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Foundation Types
- 1. ASOCIATION OF CONSULTING CIVIL ENGINEERS (I) STRUCTURAL ENGINEERING SERIES FOUNDATIONS SATISH RAIPURE 1
- 2. CONTENTS OF THE PRESENTATION 1. About Structural Design 2. Importance Of Geotechnical Investigation 3. Types Of Foundations & Its Selection 4. Reinforcement Detailing 5. Do’s N Don’ts
- 4. WHAT IS STRUCTURAL DESIGN? Manner in which the load bearing (structural) members of a physical framework support each other in sharing the load (stress). A STRUCTURE TO A BUILDING IS SAME AS SKELETON TO A HUMAN BEING FOUNDATION IS VERY IMP PART OF ANY STRUCTURE 4
- 5. LOAD PATH 5
- 6. REQUIREMENTS FOR FOUNDATION DESIGN 1. Analysis Of The Structure 2. Load Combinations 3. Critical Reactions On Columns – Vertical, Horizontal & Moments 4. Soil Investigation Report 5. Location Of The Site 6
- 7. LOAD COMBINATIONS FOR MULTISTORIED BUILDING NUMBER OF LOAD COMBINATIONS – LOAD COMB 6 1.0(DL+LL) LOAD COMB 7 1.5(DL+LL) LOAD COMB 8 1.2(DL+LL+EQX) LOAD COMB 9 1.2(DL+LL-EQX) LOAD COMB 10 1.2(DL+LL+EQZ) LOAD COMB 11 1.2(DL+LL-EQZ) LOAD COMB 12 1.5(DL+EQX) LOAD COMB 13 1.5(DL-EQX) LOAD COMB 14 1.5(DL+EQZ) LOAD COMB 15 1.5(DL-EQZ) LOAD COMB 16 0.9(DL)+1.5(EQX) LOAD COMB 17 0.9(DL)-1.5(EQX) LOAD COMB 18 0.9(DL)+1.5(EQZ) LOAD COMB 19 0.9(DL)-1.5(EQZ) LOAD COMB 20 (DL + LL) 7
- 8. DESIGN METHODS 1. WORKING STRESS METHOD 2. ULTIMATE LOAD THEORY 3. LIMIT STATE METHOD 8
- 9. FOUNDATIONS – IMP POINTS • Strength Of Any Structure Lies In Its Foundation • It Must Rest On Firm Base • It Must Safely Support & Transfer All Types Loading & Their Combination • It Must Be Strong Enough To Minimize Differential Settlement • Soil is not like concrete • Soil has the most wide range of characteristics 9
- 10. FOUNDATIONS – IMP POINTS • It Should Resists Any Chemical Attack • Depth Of Excavation Should Be Such That It Should Be Sufficient To Overcome The Detrimental Soil Movements • It Should Have Sufficient FOS Against Over Turning & Sliding • It Must Be Feasible, Both Technically & Economically And Should be Practical Enough To Build Without Adverse Effect On Surrounding Structures. 10
- 11. FOUNDATIONS – IMP POINTS • AVOID ECCENTRIC FOOTINGS, USE COMBINED FOOTINGS. • BE CAREFUL ABOUT CENTER LINES OF THE COLUMNS, SPECIALLY IN PEB STRUCTURES • AVOID CONCRETING IN WATER FILLED PITS. 11
- 12. COLUMN CENTER LINE 12
- 13. 13 CENTER LINE FOR PEB STRUCTURE
- 14. CENTER LINE FOR PEB STRUCTURE 14
- 16. Bearing Capacity • Bearing Capacity : Capacity of soil / rock to withstand load without shear failure and within limited settlements. • Max. Settlement allowed as per IS are : • Isolated footings – 50 mm to 75 mm • Raft – 75 mm to 100 mm • Piles – 12 mm • Differential settlement – L / 300 • Where L = span between adjacent footings
- 17. WHY SOIL INVESTIGATION? n Which Foundation Can Be Rest. • Excavation methodology 17
- 18. DEATILED INVESTIGATION IS DONE WITH THE HELP OF – 1. Open Trial Pits 2. Bores 3. Field Tests Sampling – Un-Disturbed, Disturbed 4. Laboratory Tests 18
- 19. Open trial pits • Depth In General 3 To 4 M • Useful For Sampling Disturbed & Undisturbed, Density Measurements, SPT, Permeability, Deciding Foundation Depth. • Advantages- Visual Observation, Large Quantity Of Sampling At One Level, Better Insight Of Stratification As Compared To Bore Logs Etc.
- 20. Bore drilling • Purpose of drilling to • Confirm Continuity of stratum in influence zone • Collection of UDS/DS samples • Conduction of SPT test • Permeability Tests • Collection of rock cores • Types • Augur boring • Rotary drilling • Percussion drilling
- 21. Approximate Tests at Site – 1. Pencil Test – Plasticity Test, To Determine Cohesiveness 2. Thumb Penetration Test 3. Pocket Penetrometer Test 21
- 22. Classification of Soil As Per Occupational Safety & Health Administration [OSHA] • Type A Soil – Include Clay, Silty Clay, Sandy Clay, And Clay Loam, Most Stable, Cohesive, High Unconfined Compressive Strength • Type B Soil – Include Angular Gravel, Silt, Silt Loam, And Soils That Are Fissured, Medium Unconfined Compressive Strength • Type C Soil – Include Gravel And Sand, Granular, Least Stable, Low Unconfined Compressive Strength 22
- 23. 23
- 25. TYPES OF FOUNDATION 25
- 26. TYPES OF FOUNDATION • Deep foundations – - End Bearing Piles - Well foundation • Shallow foundations – - Wall type or Load Bearing - Friction Piles – Single or Double Under-Reamed - Spread or Isolated – Trapezoidal, Box, Stepped - Strip Footing - Combined Footing - Mat or Raft Footing 26
- 27. FACTORS AFFECTING TYPE OF FOUNDATION • Type Of Soil – Black Cotton, Yellow Soil, Murum, Hard Murum, Soft Rock, Hard Rock • Bearing Capacity Of Soil • Level Of Strata, Ground Water Level • Type Of Structure 27
- 28. Isolated or Combined [Open] Footings • Used for most buildings where the loads are light and / or there are strong soil at shallow depth. • These footing deliver the load directly to the supporting soils. • Area of footing is = Load / SBC • Generally suitable for low rise buildings (1-5 floors) • Requires firm soil conditions that are capable of supporting the building on the area of the spread footings.
- 29. • For foundation subjected to seismic or wind load combination, stresses in steel & concrete can be increased by 33.3% as per the code. • Footings are designed for shear at D & D/2 dts from face of the column. • Footings are designed for positive pressures only, no tension is allowed • These are most widely used because they are most economical
- 31. Open Footings
- 32. WALL OR LOAD BEARING FOUNDATION 32
- 33. WALL OR LOAD BEARING FOUNDATION 33
- 34. ISOLATED BOX TYPE FOOTING 34
- 36. STRAP BEAM FOOTING 36
- 37. Raft foundation Mat or Raft foundation is a large slab supporting a number of columns under the entire structure or a large part of the structure to lower the contact pressure compared to spread footing. It is recommended for the following purposes. When the Bearing capacity of soil is very low Column spacing of the structure is so close that individual footings would overlap It is generally used for large loads.
- 38. • It can cope with mixed or poor ground condition. • It reduces differential settlement.
- 39. MAT OR RAFT FOUNDATION 39
- 40. SLAB & BEAM TYPE RAFT FOUNDATION 40
- 41. Deep Foundation • Huge vertical load with respect to soil capacity. • Very weak soil or problematic soil. • Huge lateral loads e.g. Tower, chimney. • Scour depth criteria e.g. bridge piers • For fills having very large depth. • Urban areas for future large and huge construction near the existing buildings.
- 42. Deep Foundation - Piles For soils that are compressive with heavy loads, where deep soils can not take the building load and where soil / rock strata of better capacity if found deep below. There are two types of piles. • Friction Piles • End Bearing Piles • The bearing capacity of the piles depends on the structural strength of the pile itself or the strength of the soil, whichever is less.
- 43. DEEP FOUNDATION – PILES • Number of Piles required depends on Safe Pile Load, Vertical & Horizontal • Spacing Between Two Piles – - 2.5 x Dia Of Pile For End Bearing Piles - 3.0 x Dia Of Pile For Friction Piles. • Pile Caps Are Designed For Compressive Load Cases Only, i.e. No Tension Is Allowed In Piles. 43
- 44. End Bearing Piles load transferred to greater depths on sound rock – Loads are high & good stratum is not available at shallow depths. Weathered Rock Soil Rock – for sound basalt SBC = 300 tons to 1000 tons/sq.m
- 45. TYPICAL DETAILS OF UNDER-REAMED PILE 45
- 46. 2 – PILE CAP 46
- 48. 4 – PILE CAP 48
- 49. 49
- 50. DYNAMIC PILE LOAD TESTING 50
- 52. HYBRID FOUNDATION – RAFT + PILES 52
- 53. HYBRID FOUNDATION – RAFT + PILES 53
- 55. REINFORCEMENT DETAILING IMPORTANCE OF DETAILING – 1. It’s a link between planning & execution. Very essential for proper execution of the structures. 2. For the safety of the structures. 3. Collapse of the structures can be avoided. 4. IS codes – IS:456, IS:1786, IS:13920 & SP – 34. 55
- 56. DO’s & DON’Ts FOR DETAILING – 1. Prepare the drawings properly & Accurately. 2. If possible label each & every bar. Show the shape of bar at critical locations. 3. Indicate cover, Ldc & Ldt at imp locations. 4. Try to use minimum types of bars. 5. Grade of steel & its make shall be clearly mentioned. Don’t use different types of grades & various types of reinf. Bars at one site. 6. Reinf. Left for future expansion shall be properly protected. 56
- 57. POINTS TO REMEMBER 1. Mini. Reinf. - 0.12% Of Cross Sectional Area 2. Use Lower Dia Bar With Mini 100 Mm C/C Spacing 3. Cover – 50 Mm All Around 4. Avoid Over Laps. 57 5. Depth Of Footing Should Satisfy ‘Ldc & Ldt’ Criteria. 6. Dowels, Spacer bars, Chairs, etc. shall be clearly mentioned & shown on the drawing.
- 58. 58 Ldc & Ldt
- 59. ISOLATED FOOTINGS REINFORCEMENT IN FOOTING 59
- 61. COMBINED FOOTING – STRAP BEAM REINFORCEMENT DETAILING IN COMBINED FOOTING
- 62. REINFORCEMENT DETAILS FOR COMBINED FOOTING 62
- 63. REINFORCEMENT DETAILING REINFORCEMENT DETAILING IN ECCENTRIC FOOTING 63
- 64. 64 SLAB n BEAM TYPE RAFT FOUNDATION
- 65. REINFORCEMENT DETAILING OF PILE FOUNDATION 65
- 66. END BEARING PILES 66
- 67. RAFT OT MATT FOUNDATION 67
- 68. RAFT OT MATT FOUNDATION 68
- 69. RAFT OT MATT FOUNDATION 69
- 71. Problems in Deep Foundation Construction • Deep excavation in soils . • Stability of cuts. • Cost of supporting system • Dewatering • Safety of Adjacent buildings. • Side support of foundation • Vibration , (piles by chiseling) • Excavation of rock by jack hammers. • Lowering of water table causes settlements. • Uplift pressure : Rock anchors
- 74. 74 SHORING FOR DEEP FOUNDATIONS
- 75. SHEET PILES 75
- 76. PILE WALL 76
- 77. 77 PILE WALL / SHORE PILING FOR DEEP FOUNDATIONS
- 78. 78 PILE FOUNDATIONS WITH BASEMENT FLOOR SLAB
- 79. DONT’S 79
- 82. DONT’S 82
- 83. 83 DONT’S
- 84. 84 DONT’S
- 85. 85 DONT’S
- 87. 3/25/2021 LAD COLLEGE OF ARCHITECTURE 2016 87 WHAT TO DO WITH SUCH PEOPLE??
- 88. ALL CIVIL ENGINEERS SHOULD HAVE • POSITIVE ATTITUDE • SKILLS • KNOWLEDGE • INTEGRITY • PASSION THIS WILL BE OUR REAL SERVICE TO THE NATION & TRIBUTE TO BHARAT RATNA SIR MOKASHGUNDAM VISVESVARAYA 88
- 89. SPECIAL THANKS TO – Dr. Ajit Sabnis Sir & Dr. Sudhanva Shingarey 89
- 90. THANK YOU ALL sraipure@gmail.com, 98224 65948 FOR A CIVIL ENGINEER THERE IS NO SUCH THING CALLED AS A LITTLE MISTAKE…. 90
Editor's Notes
- Normally structures on marshy land, soft clay and land that are made up of sanitary land fill or other materials (like debris, unconsolidated soil and solid waste etc. where differential settlement is suspected)-require raft foundation. Raft foundations are preferred in the soil that are suspected to subsidence like change in ground water level due to climatic change specially in case expansive soil or foundation in mining area. Can be used for buildings that are 10-20 stories tall where it provides resistance against overturning. Can be used where soil requires such a large bearing area and the footing might be spread to the extant that it becomes more economical to pour one large slab (thick)