**11. Conclusions**

*Slope Engineering*

**Figure 26.**

settlement was repaired by placing additional backfill on the top of the slope to

During the next rainy season, the slope was subjected to a significant amount of rainfall of 187 mm in May, 350 mm in June, 243 mm in July, and 563 mm in August. During this period, tension cracks and slope settlement got regenerated and gradually developed as the rainfall continued. **Figure 27** displays subsequent development

Factors that caused the slope failure from the forensic investigation are: (i) The use of marginal soil (over 60% of fines) as the backfill without provision of drainage. (ii) The original design and site investigation overlooked the existence of the weathered and fractured rock layer, which has shear strength less than that of an intact rock. (iii) Tension cracks and slope settlement developed at the top surface of the slope allowed rainwater to pond on the top and to infiltrate into the reinforced zone. (iv)The drainage system may have malfunctioned as joints were poorly and loosely connected and likely got dislocated due to the excessive deformation.

*Tension crack and settlement of slope and its failure after rains of 2012(a) tension crack; (b) onset of* 

compensate for the settlement that had occurred.

*Layout and Design of Multitier Geosynthetic Reinforced Slope (after [67]).*

of the tension cracks and slope settlement with time.

*settlement; (c) excessive settlement over 1 m (after [67]).*

**38**

**Figure 27.**

Steep slope embankment is a necessity for development of rail, road and other infrastructure projects. Safety of embankment slopes is of utmost importance which requires proper site investigation, analysis and design. Limit Equilibrium, Limit Analysis, Slip Line & Finite Element Methods are design methods for RE Slopes. Limit equilibrium method is most commonly used for design including the effect of reinforcement. Jewell's design method [14] for geosynthetic reinforced steep slope soil with granular soil is most commonly used method. Song et al. [28] proposed new approach based on LE principle to evaluate stability of reinforced slope. Slopes with cohesive backfill have been constructed due to limited availability of granular material near project site. Proper design of RE slope using cohesive backfill considering the transmissivity of draining geogrid is important. The method suggested by Giroud et al. [32] for draining geogrid reinforced cohesive back fill slope with 0.5 m/day is practical method as it takes care of pore water pressure dissipation for most common soil parameters. Abd &Utili [33] developed a semi-analytical method for uniform slope with c-ф soil using Limit Analysis (LA). The method provides the amount of reinforcement needed as a function of cohesion, tensile strength, angle of shearing resistance and slope inclination. The reinforcement length optimization from face end leads to economy in reinforcement length of the order of 20–30% without affecting factor of safety [61]. There is an interaction between slope and reinforcement [62, 64]. Inclusion of reinforcement in embankment slope results in to shifting of critical slip circle deep inside slope involving larger slide mass thus increasing factor of safety. Reinforcement also provides stabilizing moment/force. Investigation of failed slopes indicate that detailed geotechnical investigation of site to assess presence of weak layer, provision of drainage by way of draining geosynthetics in case of cohesive backfill, installation of drainage systems to capture rain and subsurface water and global stability of reinforced earth slopes are very critical for stability and performance of reinforced slope.
