaction behavior. Jha et al. [61–64] optimized reinforcement length form face of slope and identified and quantified slope-reinforcement interaction.

To study soil reinforcement interaction and length optimization reinforced embankment slope, on a competent soil, 6.0 m high with side slope of 1.5H:1 V is considered (**Figure 20**).

The embankment and foundation soil have cohesion, c, of 5 kPa, unit weight, γ , of 18 kN/m3 and angle of shearing resistance, φ , of 230. The geotextile reinforcement used has adhesion, ca, of 3 kPa, angle of interface friction between soil and reinforcement, δ, of 17° and ultimate tensile strength, Tult, of 200 kN/m.

**33**

**Figure 21.**

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

(**Figure 21**).

ment to get preferably long term FSmin of 1.5.

**8.1 Reinforcement length optimization: non-face end**

below 1.50 on reducing the length further to 7.0 m.

**8.2 Length optimization from face end**

*Critical slip circle for Z0 = 3.0 m, FSmin = 1.51, Lr = 7.27 m.*

Analysis of unreinforced embankment of 6 m leads to FSmin of 1.22 less than the required value of 1.3 and hence needs to be reinforced with geosynthetic reinforce-

Effect of varying the length, Lr, of geosynthetic placed at depth, Z0 = 3.0 m in 6.0 m high embankment is studied by curtailing it from the non-slope face to get FSmin in the range of 1.50 to 1.60. The length, Lr, of the reinforcement to intercept the failure surface at 3.0 m depth was varied from 8.0 m with FSmin of 1.6

Circles ABC and DEF are the critical slip circles of the unreinforced and the reinforced slopes. One of the effects of inclusion of reinforcement in embankment soil is to shift the critical slip circle from ABC to DEF, that is from shallower to deep inside the slope. This shift of the critical circle therefore increases the factor of safety by involving larger slide mass. PQ is reinforcement of length Lr. The length of reinforcement Lr has two components: QE = effective length, Le, in the stable zone and EP – the length, Lf in the unstable zone. Lf is further divided into lengths Lf1 (EB), the length in the failure zone between the critical slip circles of the reinforced and the unreinforced slopes and length, Lf2, between the critical slip circle of unreinforced slope and slope face (BP) as shown in **Figure 21**. The effect of varying Lr with right end fixed at point P and left end (Q ) curtailed inwards successively, leads to reduction in mobilized force in the reinforcement (Fr) from 35.8 kN/m to 19.6 kN/m corresponding to reduction in Lr from 8.0 to 7.3 m. FSmin reduces from 1.60 to 1.51. Factor of safety and the load/resistance mobilized in the reinforcement decrease with reducing length of reinforcement as is to be expected. FSmin falls

The length, Lf = (Lr - Le) is much larger than Le, the effective length of reinforcement contributing to increase in the stabilizing moment/force. The required pullout force in the reinforcement in the stable zone should equal to that mobilized by the corresponding length of the reinforcement in the unstable zone for equilibrium. It would serve no useful purpose if the length of the reinforcement in the unstable

**Figure 20.** *Schematic diagram - reinforced embankment slope.*

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

*Slope Engineering*

**8. Slope - reinforcement interaction and length optimization**

φ

quantified slope-reinforcement interaction.

δ

*Schematic diagram - reinforced embankment slope.*

and angle of shearing resistance,

considered (**Figure 20**).

*Length of reinforcement for a slope with* 

and reinforcement,

of 18 kN/m3

**Figure 19.**

The inclusion of geosynthetic reinforcement in soil slope for improving stability leads to change in behavior of reinforced soil mass due to induced stresses as compared to that in unreinforced slope so far as critical slip circle is concerned. Hence there is a need to understand slope-reinforcement interaction behavior. Jha et al. [61–64] optimized reinforcement length form face of slope and identified and

 *= 20°, c/*γ*H = 0.05 and ru = 0.*

To study soil reinforcement interaction and length optimization reinforced embankment slope, on a competent soil, 6.0 m high with side slope of 1.5H:1 V is

The embankment and foundation soil have cohesion, c, of 5 kPa, unit weight,

ment used has adhesion, ca, of 3 kPa, angle of interface friction between soil

φ

, of 17° and ultimate tensile strength, Tult, of 200 kN/m.

, of 230. The geotextile reinforce-

γ ,

**32**

**Figure 20.**

Analysis of unreinforced embankment of 6 m leads to FSmin of 1.22 less than the required value of 1.3 and hence needs to be reinforced with geosynthetic reinforcement to get preferably long term FSmin of 1.5.
