• Me gusta
Liquefaction of Soil
Próxima SlideShare
Cargando en...5
×
Subido el

 

Más en: Tecnología
  • Full Name Full Name Comment goes here.
    ¿Está seguro?
    Tu mensaje aparecerá aquí
Sin descargas

reproducciones

reproducciones totales
15,619
En SlideShare
0
De insertados
0
Número de insertados
2

Acciones

Compartido
Descargas
1,340
Comentarios
6
Me gusta
1

Insertados 0

No embeds

Denunciar contenido

Marcada como inapropiada Marcar como inapropiada
Marcar como inapropiada

Seleccione la razón para marcar esta presentación como inapropiada.

Cancelar
    No notes for slide

Transcript

  • 1. Liquefaction of soil By Dr. J.N.Jha Professor Department of Civil Engineering Guru Nanak Dev Engineering College Ludhiana Email: jagadanand@gmail.com
  • 2. Chile earthquake 1960 : An island near Valdivia- Mag. 9.5 Large settlements and differential settlements of the ground surface - Compaction of loose granular soil by EQ
  • 3. Japan earthquake 1964: Niigata- Mag. 7.5 Settlement and tilting of structures - liquefaction of soil
  • 4. Alaska earthquake 1964:Mag. 9.2 Major landslide - combination of dynamic stresses and induced pore water pressure
  • 5. Caracas earthquake 1967: Mag. 6.6 Response of building during EQ found to depend on the thickness of soil under the building.
  • 6. Observed Damage from Earthquakes
    • Chile earthquake 1960 : An island near Valdivia
    • Large settlements and differential settlements of the ground surface - Compaction of loose granular soil by EQ
    • Japan earthquake 1964: Niigata
    • Settlement and tilting of structures - liquefaction of soil
    • Alaska earthquake 1964: Turnagain heights landslide
    • Major landslide - combination of dynamic stresses and induced pore water pressure
    • Caracas earthquake 1967
    • Response of building during EQ found to depend on the thickness of soil under the building.
    • What is the inference ?
    • Influence of local soil condition on shaking and damage intensity during earthquake
    • Require a careful attention by Engineers
  • 7. Seismic waves Arrival of Seismic waves at site
    • Motion of Ground (Description): Displacement, Velocity, Acceleration
    • Motion of Ground : Depends on
    • Amount of energy release,
    • Type of slip at fault rupture
    • Geology along the travel path from fault rupture to earth surface
    • Local Soil
  • 8. Influence of local soil conditions on Acceleration(Cause for damage during EQ)
    • Some Basic Information :
    • Acceleration Response Spectrum
    • A graph showing the maximum accelerations induced in structures with fundamental period ranging from 0 to several seconds
    • Velocity Response Spectrum
    • A plot showing relationship between maximum velocity with fundamental period of the structure
    • Relation between Velocity Spectrum ( S v )and Acceleration Spectrum ( S a )
    • S v ≈ (T/2 π )S a T = fundamental period of the structure
    • Value of horizontal peak ground acceleration = 0.6g ?
    • Physical meaning :Movement of the ground can cause a maximum horizontal force on a rigid structure equal to 60% of its weight
  • 9.  
  • 10. Site approximately same distance from the zone of energy release
  • 11. Development of Peak/Max. Acceleration
    • Clay (soft): Moulded easily at natural water content and readily excavated
    • Clay (firm): Moulded by substantial pressure at natural water content and excavated
    • with a spade
    • Out of six four spectra obtained from the same city in the same EQ at a considerable
    • distance from the epicenter
    • To eliminate the influence of different amplitudes of surface acceleration, plot made
    • between period and normalized acceleration (Spectral Acceleration/Maximum
    • Ground Acceleration
    Sites (Increasing order of softness) Period (sec) (Maximum spectral acceleration) A 0.3 B 0.5 C 0.6 D 0.8 E 1.3 F 2.5
  • 12. velop
  • 13.
    • Clay layer : Amplified seismic shock of glacial till (Both event)
    • Peat deposits : Amplified seismic shocks (Only for distant shock)
  • 14.
    • Time taken for each complete cycle of oscillation is called FUNDAMETNAL NATURAL PERIOD (T) of the building
    • Time taken by the wave to complete one cycle of motion is called PERIOD OF EQ WAVE (0.03 to 33 seconds)
    • Short EQ wave have large response on short period buildings
    • Long EQ wave have large response on long period buildings
    Building Response variation during Earthquake
  • 15.
    • T (Inherent property of the building) depends on the building flexibility and mass,Any alteration made to the building will change its “T”
    • Bldg (3-5 storey); damage intensity higher in area with underlying soil cover 40-60 m thick and minimal in areas with larger thickness of soil cover
    • Bldg (10-14 storey); damage intensity maximum when soil cover in the range of 150-300m and small for lower thickness of soil cover
    • Soil plays the role of filter allowing some ground waves to pass through and filtering the rest.
  • 16. Damage potential coefficient varies with building characteristics and soil depth
  • 17. Relationship between building characteristics, soil depth and damage potential coefficient (S v /k) Structure Fundamental period Damage intensity (D r ) 2 to 3 storey 0.2 sec Remains same regardless of soil depth 4 to 5 storey 0.4 sec Max. damage intensity expected at soil depth of about 20 to 30 m 10 to 12 storey 1.0 sec Damage intensity expected to increase with soil depth up to 150 m or so 15 to 20 storey Damage intensity even greater for soil depth of 150 to 250 m & relatively low for soil depth up to 80 m or so
  • 18. Liquefaction of Soil
    • Soils behave like a liquid. How and why?
    • To understand the above phenomenon:
    • some basics required regarding:
    • Total stress,
    • Pore water pressure
    • Effective stress
  • 19. Total stress, Pore water pressure and Effective stress Figure-1 Figure-2 Case Total Pressure Pore Pressure Effective Pressure Figure- 1 475 150 325 Figure- 2 475 250 225
  • 20.  
  • 21. Liquefaction of Soil
    • Shear strength, τ = c + σ n tanø
    • Effective stress gives more realistic behaviour of soil,
    • Shear strength can be expressed as τ = c 1 + ( σ n –u)tanø 1
    • During the ground motion due to an earthquake,
    • static pore pressure may by an amount u dyn , then
    • τ = c 1 + ( σ n –u + u dyn )tanø 1
    • Let us consider a situation when u + u dyn = σ n , then τ = c 1
    • In cohesionless soil, c 1 = 0, hence τ = 0
    • Soil loose its strength because of loss of effective stress
    • Saturated sand when subjected to ground vibration, it tends to compact and decrease in volume ; if drainage is unable to occur, the tendency to decrease in volume results in an increase in pore water pressure and when this becomes equal to the overburden pressure effective stress becomes equal to zero, sand looses its strength completely and it develops a liquefied state.
    • φΦγ
  • 22.  
  • 23. Influence of soil conditions on liquefaction potential
  • 24. Liquefaction Damage: 1964 Niigata, Japan
  • 25. Tokachi-oki Earthquake: 2003 The Damage of Sewerage Structures kushiro (Town) Lifted up manhole and gushed soil during liquefaction Lifted up manhole
  • 26. The Damage of Sewerage Structures Failure Mode   (notice : this is only concept) Replaced Soil (Liquefied) Lift-up Force Crack or Residual Strain Sand Boiling Sand Boiling Manhole Flexible Pipe Rigid Pipe Residual Strain Original Soil (Liquefied)
  • 27. The Damage of Embankment Structures Toyokoro Collapsed Embankment
  • 28. Place where Embankment was collapsed Abashiri River (1) Shibetsu River (6) Kushiro River (5) Kiyomappu River (2) Tokachi River (66) Under investigation Lateral Spread was observed ( ) : the number of collapsed points Tokachi River The Damage of Embankment Structures
  • 29. Toyokoro Liquefied Soil Collapsed Embankment The Damage of Embankment Structures Liquefied Soil
  • 30. Failure Mode   (notice : this is only concept) Liquefied Stratum Embankment Settlement Land Slide Lateral Spread The Damage of Embankment Structures
  • 31. The Damage of Port Structures (at Kushiro Port) Kushiro Settlement behind Quay Wall Trace of Sand Boiling
  • 32. Alaska Earthquake ( 1964 )
  • 33.  
  • 34. Caracas ( 1967 )
  • 35. Alaska 2002 Boca del Tocuyo, Venezuela, 1989
  • 36. Lateral spread at Budharmora ( Bhuj, 2001 )
  • 37. Arial view of kandla port, Marked line sows ground crack and sand ejection (Gujrat Earthquake 2001)
  • 38. Adverse effects of liquefaction Most catastrophic ground failure Lateral displacement of large masses of soil Mass comprised of completely liquefied soil or blocks of intact material riding on a layer of liquefied soil Flow develop in loose saturated sand or silts or relatively steep slope (>3 degree) Flow failure
  • 39. Lateral Spread
    • Lateral displacement of large superficial blocks of soil as a result
    • of liquefaction of subsurface layer
    • Displacement occurs in response to combination of gravitational
    • and inertial forces generated by an earthquake
    • Develop on gentle slope (<3 degree) and move forward free face
    • Displaced ground-Break up internally causing fissures, scarps etc
    • in the form of surface failure
  • 40. Ground oscillation
    • Liquefaction at depth-decouple overlaying soil layer from the underlying ground
    • Allowing in upper soil to oscillate back and forth and up and down in the form of ground wave
    • Oscillation accompanied by opening and closing of fissures and fractures of rigid structure (Pavements, Pipelines)
  • 41. Loss of bearing strength
    • Large deformation occur within the soil allowing the structure to settle & tip
    • e.g, 1964 Niigata earthquake, Japan-Most spectacular bearing failure-Kawangishicho apartment complex, several four story building tipped as much as 60 degree
  • 42.  
  • 43. Soil conditions in Areas where Liquefaction has occurred : Case Study: Niigata Earthquake
  • 44. Survey of damaged structure(Liquefaction Zone) Zone Damage Soil Characteristics Water table Remark A No damage (Coastal dune area) Dense Sand soil up to depth of 100 ft At great depth from ground level
    • Type of structure: Same
    • Extent of damage: Different
    • Reason:
    • Characteristics of under lying sand: Different
    • Type of foundation: Different
    B Relatively light damage (Low land area) Medium to light Sand soil up to depth of 100 ft Depth of water table less than ‘A’ C Damage and Liquefaction (Low land area) Medium to light Sand soil up to depth of 100 ft Depth of water table less than ‘A’ But similar to ‘B’
  • 45. Standard Penetration Resistance Test (Zone-B & C)
    • Average Penetration Resistance: Same up to 15 ft in zone B & C
    • Average Penetration Resistance: More below 15 ft depth in zone-B
    • (Sand in zone-B are denser than those in zone- C)
    • Sand below 45 ft in both zone: Relatively dense & unlikely to be
    • involved in liquefaction
    • Conclusion : Difference in Penetration resistance of sand in depth range from 15 ft to 45 ft is responsible for the major difference in foundation and liquefaction behaviour in two zones
  • 46. Soil Foundation condition and Building Performance (Zone-C)
    • Variation of Penetration resistance with depth falls within shaded
    • area
    • Standard Penetration Resistance:
    • Top 25 ft: Generally less than 15 and sometimes less than 5
  • 47. Classification of extent of damage for each building (Zone-C)
    • Buildings Foundation: Supported on Shallow spread footing foundations (Number: 63)
    • Buildings Foundation: Supported on Piles ( 122)
    • Extent of damage due to foundation failure:
    • Category-I to Category-IV
    • Category-I:No damage to Building
    • (Tilt: upto 20 min, Settlement: upto 8 inch)
    • Category-IV: Heavy damage to Building
    • (Tilt: upto 2.3 degree, Settlement: upto 3 ft)
    • Conclusion: N =28 at the base of the foundation , required, To prevent major damage .
  • 48.  
  • 49. Relationship between depth of pile, ‘N’ of sand at pile tip and Extent of Damage (Zone-C)
  • 50. Case Study : Gujrat Earthquake, 2001
    • Soil Condition
    S.No. Region Type of Soil 1 Ahmedabad and Surrounding region Alluvial belt 2 Bhuj and Surrounding region Silty sand 3 Coastal area (Kandla) Soft clay 4 South Gujrat Expansive Clay
  • 51. Condition of soil before and after earthquake Relative density (D) of sand with depth before and after earthquake D vs depth of layer of three section charaterized by predominant period T p of microseismic vibrations
  • 52.
    • Change in density observed
    • Increase in density observed upto 5m depth from ground surface
    • Decrease in density from 10-15m depth from ground surface
    • Change in density of sand under saturation during vibration cause for liqufaction and possible reason for large differential settlement at Ahmedabad
    • Damage in Zone A-Minor, Zone B- Moderate, Zone C- Heavy
    • Direct co-relation between quality of ground, dynamic characteristics and anticipated consequences of earthquake
  • 53. Case Study: Others sites Site Soil Property Standard Penetration Mino-Owari,Tonankai and Fukui Earthquakes D 10 ~ 0.05 to 0.25 mm Uniformity coefficient < 5 <10 (upper 30 ft) Jaltipan Earthquake D 10 ~ 0.01 to 0.1 mm Uniformity coefficient ~2 to 10 Alaska Earthquake D 10 ~ 0.01 to 0.1 mm Uniformity coefficient ~2 to 4 < 20 to 25
  • 54. What are the options for liquefaction mitigations?
    • Strengthen structures to resist predicted ground movements (if small)
    • Select appropriate foundation type and depth including foundation modification of existing structure
    • Stabilize soil to eliminate the potential for liquefaction or to control its effects
  • 55. Counter measures against Liquefaction
    • Densification
    • Vibrofloatation
    • Blasting
    • Stabilization of soils
    • Filtration (drainage)
    • Lowering of Ground water Table
    • Application of dead weight
    • Mitigation of lateral flow by providing baffle walls
  • 56. Uttarkashi Earthquake, 1991
    • Site: National Highway (NH-58)at Byasi (30 km from Rishkesh towards Badrinath in Garhwal Himalaya): Agency: BRO
    • Geo-synthetic Retaining Wall (Height-11m, Length- 19.5 m)
    • Location of Existing Retaining Wall of the area
  • 57. Cross-section(Retaining Geogrid Reinforced cohesionless backfill)
  • 58. Field Performance of wall 4 O.P. Fixed in the Wall: To monitor the lateral movement of wall top away from backfill using Electronic Distance Meter for a period of 36 months
  • 59. Average Lateral Deflection of wall with time
    • Stable equilibrium: 700 days
    • Major part of total lateral movement (60~70%) : Short span of 45 days
    • Active earth pressure exerted on wall due to ground shaking by
    • Uttarkashi earth quake 1991
    • Cost: 79% of the cost of retaining wall with conventional earth fill
  • 60. Hyogoken Nambu Earthquake 1995 Height of wall – 4 to 8 m Conventional Retaining Wall – suffered maximum damage Geo-synthetic reinforced soil retaining wall –Performed very well (due to relatively high ductility of the wall)
  • 61.
    • Preloading for Grain Silos at city THESSALONIKI in north Greece
    • The continuity of settlement time curve was not upset , atleast not appreciably earthquake in 1978
    • The time rate of settlement versus time curves does not show however a kink
  • 62. Preloading for oil tanks
    • Site:500 km from the sea shore on a coastal alluvial Plain, 5 km south west of THESSALONIKI in Northern Greece, area moderately seismic active
    • Pre-loading-Aug. 1979 to June, 1980
    • Table: Change in the Variation caused by Pre Loading
    B- Before Preloading, A – After Preloading Depth Range (Metre) SPT Resistance (Bloe/0.3m) B A 0 - 5.5 6 22 5.5 - 8.0 22 34 8.0 - 26.0 10 39
  • 63. Rokko & Port (Kobe)
    • Ground improvement : Pre loading /Vertical drain/Sand compaction pile
    • Untreated ground: N - 8 to 15
    • Subsidence: 30 to 100 cm. (Avg. 50)
    • Treated ground: N - 25 or more
    • Subsidence: less than 5 cm.
  • 64. SAFETY AGAINST LIQUEFACTION Zone Depth below ground level ‘ N’ value III, II, I Up to 5 m 15 III, II, I Up to 10 m 25 I and II (For important structure) Up to 5 m 10 I and II (For important structure) Up to 10 m 20
  • 65. Liquefaction Analysis
    • Objective : To ascertain if the soil has the ability or potential to liquefy during an earthquake
    • Assumption : Soil Column move horizontally as a rigid body in response
    • to maximum horizontal acceleration a max exerted by the earthquake at
    • ground surface
  • 66.
    • At force equilibrium:
    • Horizontal seismic force = Max. shear force at the base of column ( τ max )
    • Horizontal seismic force = Mass x Accl.= [( γ t .z)/g]a max = σ vo (a max /g) = τ max
    • Mass = W/g = ( γ t .z)/g = σ vo /g
    • If effective vertical stress = σ ’ vo ,
    • Then ( τ max / σ ’ vo ) = ( σ vo / σ ’ vo )(a max /g)
    • In reality, during an earthquake, soil column does not act as a rigid body
    • ( τ max / σ ’ vo ) = r d ( σ vo / σ ’ vo )(a max /g)
    • r d ~ 1- 0.012z , also depends upon the magnitude of the earthquake
  • 67.
    • Conversion of irregular earthquake record to an equivalent series of
    • uniform stress cycle by assuming the following:
    • τ av = τ cyc = 0.65 τ max = 0.65 r d ( σ vo / σ ’ vo )(a max /g)
    • To felicitate liquefaction analysis, define a dimensionless parameter
    • CSR or SSR = τ cyc / σ ’ vo = 0.65 r d ( σ vo / σ ’ vo )(a max /g)
    • CSR = Cyclic stress ratio, SSR = Seismic stress ratio
    • FS = Factor of safety against liquefaction = CRR/CSR
    • CRR= Cyclic resistance ratio
    Time history of shear stress during earthquake for liquefaction analysis
  • 68. Cyclic resistance ratio
    • Represents liquefaction
    • resistance of soil
    • Data used: EQ ~ 7.5,
    • Line represents dividing line
    • Three lines contain- 35, 15 or ≤ 5 % fine
    • Data to the left of each line indicate field liquefaction
    • Data to the right of each line indicate no liquefaction
    • FS = CRR/CSR
    • FS = Factor of safety against liquefaction
  • 69. Foundation (Guidelines)
    • Strip foundations under masonry bearing wall
    • Necessary to ensure bond of masonry in each row and also in all corners and intersections. Depth of bond not less than one third the height of block.
    • All the individual footings or pile caps shall be connected by reinforced concrete ties at least in two direction approximately at right angles to each other or by means of reinforced concrete slabs
  • 70.
    • Footing of foundation of building or its section should be at one level. If level is different, transition of foundation from a lower level to a higher level be made in steps
    • Foundation of adjoining section of a building should have the same depth over a distance of not less than 1m from the joint. Steps should have a slope not more than 1:2 and height of not more than 50 cm.
    • Damp course of masonry wall should be made of cement mortar. Use of water proof membrane is not permitted.
    • For building with no basement the ties or the slab may be placed at or below the plinth level and for building with basement they may be placed at the level of basement floor
    • Incase of reinforced concrete slab the thickness shall not be less than (1/50)th of clear distance between the footing but not less than 10cm in any case.
    • The foundation with grillage on concrete pile reaching solid earth may be recommended for earthquake resistant buildings (including multistory) even when ground conditions are unfavourable
  • 71. Foundation of modern building that survived earthquake
    • Concrete slab without piles (b) The same at deeper depth
    • (c ) Concrete foundation grillage on wood built up piles
    • The same but with concrete piles
    • Foundation grillage suspended by bolts on concrete piles
    • 1 – Street Level; 2 – Level of compacted soil
  • 72.  
  • 73. Can Liquefaction be predicted?
    • Occurrence of liquefaction can’t be predicted
    • Possible to identify areas giving detailed information that have the potential for liquefaction
    • Mapping of liquefaction potential on a regional scale
    • Maps exists for many regions in USA and Japan
    • Liquefaction potential map : complied by superimposing a liquefaction susceptibility map with liquefaction opportunity map
    • liquefaction susceptibility: capacity of soil to resist liquefaction
    • (Controlling factor: soil type, density and water table)
    • liquefaction opportunity: A function of the intensity of seismic shaking or demand placed on the soil
    • (factor affecting opportunity: Frequency of earthquake occurrence, intensity of seismic ground shaking)
  • 74. Criteria for liquefaction potential map
    • Area known to have experienced liquefaction during historic earthquakes
    • Area containing liquefaction susceptible material that are saturated , nearly saturated or expected to become saturated
    • Area having sufficient existing geotechnical data indicating the soil are potentially liquefiable
    • Area underlain with saturated geologically young sediments (< 1000 to 15000 year old)
  • 75. Is it possible to prepare for liquefaction ?
    • Possible to identify areas potentially subject to liquefaction with hazard zone map
    • Emphasis in terms of developing appropriate public policy or selecting mitigation technique in area of major concern
    • Use of hazard map by public and private owners the seriousness of expected damage and most vulnerable structure
    • Using this map local government could designate liquefaction potential areas, and require by ordinance, site investigation and possible mitigation techniques for properties in these area particularly underground pipes and critical transportation routes
  • 76. Acknowledgements
    • The author wishes to gratefully acknowledge the various sources used during the preparation of this presentation which have aided and enhanced the quality either in the form of information, data, figure, photo, graph or table.
    • Any Question ………..
    • The End
    • Thanks for your attention