- 1.Geotechnical Aspects in Earthquake Resistant Design
- Department of Civil Engineering
- Guru Nanak Dev Engineering College
- Email: jagadanand@gmail.com
2. Conception or rather Misconception of Structure Designer
- Structure Designer believes erroneously most of the time that
superstructure needs to be strengthened more in poor soil than in a
good soil.
- Dynamic behaviour of soil rarely receives any attentionof
structure engineer as compared to dynamic behaviour of
structure.
3. Niigatta Earthquake: 1964, Mag. 7.5 4. Japan earthquake
1964:Niigata- Mag. 7.5 5. Tokachi-oki Earthquake: 2003 The Damage
of Sewerage Structures kushiro (Town) Lifted up manhole and gushed
soilduring liquefaction Lifted up manhole 6. Caracas
Earthquake1967: Mag. 6.6 7. Chile Earthquake1960 :Island
nearValdivia- Mag. 9.5 8. Alaska Earthquake1964:Mag. 9.2 9.
Observed Damage from Earthquakes
- 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
- Alaska earthquake 1964:Turnagain heights landslide- Mag.-
9.2
- Major landslide - combination of dynamic stresses and induced
pore water pressur e
- Japan earthquake 1964:Niigata -Mag.- 7.5
- Settlement and tilting of structures - liquefaction of
soil
- Caracas earthquake 1967- Mag.- 6.6
- Response of buildingduring EQ found to depend on thethickness
of soil under the building .
10. Inference and Attention:
- Influence of local soil conditionon shaking and damage
intensity during earthquakeaffects the stability of structure
.
- Large scale tilting of well built houses in
- the Niigatta earthquake of 1964 focussed
- the attention of profession onproblems
- of soil dynamics:Requiring a careful
11. Objective of Earthquake Resistant Design
- Ensuring structural reliability without structural damagedue to
ground shaking ofmoderate intensities.
- Special structureslike high level bridges, tall dams , Nuclear
Power Plantneed specific designprocedures (Site specific) supported
by detailed investigation.
12. Geotechnical Aspects of Earthquake Resistant Design
- Geotechnical Aspects of Earthquake Resistant Design of
foundation of structures and other soil retaining structuresof soil
depends on:
- Dynamic stress deformation and strength characteristics
- Earth pressure problems and retaining wall
- Dynamic bearinng capacity and design of shallow foundation
13. Influence of local soil conditions on Acceleration(Cause for
damage during EQ)
- 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 )S a T = fundamental period of the structure
- Valueof horizontal peak ground acceleration = 0.6g ?
- Physical meaning :Movement of the ground can cause a maximum
horizontal forceon a rigid structure equal to60% of its weight
14. Site approximately same distance from the zone of energy
release 1957 San Francisco Earthquake 15. Site approximately same
distance from the zone of energy release 1957 San Francisco
Earthquake 16. Effect of Soil Conditions on form of Response
Spectra Site A 17. Effect of Soil Conditions on form of Response
Spectra Site B 18. Effect of Soil Conditions on form of Response
Spectra Site C 19. Effect of Soil Conditions on form of Response
Spectra Site D 20. Effect of Soil Conditions on form of Response
Spectra Site E 21. Effect of Soil Conditions on form of Response
Spectra Site F 22. Effect of Soil Conditions on form of Response
Spectra Site A - F 23. 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
- 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
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 24.
- Clay layer : Amplified seismic shock of glacial till (Both
event)
- Peat deposits : Amplified seismic shocks (Only for distant
shock)
25.
- 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
BuildingResponse variation during Earthquake 26.
- 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 wavesto
passthroughand filtering the rest.
27. Damage potential coefficient varies with building
characteristics and soil depth 28. 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 29. Dynamic bearing capacity
- Soil dynamics: Engineering properties and behaviour of soil
under dynamic stress
- Factors to be considered for estimation of bearing capacity
under dynamic condition:
- Nature of variation of the magnitude of the loading pulse
- Strain rate deformation of soil during deformation
30.
- For both static, dynamic and seismic cases bearing capacity
failure of foundation grouped into three categories:
- Various theories concerning dynamic bearing capacity have been
presented in last 50 years butdefinition of dynamic bearing
capacity is yet to evolve till date
31. Ultimate bearing capacity of continuous shallow foundation
(static case) 32. Seismic bearing capacity 33.
- N q ,N = bearing capacity
- = tan-1[(0.67+ R D- 0.75R 2 D )tan ]
- N qE , N E= bearing capacity
- k h &k v=horizontal and vertical
- coefficient of acceleration
- AE & PE = Inclination angles for
- active and passive pressure conditions
34.
- Static bearing capacity factors
- Seismic bearing capacity factors
N q N 0 1 0 10 2.47 1.22 20 6.40 5.39 30 18.40 22.40 40 64.2
109.41 N q N 0 1 0 10 2.4 1.4 20 5.9 6.4 30 16.5 23.8 40 59.0 112.0
35.
- Variation of N qand N with
- Variation of N E /N and N qE / N qwith tan and
36. Prediction of dynamic load- settlement relationship for
foundations on clay (Jackson and Halada,1964)
- S stat /B, multiply Q/B 2 c u
- by the strain rate factor
- (=1.5) and plot it in the
37. Settlement of strip footing due to an earthquake
- (0.174)(V 2 /Ag)[k h * /A] -4 tan AE
- AE= Inclination angles for
- active pressure conditions
- design earthquake (m/sec)
- A = acceleration coefficient
- for the design earthquake
- g = acceleration due to gravity (9.81 m/sec 2 )
- k h /(1- k v ) = k h * , if k v = 0
38. 39. Geotechnical Aspects of Earthquake resistant design
- Soils behave like a liquid.How and why?
- To understand the above phenomenon: Some understandingof basics
required :
40. 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 41. 42.
Liquefaction of Soil
- Effective stress gives more realistic behaviour of soil,
- and can be expressed as= c + ( nu)tan
- During the ground motion due to an earthquake,
- static pore pressure may increase by an amount u dyn
- Let us consider a situationwhenu + u dyn = n , then= c
- In cohesionless soil,c= 0, hence= 0
- Soil loose its strength becauseofloss 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 completelyand it develops a liquefied state.
43. 44. Influence of soil conditions on liquefaction potential
45. The Damage of Embankment Structures Toyokoro Collapsed
Embankment 46. 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 47. Toyokoro Liquefied Soil Collapsed
Embankment The Damage of Embankment Structures Liquefied Soil 48.
Failure Mode (notice : this is only concept) Liquefied Stratum
Embankment Settlement Land Slide Lateral Spread The Damage of
Embankment Structures 49. The Damage of Port Structures(at Kushiro
Port) Kushiro Settlement behind Quay Wall Trace of Sand Boiling 50.
Alaska Earthquake ( 1964 ) 51. 52. Caracas ( 1967 ) 53. Alaska2002
Boca del Tocuyo, Venezuela,1989 54. Lateral spread at Budharmora
(Bhuj, 2001) 55. Arial view of kandla port, Marked line sows ground
crack and sand ejection (Gujrat Earthquake 2001) 56. 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
Flow failure 57. Lateral spread and Ground oscillation
- Liquefaction at depth-decouple overlaying soil layer from the
underlying
- Lateral displacement of large superficial blocks ofsoil as a
result of
- liquefaction of subsurface layer and Allowingupper soil to
oscillate
- back and forth / up and down in the form ofground wave
- Displaced ground-Break up internallycausing fissures, scarps
etc in the
58. 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
59. Soil conditionsin Areas whereLiquefactionhasoccurred : Case
Study:Niigata EarthquakeKawangishicho apartment complex, tipped by
60 degree 60. 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
- Extent of damage: Different
- Characteristics ofunder lying sand :Different
- ii)Type offoundation :Different
B Relatively light damage (Low land area)Medium to lightSand
soil up to depth of 100 ft Depth of water table less than A C
Damage and Liquefaction (Low land area) Medium to lightSand soil up
to depth of 100 ft Depth of water table less than A But similar to
B 61. Standard Penetration Resistance Test(Zone-B &
C-Comparison of soil condition)
- Average Penetration Resistance:Sameup to15 ftin zoneB &
C
- Average Penetration Resistance:More below 15 ftdepth
inzone-B(Sand in zone-B are denser than those in zone- C)
- Sand below 45 ft in both zone: Relatively dense & unlikely
to beinvolved in liquefaction
- Difference in Penetration resistance ofsand in depth range
from15 ft to 45 ftisresponsible for the major difference
infoundation and liquefaction behaviour in two zones
62. Soil Foundation Condition and Building
Performance(Zone-C-Range of penetration resistance:heavy damage
zone )
- Variationof Penetration resistance with depthfalls within
shaded area
- Standard Penetration Resistance: Top 25 ft: Generally less than
15 and sometimes less than 5
- Conclusion:N =28at the base of the foundation , required,
Toprevent major damage
63. Classification of Extent of Damage for each Building
(Zone-C)
- Supported on Shallow spread footing foundations
- 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)
64. 65. Relationship between N at the base of Foundation and
Extent of Damage 66. Relationship between depth of pile, Nof sand
at pile tip and Extent of Damage (Zone-C) 67. 68. 69. Case Study
:Gujrat Earthquake, 2001
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 70. Condition
of soil before and after earthquake (Relative density of sand with
depth)
- 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
71. D vs depth of layer of three section charaterized by
predominant period T pof microseismic vibrations
- Direct co-relation exists between quality of ground, dynamic
characteristics and anticipated consequences of earthquake
72. 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 maxexerted by the
earthquakeat ground surface
73.
- Horizontal seismic force= Max.
- shear force at the base of column ( max )
- Horizontal seismic force = Mass x Accl.
- = [( t.z)/g]a max= vo(a max /g) = max
- Mass = W/g = ( t.z)/g = vo/g
- If effectivevertical stress = vo,
- Then( max/ vo) =( vo/ vo)(a max /g)
- Inreality, during an earthquake, soil
- column does not act as a rigid body
- ( max/ vo)= r d( vo/ vo)(a max /g)
- r d~ 1- 0.012z ,also depends upon the magnitude of the
earthquake
74.
- Conversion of irregular earthquake record to an equivalent
seriesof
- uniform stress cycleby assuming the following:
- av= cyc= 0.65 max= 0.65 r d( vo/ vo)(a max /g)
- To felicitate liquefaction analysis, define a dimensionless
parameter
- CSR or SSR = cyc/ vo= 0.65 r d( vo/ 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 75. Cyclic resistance ratio
- Line represents dividing line
- Three lines contain- 35, 15 or 5 % fine
- Data to the left of each lineindicate field liquefaction
- Data to the right of eachline indicate no liquefaction
- FS = Factor of safety against liquefaction
76. Evaluation of liquefaction potential
- CSR= Cyclic stress ratio,CRR=Cyclic resistance ratio
- FS= Factor of safety against liquefaction= CRR/CSR=CSR L /CSR =
cyc,L/ cyc
77. Liquefaction Analysis: Niigata 1964 EQ
- Asite in Japan had the measured SPT resistance as given in the
table. The
- SPT procedure used in Japan delivered about 72% of the
theoretical free
- fall energy of the sampler. Assuming that the sands have an
average void
- ratio of 0.44 and that the water table is at a depth of 1.5m,
determine the
- extent to which the liquefaction would have been expected in
1964 Niigata
- EQ (M=7.5) if thepeak horizontal acceleration in the ground
surface
D (m) N m D N m D N m D N m D N m 1.2 7 5.2 5 9.2 14 13.2 11
17.2 5 2.2 4 6.2 9 10.2 9 14.2 11 18.2 6 3.2 3 7.2 12 11.2 23 15.2
24 19.2 4 4.2 3 8.2 12 12.2 13 16.2 27 20.2 38 78. Standard
penetration test (SPT)
- (N 1 ) 60= (N mC N )(E m /0.60E ff )
- (N 1 ) 60= Corrected standard penetration resistance (N):To
normalize the N value to an overburden pressure of 100kPa and to
correct it to anenergy ratio of 60%
- Energy ratiois the average ratio of theactual energydelivered
by safety hammer to thetheoreticalfree fallenergy
- N m= Measured penetration resistance
- C N= Overburden correction factor
- E m= Actual hammer energy
- E ff= Theoretical free fall hammer energy
79. Void ratio = 0.44, Gs = 2.7, Dry and submerged densities
1.874Mg/m 31.180 Mg/m 3
- vo = Vertical Effective stress at6.2 m depth =
- [(1.5m)(1.874 Mg/m 3 )+(4.7m)(1.180Mg/m 3 )](9.81 m/sec 2
)
- vo= Total Vertical stress at6.2 m depth =
- [(1.5m)(1.874 Mg/m 3 )+(4.7m)(2.180Mg/m 3 )](9.81 m/sec 2 ) =
128.1kPa
- C N = {1/(82kPa)[(0.01044 ton/ft 2 )/kPa]} 0.5= 1.08
- (N 1 ) 60 = N mC N(E m /0.60 E ff )
- = (9)(1.08)(0.72 E ff /0.60 E ff )= 11.7 at6.2 m depth
80. SPT overburden correction factor & values of (N 1 ) 60
81. av= cyc= 0.65 max= 0.65 r d( vo/ vo)(a max /g)r d= Stress
reduction factor = 0.960 at 6.2m depth=C D 82. Cyclic Shear Stress
cyc= 0.65 r d( vo)(a max /g)(6.2m depth)
- =0.65(0.960)(128.1)(0.16g/g)
- cyclic shear stress required
- characterized by (N 1 ) 60
- when (N 1 ) 60= 11.7 at6.2m depth
83.
- Magnitude Correction Factor for Cyclic Stress approach:
- Magnitude of Niigata EQ = 7.5
- CSR = cyc/ vo= 0.65 r d( vo/ vo)(a max /g)
- Cyclic stress ratio required for liquefaction
- cyc,L= CSR L ( vo ) = (0.130)(82.0)=10.7 kPa
- [CSR L = (CSR M=7.5 )(1.0)= 0.130(1.0)= 0.130]
- FS = Factor of safety against liquefaction
- =CSR L /CSR = cyc,L/ cyc= 10.7/12.8= 0.84
84. Details of calculation 85. Extensive liquefaction observed
for upper 8-10m & at greater depthPeak horizontal acceleration
at Niigata0.2g to 0.3g(> 0.16g) Extensive liquefaction
predictedin this problem is consistentwith actual observation in
1964 Niigata earthquake 86. Modified Chinese Criteria for
liquefactionAssessment
- Criteria for Soil to liquefy:
- Moisture Content > 0.9 LL
87. SAFETY AGAINST LIQUEFACTION Zone Depth below ground level N
value III, II Up to 5 m 15 III, II Up to 10 m 25 II (For important
structure) Up to 5 m 10 II (For important structure) Up to 10 m 20
88. Liquefaction Potential Damage Range of SPT N corrected
Potential Damage 0-20 High 20-30 Medium > 30 No Significant
Damage 89. 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
90. Counter measures against Liquefaction
- Lowering of Ground water Table
- Application of dead weight
- Mitigation of lateral flow by providing baffle walls
91. Uttarkashi Earthquake, 1991
- Site: National Highway (NH-58)at Byasi (30 km from Rishkesh
towards Badrinath in Garhwal Himalaya): Agency: BRO
- Geo-syntheticRetaining Wall (Height-11m, Length- 19.5 m)
- Location of Existing Retaining Wall of the area
92. Cross-section(Retaining Geogrid Reinforced cohesionless
backfill) 93. Field Performance of wall 4 O.P. Fixed in the Wall:
To monitor thelateral movement of wall top away from backfillusing
Electronic Distance Meter for aperiod of 36 months 94. 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
shakingby
- Uttarkashi earth quake 1991
- Cost: 79% of the cost of retaining wall with conventional earth
fill
95. Hyogoken Nambu Earthquake1995 Height of wall 4 to 8 m
Conventional Retaining Wall suffered maximum damageGeo-synthetic
reinforced soilretaining wall Performed very well(due to relatively
high ductilityof the wall) 96. Preloading for oil tanks
- Site:500 km from the sea shore on a coastal alluvial Plain, 5
km south west of THESSALONIKIin 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) BA 0-5.5 622 5.5 -8.0 2234 8.0 -26.0 1039
97.
- 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 settlementversus time curves does not show
however a kink
98. 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.
99. Foundation of modern building that survived earthquake
- Concrete slab without piles (b) The same at deeper depth
- (c ) Concrete foundationgrillage on wood built up piles
- The same but with concrete piles
- Foundation grillagesuspended by boltson concrete piles
- 1 Street Level; 2 Level of compacted soil
100. Can Liquefaction be predicted?
- Occurrence of liquefaction cant 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
bysuperimposingaliquefaction susceptibilitymap withliquefaction
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)
101. 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)
102. 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
103. Acknowledgements
- The author wishes to acknowledge all the various sources used
and especially Principle of Soil Dynamics (by Das and Ramana,
CENGAGE Learning), and paper published by Seed et al. in various
Journal/Book at different times during the preparation of this
presentation which aided and enhanced the quality either in the
form of information, data, figure, photo, graph or table.
- Thanks for your attention