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Constructing foundations on red mud
- 1. Paper No. 644 6ICEG CONSTRUCTING FOUNDATIONS ON RED MUD Ravi Sundaram Sanjay Gupta CENGRS GEOTECHNICA PVT. LTD.
- 2. Paper No. 644 6ICEG Red Mud Waste Product of Aluminium Industry Formed by washing and purifying bauxite – highly alkaline Slurry pumped into a disposal pond Over period of time, water partly evaporates, partly seeps into ground Slurry thickens to form soft deposit
- 3. Paper No. 644 6ICEG Expansion of Aluminium Industry Construction of Drum Filter Plant on Red Mud Slurry Pond Red Mud behaves as a soft clay SPT values range from 1 to 5
- 4. Paper No. 644 6ICEG Vicinity Map UTTAR PRADESH PROJECT SITE PROJECT SITE
- 5. Paper No. 644 6ICEG Stratigraphy The area formed by filling a large valley between two hills Red mud deposition with some intermediate zones of flyash, shale fragments and bauxite fragments – non uniform fill Underlying rock: Phyllitic shale – depth varies from 15 to 42 m
- 6. Paper No. 644 6ICEG Typical Borehole Data
- 7. Paper No. 644 6ICEG Engineering Properties of Red Mud Parameter Typical Range of Values Moisture Content 32 – 38 % Liquid Limit 39 – 45 % Plastic Limit 27 – 29 % Shrinkage Limit 19 – 22 % Specific Gravity 2.85 - 2.97 Gradation: Sand Size Silt Size Clay Size 10 – 14 % 43 – 57 % 32 – 39 % Undrained Shear Strength 0.4 – 1.4 kg/cm2 Effective Stress (CU) parameters c = 0.1 - 0.2 kg/ cm2 φ = 26 - 28° Apparent Electrical Resistivity 1.5-2.0 ohm-m to 5 m depth 4-8 ohm-m to 10 m depth Total Soluble Solids 0.44 – 0.56 % pH value 9.3 – 10.2
- 8. Paper No. 644 6ICEG Consolidation Characteristics Initial void ratio 0.9-1.1 Underconsolidated to about 5-8 m depth Below this, Red mud is normally consolidated
- 9. Paper No. 644 6ICEG Alternative Foundation Schemes Open Foundations / Raft Foundations: Not feasible since Red Mud is under- consolidated and SPT values are low Pile Foundations: Piles would have to be socketed into the underlying weathered rock formation. Pile length may vary from 16 to 44 m Ground Improvement: Raft Foundations on improved ground
- 10. Paper No. 644 6ICEG Ground Improvement By improving the ground to 12-14 m depth, settlements shall be within permissible limits Ground improvement done by provision of granular piles Accelerates the consolidation process so that the consolidation is complete by the end of the construction
- 11. Paper No. 644 6ICEG Construction Methodology Borehole is made to required depth Charge of gravel – 75 mm down, graded – placed in layers Each layer is rammed using a heavy rammer to obtain set Installed in a triangular grid pattern Peripheral restrainment by 2 rows of granular piles outside loaded area
- 12. Paper No. 644 6ICEG Construction Technique
- 13. Paper No. 644 6ICEG Behavior Under Load Load on Granular Pile is Resisted by: Interfacial Shear between stone and soil Lateral Compressive Strength of soil End Bearing Failure is by bulging Critical length :3 to 5D
- 14. Paper No. 644 6ICEG Granular Piles Soft Red Mud strengthened by providing 600 mm diameter granular piles to 12 m depth Spacing 2m – triangular grid pattern Each layer of gravel of height 1 m compacted using a 1 ton down-the- hole rammer 200 mm thick gravel blanket placed over the piles to distribute load
- 15. Paper No. 644 6ICEG Foundation on Improved Ground Raft foundation was constructed on the improved ground Design net bearing pressure 12 T/m2 The scheme resulted in substantial savings to the owner in comparison to the other option of providing piles.
- 16. Paper No. 644 6ICEG Verifying Performance Load test was performed on the improved ground to verify the behavior of the improved ground To ensure peripheral restrainment, six granular piles were installed surrounding the test pile
- 17. Paper No. 644 6ICEG Test Arrangement
- 18. Paper No. 644 6ICEG Load-Settlement Curve Capacity of Single Granular Pile : 42 Tonnes
- 19. Paper No. 644 6ICEG Settlement Analysis Test result analyzed to assess settlement of improved ground Settlement of underlying unimproved ground assessed from borehole data As per the analysis, total settlement of raft foundation shall be about 50 mm – STRUCTURE SAFE UNDER DESIGN LOAD
- 20. Paper No. 644 6ICEG Concluding Remarks Effective Utilization of space occupied by closed Red Mud Slurry Pond Ground improvement by granular piles is an effective option to strengthen the soft Red Mud deposition A thorough geotechnical investigation and load testing are the key to successful performance