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

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 (**Figure 21**).

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 below 1.50 on reducing the length further to 7.0 m.
