Analysis of Effect of Curtailment of Reinforcement on Stability of Steep Slopes Analyse de l'effet de la réduction du renforcement sur la stabilité des pentes abruptes Akshay Kumar Jha, Indian Railways, Hyderabad, India, akshayghungru@gmail.com Madhav Madhira, JNTU Hyderabad, Hyderabad, India, madhavmr@gmail.com G.V. N. Reddy, JNTU Hyderabad, India, gvnreddy@jntuh.ac.in ABSTRACT: Steepening of slopes for construction of rail/road embankments or for widening for other civil engineering structures is a necessity for development. Use of geosynthetics for steep slope construction or repair of failed slopes considering all aspects of design and environmental considerations could be a viable alternative to this problem. Literature survey indicates that some efforts were made for optimization of length of reinforcement. The present paper details an analysis to optimize the length of geosynthetics from the face or near end of the slope with respect to its location, length and combination of multiple layers of reinforcement to obtain the desired minimum factor of safety for a steep slope. Steep unreinforced and reinforced slopes are analyzed to obtain critical factors of safety. The effect of providing geosynthetic layer in shifting the critical slip circle has been identified and studied. The effect of interaction between layers of reinforcement has been identified and quantified. RÉSUMÉ: Le renforcement des pentes pour la construction de remblais ferroviaires / routiers ou pour l 'élargissement des autres ouvrages de génie civil est une nécessité pour le développement. L'utilisation de géosynthétiques pour la construction de pentes abruptes ou la réparation de pentes défaillantes compte tenu de tous les aspects de la conception et des considérations environnementales pourrait être une alternative viable à ce problème. L'étude de la littérature indique que certains efforts ont été faits pour l'optimisation de la longueur du renforcement. Le présent article détaille une analyse visant à optimiser la longueur des géosynthétiques à partir de la face ou près de la fin de la pente par rapport à son emplacement, la longueur et la combinaison de couches multiples de renfort pour obtenir le facteur de sécurité minimum souhaité pour une pente raide. Les pentes abruptes non renforcées et renforcées sont analysées afin d'obtenir des facteurs critiques de sécurité. L'effet de la mise en place d'une couche géosynthétique dans le déplacement du cercle de glissement critique a été identifié et étudié. L'effet de l'interaction entre les couches de renforcement a été identifié et quantifié. KEYWORDS: Reinforcement, Optimization of length, Critical slip circle, Reinforced steep slope, Geosynthetics, interaction. 1 INTRODUCTION The analysis of earth slopes is one of the oldest geotechnical engineering problem that engineers have been dealing with using various techniques. The methods can be classified as Limit Equilibrium Methods, Finite Element Method based on c and ߶ reduction, Finite Element Modeling/Finite Difference Method, combination of FEM and LEM, Limit Analysis (LA) method, etc. Geosynthetic reinforcement of earth slope results in reducing the land requirement and preservation of natural resources (land and backfill requirements) apart from time and cost. Designing geosynthetic reinforced slope with minimum length of geosynthetics leads to further economy. Jewell et al. (1985), Bonparte et al. (1987), Verduin and Holtz (1989) present design methods for earth slopes reinforced with geotextiles or /and geogrids using LEM assuming different types of failure surfaces such as circular or/and bilinear wedges. Jewell et al. (1985) used Limit Equilibrium Analysis and local stress calculation for design of reinforced slope. Jewell (1991) presented revised design charts for steep slopes valid for all polymer reinforcement materials. These revised charts lead to savings of the order of 20-30% in reinforcement quantity. Gao et al. (2016) in their study considered three dimensional effects on reinforced earth structure stability and to determine required strength and length of reinforcement using limit analysis approach. The three dimensional effects are more significant for the minimum required length of reinforcement than for the minimum required tensile strength. None of the above approaches optimizes the length of geosynthetics by curtailing the same from the slope face. The paper details analysis carried out to optimize the length of reinforcement from the face end of steep slope and also identifies interaction between layers of reinforcement and its effect on overall stability. 2 PROBLEM DEFINITION An embankment of height, H, of 6.0 m with side slopes of 1H to 1V vertical is considered (Figure 1). The embankment and foundation soil have cohesion, c, of 5 kPa, unit weight, ,ߛof 18 kN/m 3 and angle of shearing resistance, ߶ , of 23 0 . The geotextile reinforcement used has adhesion, ca, of 3 kPa, angle of interface friction between soil and reinforcement, ߜ, of 18° and ultimate tensile strength, Tult, of 200 kN/m. All the stability analyses have been carried out using Morgenstern-Price method. Figure 1. Problem Definition - 2159 -