**2.3 Composite soil reinforcement system for very high and steep fills for Sikkim airport**

For runway construction of airport at Pakyong in north eastern Indian state of Sikkim huge cutting of earth and its filling on the valley side was required to form a level platform to provide runway of 1820 m x 150 m and other related

**Figure 4.** *Schematic of reinforced slope for highway extension (sketch based on [6]).*


#### **Table 1.**

*Cost comparison of different options.*

infrastructures over 200-acre area. Retention of fill on the valley side needed construction of retaining structures with heights varying from 30 to 74 m over a length of 1480 m (**Figure 5**).

On hill side, the cut slopes have a height extending up to 100 m. To retain and stabilize this fill of varying height, a composite soil reinforcement system was employed [7]. To make optimum utilization of space available and minimize cost, combination of vertical wall and steep slope has been adopted for construction of retaining structure. Facing elements for the reinforced soil wall comprise of Gabions (**Figure 6**).

**Figure 5.** *Sikkim airport - aerial view (after [7]).*

**17**

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

parcel of land for embankments, etc.

Geosynthetics are mostly planar products manufactured from polymeric material and used with geomaterials such as soil and rock, as integral part of manmade project or system for better performance, economy, better quality control, rapid installation, cost competitiveness, lower carbon footprint, requirement of smaller

Geotextiles and Geogrids are used normally for reinforcing embankments or natural slopes either to obtain higher factor of safety or for construction with steep slopes. Allowable Geotextile/Geogrid strength is arrived at using several factors to account for degradation, creep, installation damage, etc. The allowable tensile

Where Tall and Tult - allowable and ultimate tensile strengths respectively, RFID, RFCR and RFCBD - reduction factors (all >1.0) for installation, creep and chemical and biological damage respectively. The combined or overall reduction factor is

Jewell et al. [8], Bonaparte et al. [9] and Verduin and Holtz [10] present design methods for earth slopes reinforced with geotextiles and/or geogrids using limit equilibrium method considering circular or/and bilinear wedges. Leshchinsky and Reinschmidt [11] and Leshchinsky and Boedeker [12] present an approach based on limit equilibrium and variational extremization of factor of safety of multilayer reinforced slope. Schneider and Holtz [13] present a design procedure for slopes reinforced with geotextiles and geogrids for a bilinear surface of sliding, considering porewater pressures and the initial stress conditions in the slope. Jewell [14] presented revised design charts for steep slopes valid for all reinforcement materials. Leshchinsky [15] and Leshchinsky et al. [16] used log-spiral failure mechanism to determine the required reinforcement long term strength. Zhao [17] and Michalowski [18] present kinematic limit analyses solutions for the stability of reinforced soil slopes. Shiwakoti et al. [19] conducted parametric studies to investigate the effect of geosynthetic strength, soil–geosynthetic interaction coefficients, vertical spacing of geosynthetics for soil slope/wall on competent foundation. Baker and Klein [20, 21] modified the top-down approach of Leshchinsky [15] to obtain the reinforcement force needed for a prescribed factor of safety everywhere within the reinforced mass. Han and Leshchinsky [22] present a general analytical framework for design of flexible reinforced earth structures, i.e., walls and slopes. Leshchinsky et al. [23] present a limit equilibrium methodology to determine the unfactored global geosynthetic strength required to ensure sufficient internal stability in reinforced earth structures. Leshchinsky et al. [24] introduced a limit state design framework for geosynthetic reinforced slopes and walls. Leshchinsky and Ambauen [25] present use of upper bound limit analysis (LA) in conjunction with discretization procedure known as discontinuity layout optimization (DLO). DLO-LA is an effective tool for establishing a critical failure mechanism and ensuing stability of the slope without the constraint or assumptions required in LE analysis. Shukla et al. [26] presented a review of design of reinforced slope and covers basic of methods in detail. Gao et al. [27] in their study considered three-dimensional effect on reinforced earth structure stability and to determine the required

T T / R R RF all ult FID FCR CBD = ∗∗ (1)

**3. Geosynthetics**

strength, Tall, is

about 2.0 for design.

**4. Literature review**

**Figure 6.** *Slope face completely covered with vegetation few months after installation (after [7]).*
