Geosynthetics y and Reinforced Soil Structures Reinforced Soil Walls … continued Prof K K. Rajagopal Department of Civil Engineering IIT Madras, Chennai e-mail:
[email protected]
Outline of the Lecture • Different Standards for Reinforced Soil Retaining walls • Materials required • Fundamentals of earth pressure theories • Stability Analysis of Reinforced Soil R t i i Walls Retaining W ll
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Codes and Design Standards for the Reinforced Soil Retaining Walls Soil Retaining Walls • •
• •
BS 8006 Strengthened/Reinforced Soils and Other Fills, British Code of Practice (1995 & 2006) FHWA Mechanically Stabilised Earth Walls and Reinforced Soil Slopes: Design and Construction Guidelines, FHWANHI 0043 (2001) NHI-0043 Segmental Retaining Walls, National Concrete Masonry Association, Herndon, Virginia, USA(2009) Seismic Analysis and Design of Retaining Walls, Buried Structures, Slopes, and Embankments, NCHRP National Cooperative Highway Research Project, Project Transportation Research Boads, Washington, DC USA (2008)
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Comments on Design Codes BS 8006-1995 • Limit State Based code • Covers both polymeric and metallic reinforcements • Reinforced walls, slopes and Anchored Earth are discussed elaborately • Seismic Loads are not considered FHWA NHI-00-0043 • Lumped factor of safety approach • Covers metallic and polymeric reinforcement materials, but not anchored earth • Slightly more tolerant of fine soils • Seismic design Reinforced Soil Walls - 3
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Major differences between BS 8006 and d FHWA BS 8006 BS 8006
FHWA
• Limit Limit state state • No check for overturning and overturning and eccentricity • Vertical stress – simple p static pressure
• Lumped Lumped Factor of Safety Factor of Safety • Checks for overturning and eccentricity and eccentricity • Vertical stress – Meyerhoff y pressure p
v
z ws
v
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Rv L 2e 5/25
Soil gradation requirements Percent passing Particle size (mm) 125mm 90mm 75mm 37 5 37.5 10mm 5mm 600 microns 63 microns
BS8006‐1995 100% 80‐100 65‐100 45 100 45‐100 15‐60 10‐45 10 45 0‐25 0 to 12
particle size FHWA 102 mm 100% 0.425 mm 0‐60% 0.075 mm 0‐15% Pl i i i d Plasticity index 3000 Ohm‐cm pH 5 10 5‐10 Chlorides
