Ground improvement techniques compaction vibration
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This document discusses various ground improvement techniques used to treat poor ground conditions. It begins by classifying ground conditions as hazardous, poor, or favorable. Poor ground conditions that cannot be used in their insitu state but can be treated include expansive soils, organic soils, loose sands and silts, and fissured rocks. The document then discusses various ground improvement techniques including compaction methods, preloading, grouting, geosynthetics, soil reinforcement, stone columns, and thermal methods. It provides details on techniques like dynamic compaction, vibrocompaction, vibrodisplacement, prefabricated vertical drains, and compaction piles. The objectives, principles, factors affecting selection, and design of various techniques are
Ground improvement techniques compaction vibration
- 1. CE 14 805 (D) Ground Improvement Techniques
- 2. Why??
- 3. Failures due to poor ground conditions
- 4. Types of Ground Conditions Hazardous Poor Favourable
- 5. • HAZARDOUS: Totally unsuitable and hazardous, hence should be avoided – Locations close to faults, or seismically active regions – Loose to medium fine sands subject to liquefaction – Any landfill of hazardous waste – Soils near volcanic active regions • POOR: Cannot be used in the insitu condition, but can be used after suitable treatment – Expansive soils – Organic soils – Loose sands and silts – Fissured rocks • FAVOURABLE: – Cohesive granular soils- sand clay mixtures – Shallow rock without discontinuities
- 6. Reject Redesign (structure is redesigned to suit the insitu condition) Remove and replace Treat the soil- Ground Improvement Solution for Poor Ground conditions???
- 7. Ground Improvement • Alteration of any property of soil or rock, to improve its engineering performance, to match the desired results of a project • Depends upon: – Type of soil – Area and depth to be treated – Economy – Type of structure and load distribution – Resource availability-men, material – Environmental considerations
- 8. Objectives of Ground Improvement Increase strength Control Permeability Reduce erodability Reduce compressibility Reduce liquefaction susceptibility Reduce distortion
- 9. Factors affecting suitable GIT • Soil type • Area and depth of treatment • Type of structure and load distribution • Soil properties • Permissible total and differential settlements • Material availability • Availability of skills and equipment • Environment considerations • Economy
- 10. Types of ground improvement techniques • In-situ ground improvement methods without the addition of new materials (Module 1) • With the addition of new material (Module 2) • Geosynthetics (Module 3) • Inclusions- soil reinforcement (Module 4)
- 12. Ground Modification principles Mechanical Hydraulic Physical/ chemical By inclusions
- 13. Major Techniques • Compaction-static, dynamic, vibratory • Preloading- with and without drains • Thermal treatment • Biotechnical stabilization • Blending • Grouting • Geosynthetics • Soil Reinforcement
- 19. COMPACTION • Most common and visible technique used in field • Involves improving mechanical properties of soil by densifying the particles using compactive effort • Soil strength and density will be maximum when compacted at optimum moisture content • Compaction causes densification, reducing the voids thereby improving the strength and stability of the soil
- 20. Principle /Mechanism • Reorientation of particles • Fracture of grains or bonds followed by reorientation • Bending and distortion of particles and their adsorbed layers • For cohesive soils: particle distortion followed by reorientation • Cohesionless soils: Reorientation and readjustment of particles to a closer packing
- 21. Objectives of Compaction • Increase density • Increase shear strength • Reduce compressibility • Reduce permeability • Reduce liquefaction potential • Reduce swelling and shrinkage potential • Increase long term stability
- 22. Compaction mechanics • At very low moisture content- capillary tension causes increase in contact pressure and friction • As moisture content content increases capillary tension decreases causing densification due to lubrication effect particles reorient themselves to form a packed condition reducing voids density increases • After OMC neutral stresses develop density reduces
- 23. Laboratory Compaction Standard proctor test Modified proctor test 1000ml mould 100ml mould 3 layers 5 layers 25 blows 25 blows 2.7Kg hammer 4.89 Kg hammer 300mm free fall 450mm free fall Compactive energy 570KJ/m3 (4.5 times extra)
- 24. Engineering behaviour of compacted fine grained soils • Depends on • Type of soil • Moisture content • Density • Soil structure • Addition of admixtures • Features: • Soil structure • Permeability • Compressibility • Rigidity • Swelling and shrinkage
- 25. Property Dry side Wet side Soil structure flocculated Dispersed Less void ratio More void ratio Permeability More permeable Less permeable Increase in m.c. reduce permeability Slight effect Compressibility More compressible at low stress More compressible at high stress Rigidity Rigid and strong Less rigid Swelling and shrinkage Swells more, shrinks less Swells less, shrinks more
- 26. Field Compaction • Different means: Kneading, tamping , vibrating, impact – Cohesive soils: Kneading tamping and impact – Cohesionless: vibration • Compaction specification 1. Performance type: specifying some physical properties of the compacted layer – Eg. 95% of maximum dry density achieved in lab 2. Work type: includes specification of type of equipment, lift thickness, moisture content, and amount of work required
- 27. a)Smooth wheeled rollers • Bicycle or tricycle configurations • Ballasted or unballasted • self propelled • Static or vibratory • Large contact area hence less pressure(300-400kPa) • Only for thin layer compaction- subgrade, pavement layers etc. • Each layer to be scarified before next- to prevent weak planes • Vibratory roller for granular soils • 3-6km/hr speed • Lift thickness 10-20cm • Relative compaction can be monitored
- 29. b) Sheepsfoot rollers • Tamping foot rollers • Protruding studs /feet that penetrate into soil • Tamping and kneading action • Suitable for predominantly clayey soils, not for coarse grained soils • Ballasted or unballasted • Contact pressure: 1500-7000 kPa • Walkout process • Self propelled or towed • Usual roller speed 3-6km/hr, self propelled upto 9km/hr • Vibrating tamping foot rollers can be used for silty and clayey sands
- 30. b) Sheepsfoot rollers(cntd..) • Advantages over smooth wheeled rollers – More suitable for cohesive sols – Kneading action – Increased blending – Simpler moisture control – Soil compaction over wider moisture range – Effective in breaking down rock pieces • Disadvantages: – Slow – Lower compacted density – Large entrapped air – soft zones not revealed easily
- 31. c) Grid rollers • Intermediate between smooth wheeled and sheepsfoot rollers • Wheels made of steel bars forming a grid with square holes • Less kneading action but high contact pressure • More suitable for coarse grained soils
- 32. d) Pneumatic tyred rollers • By Kneading action • Suitable for both cohesive and cohesionless soils • Can be ballasted • Wobble-wheel effect • Front and rear wheels not in alignment for better efficiency • Speed 6-12 km/hr • Smoother finish • Lift thickness: 15-30 cm based on roller weight • Heavier in weight hence lesser no; of passes required; thicker lifts, reveal weak zones
- 34. Other surface compaction devices • Heavy rubber tired trucks • Crawler type tractors- for cohesionless soils • Smaller ones: air tamps, impact rollers, vibratory plate devices etc.
- 35. Roller selection • Economy • Type of soil and relative compaction required • Sheepsfoot and smooth wheeled cohesive • Vibratory and crawler type cohesionless
- 36. Deep compaction techniques • Vibrocompaction • Dynamic compaction • Compaction grouting • Prefabricated Vertical drains • Blasting
- 37. Dynamic compaction • Repeated blows of a heavy weight (10-50 tonnes) from height (10-40m) • Type of deep compaction • Densification depends on: ? • Compacted in intervals • Top surface craters formed compacted later • Spacing depends on:? • Energy transfer by Seismic wave propagation • Merits?
- 39. Methods of dynamic compaction • Dynamic compaction- granular • Dynamic consolidation- saturated cohesive soils • Dynamic replacement- soft saturated soils
- 40. Compaction Control • Effective Depth of compaction: Empirical relation Dmax = n√(W H) Where, Dmax = Max depth of improvement, m n = Coefficient that caters for soil and equipment variability W =Weight of tamper, tons H = Height of fall of tamper, m • Compacted materials tested for moisture content and density Nuclear density meter Hill’s Method
- 42. Other Insitu Evaluation Techniques • Pore pressure, settlement , energy consumed by the equipment etc. can be monitored • Values before and after compaction is compared • SPT and CPT • Pressuremeter and dilatometer tests stress strain behaviour • Shear wave velocity measurements
- 44. Flat dilatometer
- 45. Shear wave velocity monitoring
- 46. VibrationMethods Vibrocompaction Blasting Terraprobe Vibratory compactors Vibro- displacement Compaction piles in sand Vibrofloatation Sand compaction piles Stone columns
- 47. VIBRODISPLACEMENT • Vibrations with active displacement of particles subsequent backfilling • Vibro displacement and vibro replacement
- 48. 1. Sand Compaction Piles
- 49. Sand compaction piles • Also called vibro-composer method • Effect decreases radially outwards, and vertically upwards • Economical for depths upto 15m • Square or rectangular pattern • Pile spacing: s/d varies from 2.5 to 4
- 50. 2. Compaction Piles in sand • Simplest vibro-displacement techniques • Driving piles into sand to densify it- usually timber piles • Most effective in cohesionless sands above WT • Effect decreases with increase in fines content and decrease in permeability • Effective to a distance upto 8d from center of pile.
- 51. 3. VIBROFLOATATION • Mainly for cohesionless soils • Equipment: Vibratory probe, power supply, water pump, crane, feeder • Probe dimensions: dia 0.3-0.5 m, l= 2-3m • 2Parts: Vibratory probe+ follow up pipe • Procedure: 4 stages • Water is pumped at 225-300 l/min at 400-600 kPa • Vibrofloat moves down due to weight + jet action • Jet creates sand boiling momentarily • Efficiency depends upon: • Continuous monitoring required
- 53. • Backfill required: almost 10% of compacted volume • In one penetration, cylindrical columns of 2.5-3m diameter will be formed • Withdrawal rate: 0.3-0.6/min • Effective upto 20m normally 70% rel.den • Soil suitability: – Zone A,B,C (refer ) – Most suitable for soils under zone B • Suitable for granular soils with silt content less than 10% • Linear, square or triangular pattern • Spacing depends on : • Backfill suitability: Brown’s suitability Number
- 55. Vibrofloatation in clays • Used in soils that do not respond well to vibration alone. (to stiff, more than 15% silt) • The improvement is achieved by creating columns of either crushed stone or concrete (of which can be reinforced). • The process enables increased load bearing, reduces settlement and even improves the shear resistance of the ground being treated. • The process is technically proven worldwide and very cost effective
- 56. VIBROCOMPACTION • Rapid densification technique for saturated cohesionless soils • Localized liquefaction followed by densification and compaction • Effectiveness decrease with increase in percentage fines • Blasting, Terraprobe, Vibratory Compactors
- 57. 1.EXPLOSIONS IN SAND • Controlled blasting • Explosive charge buried in soil and detonated • Principle: shock waves produced by blasting--. Densification • Procedure: • Detonated large holes created by lateral displacement Backfilled • Spacing - • Spacing , pattern and blast timing must be carefully planned • Depth less than 10m blast in one tier • 70-80% relative density achieved • Adequate data regarding soil type, depth , degree of saturation, relative density to be achieved, is required
- 58. 2. Vibratory Compactors • Vibrating drums, pneumatic tyred rollers, vibrating plate etc. • 1500-2500 cpm • 3-6 km/hr • Rel.densities 85-90% • Lift thickness, roller type and soil type should match
- 59. 3.Vibratory probe/Terraprobe • Vibrodriver with open ended steel tubular probe of 760mm dia and 15m length • Vibration: 15Hz • Held 30-60 seconds before extraction • Spacing 1-3m- square pattern • Influence area- 1m cylinder and 1m deeper than probe depth • Great depths • Saturation preferrable • Less cost • More useful in offshore locations • faster • Less effective than vibrofloatation
- 60. STONE COLUMNS • Most versatile • Applicable to wide range of soils • Multiple functions: – Densification- Increase shear strength & BC – Drainage path- Accelerates consolidation– reduce settlement – Increase stiffness- reinforcement – Prevents pore pressure built up Reduce liquefaction potential • Applications- – Embankment fill stability – Foundation in soft soils
- 61. Suitable soils • Weak Cohesive Soils • Granular Soils with High Fines Content (in excess of 15%) • Organic Soils • Marine/Alluvial Clays • Liquefiable Soils • Waste Fills
- 62. Methods of installation Cased Borehole method/ Rammed stone column Vibration Methods- Vibrofloatation / Vibrocomposer
- 63. Cased Borehole Method/ Rammed stone column • Proposed by Datye and Nagaraju (1977) and developed by Nayke (1982) • Uses a bored piling rig to dig the borehole and granular fill is placed and compacted in stages
- 64. Cased Borehole Method/ Rammed stone column • Proposed by Datye and Nagaraju (1977) and developed by Nayke(1982) • Uses a bored piling rig to dig the borehole and granular fill is placed and compacted in stages Construction steps: 1. Cased borehole is prepared 2. Granular material (2-75mm ) filled upto 2-3m depth from surface 3. Each layer compacted using rammer of 15-20kN from height about 1.5m 4. Casing is withdrawn in stages
- 65. Rammed stone column- procedure Cased borehole Granular materal (2-75mm) backfilled upto 2-3m from surface Each layer compacted using rammer (15- 20kN from height 1-1.5m Casing withdrawn in stages • Simpler method without casing can also be used
- 66. Stone columns after installation
- 67. Vibrocomposer method • Vibrofloat- assisted with water jet or compressed air • Backfill gravel- 12-75mm • More effective but costly
- 68. Conventional method • Auger boring followed by manual cleaning • Gravel-sand mixture (2: 1) proportion preferable for more densification • Granular piles 20-30mm stone aggregate + 20-25% sand on top of each layer • Each two layer unit compacted by 1250kN hammer with free fall 750mm
- 69. Design Criteria • Unit cell concept
- 70. • Area replacement ratio • Spacing and diameter • Length • Load carrying capacity
- 71. Preloading
- 74. Types of vertical drains • Unenclosed Sand drains- 200-400mm dia • Wick drains- 60-100mm dia • Prefabricated vertical drains- 90-100mm
- 75. Advantages of PVD • Easy installation • Quality control • Efficiency • Economy • Assured continuity • Less material storage • Minimal displacement • No spoil removal
- 76. Design of PVD
- 78. Stabilisation by Heating • More Suitable for partially saturated fine grained soils • Effects: – Reduces electric repulsion – Increased pore water flow rate – Reduced moisture content – Reduces compressibility and swelling potential – Produces cementation effect in sands • 1000 c Drying strength enhanced • 5000 c permanent structural change decrease in plasticity and moisture adsorption capacity • 10000c fusion of clay particles into solid brick
- 79. • Methods – Burning of liquid or gas fuels in boreholes at high pressures – Injection of hot air • Stabilises 1.3-2.5m dia holes after about 10 days • Effective only when fuels are easily accessible- otherwise uneconomical Temperature range for different applications
- 80. Schematic view of ground heating
- 81. GROUND FREEZING Developed by German scientist F. Hermann Poetsch in 1863 Making water-bearing strata impermeable, by freezing the pore water into ice Increases strength and decreases permeability On freezing, grain structure binds stronger, hence more strength and less impermeability Pore water ice ice wall Suitable in all soils Strength and freezing time, depends on temperature and moisture content of soil
- 82. Strength Vs Temperature for different soils
- 83. • Freeze pipes installed at suitable intervals • Coolant (brine or liquid nitrogen) pumped into the pipe • Absorbs heat energy from soil • Ice formation starts around pipes, developing into wall, • Sands-at +20 °F , while clay: - 20 °F • After freeze wall formation, operated at reduced rate to maintain the condition • Pipes removed, ground back to normal condition PROCEDURE
- 84. Freeze wall formation in different strata Process of freeze wall formation
- 87. b) LIN freezing
- 88. ADVANTAGES • Minimum disturbance to ground • Suitable to all types of soil and rock • Provides ground water control, and protection • No waste products, little noise or tremor • No disturbance to underground utilities • Can be used in combination with other materials • Cost effective
- 90. Frozen structure in ground containing boulders Synergetic function between frozen ground and sheet pile wall
- 91. Tram rails passing unaffected across frozen ground retaining walls.
- 92. Parameters Design parameters- • Soil and groundwater conditions; • Shape of structure, and pipe spacing Monitored parameters • ground and coolant temperature • Groundwater level • Coolant flow and pressure • Refrigeration data
- 94. 2)Tunneling.. Horizontal and vertical layout of freeze pipes
- 95. 3) Excavations
- 96. 4) Groundwater cutoff •Prevents entry into open pits, landfills, etc • No need of dewatering •Stops migration of contaminated groundwater •Inexpensive maintenance
- 97. • Protects ground from contaminants • Industries- toxic products in ground • Acts as an impervious seal • Freeze pipes installed around – isolates groundwater within-pumped and treated • Minimum disturbance and noise or leakage 5) Environment remediation
- 98. Biotechnical stabilisation • Sometimes called bioengineering - combines live and dead plant materials with structural engineering techniques to stabilize slopes and stream banks. • now emerging as a more cost-effective, aesthetically pleasing, and environmentally acceptable solution. • natural process of soil stabilization and plant regeneration following erosion or slope failure events.
- 99. Methods • Pole cuttings or live staking • Fascine bundles • Brush layering • Branch packing • Tree revetments
- 103. Benefits of Biotechnical soil stabilization techniques • Soil structural reinforcement • Provides for hydraulic wicking (water absorption) • Provides barrier to sedimentation • Produces shade – temperature control • Provides habitat • Aesthetics – minor site disturbance and less obtrusive • Cost-effective for small scale projects • Long-lasting, strengthening over time
- 104. Drawbacks to Biotechnical soil stabilization techniques: • Results are not immediate – Time variant as plants establish • Applications are difficult to engineer for precise calculations • Large scale projects are more costly and less popular. • Availability of plant material • Soils must support plant growth • Difficult to duplicate – each site requires specific design considerations • Maintenance may be required